afp reference guide

Version 2.7.1

AFPReference

Guide

AT271_ARG_E4

AtollRF Planning and Optimisation Software

AFP Reference Guide

Contact Information

Atoll 2.7.1 AFP Reference Guide Release AT271_ARG_E4

© Copyright 1997 - 2008 by Forsk

The software described in this document is provided under a licence agreement. The software may only be used/copiedunder the terms and conditions of the licence agreement. No part of this document may be copied, reproduced ordistributed in any form without prior authorisation from Forsk.

The product or brand names mentioned in this document are trademarks or registered trademarks of their respectiveregistering parties.

About AFP Reference Guide

This document is aimed at frequency planning engineers using Atoll AFP module to perform automatic frequency planningof their networks. This document introduces the AFP with a high level description of the frequency planning process inAtoll. Then descending lower to the practical level, this document describes in detail every aspect of frequency planningin Atoll. Main topics covered in this document include AFP pre-requisites, AFP usage, AFP minimization target and somepossible problems that may come up during training.

This document begins with a basic user guide containing a short operational introduction to the AFP process in Atoll. Thenit goes on to summarize most aspects of the practical planning process and provides detailed discussions on certaintopics. It also explains the means to evaluate a frequency plan. Furthermore, a chapter is dedicated to advanced topicsand troubleshooting in the end.

The appendices describe the technical aspects of the cost function, the BSIC allocation algorithm, the IM calculation, andthe dimensioning process.

Forsk (Head Office) 7 rue des Briquetiers 31700 Blagnac France

[email protected]@forsk.com+33 (0) 562 74 72 10+33 (0) 562 74 72 25+33 (0) 562 74 72 11

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[email protected][email protected]+1 312 674 4846+1 888 GoAtoll (+1 888 462 8655)+1 312 674 4847

Sales and pricing informationTechnical supportGeneralTechnical supportFax

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[email protected]+86 20 8553 8938+86 20 8553 8285+86 10 6513 4559

WebInformation and enquiriesTelephoneFax (Guangzhou)Fax (Beijing)

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Table of Contents

Table of Contents

1 Overview ......................................................................................... 131.1 Introduction to AFP ................................................................................................................................ 13

1.1.1 Frequency Assignment as a Cost Minimization Problem ................................................................. 131.1.2 Abbreviations.................................................................................................................................... 13

1.2 Architecture ............................................................................................................................................ 14

2 Basic AFP Tutorial .......................................................................... 192.1 AFP Process in Atoll .............................................................................................................................. 192.2 Loading and Validating the Network ...................................................................................................... 202.3 Definition of the AFP Scope ................................................................................................................... 222.4 Preparing to Launch the AFP................................................................................................................. 232.5 Launching the AFP and Monitoring its Progress.................................................................................... 252.6 AFP Outputs........................................................................................................................................... 27

2.6.1 Partial Commit Functionality............................................................................................................. 292.6.2 Automatic Constraint Violation Resolution ....................................................................................... 30

2.7 Visualising and Manipulating Results..................................................................................................... 312.8 Manual Frequency Allocation................................................................................................................. 31

2.8.1 Manual Frequency Allocation for SFH Case .................................................................................... 312.8.2 Manual Frequency Allocation for NH Case ...................................................................................... 31

3 Frequency Planning Prerequisites .................................................. 353.1 Atoll Data Model..................................................................................................................................... 35

3.1.1 Reliability and Propagation............................................................................................................... 353.1.2 HCS Layers ...................................................................................................................................... 353.1.3 Subcells ............................................................................................................................................ 36

3.1.3.1 Key Roles of Subcells................................................................................................................. 363.1.3.2 Concentric Cells and Dual-band Cells ........................................................................................ 363.1.3.3 Minimum C/I................................................................................................................................ 36

3.1.3.3.1 Quality Targets...................................................................................................................... 363.1.3.4 Traffic Loads ............................................................................................................................... 363.1.3.5 Local Domain Restrictions .......................................................................................................... 37

3.1.4 TRXs ................................................................................................................................................ 373.1.5 Freezing Flags.................................................................................................................................. 373.1.6 AFP Weights .................................................................................................................................... 373.1.7 Spectrum Administration .................................................................................................................. 373.1.8 Redundancy and Subcell Audit ........................................................................................................ 373.1.9 Neighbour Importance ...................................................................................................................... 383.1.10 SeparationConstraints Table ............................................................................................................ 383.1.11 SeparationRules Table and Rule Priority ......................................................................................... 383.1.12 Adjacency Suppression .................................................................................................................... 38

3.2 AFP Performance Indicators .................................................................................................................. 383.2.1 AFP TRX Rank ................................................................................................................................. 38

3.2.1.1 TRX Rank Usage........................................................................................................................ 393.2.2 Total Cost and Separation Violation Cost Component ..................................................................... 39

4 Frequency Plan Optimisation.......................................................... 434.1 Step 1 (Optional): Traffic Model Usage.................................................................................................. 43

4.1.1 Creating a Traffic Map Based only on Clutter Weighting ................................................................. 434.1.2 Performing a Traffic Capture ............................................................................................................ 434.1.3 Creating IMs Based on Traffic .......................................................................................................... 44

4.2 Step 2 (Optional): Neighbour Relations and Relative Weighting ........................................................... 444.2.1 Automatic Neighbour Allocation ....................................................................................................... 444.2.2 Importing Neighbour Importance ...................................................................................................... 454.2.3 Extending Existing Neighbour Relations .......................................................................................... 454.2.4 Importing Partial Sources of Neighbour Importance ........................................................................ 46

4.3 Step 3 (Optional): Using Dimensioning .................................................................................................. 474.3.1 Optimal Dimensioning of an Existing Network ................................................................................. 47

4.4 Step 4: Optimal Usage of the Atoll AFP ................................................................................................. 48

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4.4.1 Introduction to the AFP Cost Function ..............................................................................................484.4.1.1 Combination of Separation Violation and Interference Probabilities ...........................................484.4.1.2 Counting TRXs (Nodes) Instead of Relations (Edges) ................................................................484.4.1.3 Each TRX Cost............................................................................................................................494.4.1.4 Separation Violation Cost ............................................................................................................494.4.1.5 Interference Cost .........................................................................................................................504.4.1.6 Probabilistic Cost Combination ...................................................................................................504.4.1.7 Missing TRX Cost........................................................................................................................504.4.1.8 Corrupted TRX Cost ....................................................................................................................514.4.1.9 Out-of-domain Frequency Assignment Cost ...............................................................................514.4.1.10 Quality Target ..............................................................................................................................514.4.1.11 Modifiable and Non-Modifiable Costs..........................................................................................51

4.4.2 Most Important Cost Function Parameters and Tuning ....................................................................524.4.2.1 Interference Weight vs. Separation Weight .................................................................................524.4.2.2 Cost of Changing a TRX .............................................................................................................524.4.2.3 Quality Target and C/I Weighting ................................................................................................53

4.4.2.3.1 Quality Target ........................................................................................................................534.4.2.3.2 C/I Weighting .........................................................................................................................53

4.4.2.4 Separation Weights Settings .......................................................................................................54

5 Means to Evaluate Frequency Plans ...............................................575.1 Estimating Frequency Plan Quality.........................................................................................................57

5.1.1 Using Interference Studies................................................................................................................575.1.1.1 Various Interference Studies .......................................................................................................57

5.1.1.1.1 TRX Based Interference Study ..............................................................................................575.1.1.1.2 Worst Case Interference Study..............................................................................................58

5.1.1.2 Visualising TRX Ranks with a TRX Based Interference Study....................................................585.1.1.3 Visualising C/I Distributions with a TRX Based Interference Study.............................................58

5.1.2 Using Audit........................................................................................................................................595.1.2.1 Global Separation Fitness Expression ........................................................................................59

5.1.2.1.1 Forsk Independent Separation Fitness Expression (FISFE) .................................................595.1.2.1.2 Main Separation Violation Item Summary .............................................................................59

5.2 Using Point Analysis ...............................................................................................................................605.2.1 Example 1: Combination of Interference Effects...............................................................................615.2.2 Example 2: Counting Strong Interference Only Once .......................................................................61

5.3 Uniform Frequency Usage Distribution ...................................................................................................615.3.1 When Uniform Distribution and Quality do not Coincide ...................................................................62

5.3.1.1 Domain Range Effect and Adjacent Constraints .........................................................................62

6 Advanced Topics and Troubleshooting ...........................................656.1 Various AFP Related Features ...............................................................................................................65

6.1.1 SFH (HSN, MAL, MAIO) ...................................................................................................................656.1.2 Definition of Atom..............................................................................................................................656.1.3 Synchronous Networks .....................................................................................................................656.1.4 Optimising Hopping Gains ................................................................................................................656.1.5 Fractional Load .................................................................................................................................656.1.6 Domain Use Ratio .............................................................................................................................666.1.7 User Defined MAL Length.................................................................................................................666.1.8 HSN Allocation ..................................................................................................................................666.1.9 MAIO Allocation ................................................................................................................................66

6.1.9.1 Staggered MAIO Allocation .........................................................................................................666.1.10 BSIC Allocation .................................................................................................................................666.1.11 Robustness of Atoll AFP ...................................................................................................................67

6.1.11.1 Value Ranges and Limitations at Validation ................................................................................676.2 Managing Consistency in Atoll and the AFP...........................................................................................68

6.2.1 Service Zone of a Subcell .................................................................................................................686.2.1.1 Specifying Correct Interference Study Coverage Criteria ...........................................................686.2.1.2 Selecting “All servers” or “Best Server” Service Zone .................................................................69

6.3 Event Viewer...........................................................................................................................................696.4 Interference Study Quality Criteria..........................................................................................................696.5 Calculation Zone Border Effect...............................................................................................................696.6 Frequency Planning Techniques ............................................................................................................70

6.6.1 Basics................................................................................................................................................706.6.2 Post-processing of Hot Spots............................................................................................................706.6.3 Learning the Network and Solving for Hot Spots ..............................................................................70

6.7 Performance and Memory Issues in Large GSM Projects......................................................................70

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Table of Contents

7 Interference Matrices ...................................................................... 757.1 Types of Supported Interference Matrices ............................................................................................. 767.2 Interference Matrices Storage................................................................................................................ 767.3 Multiple File Import................................................................................................................................. 777.4 Maximum Likelihood Combination ......................................................................................................... 77

7.4.1 Scope and Context of Interference Matrices .................................................................................... 777.4.1.1 Interference Matrix Context ........................................................................................................ 777.4.1.2 Interference Matrix Scope........................................................................................................... 797.4.1.3 Keeping the Scope and Context Up to Date ............................................................................... 80

7.4.2 Interference Matrix Combination in Atoll AFP Module...................................................................... 807.5 Interference Matrix Calculation .............................................................................................................. 81

8 Appendices ..................................................................................... 858.1 Appendix 1: Description of the AFP Cost Function ................................................................................ 85

8.1.1 Notations .......................................................................................................................................... 858.1.2 Cost Function ................................................................................................................................... 858.1.3 Cost Components............................................................................................................................. 87

8.1.3.1 Separation Violation Cost Component........................................................................................ 878.1.3.2 Interference Cost Component..................................................................................................... 88

8.1.4 I_DIV, F_DIV and Other Advanced Cost Parameters ...................................................................... 908.2 Appendix 2: Interferences ...................................................................................................................... 91

8.2.1 Using Interferences .......................................................................................................................... 918.2.2 Cumulative Density Function of C/I Levels....................................................................................... 918.2.3 Precise Definition ............................................................................................................................. 918.2.4 Precise Interference Distribution Strategy ........................................................................................ 92

8.2.4.1 Direct Availability of Precise Interference Distribution to the AFP .............................................. 928.2.4.2 Efficient Calculation and Storage of Interference Distribution .................................................... 928.2.4.3 Robustness of the IM.................................................................................................................. 92

8.2.5 Traffic Load and Interference Information Discrimination................................................................. 928.3 Appendix 3: BSIC Allocation .................................................................................................................. 94

8.3.1 Definitions......................................................................................................................................... 948.3.2 Hard Criterion ................................................................................................................................... 948.3.3 Soft Criterion .................................................................................................................................... 948.3.4 Behaviour ......................................................................................................................................... 94

8.4 Appendix 4: Traffic Capture and Dimensioning...................................................................................... 958.4.1 Introduction....................................................................................................................................... 958.4.2 Traffic Map Generation..................................................................................................................... 958.4.3 Traffic Capture Process.................................................................................................................... 95

8.4.3.1 Inputs .......................................................................................................................................... 958.4.3.2 The Engine ................................................................................................................................. 96

8.4.3.2.1 Traffic Distribution ................................................................................................................. 968.4.3.2.2 Average Timeslot Capacity ................................................................................................... 978.4.3.2.3 Integration ............................................................................................................................. 97

8.4.3.3 Outputs ....................................................................................................................................... 988.4.4 Network Dimensioning Process ....................................................................................................... 99

8.4.4.1 Inputs .......................................................................................................................................... 998.4.4.2 Dimensioning .............................................................................................................................. 998.4.4.3 Outputs ....................................................................................................................................... 99

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List of Figures

List of Figures

Figure 2.1: AFP Process in Atoll .................................................................................................................................. 19Figure 2.2: Interaction of the AFP with Other Elements............................................................................................... 19Figure 2.3: AFP Outputs .............................................................................................................................................. 20Figure 2.4: AFP Launch Wizard - AFP Session Tab.................................................................................................... 20Figure 2.5: AFP Launch Wizard - Separations Tab ..................................................................................................... 20Figure 2.6: AFP Launch Wizard - Global Parameters Tab .......................................................................................... 21Figure 2.7: Event Viewer - Sample Messages............................................................................................................. 21Figure 2.8: Message 1 ................................................................................................................................................. 22Figure 2.9: Message 2 ................................................................................................................................................. 22Figure 2.10: AFP Launch Window ................................................................................................................................. 23Figure 2.11: Partial Interference Matrices - Report........................................................................................................ 23Figure 2.12: Complete Interference Matrices - Report................................................................................................... 24Figure 2.13: AFP Progress Window............................................................................................................................... 25Figure 2.14: Event Viewer Message - Solution Kept ..................................................................................................... 25Figure 2.15: AFP Progress Window............................................................................................................................... 26Figure 2.16: Cost Distributions on Frequencies............................................................................................................. 27Figure 2.17: Frequency Usage Distributions.................................................................................................................. 27Figure 2.18: AFP Results Window ................................................................................................................................. 28Figure 2.19: Separation Constraint Violation Details Message...................................................................................... 28Figure 2.20: AFP Results Window - Partial Commit Feature......................................................................................... 29Figure 2.21: AFP Results Window - Partial Commit Feature......................................................................................... 30Figure 2.22: Constraint Violation Resolution Tool.......................................................................................................... 31Figure 2.23: Scanning for Frequencies.......................................................................................................................... 32Figure 2.24: Scanning for Frequencies.......................................................................................................................... 32Figure 3.1: Model Standard Deviation - Default Value................................................................................................. 35Figure 4.1: Automatic Neighbour Allocation................................................................................................................. 45Figure 4.2: Automatic Neighbour Allocation Results.................................................................................................... 46Figure 4.3: Neighbours Table ...................................................................................................................................... 46Figure 4.4: Dimensioning Process ............................................................................................................................... 47Figure 4.5: Atoll AFP Module Properties - Separation Weights Tab............................................................................ 49Figure 4.6: Atoll AFP Module Properties - Cost Tab.................................................................................................... 52Figure 4.7: C/I Weighting ............................................................................................................................................. 53Figure 4.8: Atoll AFP Module Properties - Separation Weights Tab............................................................................ 54Figure 5.1: Interference Study Report.......................................................................................................................... 57Figure 5.2: TRX Based Interference Studies ............................................................................................................... 58Figure 5.3: TRX Based Interference Study - C/I Distributions ..................................................................................... 59Figure 5.4: Event Viewer Messages ............................................................................................................................ 60Figure 5.5: Event Viewer Message 1 ........................................................................................................................... 60Figure 5.6: Event Viewer Message 2 ........................................................................................................................... 60Figure 5.7: Combinatin of Interference Effects ............................................................................................................ 61Figure 5.8: Counting Strong Interference Only Once................................................................................................... 61Figure 6.1: Hopping Sequence Numbers..................................................................................................................... 66Figure 7.1: Interference Matrix Properties Dialog - General Tab ................................................................................. 78Figure 7.2: Interference Matrix Properties Dialog - Advanced Tab.............................................................................. 78Figure 7.3: Interference Matrix Scope.......................................................................................................................... 79Figure 7.4: AFP Interference Matrices Parameters ..................................................................................................... 81Figure 8.1: Atoll AFP Module Properties - Advanced Tab ........................................................................................... 90Figure 8.2: The cumulative density of C/I levels between [TX1, BCCH] and [TX2, BCCH] ......................................... 91Figure 8.3: Traffic Maps Overlay.................................................................................................................................. 96Figure 8.4: Traffiic Overflow......................................................................................................................................... 97Figure 8.5: Intra-Layer Distribution .............................................................................................................................. 97Figure 8.6: Traffic Distribution in Atoll .......................................................................................................................... 98Figure 8.7: Network Dimensioning Process................................................................................................................. 99

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Chapter 1Overview


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AFP Reference Guide

Chapter 1: Overview

1 OverviewThis document describes every aspect of frequency planning in Atoll, from high level description of the frequency planningprocess to the practical level detail. Main topics covered in this document include AFP prerequisites, AFP usage, AFP mini-misation target and some possible problems that may come up during training.

This document begins with a basic user guide, a short operational introduction to the AFP process in Atoll, and goes onto summarize most aspects of the practical planning process with detailed discussions on certain topics. It also explainsthe means to evaluate a frequency plan available in Atoll. A chapter is dedicated to advanced topics and troubleshootingin the end.

Four appendices contain in-depth information on technical aspects of the cost function, the BSIC allocation algorithm, theIM calculation and the dimensioning process respectively. All in all, this document is almost self sufficient with respect tothe use of Atoll AFP.

1.1 Introduction to AFPThe main role of an Automatic Frequency Planner (AFP) is to assign frequencies (channels) to the network such that theoverall network quality is optimised. With the evolution of GSM over the years to integrate many improvements, additionalrequirements have emerged in the process of radio network planning. The implementation of baseband and synthesisedfrequency hopping, discontinous transmission and network synchronisation, for example, has led to higher sophisticationin the process of frequency planning. These enhancements require that an AFP also be intelligent and advanced enoughto help the frequency planner through out his tedious task.

The Atoll AFP considers a large number of constraints and directives; for example, ARFCN separation requirementsbetween transmitters, interference relations, HSN assignment methods, frequency domain constraints, a certain fractionalload to maintain etc. Hence, the AFP depends on a variety of input data, such as the interference matrix, neighbourhoodrelations, traffic information and so on.

This document not only explains how to use the Atoll AFP, by describing the AFP GUI, but also includes detailed descrip-tions of the various constraints, directives, and data sources. The primary target of this document is to explain the technicalbackground of the AFP.

1.1.1 Frequency Assignment as a Cost Minimization ProblemFrom the technical point of view, the Frequency Assignment Problem (FAP) is considered as a minimization problem. Thismeans that the AFP will generate a set of Frequency Plans (FPs), and propose the one that has the lowest cost as the“Best Solution”. Therefore, the AFP cost is the equivalent of AFP quality estimation: the lower the cost, the better shouldbe the quality from the AFP point of view.

The approach of cost minimization is not only the most common approach to the FAP but probably also the easiest tounderstand and control. It provides the user with means of guiding the AFP in its task. For example, by setting the cost ofinterference violation low, the AFP will concentrate its efforts on resolving the separation violations.

There are AFP tools in which certain types of objectives are presented as “hard constraints”. If a hard constraint is notsatisfied, the AFP does not offer any solution or offers a partial solution (with fewer frequencies and satisfying hardconstraints). The philosophy of hard constraints vs. soft constraints has nothing to do with the quality of an AFP engine, itis merely a behaviour convention. In Atoll, we prefer always offering a solution to offering partial assignments or violatingdomain limitations. This ensures that you will always get a result when you launch the Atoll AFP. This result will very welldepict the difficulty of the FAP. The cost of this solution will clearly indicate if unacceptable violations have occurred or ifthis plan has improved the current frequency plan.

The cost function definition permits you to place as much emphasis as required on certain elements of the cost function.This manipulation will make the AFP behave as if it were guided by hard constraints, from the optimisation viewpoint, whileretaining its property of being a quality monitor and a hardness-of-assignment monitor both.

1.1.2 AbbreviationsSome abbreviations and terminologies used in the document are listed below:

GSM Global System for Mobile Communications (Groupe Speciale Mobile)

GPRS General Packet Radio Service

EDGE Enhanced Data rates for GSM (or Global) Evolution

EGPRS EDGE based GPRS

TSL Timeslot

TX Transmitter or sector

TRX Transceiver

BCCHBroadcast Control CHannel. A term usually employed in Atoll to refer to the TRX carrying this channel.

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AFP Reference Guide

1.2 ArchitectureThe Atoll Automatic Frequency Planning (AFP) module is an optional module that enables you to generate frequency plansfor GSM and TDMA networks automatically. The Atoll AFP module can allocate the following parameters:

• Frequencies• Frequency hopping groups (MAL)• HSN, MAIO• BSIC (TSC planning)

TCHTraffic CHannel. A term usually employed in Atoll to refer to a TRX carrying traffic with usually the same coverage area as the BCCH.

TCH_INNERInner Traffic CHannel. A term usually employed in Atoll to refer to a TRX carrying traffic but usually having a coverage area less than that of a TCH.

HR/FR Half Rate/Full Rate

CS Circuit-switched

PS Packet-switched

HCS Hierarchical Cell Structure

Subcell An entity defined by the pair [TX, TRX Type]

HO Handover

kbps Kilobits per second

GoS Grade of Service

QoS Quality of Service

KPI Key Performance Indicators

TL Traffic Load

P Probability

C Carrier power (Signal strength)

C/I Carrier to Interference ratio

AFP Automatic Frequency Planner/Planning

DTX Discontinuous transmission

GUI Graphical User Interface

FP Frequency Plan

BBH Baseband Hopping

SFH Synthesized Hopping

NH No Hopping

MALMobile Allocation List. In the context of SFH, MAL is the group of frequencies used by the frequency hopping TRX.

AMR Adaptive Multi-Rate

CC Concentric Cells

Transmitter Atoll synonym for cell or sector in conventional GSM jargon

FER Frame Erasure Rate

FH Frequency Hopping

DLPC Down Link Power Control

RRM Radio Resource Management

Synchronised transmitters

Transmitters that are synchronised and can, therefore, share the same HSN.

Data ModelA project can be saved in a filename.ATL file or as a database. In both cases, most of the project’s information is saved in database tables. We refer to these tables as the data model.

IM, IMco, IMadj Interference Matrix, Co-channel / Adjacent-channel Interference Matrix

FN Frame Number

CDF Cumulative Density Function

TSC Training Sequence Code

FAP Frequency Assignment Problem

# Number of

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Chapter 1: Overview

• TRX rank (can be used to prioritise the use of good frequencies)• Performance Indicators at Site/Cell/TRX levels

Atoll works with an open AFP interface. Any AFP built using this interface can be able to allocate the following additionalparameters. Future versions of the Atoll AFP module are planned to assign the following parameters as well:

• Group ID (better administration of the frequency resources)• TN offsets• FN offsets

Atoll AFP implements simulated annealing, taboo search, graph heuristics and machine learning. It manages its timeresources to match the users time directive. If allowed enough time, the AFP will employ a major part of this time in “learn-ing” the network. During the learning phase, the AFP tunes up its internal parameters. Towards the end of the user-definedtime, the AFP switches to a randomised combinatorial search phase.

Network learning is performed by executing numerous fast and deterministic instances of the AFP. The one that obtainsthe best performance is memorized in the document and is, therefore, the most suitable for the specific network. The nexttime an AFP is executed it will start where the learning process ended and it will use the parameter profile of the best solu-tion stored in the document.

The Atoll AFP is built based on a specified COM interface designed as a part of Atoll’s open platform strategy. The interfaceis designed in such a way that puts aside elements that are not inherent to the AFP process. At the same time, throughthe modelling capabilities of the planning tool, the AFP can support complete list of features expected from an AFP.

Remark:The role of this learning phase is extremely important in order to get good results. You should often let the AFP run over a night or a weekend by specifying corresponding target time. If you never run the AFP specifying a long time period, it will never be able to calibrate itself and will always perform from 10 to 70 solutions and stop.

Note:

• The following scenario will demonstrate the usefulness of AFP learning capabilities:

- Create a GSM GPRS EGPRS project and import its network elements and maps.

- Create a copy of “Atoll AFP module” and name it “Atoll AFP module 2”.

- If the network has X transmitters, run “Atoll AFP module 2” for X / 10 minutes to obtain acost Y. (Short execution)

- Now run “Atoll AFP module 2” for a longer time (for example, X / 5 hours).

- Another cost, Z, is obtained, which is better than Y (i.e. Z < Y). The network dependentinformation is memorized in the “Atoll AFP module 2” instance whereas the “Atoll AFPmodule” instance remains unchanged.

- Now if you perform a short execution with “Atoll AFP module 2”, you can get the improvedresult (Z) right away. While a short execution of the “Atoll AFP module” instance will givethe initial cost (Y).

- If X / 5 hours is too long, you can perform the “learning” on a small (representative) part ofthe network.

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Basic AFP Tutorial

Chapter 2


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AFP Reference Guide

Chapter 2: Basic AFP Tutorial

2 Basic AFP TutorialAtoll AFP framework complies with its global open architecture strategy. Any AFP module, Atoll AFP or 3rd party AFP, canbe interfaced and made available to RF planning engineers through Atoll. Furthermore, different AFP modules are acti-vated, accept their main inputs and generate their main outputs in the same manner. This section teaches the basics ofactivating an AFP in Atoll.

2.1 AFP Process in AtollThe AFP process is a cycle in which the AFP is only one of its many steps:

The figure below gives a better view of interaction of the AFP with other elements in Atoll:

The following figure depicts the outputs of the AFP:

Figure 2.1: AFP Process in Atoll

Figure 2.2: Interaction of the AFP with Other Elements

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AFP Reference Guide

2.2 Loading and Validating the NetworkTo launch the AFP, choose the Automatic Allocation… command from the Frequency Plan menu of the Transmittersfolder context menu. This initiates a series of dialogs called the AFP wizard.

Figure 2.3: AFP Outputs

Figure 2.4: AFP Launch Wizard - AFP Session Tab

Figure 2.5: AFP Launch Wizard - Separations Tab

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Here you can,

• Specify the AFP module you would like to use and set its parameters,• Choose the network parameters and AFP performance indicators you want the AFP to allocate,• Specify the network’s default separation requirements,• Consult the network’s “Exceptional Pairs” and define other separation constraints for them, and• Indicate whether interferences are to be included in calculations or not.

For explanations of AFP performance indicators, refer to "AFP Performance Indicators" on page 38. The last wizard dialogcontains some global parameters that often vary from one AFP instance to another:

The most important option here is the one proposing the two sources of the traffic load information. Traffic load can beread directly from the subcells table, which could have been filled manually, by the dimensioning process or by a KPI calcu-lation. You can also specify that the traffic load should be read from the default traffic capture (explained later).

Clicking Validate will start the data verification and storage optimisation aimed at providing fast access to data needed bythe AFP. This stage may generate many warnings for real-life networks (for example, values out of range). These aredisplayed in the Event viewer. It is recommended to revise the network data according to these messages and continueonce all the data are clean and coherent. If a certain message is not clear or self evident, you can always contact Forsk’stechnical support. The figure below depicts the Event viewer with some sample messages:

Let us look at two of these messages:

Figure 2.6: AFP Launch Wizard - Global Parameters Tab

Notes:

• In case the traffic load is taken from the Subcells table, committed after a KPI calculation,you must be aware of a certain difference: in the KPI calculation, Atoll divides the capturedtraffic by the timeslot capacity of the existing number of TRXs, while the AFP requires it tobe divided by the timeslot capacity of the required number of TRXs.

• The traffic load is artificially increased to 0.1, if it is too low (less than 0.1), in order tomaintain the AFP robust against partial data conditions. Hence, the AFP cannot completelyignore the existence of a frequency in a TRX.

Figure 2.7: Event Viewer - Sample Messages

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AFP Reference Guide

This means that the value entered in the AFP weight column of the Transmitters table for the transmitter 19941 is invalid.In the database, this field’s name is “COST_FACTOR”. A value of –2 for the cost factor implies that the AFP should gener-ate the worst assignment possible for the transmitter. It would be interesting to investigate the origin of this erroneous valueas it may avoid possible errors in the future. Atoll automatically resets this value to 1 in order to avoid such calculationerrors.

This message informs that 3678 subcells were loaded successfully. The next section explains the significance of the term‘effectively selected’ and why 3678 subcells were loaded and only 6 selected for the AFP process.

2.3 Definition of the AFP ScopeIn the example above, the 6 subcells effectively selected for the AFP process had many potential interferers, neighbours,neighbours of neighbours, and/or transmitters with exceptional separation constraints with them. No AFP can perform agood allocation for these 6 subcells without “dragging in” a large part of the network. The AFP considers the part that is“dragged in” to be “frozen”. On the other hand, there are many other ways to freeze network elements in Atoll. Someprecise definitions are provided in order to avoid misconceptions.

Let us define 4 groups of transmitters (ALL, NET, SEL, RING):

• ALL = All the transmitters in the project.• NET = Active transmitters that pass the filters on the main Transmitters folder and on the main Sites folder.• SEL = Transmitters belonging to the (sub)folder for which the AFP was launched and that are located inside the

focus zone.• RING = Transmitters belonging to NET, not belonging to SEL and having some relationship with the transmitters

in SEL:- If interferences are to be taken into account (see the dialog above), all transmitters whose calculation radii

intersect the calculation radius of any transmitter in SEL will be included in RING. For large calculation radii(20 km for example), a single site can have a very large RING loaded.

- Neighbours are always included in RING.- If one transmitter of an Exceptional Pair is included in SEL and the other is not, then the other will be included

in RING as well.- If BSIC assignment is required, then all the second order neighbours (neighbours of a neighbour) will be

included in RING as well.

Both the RING and the SEL parts of the network are loaded. It is important to know which subcells are loaded as the costis calculated for all loaded subcells. The RING part is frozen for all assignments (BSIC, HSN, MAL, MAIO and channels).The SEL part may be assigned some parameters but only the ones specified in the dialog above. For example, if the userdid not select BSIC, it will not be assigned.

In addition to the generic freezing options above, there are some finer freezing options available in the data structure:

1. Individual transmitters can be frozen for channel (and MAL), HSN and/or BSIC assignment.2. Individual TRX’s can be frozen for channel (and MAL) assignment.

In an Atoll project, it is strongly recommended to avoid TRX’s without channels. For this reason, never create transmittersautomatically if there are no channels to assign to them. Therefore, if the user does not ask for MAL/MAIO assignment, allSFH subcells are considered frozen and no TRX will be created for them. The same occurs when only a MAL/MAIOassignment is requested. In this case, all NH and BBH subcells will be considered frozen and no TRXs will be created.

Figure 2.8: Message 1

Figure 2.9: Message 2

Note:

• See Developer Reference Guide for details on the TO_ASSIGN and FROZEN assignmentstates available in the AFP API.

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2.4 Preparing to Launch the AFPOnce the network is loaded and all warnings resolved, the AFP launch dialog will appear. This dialog contains a shortsummary of the state of the loaded network, SEL + RING.

Interference matrices can be managed through the Interference Matrices folder. You can have more than one interferencematrices in your document. The top most active interference matrices set is used by the AFP. You can either embed theinterference matrices in the document or store them in external files. Atoll compresses the interference matrices if storedin the .atl document itself. It is not necessary to load IMs or look for them each time AFP is launched. You can view thereports on different interference matrices available in the Interference Matrices folder. This report has a summary sectionwhich indicates the current state of the IMs.

Figure 2.10: AFP Launch Window

Example 1: When partial IM info exists, we can see that 9 transmitters out of 24 do not have any interferers.

Figure 2.11: Partial Interference Matrices - Report

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AFP Reference Guide

The AFP launch dialog also lets you define a generator initilialisation number. This number serves as a directive ofrandomness for the AFP process being launched. If the generator initialisation is set to 0, the AFP will be fully random. Aninteger other than 0 will define a given deterministic sequence for the AFP process. Each generator initialisation number(other than 0) corresponds to a deterministic sequence. Therefore, each AFP instance launched with the same generatorinitialisation number will yeild the same results.

You can use this option if you want to have the same set of solutions every time you launch the AFP for the same part ofthe same network.

The Atoll AFP has a single algorithm with a number of steps. The AFP ignores some of these steps if the alloted targetcalculation time is too short. One of these steps is deterministic, i.e. independent of the generator initialisation number,while the other steps are initialized by this number.

• Generator Initialisation = 0 (default value) signifies that this intialisation number will be calculated randomly.

• Generator Initialisation 0 means that the number will be the one set by the user. Every time you define the same

number, the AFP algorithm will be initialised in the same way, and hence the set of solutions will be the same.

It is advised to set Generator Initialisation = 0, and let the AFP reach the end of the Target Computation Time defined.

However, you must keep in mind that all the AFP computations are deterministic in the start, independent of the generatorinitialisation. The AFP must be allowed to compute during the target time to observe the effects of randomness.

Example 2: When complete IM info exists, observe that the IM topology is more or less normal.

Figure 2.12: Complete Interference Matrices - Report

Notes:

• Since the method chosen by the AFP depends on the target time provided, you might notget the same results using the same generator initialisation number if the defined targettimes are different. Therefore, to actually get the exact same results from the AFP process,you must define a certain target time and a certain generator initialisation.

• The AFP may be perfectly deterministic during a portion of the target computation time (5 -15%). During this period, the randomness seed will have no effect on the solutions. If youwant to see the effect of randomness, let the AFP calculate until the end of the target time,or set a shorter target time.

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2.5 Launching the AFP and Monitoring its ProgressProvide a time quota and a generator initialisation number in the above dialog and launch the AFP by clicking Run. It isimportant to set a long time quota from time to time to allow the AFP to calibrate itself. If not stopped, the AFP will usuallycontinue for a while before stopping by itself.

The window below opens when the AFP is started, and displays information about the AFP process:

The Progress section of this window in the top left displays the target time allocated to the AFP, the time elapsed and thenumber of AFP solutions that have been evaluated so far.

The general information and interference matrices report section in the top right gives some general information about thecurrent solution in real time. This display depends on the selected AFP module. This section lists the status of the currentsolution, the initial cost, the cost of the current best solution, the cost of the previous solution and whether the previoussolution was kept or rejected. You can use the >> button to switch to the report on the currently used interference matrices.

The Event viewer has been made accessible through the AFP progress dialog in order to help the user keep track of allthe important warnings and messages generated before and during the AFP process. This also enables you to exportthese messages as an AFP log file.

If a solution is kept, a corresponding message appears in the Event viewer. Double-clicking the message in the Eventviewer will open a dialog with the full details of this message, which will look something like the following figure.

After the AFP is allowed to compute solutions and try to optimise the network for a while, the AFP progress dialog wouldlook somewhat like this:

Important:

• If only a short time is specified, the full optimisation potential of the AFP will not be utilised.

Figure 2.13: AFP Progress Window

Figure 2.14: Event Viewer Message - Solution Kept

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AFP Reference Guide

The Best Frequency Plan Costs section displays the current values of modifiable and total costs, and their respective sepa-ration components. This section also displays the total weighted Erlangs of the network concerned in the AFP process,i.e. the total cost of a 100% interfered frequency plan). It gives a general idea of how good the cost of a certain frequencyplan is. The cost of any solution remains between 0 and the Network Weighted Erlangs. The cost is as better as it is closerto 0.

Apart from the above information, this section also contains a table listing the initial frequency plan and all the AFP solu-tions kept so far sorted in ascending order of cost. This table can display:

• Modifiable costs• Total costs• Frozen costs• Summed components• Main components (separation violation cost component, interference component and modified TRX component)• Additional taxes (corrupted, missing or out of domain TRXs)

For detailed description of modifiable and non-modifiable parts of the total cost, please refer to "Modifiable and Non-Modi-fiable Costs" on page 51.

Using the buttons available in the Plan comparison section in the bottom right, it is possible to visually compare the initialfrequency plan and the current best solution (with the Best Plan column in the AFP cost details table checked). Clickingthese buttons opens dialogs containing graphs corresponding to ’Cost Distribution on Frequencies’ and ’Usage Distribu-tion on Frequencies’.

The cost of a frequency f is given as:

Where, FL(i) is the fractional load of frequency f in the MAL of i, and cost(i) is the AFP cost of TRX i in Erlangs.

Figure 2.15: AFP Progress Window

Cost f FL i Cost i i TRXs using f

=

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You can pause or stop the AFP process any time to check the current best solution, and resume optimising the networkafter you have checked it. Pausing the AFP process opens the AFP results window with the current best solution resultslisted.

2.6 AFP OutputsWhen calculations stop (completed or paused to view the current situation), Atoll displays the frequency plan proposed bythe AFP. All results/violations are listed in a dialog window. This window contains a table listing all the assigned resources.Transmitters located within the Focus zone are listed in the results dialogue. If a Focus zone is not available, the resultsare displayed for all the transmitters within the Computation zone. These resources and related items (transmitters,subcells) are coloured differently to indicate different reasons:

• Arctic blue: frozen resource• Red: resource modified compared to the previous allocation but with separation violation• Green: resource modified compared to the previous allocation respecting the separation constraints• Black: resource not modified• Blue: resource assigned with no separation violation• Purple: resource assigned but with separation violation• Grey: items and resources involved in computation but not available for allocation

Positioning the cursor over a resource in the table displays the reason for its colour in a tool tip.

The AFP result dialog is a non-blocking dialog. It enables the user to access other Atoll windows while the AFP is still pend-ing. Thus, it is possible to view other data or warning/error messages in the Event viewer (for example, the history of AFPsolutions). From this stage, it is possible to commit, to resume or to quit the AFP. It is good practice to keep a report throughthe export option before resuming the AFP. The user can also partially commit some of the results as explained in the nextsection.

The results window displays all the results of the AFP session. It is possible to only display some of the results by checking/un-checking the relevant choices in the Display options menu. You can choose to display the results related to:

• Cells (BSICs)• Subcells (HSNs)• TRXs (Channels/MAL, MAIO) and related separation violations

Selected AFP performance indicators (AFP TRX ranks, and total and separation costs at TRX, subcell, transmitter andsite levels) will also be available in the results window. These AFP performance indicators are also available to export.You can choose whether to display the AFP indicators in the results as separate columns. The Show AFP Indicatorscommand in the Display options menu controls the display of AFP TRX ranks, and total costs and separation cost compo-nents at TRX, subcell, transmitter, and site levels.

Figure 2.16: Cost Distributions on Frequencies

Figure 2.17: Frequency Usage Distributions

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As the network had been loaded according to both the items to assign and the ones they relate to, it is possible to displaythe frequency plan of either:

• Items belonging to the selected transmitters (see the definition of SEL), or• Items belonging to the loaded transmitters (see the definition of SEL + RING). In the preceding example, there

were no transmitters in the RING set, so the option is not available.

It is also possible to display detailed information about separation constraint violations, i.e. the co-channel and adjacentchannel collision probabilities for relevant TRXs. You can choose to display these separation constraint violations throughthe Display options menu.

The Separation violations column lists each each type of separation constraint violation realted to a given TRX, i.e. excep-tional pair, co-transmitter, co-site, or neighbour. Another column titled ’With the TRX’ contains a button for each type ofseparation constraint violation. This caption of this button shows the TRX with which the separation constraint violationoccurs. Clicking this button takes you to the corresponding TRX row in the table. Right-clicking a row with a separationconstraint violation opens a Separation Constraint Violations context menu, which opens a dialog mentioning the reasonof violation when clicked. For example:

Use the Commit button to assign the allocated resources and AFP performance indicators. The resume button permitsresuming the AFP optimisation from where it stopped the last time.

Figure 2.18: AFP Results Window

Figure 2.19: Separation Constraint Violation Details Message

Note:

• At the bottom of the AFP results window, messages related to the last solution aredisplayed, which may list problems as well.

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2.6.1 Partial Commit FunctionalityIt is often required to commit only a part of the automatically generated frequency plan rather than committing it entirely.The purpose is to avoid committing TRXs that violate separation constraints (sometimes referred to as “not closing thefrequency plan”). Future Atoll versions will incorporate advanced automatic filters for partial commit.

The dialog examples below depict a case where removing a TRX eliminates a separation constraint violation on neigh-bours. Once a TRX is manually removed from the resulting plan, separation violations are recalculated (may take a fewseconds). If the TCH TRX of transmitter Site36_3, causing neighbour separation constraint violations, is removed from thesample frequency plan below, the resulting frequency plan has no neighbour separation constraint violations on the TCHTRX of transmitter Site36_1.

It is possible to specify the action to be taken with each TRX individually, or globally delete all TRXs with separation viola-tions. It is also possible to mix the old plan and the new plan. Though this is not recommended, since it can cause inter-ferences of which the user might be unaware. The dialog examples below depict how this operation can be carried out.

The Delete the TRX option implies that the resulting frequency plan will not respect the number of required TRXs. In theabove example, note than the neighbour separation constraint violations at transmitter Site36_1 vanished once the TCHTRX at Site36_31 was deleted.

Figure 2.20: AFP Results Window - Partial Commit Feature

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AFP Reference Guide

2.6.2 Automatic Constraint Violation ResolutionDifferent types of constraint violations, i.e. co-transmitter, co-site, neighbour, and exceptional pair, can automatically beeliminated from the propsed frequency plan using the Automatic Constraint Violation Resolution tool. This tool is accessi-ble from the Actions button menu.

The aim of this tool is to find the TRXs in the currently proposed frequency plan that cause constraint violations of any ofthe four following types:

1. Co-transmitter2. Co-site3. Neighbour4. Exceptional pair

Once it finds the TRXs that satisfy the criteria, it sets their corresponding values to Delete the TRX in the Channel Assign-ment column of the AFP results window.

This tool lets you resolve any type of constraint violations for different types of TRXs, control or traffic. You can also definea threshold of co-channel and adjacent channel collision probabilities. This restriction will only set those TRXs to Deletethe TRX, which have a co-channel or adjacent channel collision probability higher than the threshold you defined.

Figure 2.21: AFP Results Window - Partial Commit Feature

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2.7 Visualising and Manipulating ResultsThe Commit button copies the frequency plan to the data structure. It is not necessary to save the document or committhe changes to the database right away as the AFP cycle has not yet ended. At this stage, various generic and specifictools are available in Atoll, and can be used to inspect the candidate frequency plan. Interference and C/I prediction studiesand various consistency checks are described in the following chapters of document. In addition to these, a useful tool isalso available in Atoll, called the Search tool. Its function is to facilitate visualising co-channel and adjacent-channel trans-mitters. This tool is explained in detail in the User Manual. Other means of inspection include the common grouping, filter-ing, advanced filtering, display and tool tip management features.

2.8 Manual Frequency AllocationThis section describes quick and useful techniques for performing manual frequency allocations in Atoll.

2.8.1 Manual Frequency Allocation for SFH CaseIt is possible to perform frequency allocations for irrgular pattern networks, i.e. patten allocation of type 1/N. The followingset of operations will results in a frequency allocation even if the network is not a 100% regular pattern network.

1. Run the AFP so that it creates the required number of TRXs.2. Group the transmitters by azimuth and manually assign the MALs to the most important azimuth groups.3. Filter out these azimuth groups and delete the TRXs of all transmitters that were not assigned a MAL manually.4. Run the AFP again selecting MAIO assignment only. This will assign proper MAIOs to the TRXs to which MAL

was manually assigned.5. Remove the filter and freeze the existing TRXs. Now use the AFP to complete the assignment (assigning all

resources).

2.8.2 Manual Frequency Allocation for NH Case To carry out manual frequency assignment:

1. Create a Best Server map and display it,2. Display neighbours of the transmitter for which you want to find a frequency manually,3. Open the Search tool,4. By scanning the spectrum a good frequency can easily be found and can be allocated to the transmitter.

Figure 2.22: Constraint Violation Resolution Tool

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AFP Reference Guide

In this example, frequency 11 is not a good choice since it is used as a neighbour co channel. Frequencies 10 and 12present similar characteristics.

On the other hand, frequency 14 is a good one and can be possibly allocated. None of the frequencies {13, 14, 15} areallocated at the selected transmitter of at its neighbours.

Figure 2.23: Scanning for Frequencies

Figure 2.24: Scanning for Frequencies

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Frequency Planning Prerequisites

Chapter 3


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Chapter 3: Frequency Planning Prerequisites

3 Frequency Planning PrerequisitesThe principal difference between AFP and other planning activities is that the impacts of poor frequency planning are morewidespread in a network. For example, poor planning of a site or a cell will have somewhat local influences, while imple-menting a poor frequency plan will affect a much larger part of the network. Moreover, creating a poor frequency plan israther relatively easy, the presence of a single faulty parameter in the process can be sufficient for the damage the entireplan.

Therefore, it is mandatory that the AFP user acquires a minimum level of knowledge regarding Atoll data model. This chap-ter familiarises the user with the essentials of the data model and depicts their relations with the AFP.

3.1 Atoll Data Model

3.1.1 Reliability and PropagationOften the user senses that the AFP does not have enough constraints:

• The unfrozen part of the AFP cost is 0 and the AFP stops due to this fact.• There appear to be close frequency reuses in the resulting frequency plan.

This means that the problem is too “easy” for the AFP and the user would like to create a more difficult IM in order for theAFP to have a more difficult problem to solve.

The best method to accomplish this is to increase the cell edge reliability and recalculate the IMs. When the reliabilityrequirement is elevated, a larger part of the standard deviation is reduced from “C” when calculating the C/I for each IMentry.

The user should also verify that the standard deviation is properly defined in all clutter classes and its default value. Thisverification is more important in the case of Atoll documents converted from older versions or connected to a database.

3.1.2 HCS LayersHCS layers have several roles in Atoll. Their most important role is related to the way Atoll manages traffic maps. Differentlayers have different priorities and mobility limitations. There is also the possibility to manage traffic overflow from one layerto another. The objective of all these options is to model the behaviour of a real network, where two potential servers thatdo not belong to the same layer usually do not compete for best server.

When calculating an IM, or when generating an interference study, HCS layers are used in generating service zone maps,the basis of these calculations. If two transmitters belong to different layers, they can both serve the same pixel even ifreceived signal from one is much stronger than the other’s. For equal HO margins, more HSC layers mean higher over-lapping levels in the network. As the overlapping level increases, the constraint level in the IM and the amount of interfer-ence in an interference study also increase.

Figure 3.1: Model Standard Deviation - Default Value

Note:

• Be sure to study the priority mechanism in your network, both in the re-selection processand in the handover process. Define the corresponding HCS layers once you know itsworking. When using a traffic model, make sure that there are a few levels of mobility inorder to model high speed / low speed mobility behaviours.

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3.1.3 SubcellsSubcells are defined as a group of TRXs in the same transmitter. Two subcells of the same transmitter can requestfrequencies from different domains, require different C/I qualities, have different downlink power offsets and even havedifferent Radio Resource Managements (RRM). Different RRMs can lead to different service zones under the same cell.Subcells are crucial for modelling concentric and dual band transmitters. In these cases, the TRXs belonging to the “inner”subcell serve traffic within a limited zone.

3.1.3.1 Key Roles of Subcells• Associating TRX groups with required quality definitions• Associating TRX groups with weak / strong constraints (interference , separation)• Associating TRX groups with different domain limitations• Visualising and filtering by TRX Type• The following additional parameters are also defined in the Subcells table:

- HSN (since the inner zone HSN may be different from the outer zone HSN)- Power offset- Reception threshold (can limit the zone of the inner subcell)- Hopping mode- Assignment mode (in SFH, “group constrained mode” limits the choice of MAL to one of the groups in the

domain)- Support of DTX- Traffic load and supplementary AFP weight- Some other parameters influencing the AFP indirectly (for example, the overflow rate)

3.1.3.2 Concentric Cells and Dual-band CellsConcentric cells were created in order to exploit downlink power control (DLPC) and radio resource management (RRM)in frequency planning. This is accomplished by associating channels with subcells. Subcells may have different servicezones with respect to the transmitter’s geographic coverage. For example, a subcell TCH_INNER covers a zone requiringminimum reception level of –75 dBm and TCH_OUTER covers a zone with minimum reception level of –94 dBm. In thiscase, the inner zone has a higher resistance to increasing interference. The AFP has the possibility ot assign a relativelyinterfered frequency to the TCH_INNER zone to give more choice to the outer zone.

The other important property of concentric cells is the fact that a downlink power offset is associated with each subcell.The inner subcells can have higher DLPC implying that the frequencies assigned to the inner zones will interfere less withother transmitters. Concentric cells permit a higher reuse pattern between inner zones, providing up to 40% increase incapacity.

Atoll can fully exploit this increase in capacity since it calculates interferences between subcells. It uses the power offsetand the C/I threshold that defines the subcell boundaries. Furthermore, it is also possible to define separation constraintsat subcell level.

3.1.3.3 Minimum C/IThe required quality thresholds for BCCH and TCH are usually 12 and 9 dB respectively. But, since the GSM standardtests this behaviour under the comfortable reception conditions of 20 dB above thermal noise, it does not reflect the behav-iour for, for example, received signals being only 15 dB above thermal noise.

Atoll provides the possibility to define these thresholds at subcell level allowing maximum flexibility and possibility tosupport a mixture of old and new equipment. Moreover, the safety margins corresponding to these values can be definedin the AFP cost definition. Refer to "Quality Target and C/I Weighting" on page 53 for more information.

3.1.3.3.1 Quality TargetsVarious quality targets can be set in Atoll by defining a C/I threshold value “min C/I”, with a probability threshold “% maxinterference”. These two values combined together define a quality target which implies that in order to have acceptablequality, the probability of having C/I lower than the “min C/I” value must be less than “% max interference”.

This method enables Atoll to exploit the fact that a larger number of TCH channels can be assigned with quality require-ments lower than the BCCH quality. This results in less constraining interferences and an easier and faster assignment.Refer to "Quality Target and C/I Weighting" on page 53 for more information.

3.1.3.4 Traffic LoadsTraffic loads of all the subcells are used as input to the AFP. These traffic loads can be calculated by Atoll (default trafficcapture) or imported from another source to the Subcells table. Atoll calculates the traffic loads as values from 0 to 1.However, the AFP can work with traffic load values from 0 to 1000. If the values imported to the Subcells table from anyother source than Atoll are less than 0 or greater than 1000, the AFP returns an error message and stops. If the importedvalues are from 0 to 1000, they are converted to values from 0.1 to 1 using the following equation:

Note:

• All TRXs in a subcell share the same TRX type.

VNew 0.11.8

-------- 3 VOld 2 VOld2+ tan+=

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3.1.3.5 Local Domain RestrictionsLow level domain restrictions can be introduced at subcell level through the excluded channels column in the Subcellstable.

3.1.4 TRXsAtoll’s TRX table enables the following:

• Support of an external ID space of the TRXs of a transmitter (important for import and export utilities).• MAL / channel at TRX level.• MAIO at TRX level.• Fine freezing: The user can freeze specific TRXs in an unfrozen transmitter.

The TRX table does not contain an “active” field. Therefore, all TRXs in it should contain a valid frequency or MAL and areall considered to be on air. It is better to remove an entire TRX record than removing only the frequency or MAL from itschannels list.

3.1.5 Freezing FlagsA multilevel freezing mechanism enables freezing resources at TRX level as well as at transmitter level. This, in turn,enables the user to use an existing plan while assigning only newly added demand for channels. These options are inaddition to the working zone limitations.

3.1.6 AFP WeightsThe AFP weight field in the Transmitters table enables the user to assign high or low weightings to certain transmitters. Itcan be used to improve quality at a problematic location or to boost quality in a particular covered region of the network.An additional AFP weight field exists at the subcell level. It enables the user to assign weighting to subcells. A conventionalidea could be to assign a higher weight to the BCCH. The AFP uses the multiplicative product of transmitter level AFPweight and subcell level AFP weight.

3.1.7 Spectrum AdministrationMany levels of administration exist relative to frequency planning. In order to avoid confusion, here is a comprehensive list:

• ARFCNs

ARFCN is the method employed by the GSM/DCS standards to enumerate 200 kHz frequency carriers.

• Frequency Bands

Frequency Bands are subgroups of ARFCNs. Different equipment may be limited to different frequency bands(BTS, MS, …). In addition, propagation models use the central frequency of the band for calculating propagation.

• Frequency Domains

Domains are used for managing the usage of the Frequency Bands. For example, an operator may use frequen-cies 1 to 50 while the other uses 52 to 100. Splitting the band on channel usage basis is of great importance aswell (BCCH frequencies, TCH frequencies, Hopping layer).

• Domain Groups

Domain groups are used for further managing the use of the frequencies in a domain. For example, f1 and f2 canbe assigned at the same transmitter if and only if they belong to the same group. Another frequent use for groupsis in the MAL assignment.

In Atoll, a domain is defined as a union of groups. It points to a frequency band and must be included therein. The AFPrespects domain limitations at subcell level.

3.1.8 Redundancy and Subcell AuditAtoll incorporates some deliberate redundancies between the subcells and TRX levels, and the Transmitters table:

• The channel list in the Transmitters table is the intersection of all channels appearing in the TRXs of a transmitter.• The hopping mode of a transmitter is the hopping mode of it’s default traffic carrier (the TCH TRX Type)• The frequency band of the transmitter (the one used by the propagation model to deduce the central frequency),

is read from the domain of the BCCH subcell of the transmitter.

Atoll considers the low level to be the accurate source of information. For example:

• Atoll will automatically update the TRX table if the channel list of a transmitter in the transmitter table is changed.• The frequency band of a transmitter cannot be edited.

Note:

• When freezing channels, keep in mind that the MAIOs are not frozen.

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These redundancies provide some additional features (for example, grouping transmitters according to the frequencybands).

On the other hand, there is a chance of mistakes and bugs which may damage a redundancy in the ATL file. Therefore, itis recommended that the audit tool be used from time to time in order to fix these problems (right click the Transmittersfolder, choose Audit from the Subcells menu).

3.1.9 Neighbour ImportanceNeighbour importance field exists in the neighbour relation tables. It is also available in the AFP and can assist in resolvingcongestion situations. This is discussed in detail in subsequent chapters.

3.1.10 SeparationConstraints TableIt is a separation exceptional-pair table containing pairs of subcells with associated separation requirements. Special sepa-rations have a higher priority with respect to all other separations and can be used to relax separation constraints as well.

3.1.11 SeparationRules Table and Rule PriorityThe SeparationRules table is simple to understand once the order of priority that exists between various separation rulesis kept in mind:

1. Highest priority: exceptional pairs

2. Second higher: co-transmitter

3. Third priority: co-site

4. Last priority: Neighbour.

For example, if two subcells are neighbours and at the same site, their associated separation requirement will be accordingto the co-site separation rules. And, if this separation requirement is not fulfilled, their separation violation costs will beweighted by the co-site weight.

Separation rules depend on equipment, and refer to the non-hopping configuration. Separation rules are "administrationrules" that are set once according to the equipment and are not meant to be modified during routine operations. Separationrules do not depend on whether SFH is available in the network or not. Atoll and the AFP consider SFH independent ofthe separation rules. If you relax the separation constraints, and have SFH TRXs, this means that you are asking the AFPand Atoll to take into account the effect of SFH twice.

3.1.12 Adjacency SuppressionAdjacency suppression is defined as the difference between the required C/I and the required C/A (C/A being the “Carrierto Adjacent Intensity ratio”). By default this is set to 18 dB following the standard. It is available in the Predictions folderproperties dialog window under the name “Adjacent channel protection level”.

The GSM standard requires this desired behaviour but does not specify any amplification level. It is recommended to besure that the physical equipment in the network support this value. The value of this parameter is used in the AFP whenextracting the interference caused by an adjacent channel, and in Atoll in interference and C/I studies.

It might be a good idea to use a safety margin for this parameter and set it to 16 dB, for example.

3.2 AFP Performance IndicatorsThe AFP can be used to generate different AFP performance indicators and listing them in the AFP results window. Theseperformance indicators describe the states of different network entities, such as TRXs, subcells, transmitters and sites.

3.2.1 AFP TRX RankAFP TRX Rank provides a ranking of the TRXs in a subcell. If a TRX rank is high, it implies that the frequency (channel)corresponding to this TRX has bad usage conditions. TRX ranks indicate the best and worst quality TRXs in each subcell,which maybe candidate GPRS TRXs or potentially removable TRXs to improve overall network quality. The OMC mightuse rank (or preference) information for better RRM.

As it is during an AFP process that frequencies and MALs/MAIOs for different TRXs of a subcell are chosen, the AFP toolstores and manipulates the information about TRXs in good and in bad conditions.

If you choose AFP Rank indicator to be allocated when starting an AFP session, each cost improving solution will gothrough a TRX rank assignment. If no improving plan is found, TRX rank will be assigned for the initial plan (like BSIC).TRX ranking within a subcell is performed on the basis of TRX costs.

Notes:

• Rank = 1 is the best rank.

• TRX Rank is the corresponding field in the TRX table.

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In many cases of MAL/MAIO assignment, only one or two of a TRX’s MAIOs violate separation constraints. Therefore, ahigher ranking will be assigned to the MAIO violating the separation constraints.

3.2.1.1 TRX Rank UsageThis information can help increase performance in certain cases where a cell and its neighbour are not loaded with trafficat the same time (for example, a stadium and its parking lot). In such cases, it is possible to decrease call blocking byadding the TRXs in bad conditions to the concerned cells. If the BTSs do not recognize TRXs in bad conditions, the overallnetwork behaviour will either be very poor or difficult to predict even if the BTS knows how to track ranking in real time.

TRX ranks may be required by the OMC in order to optimise the spectral efficiency. In some networks, a part of the deci-sion-making process at the OMC may be transferred to the BTSs when this information is available. Even if such a “smart”system exists, it might be better to know the TRX ranks in advance to improve predictability and consistent behaviour.

Apart from these uses, AFP TRX ranks can be used in post-AFP optimisation. For example, once you perform AFP, youcan freeze all TRXs with ranks less than or equal to X. So that a new AFP instance will concentrate on a smaller subsetof the most interfered TRXs in the most loaded subcells.

A TRX will not be considered frozen for TRX Rank assignment if and only if it is selected for AFP allocation and has notbeen frozen at Transmitter level or by the AFP launch Wizard.

3.2.2 Total Cost and Separation Violation Cost ComponentTotal cost and separation violation cost component at the TRX, subcell, transmitter and site levels can be computed anddisplayed as AFP performance indicators. These are the cumulated total costs and the cumulated separation violationcosts of each TRX, subcell, transmitter and site.

In order to be able to compute and display these results, you must add AFP_COST and AFP_SEP_COST fields (of typeSINGLE) to the TRX, Subcells, Transmitters and Sites tables. AFP_COST field and AFP_SEP_COST field correspond tothe total cost and separation cost component respectively. These AFP performance indicators are available in the list ofAFP performance indicators to be computed available when launching the AFP tool.

The AFP cost assignment to the TRXs, subcells, transmitters and sites is carried out at the same time as the TRX rankassignment. Once a frequency plan is committed, the next instance of the AFP can concentrate more on the problematicTRX/subcell/transmitter/site to improve results. Another use of this feature can be to automatically limit the modificationscope to the problematic cells/sites. This feature can deliver a significant quality gain.

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40 AT271_ARG_E4 © Forsk 2008

Frequency Plan Optimisation

Chapter 4


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Chapter 4: Frequency Plan Optimisation

4 Frequency Plan Optimisation

4.1 Step 1 (Optional): Traffic Model UsageIt is not possible to solve a difficult optimisation problem without having a traffic model. Following are the 4 principal rolesof a traffic model:

1. To reduce the required number of TRXs where they are least needed and spectrum not available.

2. To indicate the least loaded TRXs, since they are less important and interfere less with others TRXs.

3. To reduce the constraint level of the IM (for example where interferences are limited to low density surface).

4. To provide an accurate quality estimation of the resulting frequency plan.

The first point is currently implemented through a dimensioning model, which is explained in this chapter. Moreover, it willbe available as an AFP option in one of the future versions (i.e. the AFP will optimise the decisions so as not to respectthe required number of TRXs. In other words, it will perform a spectrum oriented dimensioning). The second role is carriedout by the traffic loads. In order to understand traffic loads better, traffic capture is also described subsequently. The thirdpoint is explained alongwith the description of the IM and the last point is detailed in chapter 5.

The Atoll traffic model is quite advanced. To gain familiarity with the concepts of user profiles, environments, services,mobile types, terminal types etc. a new user should refer to the Atoll User Manual. These traffic model entities can be usedto benefit from all possible capacity gaps in a network. The simplest application here, would be to use a clutter weightoriented model. The more advanced models and techniques of creating traffic maps, based on traffic-by-transmitter etc.,are also explained in detail in the Atoll User Manual. This chapter provides with the basic know-how on creating thesimplest model using clutter information and clutter weights.

4.1.1 Creating a Traffic Map Based only on Clutter WeightingThere are two simple methods:

• Using a raster map

- Define a simple user profile for an active user with voice service, speaking 3600s per hour (i.e. consuming 1Erlang).

- Create a traffic environment of this kind of user profile with a density of 1 and pedestrian mobility. Any mobilitycan be used (e.g. 1), as it will be used for calculating IM where only the relative weight matters.

- Assign appropriate clutter weighting to this traffic environment.- In the Geo tab, create a new traffic map based on environments through the GSM GPRS EGPRS Traffic folder

context menu. On the drawing toolbar, select the traffic environment created earlier, click the polygon buttonand draw a polygon surrounding the computation zone. This raster map will appear in the Traffic folder.

• Using a vector map

- Define a simple user profile for an active user with voice service, speaking 3600s per hour (i.e. consuming 1Erlang).

- In the Geo tab, create a new traffic map based on user profiles through the GSM GPRS EGPRS Traffic foldercontext menu. Select the user profile just created with pedestrian mobility and assign density to the Densityfield.

- Assign appropriate clutter weighting.- Click the polygon button on the drawing toolbar and draw a polygon surrounding the computation zone.

Double-click it and assign a density of 1. This vector map will appear in the Traffic folder.

Both traffic maps are stored in the document and can be exported. An exported vector map is smaller than a raster one.

4.1.2 Performing a Traffic CaptureTraffic capture is a means to cumulate one or more traffic maps, for voice and/or data services, for different terminals andprovide a spreading of traffic per sector respecting layer priorities, frequency bands and other rules that can be defined bythe user. The details of this process are described in "Appendix 4: Traffic Capture and Dimensioning" on page 95. Oncetraffic analysis is performed, a traffic capture object is available in the Explorer window Data tab. This traffic capture objectcontains traffic demand per [service, subcell] pair in terms of Erlangs for CS traffic and kbps for PS traffic. This trafficdemand provides Atoll with an estimate of average demand in terms of # TSL used.

The AFP combines this traffic capture with the number of required TRXs and their timeslot configurations to generate trafficloads (assuming the AFP will create the required number of TRXs indicated in the subcell table).

The dimensioning process reads the basic information contained in the traffic capture to find out the number of TRXsneeded to support a user defined blocking rate, HR ratio etc. See "Appendix 4: Traffic Capture and Dimensioning" onpage 95 for details.

The KPI calculations combine traffic capture with the current number of TRXs in the network and their timeslot configura-tions to generate current traffic loads.

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4.1.3 Creating IMs Based on TrafficIM calculation is either based on uniform distribution or on the maps used to perform the default traffic capture. In order tocalculate IMs based on a traffic clutter weighting,

• Create the traffic map as described earlier,• Perform a traffic capture using only this traffic map,• Make this traffic capture the default one, and• Select the option "Traffic spreading based on the maps used in the default traffic capture" in the IM calculation

dialog.

This option has the following advantages:

• Interference over “hot spots” will have more weight

- Example: Sites covering an important highway will interfere over the highway but the interfered surface willbe less compared to the coverage. Therefore, not significant if no traffic is used.

• Interference over dead spots will not create overhead constraints

- Example: A large hilly park in the middle of a city is often not covered by a dedicated site since it has lowtraffic. The slopes of this hill are covered by many overlapping cells and tend to create many undesirable IMentries. If the weight of these slopes is reduced due to very little traffic, this can simplify an over-constrainedproblem.

See "Appendix 3: BSIC Allocation" on page 94 to understand further why traffic loads and interference information are notcombined together in Atoll.

4.2 Step 2 (Optional): Neighbour Relations and Relative WeightingIn many cases, neighbour relations are the most constraining elements for the AFP. Neighbour importance field of theneighbours table permits the AFP to partially ignore weak / far-away neighbours and concentrate more on the more impor-tant neighbours.

This section details the use of this new feature in various scenarios.

4.2.1 Automatic Neighbour AllocationNeighbour importance has two major roles in Atoll:

1. Weighting the neighbour relation in the AFP.

2. Ranking the neighbours so that Atoll can select the n most important neighbours.

The configuration presented below is recommended in order to use the resulting neighbour importance in the AFP.

• Coverage Factor: 1% to 81%• Adjacency Factor: 20% to 90%• Co-site Factor: 70% to 100%

Important:

• Keep in mind that the required number of TRXs is the number of TRXs required to carry agiven traffic. This is the number of TRXs (usually) calculated through the dimensioningprocess. The number of existing TRXs is the current actual number to TRXs at atransmitter.

Tip:Check neighbour allocation before running the AFP. Often a bad neighbour relation definition causes poor frequency plan performance.

Notes:

• The default values for computing importance values are:

- Coverage Factor: 1% to 30%

- Adjacency Factor: 30% to 60%

- Co-site Factor: 60% to 100%

• The neighbour allocation algorithm works as in earlier versions with these default values.Changing these values changes the priority definitions of the neighbour allocationalgorithm. Refer to the Technical Reference Guide for more details.

44 AT271_ARG_E4 © Forsk 2008


AFP can be launched once the results of the neighbour allocation have been generated and committed.

4.2.2 Importing Neighbour ImportanceVarious sources of neighbour importance exist:

• OMC HO statistics• Test mobile data measurements (which ignore interferences between non-neighbours)• Other

As with any other source of information, it is the user’s task to prepare and import this external data. The units of the neigh-bour importance are probabilities and are expected to reamin between 0 and 1.

4.2.3 Extending Existing Neighbour RelationsExtending an existing neighbour relation should be performed often either to solve some HO problems or because of addi-tion of new sites. Such operations usually imply that a fresh frequency allocation be carried out. The AFP would be requiredto use the original neighbour relations as well as the new additional neighbours, yet in a different way (with a differentweight). In addition, the AFP would require access to the former (complete or partial) source of neighbour importance aswell as to the new values of neighbour importance calculated for the recently added relations.

The neighbour importance of the original neighbour assignment is probably more reliable than the one calculated usingpath loss calculations.

This section explains how this can be done:

1. Export the current neighbour relation into a file called AllCurrentNei.txt using the generic export feature availablethrough the context menu of the table,

2. Export all the relations for which there are reliable neighbour importance into a file namedAllCurrentNei_Importance.txt,

3. Import the file AllCurrentNei.txt into the neighbour exceptional pairs so that the existing neighbour allocation isforced (usual operation for extending an existing allocation),

4. Run automatic neighbour allocation in order to extend your neighbour relations and/or assign importance whereit was not already assigned. To keep important values lower than X%, all Max% values in the importance part ofthe dialog should be kept less than X. For example, if X is 50%, the configuration shown below can be used,

Figure 4.1: Automatic Neighbour Allocation

Note:

• In the results generated by Atoll after neighbour allocation, the sum of importance values ofall neighbour relationships of a sector is not 1.

© Forsk 2008 AT271_ARG_E4 45

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As can be observed in the figure above, all new neighbour relations have weak importance values.

5. Commit the allocation,

6. Import the file, and answer “no” if asked to remove neighbours of modified transmitters.

The screenshot below shows that the neighbour relations now comprise old neighbours with a higher importanceand new neighbours with a lower importance automatically calculated by Atoll.

4.2.4 Importing Partial Sources of Neighbour ImportanceAtoll’s generic import feature can be used to import the data easily. In order to import, the user should know the locationto place this imported data (Importance column of the Neighbours table) and the data units (probabilities between 0 and 1).

If your network statistics do not provide you directly with the importance of neighbours, you can calculate neighbour impor-tance from other statistics. Then, this calculated importance can be imported to Atoll and provided to the AFP as input.

For example, if you have statistics about the number of handovers between two sectors, you can calculate the importanceof the different neighbours of each cell from these statistics. Consider two sectors, A and B. Let X be the "Average Activityof a Relationship" in the network, i.e., the sum of all handovers of all the sectors divided by the number of neighbour rela-

Figure 4.2: Automatic Neighbour Allocation Results

Figure 4.3: Neighbours Table

46 AT271_ARG_E4 © Forsk 2008


tionships. If the number of handovers from sector B (neighbour of sector A) is Y, the importance of sector B for sector Acan be given by:

In this way, when a relationship has more than the average number of handovers, its importance will be the highest it canbe in Atoll, i.e., 100%. Otherwise, the importance will be less than the average.

4.3 Step 3 (Optional): Using DimensioningThe Atoll dimensioning model, combined with the traffic capture, is a strong tool for frequency plan optimisation. In mostcases, where a spectrum problem exists and the problem does not originate from the neighbour relation, the second mostimportant task is to reduce the number of required TRXs in a selective and careful way.

This optimisation can currently be carried out with the help of the dimensioning model. In future versions, it may be avail-able directly through the AFP.

4.3.1 Optimal Dimensioning of an Existing Network1. Run the AFP and commit the resulting frequency plan. Proceed to the next step if this frequency plan is not satis-

factory and the TRX demands have to be reduced.

2. Increase the service blocking rates (from 2% to 4% for example). The screenshot below shows:

- Where this can be done (Services table).- That the dimensioning model is based on blocking.- The effect this change has on the required number of TRXs (the number of existing TRXs being the previous

number of required TRXs for 2% blocking rate committed in Step 1).

3. Recalculate the traffic capture since service definitions have changed and then launch dimensioning. Some trans-mitters will have less required TRXs while others, which were more loaded, have the same number of requiredTRXs as before.

Impor cetan1 If Y XYX---- If Y X

=

Figure 4.4: Dimensioning Process

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Running the AFP once more can return an improved frequency plan, as the following example shows:

The above experiment proves that the capacity difference between the two networks is very low (first column, around 2Erlangs). This means that the reduction of 5 TRXs leads to a very minor decrease in capacity. This is due to the fact thatthis was done by dimensioning considerations rather than other possible considerations.

The AFP generates a better plan after this decrease in the number of TRXs. The AFP cost units are Erlangs, therefore,we can compare the 2 Erlangs lost because of capacity to the 10 Erlangs gained because of better AFP cost.

4.4 Step 4: Optimal Usage of the Atoll AFP

4.4.1 Introduction to the AFP Cost Function

4.4.1.1 Combination of Separation Violation and Interference ProbabilitiesThe cost function of Atoll AFP has two main components. The first component is the cost for violations of separationconstraints and the second component is the cost for creating interference.

Atoll AFP gives each separation violation a cost equivalent to a certain amount of interference, making it possible to sumboth costs and minimize their sum. For example, the user can define that a separation violation of 1 costs the same as x%of interfered traffic. This is weighted by the type of violation (co-transmitter separation violations have higher impact thanneighbour separation violations). Through this equivalence, It is possible to sum separation violation and interferencecosts that share a common unit, i.e. percentage of interfered traffic.

Following this principle, all other cost elements are also calculated in the same manner, the cost of Missing TRXs, the costof corrupted TRXs, the cost of a TRX assigned out-of-domain frequencies and the cost of changing a TRX’s assignment.

4.4.1.2 Counting TRXs (Nodes) Instead of Relations (Edges)In the following example, each separation violation represents an edge and each TRX a node. All the 3 frequency plansproposed in this example do not respect all separation requirements for all TRXs, meaning that they all have bad nodesand bad edges. Now the question is that whether the AFP minimization target should try to minimize the number of badedges or the number of bad nodes.

Example:

• Imagine a network with 6 TRXs, all having a separation constraint of 1 with each other (i.e. 6 nodes, 15 Edges).• The following 3 cases demonstrate the way the AFP calculates the cost of an allocation.

• Atoll AFP prefers Case 1 by default. Nevertheless, it can be configured to opt for Case 3.

Action performed

AFP cost for the empty network, indicating the

number of weighted Erlangs

Sum of Number of Required

TRXs

Separation Violation

Cost

Interference Cost

Missing TRX

Erlangs

Original network 603.6 100 106 9.7 0

After increasing the Blocking Probability to 4% and dimensioning

601.4 95 96.6 9.4 0

Note:

• It is possible to set a “Maximum number of TRXs” in the Transmitters table. You can copyand paste the current demand to this column, thus forcing the dimensioning process torespect the current state of the network as an upper bound. This possibility is a handy in allpossible cases of difficult frequency allocation.

Case 1 Case 2 Case 3

F1 is used 4 times, F2 and F3 are used one time each.

F1 is used 3 times, F2 twice, and F3 is only used one time.

F1, F2, and F3 are used two times each.

Number of separation violations is 6(6 bad edges)

Number of separation violation is 4(4 bad edges)

Number of separation violations is 3(3 bad edges)

Two TRXs have good assignments Only one TRX has a good assignment No TRX has a good assignment

The spectrum is not equally used The spectrum is equally used

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The parameters that control the capability of Atoll AFP to be more Edge-oriented than Node-oriented are explainednext. But, before this explanation, following are the three main advantages of the Node-oriented approach:

a. The cost function has meaningful units, i.e. Interfered Erlangs.

b. The ability to focus problems on a TRX that is already 100% interfered and to improve the others instead ofspreading interference on several TRXs.

c. The capability to respect a TRX based quality target, i.e. dismissing interference at a TRX that does not sumup to a certain considerable value (explained below).

The Node-oriented approach is an important feature of the Atoll AFP and provides a tighter correspondence between theAFP cost and the network quality.

4.4.1.3 Each TRX CostThe AFP cost function is summed up for each TRX according to the following logic:

• If TRX is corrupted, the tax of being corrupted is added to the cost, and multiplied by T().• If TRX is missing (the required number of TRXs and the actual number of TRXs being different), the tax of

missing TRX is added to the cost, and multiplied by T().• If TRX has out-of-domain frequencies assigned to it, the tax of out-of-domain frequency assignment is added to

the cost, and multiplied by T().• Otherwise, the separation cost, the interference cost and the changing load of this TRX are summed up (probabi-

listically) and added to the cost, and multiplied by T().• If this sum is very small, it is discarded (see "Quality Target" on page 51)

Here, T() is an estimation of the traffic Erlangs using TRX weighted by the AFP weight for this TRX.

The user can fully control the AFP cost target by determining the value of the cost function parameters. Some of theseparameters belong to the data model, e.g. “Maximum MAL Length” and “Minimum C/I”, while others are present in thespecifc AFP GUI. Appendix 2 explains how to find each of these parameters.

4.4.1.4 Separation Violation CostIn this section, interference cost is ignored in order to understand the separation violation cost. A TRX having only oneseparation violation is considered.

Let Sij denote the required separation between two transmitters. If f1 is assigned at i and f2 at j such that , this

means that the separation constraint is not satisfied. Separation constraints can be violated strongly or weakly:

• For example, the pair of frequencies (1, 2) violates a separation requirement of 3. The pair of frequencies 1 and 3violate this requirement as well but is still a better solution than (1, 2) and, therefore, should have a lower cost.

Frequencies that are part of a MAL with a low fractional load and that disobey a separation constraint, should not beweighted the same as in non-hopping separation violation. In fact, the separation component is weighted by the burst colli-sion probability, which is the multiplication of the victim’s fractional load and the interferer’s fractional load.

Note:

• The AFP cost is the cost of the entire loaded network, not only the cost of the selected ornon-frozen TRXs. In many cases, the AFP is authorized to change only a part of thenetwork. Therefore, the part of the cost corresponding to the non-frozen part of the networkand the part of the cost corresponding to the frozen part of the network are indicated.

Figure 4.5: Atoll AFP Module Properties - Separation Weights Tab

f1 f2– Sij

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Example: Let us consider the following simple case of a network comprising two TRXs in the same cell. The first, TRXi,

has a MAL denoted as MALi. It is interfered by TRXk having MALk. TRXi and TRXk have a separation requirement of 2.

Their MAL lengths are respectively 5 and 4. Unfortunately, one of their frequencies is the same (i.e. separation = 0), whileall other frequencies are correct. For the case of a co-channel violation when the required separation is 2, the cost of theseparation violation is 90%, as shown in the dialog above.

Since only one channel of each TRX causes interference, with length(MALi)=5 and length(MALk)=4, the collision proba-

bility is 1/20. Hence, the cost to consider is divided by 20, i.e. 90/20 = 4.5% for each TRX.

In addition, since the two TRXs have different MAL lengths, they have different interferer diversity gains: a gain of 1.4 forMAL length of 5 and a gain of 1.2 for MAL length of 4 (see "Appendix 2: Interferences" on page 91 for details).

Applying interference diversity gain of 1.4 dB means that the cost will be divided by the value: . For TRXi,

this will give 4.5% / 1.38 = 3.25%.

For TRXk, the cost to consider will be .

Now, in order to get the exact contribution to the separation cost component, these values are multipilies by the traffic load(Erlangs / timeslot) and by the number of traffic carrier timeslots in each TRX. Assuming the traffic load to be 1 and thateach TRX has 8 traffic carrier timeslots, we will get (8 x 3.25 + 8 x 3.41), i.e. about 0.5 Erlangs for the two TRXs together.

4.4.1.5 Interference CostTraffic on a TRX will be interfered if and only if co/adjacent-channel reuse exists within interfering transmitters. Each suchreuse will reduce the amount of good traffic and increase the interference cost. It will be weighted by the global interferenceweighting factor, and will take into account the burst collision probability in the same way as in the example above. Formore information, see "Interference Cost Component" on page 88.

4.4.1.6 Probabilistic Cost CombinationAssume that TRX is subject to a separation violation causing a cost of 30% of T() (T() = Traffic of TRX ) and in addi-tion, a co/adjacent-channel reuse causing this TRX to be 40% interfered. This section explains how these two events aresummed together.

The solution to this problem is provided by a probabilistic approach: all different costs are considered as bad events andare combined as if these events were independent.

The probabilities of events in this example are p(Violation) = 0.3 and p(Interference) = 0.4. The cost of the two together isgiven by:

Let P1, P2, ….Pn be the violation probability costs of the given TRX (one for each of its n violations).

Let Pn+1, Pn+2, ….Pm be the interference probability costs of the given TRX (one for each of its (m-n) interferences).

Let Pm+1 be the “changing TRX cost” described below.

The separation cost of this TRX will therefore be:

The additional cost of this TRX will be

The interference cost uses the “min C/I” value, defined at subcell level, for which it may have precise pair-wise interferenceinformation. It may apply various gains to this C/I quality target due to frequency hopping and/or DTX.

4.4.1.7 Missing TRX CostIt is easy to have a 0-cost solution if the required number of TRXs criterion is not fulfilled (by removing all TRXs, for exam-ple). This is the main purpose of missing TRX cost. By default, the exact traffic that a missing TRX was supposed to carrywill be counted by the cost function. However, the user can increase this tax (to 200% for example) if needed.

In certain cases, creating more TRXs will not only generate interferences for the newly assigned TRXs but also for otherTRXs that, otherwise, would have correct assignments. This parameter enables the user to tune the AFP in its tradeoffsbetween respecting the number of required TRXs and optimising quality.

Note:

• In this example, the AFP weight was assumed to be 1, the traffic loads were assumed to be1, no DTX was involved, no other interference or violation was combined with the above,the global separation cost was set to be 1, and the co-transmitter separation weight wasset to 1 as well.

101.4 10

1.38

120------ 90

101.2 10

------------------------ 3.41%=

1 1 p Violation – 1 p Interference – – 0.58 or 58%=

1 1 Pi–

i 1=

n

–

1 1 Pi–

i 1=

m 1+

–

1 1 Pi–

i 1=

n

–

–

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4.4.1.8 Corrupted TRX CostIt is easy to generate a 0-cost solution if frequency domain constraints are not satisfied (by putting an arbitrary channel,for example). This cost component exists in order to avoid this behaviour. By default, 1000% of the traffic that a corruptedTRX is supposed to carry will be considered impaired.

In some cases, fixing the assignment on a group of corrupted TRXs will not only result in an interfered assignment for theseTRXs but also for many other TRXs that, otherwise, would have correct assignments. It is for this reason that this tax ishigher than 100%.

In future versions, different corruption reasons will have different tax levels and the assignment of a corrupted TRX will notalways be ignored.

4.4.1.9 Out-of-domain Frequency Assignment CostTRXs may have proper ARFCN assigned yet may not comply with the frequency domain definition. In many cases, thefrequency domain limitations are not fully respected in the surroundings of the zone considered for frequency planning.This cost component can not be ignored or be modelled by the corrupted TRX cost because such a corrupted TRX caninterfere and be interfered, which will be ignored in both the cases.

If a TRX is assigned out-of-domain frequencies (channels) but has correct ARFCNs, it will have dual influence on the cost:

1. The normal cost of interference, separation and/or modification.

2. An additional cost of having out-of-domain channels, multiplied by the number of frequencies out of domain anddivided by the MAL length.

4.4.1.10 Quality TargetIt is often required to handle small and large amounts of interference in different manners. For example, an operator mightprefer to have 10 transmitters with 2% interfered traffic in each, rather than to have 2 transmitters with 10% interfered trafficin each.

The Global Cost section of the Atoll AFP properties dialog window’s Cost tab provides an option to dismiss interferenceand separation costs that do not sum up to the value of the parameter "% Max Interference" defined in the Subcells tablefor each subcell. TRXs having less percentage of interference than that defined in the "% Max Interference" are consideredto have 0 interference and are excluded from the cost.

This feature can be used to distribute the interferences equally among some transmitters in stead of having a few with verylow interferences and others with high interferences.

4.4.1.11 Modifiable and Non-Modifiable CostsInterfered Erlangs or separation constraint violations between frozen TRXs can not be resolved by the AFP. The AFP canonly reduce the non-frozen cost, which is the modifiable cost.

Modifiable and non-modifiable parts of the total netwok cost are linked in concept with the definition of the AFP scope. See"Definition of the AFP Scope" on page 22 for more information. Four groups of transmitters can be defined with respect toAFP:

• ALL = All the transmitters in the project.• NET = Active transmitters that pass the filters on the main Transmitters folder and on the main Sites folder.• SEL = Transmitters belonging to the (sub)folder for which the AFP was launched and that are located inside the

focus zone.• RING = Transmitters belonging to NET, not belonging to SEL and having some relationship with the transmitters

in SEL:- If interferences are to be taken into account, all transmitters whose calculation radii intersect the calculation

radius of any transmitter in SEL will be included in RING. For large calculation radii (20 km for example), asingle site can have a very large RING loaded.

Note:

• The Atoll AFP always assigns as many TRXs as the “Required TRXs” field indicates. Theuser can only decide regarding the better plan, i.e. the previous plan having a better qualitybut some missing TRXs or the new plan having lower quality but having all required TRXsassigned. In future versions, the AFP will be capable of optimising these decisions as well.

Note:

• A TRX is corrupted not only if it contains frequencies that are out of domain but also when:

- An NH TRX has a MAL with more than one frequency

- A TRX has no channel at all

- A group constrained SFH TRX is assigned a MAL that is not strictly a group of its domain

- An SFH TRX has no MAIO, or no HSN, or has an out of domain HSN / MAIO value.

Note:

• If SFH and group constrained subcells have out-of-domain channels, and are frozen, thefrozen TRX will be ignored altogether.

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- Neighbours are always included in RING.- If one transmitter of an Exceptional Pair is included in SEL and the other is not, then the other will be included

in RING.- If BSIC assignment is required, then all the second order neighbours (neighbours of neighbours) will be

included in RING.

The total cost of the network corresponds to SEL+RING. It contains the modifiable as well as the non-modifiable parts ofthe network costs.

The modifiable part of the total cost of the network corresponds to SEL. However, this cost does not include costs corre-sponding to frozen entities of transmitters in SEL.

The non-modifiable part of the total cost of the network corresponds to RING. It includes the costs corresponding to frozenentities of transmitters in SEL.

In each instance of an AFP process, there might be entities frozen by the user. In addition to the generic freezing options,there are finer freezing options available in the data structure:

1. Individual transmitters can be frozen for channel (and MAL), HSN and/or BSIC assignment.

2. Individual TRX’s can be frozen for channel (and MAL) assignment.

4.4.2 Most Important Cost Function Parameters and TuningIt is strongly advised that the user should fully understand the different cost function parameters before manipulating them.In order to understand the parameters that are not explained in this section, please refer to "Appendix 1: Description of theAFP Cost Function" on page 85 and "Appendix 3: BSIC Allocation" on page 94.

The figure below depicts the Cost tab of the AFP properties dialog:

4.4.2.1 Interference Weight vs. Separation WeightThe most important parameters are the ones outlined by rectangles in the figure above. Interference and separationweights are used as multiplicative factors before each interference or violation event. Therefore, these parameters havethe ability to reduce one type of event cost compared to the other. If these two parameters are set to low values (for exam-ple, 0.1 and 0.035 respectively), AFP will be forced to work according to the edge-oriented strategy, which is probably notthe recommended approach. By default, interference events are less important than separation violation events.

4.4.2.2 Cost of Changing a TRXThe second most important parameter (also outlined with a rectangle in the figure above), is the cost of modifying a TRX.This is recommended to be used if the non-frozen part of the network should be changed as little as possible. The followingexperiment shows the effects using this parameter can have:

Figure 4.6: Atoll AFP Module Properties - Cost Tab

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4.4.2.3 Quality Target and C/I Weighting

4.4.2.3.1 Quality TargetThe Global Cost section (outlined with a rectangle in the figure above) lets you define the quality target mechanism for theAFP cost.

1. If you select "Do not include the cost of TRXs having reached their quality targets (% Max Interference)", Atoll willnot take into account the cost of those TRXs which have less % of interference than that defined in their corre-sponding "% Max Interference" in the Subcells table. The total cost will only include the costs of TRXs whose inter-ference is still higher than this threshold value.

2. If you select "Take into account the cost of all TRXs", Atoll will consider the cost of all the TRXs ignoring whetherthey have reached their quality targets, defined in the "% Max Interference" in the Subcells table, or not.

For example, consider a frequency plan with only one interfered TRX with 10% interfered traffic, and another frequencyplan with 10 interfered TRXs with 1.5% interfered traffic in each. Assume that you have set the "% Max Interference" forall the TRXs in both the cases to 2%. If you choose the 1st option in the AFP global cost settings, Atoll will prefer the solu-tion with 10 interfered TRXs with 1.5% interfered traffic rather than having 1 interfered TRX with 10% interfered traffic.

4.4.2.3.2 C/I WeightingWhen the C/I weighting option (the bottom rectangle), related to the quality threshold, is used, the AFP takes into accountthat the traffic having close-to-threshold C/I conditions is neither 100% satisfactory nor 100% corrupted.

In this way, safety margins on the threshold C/I conditions can be avoided. Therefore, the user must specify a marginaround which a “slope” is created, as illustrated in the figure above. This figure corresponds to an interference relationbetween two TRXs. It describes the distribution of traffic according to C/I conditions. It depicts the effect of 3 different qual-ity requirements on the interference cost of a co-channel frequency reuse.

It can be observed that, when a low quality (C/I > 8 dB) is required, less traffic is considered as interfered than for a highquality (C/I > 11 dB).

The option ‘C/I >10 dB + 2dB margin’ has the advantage of not being too strict on one hand, and yet trying to achieve highquality if possible. It is visible from the above figure how it integrates the different traffic classes into the interference cost.

Test case:

A network with 90 transmitters in total, 15 frozen transmitters and sum of required TRXs = 257.

Only 193 good TRXs were already allocated.

64 TRXs should be created / newly allocated with as little influence as possible on the other 193 TRXs.

For a cost of changing a TRX = 1 AFP changed only 98 TRXS

For a cost of changing a TRX = 0.3 AFP changed only 129 TRXS

For a cost of changing a TRX = 0.1 AFP changed only 139 TRXS

For a cost of changing a TRX = 0 AFP changed 162 TRXS

Figure 4.7: C/I Weighting

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4.4.2.4 Separation Weights SettingsThe Separation Weights tab enables the user to define relative weights of different separation types with respect to eachother and of one co-channel violation with respect to an adjacent channel violation and so on.

The figure below shows the Separation Weights tab of the AFP properties dialog.

Other tabs of the AFP module properties dialog are more advanced. Please refer to the Atoll User Manual for more infor-mation on AFP module properties tabs.

Figure 4.8: Atoll AFP Module Properties - Separation Weights Tab

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Means to Evaluate Frequency Plans

Chapter 5


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Chapter 5: Means to Evaluate Frequency Plans

5 Means to Evaluate Frequency Plans

5.1 Estimating Frequency Plan Quality

5.1.1 Using Interference StudiesThe full description of the interference study features is outside the scope of this document. Nonetheless, it is importantto understand that a geographically based interference study has an important advantage over any simulation based onpair-wise interference matrices (or histograms).

Atoll interference studies are geographic studies that analyse each point on the map. For each point, an interference studyestimates the carrier power and then sums up the interference powers taking burst collision probabilities, DTX, and trafficload into account.

As the AFP works with interference matrices, it is limited to coarse estimations of interference combination and losesknowledge of the geographical location of interference events. It is due to this reason that the interference study output ismuch more accurate than the AFP cost.

The column “Erlangs (based on traffic load)” is available in the interference study report as seen above. This column usesa traffic model similar to the one used by the AFP:

• It spreads the traffic of each subcell (#TRX x traffic load x # timeslots) on the service zone of the subcell.• Then, it sums up the interfered traffic (in Erlangs) of each interfered TRX.

This means that it is a TRX based estimation of interference and is much more accurate than any other tool available inAtoll. In order to be able to use this option, you must check the “Detailed results” option when specifying conditions for aninterference study.

5.1.1.1 Various Interference StudiesFollowing are the main differences between a TRX based interference study and a transmitter level worst case interferencestudy.

5.1.1.1.1 TRX Based Interference StudyIf there are more than one TRXs per cell, a “TRX based” frequency plan analysis is usually required. This can be performedin Atoll using the “Detailed results” option of an “Interfered zones” study. The following figures depict this function:

Figure 5.1: Interference Study Report

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For each TRX, Atoll retains a map of all the pixels that do not comply with the quality threshold (one map for each TRX).The threshold can be global or dedicated to each subcell (from the Subcells table). The maps can be visualised by theuser and contribute to the overall statistics. The column mentioned earlier weighs the “bad” surface of each TRX map bythe traffic carried by the TRX as seen by the AFP. Therefore, it is the most appropriate tool for frequency plan interferenceevaluation.

5.1.1.1.2 Worst Case Interference StudyA Worst Case Interference study allows generating the Worst C/I (I being the worst interferer) per pixel or per serving trans-mitter at pixel. Statistics on these maps are available with or without traffic weighting. The principal drawback is that pixelsare coloured in both cases: when 1 out of n TRXs is interfered and when n out of n TRXs are interfered. Moreover, thereis no information about TRXs (channels or frequency) responsible of these worst C/I values.

5.1.1.2 Visualising TRX Ranks with a TRX Based Interference StudyYou can also visualise and compare the AFP TRX ranks with the results of a detailed interference study. In the interferencestudy report table, as shown in the earlier figure, the “Erlangs (based on traffic load)” column should rank the TRXs in thesame order as the AFP TRX ranks. Make sure that the AFP cost is based on interferences and not separation constraints.

In case of large networks, where it might be easier to compare these results using MS-Excel, you might not get a 100%match between these results and small variations in the order may exist.

5.1.1.3 Visualising C/I Distributions with a TRX Based Interference StudyThe figure above and the example below show how to get very detailed information about the various C/I conditions atTRX level.

The different information seen in this screen-shot is part of the report obtained by creating several instances of an inter-fered zone study. The interfered zone study whose properties dialog is shown, is the closest to the default configuration.Its interference definition references the subcell quality threshold.

In the two other interfered zones studies, the global threshold for the minimum and maximum TRX C/I to be included ineach TRX’s map were fixed at the reference values. These studies show that there are more “weak interferences” (11.3Erlangs) than “strong interferences” (6.3 Erlangs). The “weak interferences” being 8 < C/I <= 12 and the strong interferencebeing C/I <= 8.

Figure 5.2: TRX Based Interference Studies

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5.1.2 Using AuditThe consistency checking tool gives precise information about separation constraint violations:

• Number of constraints violated• Types of constraints violated (co-transmitter, co-site, neighbour, special)• Transmitters and TRXs affected• Synchronisation, HSN, MAL and MAIO are taken in to account.

The consistency check tool is described in detail in the Atoll User Manual. A quantified summary of separation constraintviolations is available. It makes the evaluation of a frequency plan much easier than before. The section below demon-strates how this evaluation can be carried out.

5.1.2.1 Global Separation Fitness ExpressionIt is often interesting to quantify the “amount” of separation violation in a frequency plan. The difficulty in this is that manydifferent cases and subcases exist. It is not possible to simply count the violating pairs since the SFH violation with lowfractional reuse will affect the count. Another complexity is the difference between co-channel and adjacent-channel viola-tions. Therefore, a Separation Fitness Expression that tries to assign relative weights to different types of separation viola-tions is defined. It is composed of 7 separate summations (N1 through N7), each assigned its respective weight. It is calledForsk Independent Separation Fitness Expression (FISFE) and it is described below.

The FISFE expression is part of our open architecture AFP strategy. There are more than one AFP integrated with theAtoll platform and, therefore, it is interesting to know the frequency plan FISFE values. The answer must be independentof the AFP used to generate the plan.

5.1.2.1.1 Forsk Independent Separation Fitness Expression (FISFE)

The value “7.5” is arbitrary. It is used to upscale the FISFE(FP) value to “close to Erlang” units. On the other hand, theweights specified for each component reflect the idea of their relative importance.

N1 through N7 are now available in the summary of the consistency checking tool.

5.1.2.1.2 Main Separation Violation Item Summary• N1 is the number of TRXs subject to a co-channel reuse violation where the separation violation concerns two non

SFH TRXs.

Figure 5.3: TRX Based Interference Study - C/I Distributions

FISFE FP 7.5 0.8 N1 0.3 N2 0.2 N3 0.1 N4 0.07 N5 N1– N2– N3– N4– ++++ 0.3 N6 0.15 N7++ =

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• N2 is the additional number of TRXs subject to an adjacent-channel reuse violation where the separation violationconcerns two non SFH TRXs.

• N3 is the additional number of TRXs subject to a co-channel reuse violation where the separation violation con-cerns two TRX where at least one is SFH.

• N4 is the additional number of TRXs subject to an adjacent-channel reuse violation where the separation violationconcerns two TRX where at least one is SFH.

• N5 is the number of TRXs subject to whatever separation violation that exists.• N6 and N7 correspond to a different counting system, the pair-wise counting system. N6 and N7 are only used in

cases where the fractional load is less than 1, which means that at least one of the TRXs in the pair is SFH.

The pair-wise violation counting is less important than TRX counting and therefore has a low weight coefficient.On the other hand, it cannot be ignored, since in 1/1 SFH plans, all TCH TRXs will have violations with neighboursand yet it would be required to minimize the volume of these violations. N6 and N7 are defined as following:

• N6 is summed over all pairs subject to a co-channel reuse violation, where at least one TRX in the pair is SFH andwhere the probability of a burst having a co-channel violation is summed.

• N7 is summed over all pairs subject to an adjacent-channel reuse violation, where at least one TRX in the pair isSFH and where the probability of a burst having an adjacent-channel violation is summed.

In the following example, the values of N1 through N7 are {0, 23, 62, 35, 123, 7.695, 2}

5.2 Using Point AnalysisIt is often useful to know what exactly causes interference conditions at a point. This is one of the important roles of thepoint analysis tool. Yet because of it’s complexity, some users are afraid to use it, which is a pity. The point analysis iscomplicated only because it is a very rich tool. It provides the user with the information of how are the interferers of a TRXat a point, what are the different gains (power offsets, burst collision probability, DTX, adjacency suppression), and howdo the different components combine to a “total interference”.

Notes:

• If a TRX is counted in N1 it will not be counted in N2.

• If a TRX is counted in N1 or N2 it will not be counted in N3.

• If a TRX is counted in N1, N2 or N3 it will not be counted in N4.

Figure 5.4: Event Viewer Messages

Figure 5.5: Event Viewer Message 1

Figure 5.6: Event Viewer Message 2

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5.2.1 Example 1: Combination of Interference EffectsThis figure depicts the case where two adjacent interferences are combined to create total interference (the gain value(the empty part – 18 dB) shows that they are adjacent). For each of the two adjacent interferers, C/I > 11 dB, while for theircombination, the total interference, C/I < 11 dB. This example demonstrates the fact that geographic interference combi-nation is more accurate than the interference cost of the AFP. Assuming the required quality to be 11 dB, this specific pointwould not contribute to the AFP cost, while it would be considered as interfered in the interference study.

5.2.2 Example 2: Counting Strong Interference Only OnceIn this case, two strong interferences are combined to create an extra strong total interference. C/I is very weak for bothinterferers. Therefore, the point under analysis contributes to both IM entries, which are considered in the AFP cost. Thisexample demonstrates the fact that geographic interference combination is more accurate than the interference cost ofthe AFP because of counting this point only once as an interfered point (and not twice as in the AFP).

5.3 Uniform Frequency Usage DistributionA frequency distribution analysis tool is available. This feature is accessible through the Frequency Distribution commandfrom the Frequency Plan menu in the Transmitters folder context menu. The output of this tool consists of a 3 column tablelisting,

• The ARFCN,• The number of TRXs in which the ARFCN appears• Its relative load.

Figure 5.7: Combinatin of Interference Effects

Figure 5.8: Counting Strong Interference Only Once

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The relative load is the same as the number of TRXs if no synthesised hopping is involved. When synthesised hoppingexists, the frequency load is the sum of 1/(MAL size) of all the TRXs using this frequency.

The scope of this tool is the same as the AFP scope.

5.3.1 When Uniform Distribution and Quality do not CoincideWhile it is clear that in some cases the frequency usage distribution can be a quality indicator, it is not always the case.The following two examples prove the same. Therefore, a cost has not been dedicated to non-uniformity of spectral usein Atoll and thus marking it an “objective” of the AFP. As a result Atoll AFP will create non-uniform frequency distributionsin the following cases:

1. When the FAP is easy, the AFP reaches a 0-cost solution and stops immediately. If it was instructed to use theminimum possible spectrum, the AFP will use the smaller ARFCNs more than the larger ones (and will leave thelargest ARFCNs untouched, for future use). Otherwise, the AFP will try to spread the spectrum usage. By defaultthis directive is free for AFP tuning. Therefore, the AFP will not create a uniform frequency usage distribution whenthe FAP is easy.

2. If the FAP is somewhat difficult, the frequency usage distribution will be somewhat non-uniform. In order for it tobe uniform, the corresponding directive must be set in the Spectrum tab of the AFP properties dialog.

3. If the FAP is difficult, all frequencies will be used and the allocation heuristics will result in a balanced allocation.Lastly, when the FAP is extremely difficult (many separation violations, for example), an unbalanced allocationmay result because of the reason explained in chapter 7.1, concerning the fact that the AFP cost is a TRX (node)based cost.

4. AFP can also create non-uniform frequency distributions due to the domain range effects described below.

5.3.1.1 Domain Range Effect and Adjacent ConstraintsOther sources of unbalanced frequency distribution are the domain range limits. The first and the last frequencies in adomain have lesser separation constraints related to them. Consequently, they are used more than other frequencies. Thesecond and the second last are used less since frequencies adjacent to them are used more and so on. This effect isstronger for more regular networks. If the domain is small, if ((first – last) / 2) is an integer and if the network is regular, theAFP may hardly use a part of the spectrum. This will happen if and only if there are many adjacent constraints.

The following example can be interesting:

In a domain of 1 to 7 in a typical hexagon network with 6 neighbours for each transmitter, one solution can be a 1/4 patternusing only the frequencies 1, 3, 5 and 7, while 2, 4 and 6 will not be used at all. Another solution for the same can be a 1/7 pattern. Although, if the separation constraints between neighbours are 2, the 1/4 pattern (based on odd number frequen-cies only) will give a better result.

Advice:Do not expect a balanced distribution of frequencies in every case. Sometimes the best solution requires an unbalanced assignment.

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Advanced Topics and Troubleshooting

Chapter 6


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Chapter 6: Advanced Topics and Troubleshooting

6 Advanced Topics and Troubleshooting

6.1 Various AFP Related Features

6.1.1 SFH (HSN, MAL, MAIO)Atoll AFP is capable of performing free MAL assignment and predefined MAL assignment both. The instruction indicatingthe assignment mode to be used is at subcell level. In free assignment mode, the AFP is free to assign any MAL that satis-fies the requirements of the TRXs. The length of MAL, the HSNs and the MAIOs are assigned in compliance with the user’sdirectives. If the assignment mode is group constrained, the AFP can assign one of the predefined groups in the domain.

The success of the assignment depends on the definition of groups in the domain. Each MAL length, represented by oneor more groups in the domain, is supposed to fulfil the conditions:

• that there must be a number of other groups having the same length, and• that on the whole they cover the domain as much as possible.

For example, a domain containing groups of lengths 3, 5 and 8 will be a badly planned domain if there are many groupsof length 3, many of length 8 and only one of length 5.

If restricted to such a domain, the AFP will not produce an optimum plan. On the other hand, by adding a few more groupsof length 5, the quality can be much improved. Another solution could be to simply remove the single group of length 5.When many groups are defined, the quality is almost as good as with free assignment.

6.1.2 Definition of AtomAn atom is a set of synchronised subcells that share the same HSN, the same frequency domain and have the same lengthMAL. The MAIO assignment of an atom manages the frequency collisions between the MALs of the atom. If an atomcontains more than one subcell, the AFP may assign to it partially different MALs (depending on a user-definable option)but it will always consider the fact that the subcells are synchronised. Atoms can be determined by the user or by the AFPvia the HSN allocation. Some restrictions on this definition exist due to some extreme cases:

1. If two subcells have different domains, they cannot belong to the same atom.

2. If two subcells have different limitations on “Max MAL Length”, they cannot belong to the same atom.

A warning is generated when HSN assignment directives contradict with these restrictions.

An important feature is the possibility to force the AFP to always assign the same MAL among subcells of an atom. Further-more, improved results can be obtained by post-relaxation of this constraint, performed on a carefully selected and smallsubset of transmitters.

6.1.3 Synchronous NetworksThrough working at atom level, and consulting a user defined synchronisation reference given in the subcell table, the AFPcan fully exploit the benefits of synchronisation in a GSM network. It is capable of extending Atoms beyond the limit of asite and, by doing so, using the MAIO assignment to further resolve violations or interference.

6.1.4 Optimising Hopping GainsIf the AFP has a certain degree of freedom when choosing MAL lengths, it may opt for longer MAL lengths. In this way, itcan profit more from the hopping gains. On the other hand, it may be increasingly hard to find frequencies for these MALs.

6.1.5 Fractional LoadBoth HSN assignment and MAL length determination processes are tuned to obtain a user defined fractional load. A frac-tional load of is obtained if the number of TRXs using a certain MAL is only times the size of the MAL. Atoll’s notion offractional load does not require the traffic load to be taken into account.

Since fractional load cannot always be obtained, this parameter is considered as a guide rather than a constraint. Whenit can be obtained, AFP chooses either a MAL length 1/ times longer than the number of TRXs in the biggest subcell ofthe atom or a MAL length 1/ times longer than the sum of all TRXs in the atom. These are called “the short MAL strategy”and “the long MAL strategy” respectively. You can choose between the two in the MAL tab of the properties dialog. Thevalue of the fractional load parameter can also be edited and, furthermore, it can even be automatically calibrated by theAFP.

Notes:

• Currently, the AFP always assigns the same MAL to all TRXs within a subcell.

• The “group constrained” assignment mode is applicable for SFH only. In NH and BBH, theassignment mode is always free.

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6.1.6 Domain Use RatioBoth HSN assignment and MAL length determination processes are tuned to avoid exceeding a user defined Domain UseRatio. Domain Use Ratio is the MAL length divided by the total number of frequencies in the domain. For example, a 1/1reuse pattern has a frequency reuse ratio of 1. A 4/12 reuse pattern can have a reuse ratio between 1/4 and 1/12, depend-ing on whether all TRXs in a site have the same MAL (and HSN) or not.

6.1.7 User Defined MAL LengthThe MAL length has an upper limit defined in the “Max MAL length” parameter of the subcell table. The user can instructthe AFP to strictly use this value.

6.1.8 HSN AllocationThe AFP assigns HSNs at subcell level. It chooses different HSNs for interfering and non-synchronous subcells. Forsynchronous subcells (usually within a site), the AFP can opt to assign the same HSN and different MAIOs within the setof same-HSN subcells.

According to the adapted convention on HSNs for BBH TRXs, the AFP allocates different HSNs to the BCCH TRX andTCH TRXs. The 1st HSN corresponds to timeslots 1 through 7 of the BCCH and TCH TRXs, and the second HSN corre-sponds to the timeslot 0 of the TCH TRXs only. The second HSN is used in studies.

The user can control the HSN allocation so that it performs one of the following:

• Assigns the same HSN to all subcells of a site• Assigns the same HSN to all subcells of a transmitter• Assigns pair-wise different HSNs if a pair of subcells has mutual interference.• Optimise HSN assignment so that the frequency assignment is better (free HSN).

6.1.9 MAIO AllocationThe AFP assigns MAIOs to TRXs so that the same MAL can be reused within a subcell, within a transmitter or even withina site. The separation requirements must be satisfied for frequencies that are on air, at all frame numbers. The cost func-tion averages the cost upon all frame numbers in the synchronised case and upon all collision probabilities in the non-synchronised case. See "Appendix 1: Description of the AFP Cost Function" on page 85 for details.

6.1.9.1 Staggered MAIO AllocationIf this option is selected, the AFP will allocate a MAIO set of 3 numbers: {First, step, total Number}. For example:

• {17, 85} OK, Step is 68• {2, 3, 4, 5} OK. Step is 1• {2, 3, 5} Not OK, 4 is missing• {2, 4, 6} OK. Step is 2

6.1.10 BSIC AllocationAtoll AFP allocates BSICs according to two criteria, a soft criterion and a hard criterion. Not respecting the hard criterionis considered an error, while not respecting the soft criterion provokes a warning. The soft constraints are logicallystronger, meaning these have a higher probability of not being satisfied. The hard criterion is easier to satisfy but must notbe broken as it will cause handover failures. The hard criterion is based on the second order neighbour relation and BCCHco-channel reuse. The soft criterion uses interference information as well and tries to induce a larger [BSIC, BCCH] reusedistance. Appendix 4 details the new algorithm and both criteria.

Note:

• Fractional load is 1 for Baseband hopping.

Figure 6.1: Hopping Sequence Numbers

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The BSIC allocation is compliant with the BSIC domains of transmitters and the strategy indicated in the BSIC tab of theAFP module property dialog. Either the algorithm selects a minimum number of BSICs in the related BSIC domain (Minimaloption), or it chooses as many BSICs as possible while keeping them evenly distributed in the related BSIC domain (Maxi-mal and homogeneous option).

6.1.11 Robustness of Atoll AFPThere are three main checks to avoid corrupt data entries and illegal data manipulations in Atoll:

• The first is available in the GUI and protects Atoll’s tables from NULL and out of range values, non-existing refer-ences and other inconsistencies. The deficiency of these checks is that these can be partially bypassed by auto-mated import procedures and external database manipulations.

• The second comprises Network Validation processes as described in the User Manual. The setback of this checkis that the user can ignore it altogether.

• The third check is available when launching the AFP. As the AFP puts together information collected from manydifferent sources, it is quite possible that some elements be conflicting and/or missing. Before launching the AFP,a validation process is launched that controls the possibility to launch the AFP.

If possible, missing / incorrect data are changed and default values are used (with warnings for each in the Event viewer).If any serious problem is detected, an error message appears and access to the AFP is denied. The table below lists themost common data limitations enforced in order to protect the frequency planner.

6.1.11.1 Value Ranges and Limitations at Validation

Notes:

• In the Atoll AFP, the directions of neighbour relations are all considered equivalent, so thatthe BSIC allocation is subject to harder constraints. Let us consider the following twoexamples:

From the operational point of view, the first case is much more critical in terms of (BSIC,BCCH) collision. However, both cases are considered as violations of hard constraints bythe AFP and error messages are generated (if the domain limitation provokes violations).

• The soft criteria add additional constraints due to interference and adjacent reuse betweenBCCH channels. Warning messages are generated when soft criteria are not fulfilled.

• Atoll AFP also considers Training Sequence Code collisions for synchronous networks.The AFP tries to avoid having the same TSC when interference exists (i.e. TCHinterference, not only BCCH reuse).

• BSIC assignment cannot be performed if the BSIC domain is empty or not assigned. Whenno BSIC domain is assigned, Atoll dislays a warning message that says that the BSICdomain is either null or empty. When an empty BSIC domain is assigned, Atoll displays anerror message telling the user that BSIC allocation is not possible, and the network loadingis stopped.

A

B C

NN

A

B C

NN

1st case: B and C neighbours of A 2nd case: A neighbour of B and C

Limitation Value Comments

Maximum number of subcells in the loaded part of the network

1,000,000

Highest possible HSN 63

Lowest possible HSN 0

Limitation on the number of different frequency domains

10,000Each exclusion of frequencies at a transmitter may create a new domain

Highest possible BSIC 77

Lowest possible BSIC 0

Longest possible MAL length 62So that with the BCCH frequency there are not more than 63 frequencies in a list to avoid exceeding the 255 character limit in Access.

Shortest possible MAL length 0

Default Max MAL length 62 Used if the parameter is out of range.

Interference calculations are performed for co-channel and adjacent interference only.

If separation <= 1 Performance

Highest frequency ARFCN 1024

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6.2 Managing Consistency in Atoll and the AFPAtoll can generate many prediction studies, some of which can be used to analyse the AFP results. In each case, it is thetask of the user to ensure consistency between the prediction study settings and the AFP settings.

6.2.1 Service Zone of a SubcellTo render flexibility, optimised storage, validity checking and backward compatibility, each of the following Atoll processeshas its own definition of service zone:

1. Neighbour allocation

2. Network dimensioning

3. Prediction studies

4. Interference calculation

To avoid confusion, it is recommended that the user be aware of service zone model being used. In fact, the user shoulddecide a unique service zone definition to use throughout a project.

6.2.1.1 Specifying Correct Interference Study Coverage CriteriaThe AFP reads required interference information from either calculated or imported interference histograms. For interfer-ences calculated by the AFP, the service zone is determined by the minimum reception level found in the Subcells table,and by the option, “all servers” / “best server”. Atoll interference study has a wider range of options to determine the servicezone. A small service zone in the AFP interference calculation and a large one in the Atoll interference study will implygreat amount of interferences in the interference study, even if the AFP had declared the cost to be 0.

Moreover, for imported interference matrices, there is no means to check whether the imported files are a complete sourceof information. The user could very well calculate interference matrices for a part of the network, export it, and later importit as interference data for the entire network. This would result in an interfered frequency plan.

Maximum required channels at a subcell 62

Highest value of AFP weight 100

Lowest value of AFP weight 0

Default value of AFP weight 1 Used if the parameter is out of range.

Highest value of Traffic Load 10

Lowest value of Traffic Load 0.1

Default value of Traffic Load 0.1 / or 1 if the field is NULL. Used if the parameter is out of range.

Highest value of “% max interference” 100 Appears in subcell and cell type configuration tables.

Lowest value of “% max interference” 1 Appears in subcell and cell type configuration tables.

Default value of “% max interference” 2Used if the parameter is out of range. (The parameter appears in subcell and cell type configuration tables).

Highest value of “min C/I” 25

Lowest value of “min C/I” 2

Default value of “min C/I” 12 Used if the parameter is out of range.

Maximum power offset 25

Highest value of “Reception threshold” -50

Lowest value of “Reception threshold” -116

Default value of “Reception threshold” -94 Used if the parameter is out of range.

Limitation on separation requirements Must be <= 7 Will be eliminated in the future.

Limitation on the actual number of TRXs in a transmitter

50

Limitation on the number of interfering and neighbour subcells

1000

Advice:Before running the AFP, select the definition of the service zone to use for the AFP and all Atoll prediction studies intended for AFP results analysis.

Advice:1. Check that the options in the Atoll interference study are consistent with the AFP interference calculation settings.

2. Verify that the small IM report does not indicate the existance of many non-interfered transmitters.

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6.2.1.2 Selecting “All servers” or “Best Server” Service ZoneExcept neighbour allocation, all other calculations and processes allow choosing their service zone models through theoptions “All” or “Best server” with a margin. It is important to understand the difference between these options and whythese options exist in Atoll.

The “All servers” option implies that a transmitter is assumed to serve the region where its signal is stronger than a mini-mum reception threshold. This means that more than one transmitter can be serving a given point. The service zone isbased on the minimum reception level “C”.

The “Best server” option implies that a transmitter is assumed to serve the region where its signal is the strongest amongall signals stronger than a minimum reception threshold. In other words, where C/N > 0 (C being reception level and Nbeing the strongest neighbour reception level). If a margin M is defined, then the condition translates to C/N > – M. Theremay be more than one serving transmitters at a point but only one best server.

By tuning the minimum reception level and the margin value, any desired server overlapping can be achieved. Large over-laps will result in a denser interference relation, more neighbours and a rather pessimistic analysis of C/I levels or interfer-ences. It might be interesting to manipulate the overlapping zones study and the coverage by transmitter study todetermine the correct service zone model.

Coming back to the question of choosing between the two models, since both “C” and “N” values contain errors, the bettermodel would be the one with the least error. The choice depends on the correlation between the errors in “C” and in “N”.If these errors are geographically correlated, the “C/N > – M” model should be preferred. Moreover, the error in “C” andthe one in “N” are not evenly distributed: the further you are from the site, the bigger the error is. Therefore, when “N” ismuch stronger than “C” it is probably more reliable as well. For these reasons, it is recommended to use the “C/N > – M”model. As a final argument, it should be kept in mind that the C/N > – M model is bound by the C model.

The fact that “C/N > – M” is bounded by the “C” model might incur misunderstandings. For example, increasing the marginwill not essentially increase the service zone, but change nothing because service zones are limited by coverage and notby other best servers.

6.3 Event ViewerThe AFP outputs various messages in the Event viewer. For example, when it finds a zero cost solution, when it stopsbecause of a data problem or when it finishes without improving. The events, warnings and errors may be helpful in under-standing the AFP behaviour, especially when a problem occurs.

6.4 Interference Study Quality CriteriaThe AFP uses the quality specified in the data model (min C/I field in the subcell table). In Atoll interference study, thereis a wider range of quality criteria determination. To assess a frequency plan quality in accordance with AFP calculations,ensure that the interference study quality threshold has been specified accordingly (use subcell C/I threshold as studysetting).

6.5 Calculation Zone Border EffectIf a calculation zone is used to geographically select a set of transmitters for assignment. The following problem will occurwithout the user being aware of it:

Since the calculation zone limits the influence area in the interference studies (and IM calculation), all subcell servicezones are, therefore, limited to the calculation zone. Hence, the transmitters at the borders will have very small servicezones. All of the traffic corresponding to these transmitters will be considered as if concentrated in these few pixels andtheir interference matrix entries will be calculated so.

3. If AFP interferences have been imported, check that they are consistent with the service zone of Atoll interference study.

Advice:

Advice:Use a "Best server with margin" coverage study as service zone for both AFP and Atoll studies dedicated to analyse AFP results.

Note:

• For simplicity, hierarchical layers have been ignored in this discussion.

Advice:Select "Subcell min C/I threshold" instead of "Specified min threshold" in the Atoll interference study Condition tab.

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6.6 Frequency Planning Techniques

6.6.1 BasicsFor any network and any amount of available time, fill in the target computation time field to instruct the AFP to behaveaccording to its default and basic allocation strategy.

6.6.2 Post-processing of Hot SpotsAssuming X hours of available computation time, the strategy is as following:

• Launch the AFP during X * 30 minutes (half of the time), then stop it and commit the results (if good).• Freeze all TRXs in the network.• Find the areas that generate problems. For example, some sites with separation violations.• Unfreeze the worst 10 sites.• For each such site, unfreeze 2 – 4 neighbouring transmitters.• Run the AFP for an additional X * 30 minutes (the remaining half of the time).

AFP is also capable of committing cell level and TRX level quality indicators into the data structure. This makes the selec-tion of hot spots a much easier task.

6.6.3 Learning the Network and Solving for Hot Spots• Apply this technique to networks having 4000 to 40000 Erlangs (500 to 5000 TRXs).• Run the AFP for at least 10 solutions, specifying a short time period.• Find the areas that generate problems. For example, some sites with separation violations.• Create a calculation zone around these areas (referred to as the network core).• Make sure that this network core is not too big or too small. For example: 100 to 150 transmitters, in one chunk, if

possible. The network core should not be too small because it is representative of the entire network.• Specify a long execution time (1000 to 5000 minutes) and let the AFP work on the core over a weekend.• Commit the plan and run the AFP on entire network. Specify a short time (between 5 and 40 minutes) but let the

AFP run for a long time (a night if possible, to get at least 50 solutions).• Optional: You can freeze the network core before this last AFP execution.

6.7 Performance and Memory Issues in Large GSM ProjectsMemory problems might be experienced in the C/I coverage prediction studies, interference matrices calculations, and theAFP, while working on large GSM networks. Large network projects are more susceptible to these problems. Although, ifthe network is large though homogeneous, these problems may only appear if the number of transmitters is more than15,000 or so. But, if there are large city centers involved, with each pixel having many overlapping path loss matrices, thenthis size limit might decrease to around 5,000 transmitters or so.

Advice:Use a focus zone inside the calculation zone in order to focus the study on properly modelled transmitters. Preferably, use calculation zones that are geographically isolated. See the example below:

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Also, if the Atoll session has been open for a long time, memory problems may even appear while working on smallernetworks. This is because the process memory space (memory space allocated to Atoll by the operating system) becomesfragmented.

Following is a list of advices, which you can follow in order to avoid such problems:

• Use regionalisation or site lists: If you load a large network, Atoll will be required to load a lot of data that might notbe useful all of the time. For example, in a typical large GSM network, you might have around 10,000 transmitterrecords, 20,000 subcell records, 50,000 TRX records, and up to 150,000 neighbor records.

• Externalise embedded interference matrices: In Atoll 2.4.1 and 2.5.0, embedded interference matrices can beexported to external files and then removed from the .atl file to free up some memory. This might be interesting todo before launching a large C/I coverage prediction study. In Atoll 2.5.1 and above, you can externalise or embedeach separate interference matrix in the IM folder. Atoll manages the loading of interference matrices from the diskto RAM so that it occupies memory only when needed. You will also reduce the .atl file size by externalising theinterference matrices.

• Try to adapt calculation radii to the cell type and the EIRP: Before calculating path loss matrices, take care in cor-rectly associating calculation radii and resolutions to different types of cells. If you calculate path loss matrices forall types of cells over a large calculation radius, it will unnecessarily burden the C/I and interference matrices com-putations.

• Properly configure the interference thresholds: These thresholds indicate the level from which onwards an inter-ferer can be ignored. The default value for this threshold (-130 dBm), defined in the Predictions tab of the Predic-tions folder’s Properties dialog, implies that the computations will take into account all the intererers. However, ifyou set it too high, you might lose important interference information. The proper value for this threshold dependson the Reception Thresholds and the C/I Thresholds defined in the Subcells table. The optimum value would be

. Which means the minimum value of the factor computed for all

subcells, i. Where, RTi is the reception threshold of the subcell i, CITi the C/I threshold of this subcell, and M is a

safety margin.

Since this interference threshold is used both in interference matrices calculation and in interference predictions,it is important to take at least 3 dB margin for the interference energy aggregation in C/I studies. We recommenda safety margin of 5 dB, which can be reduced any problem is encountered.

• Do not define very high C/I quality thresholds (Default values: 12 dB for BCCH and 9 dB for TCH). If you want acertain TRX type to carry GPRS/EDGE traffic, you can add 1 or 2 dB to this value for that TRX type, and use theoption of safety margin in the AFP module’s Cost tab. The 12 dB and 9 dB default values already include safetymargins. If you increment these values too much, it will unnecessarily load the interference matrix generation andthe AFP.

• Do not start an AFP session if the interference matrices report indicates problems: All the transmitters should haveinterferers and very few of them (not more than 20%) should have more than 70 interferers. If there are too manyor too few entries in your interference matrices, the AFP plan will not be optimum.

• If the memory-critical task is interference matrices generation: You can generate interference matrices in a piece-wise manner.

This means that you can generate nation-wide interference matrices with low resolutions based on the % of inter-fered area (to improve computation time), with a cell edge coverage probability of 50% (which implies no accessto clutter forreading standard deviation values), and an interference threshold of -112 dBm. This will provide roughglobal interference matrices which can be locally improved. These interference matrices will be less memory-consuming.

Then, use polygon or site list filters to focus on each important location, and calculate local interference matriceswith higher resolutions and reliabilities. Make sure that the computation zone in your project completely encom-passes the filtering zones that you define.

If you are working with Atoll 2.3.1 upto 2.5.0, you must first import the high resolution interference matrices, andthen the low resolution matrices. This is automatically performed by Atoll 2.5.1 and above.

• If the memory-critical task is the AFP session: Try to make the document lighter, e.g. remove coverage predictionstudies, exit and restart Atoll, and try to generate interference matrices having less number of entries.

• If the memory-critical task is the traffic capture: You can use traffic load field of the Subcells table to provide trafficloads directly to the AFP, and possibly skip this step.

MinAllSubcells RTi CITi– M– RTi CITi– M–

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Interference Matrices

Chapter 7


Chapter 7: Interference Matrices

7 Interference MatricesAtoll can simultaneously use more than one interference matrices. There is no size limit to the interference information thatyou can use. And, it is possible to keep the interference matrices updated when transmitters are renamed or deleted, orthe radio network data is reloaded from a database.

You can create different scenarios in Atoll, such as:

• Working with many small (regional) interference matrices instead of one country wide matrix

- If recalculation is required, you can recalculate just the concerned matrices instead of recalculating an entirecountry-wide matrix. The calculation of smaller matrices is quicker as well.

- Using the AFP for a certain region only requires to load the interference information for that region.

• Working with interference matrices of different resolutions

- You can have, for example, a country-wide matrix of lower resolution completed by high resolution regionalmatrices. The AFP can use the country-wide matrix where the high-resolution matrices are not available.

• Working with interference matrices of different types

- Interference matrices based on drive tests can be updated from the measurements as they are carried outfrom time to time in each region.

- Interference matrices based on RXLEV statistics from the OMC can be updated as the statistics are madeavailable from the OMC. Each time the information will be collected with a different list of (dummy) neighbours.The actual neighbours remain the same; therefore, these interference matrices can be combined based on a"Worst case combination". If they are combined by averaging, a neighbour interferer will be n times strongerthan an equivalent non neighbour interferer.

You can combine interference matrices of the same type and import for use in Atoll, or you can import these interferencematrices in Atoll as lower bound interference matrices. In both cases, the AFP uses the interference information correctly.

Interference matrices of the different types, resolutions, and sizes are listed under the Interference Matrices folder. Thefollowing sections describe how interference matrices can be stored, imported, combined, and calculated.

Features in Atoll

The following features are available concerning interference matrices in Atoll.

• Support of different types of interference matrices.

You can import and work with interference matrices from different sources:

- Based on path losses (propagation)- Based on data from the OMC- Based on drive test data

• Support of different sizes of interference matrices.

You can work with either a lot of of small (local) or fewer large interference matrices, with different resolutions.

• Support of more than one interference matrix with the possiblity to activate and deactivate the matrices.

You can import and work with more than one interference matrix. All the interference matrices, available in theInterference Matrices folder, correspond to a network state.

- You can work with interference matrices with different interference information about the same pixel. Duplicateinformation is managed by Atoll.

- The information in the interference matrices is compressed.- Interference matrices only require memory (RAM) when in use.- Interference matrices can be saved to external files, without any loss in performance, so that the .atl file size

is not impacted.- Each interference matrix has its own scope and context.

• Support of maximum likelihood combination.

The Atoll AFP module can combine interference matrices, using their scopes and contexts and a maximum likeli-hood combination method.

- The Atoll AFP module has access to the the scopes and contexts of interference matrices, and can intelligentlycombine different interference matrices.

- The combination process takes into account no-interference and interference information from interferencematrices.

- The Atoll AFP only loads the active and relevant interference matrices in memory during calculations. Inactiveinterference matrices and interference matrices that do not belong to the studied area are not loaded.

General API Features

Atoll’s general API can be used to manage interference matrices. You can read and write interference data, and the scopeand context of interference matrices via the API. It is also possible to run interference matrix calculations (in batch mode)using the API, which allows you to automatically prepare the interference matrices for the AFP in the background.

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AFP API Features

Automatic frequency planning tools can access active interference matrices through the AFP API. The AFP can select theinterference matrices to load, and has access to the scope and context parameters of each IM. The AFP can also readthe different interference values predicted by each of the loaded interference matrices.

7.1 Types of Supported Interference MatricesInterference matrices can be generated based on different sources of information and propriety software. The followinglist includes 9 typical information sources that can be used to create interference matrices supported by Atoll.

1. Based on path loss (propagation data) matrices

Reliability depends on the accurate and correct network and geo data.

2. Based on reselection statistics from the OMC

Reliability usually low due to difference between the locations where mobiles are switched on and where they areactually used to access the network.

3. Based on handover statistics from the OMC

Reliability usually low due to the fact that interference is measured only among existing neighbours, which mightnot be correctly assigned. This type of interference matrices are highly correlated with the neighbour relations. Itcan be used as a measure to remove excess neighbour constraints. However, it can not be used to complete anymissing neighbour information. Another reason for low reliability is that interference information is collected fromthe handover regions only, which is different from the service area.

4. Based on RXLEV statistics from the OMC

Can be a very good source of interference information if it is statistically stable because it is not sensitive to dataerrors. On the other hand, it has many disadvantages, such as:

- Transmitters with the same BSIC and BCCH cannot be differentiated.- Transmitters having the same BCCH will never have an interference entry.- Information is lost when more than 6 interferers exist at a location.- If many interferers share the same BCCH, they increase the interference levels of each other.- HCS layers may cause problems: more servers at a point, macro layer servers are stronger, a correction

margin might be introduced in some equipment, etc.

This type of interference matrices can be created using an extended neighbours list.

5. Based on test mobile data

Reliability can be low because usually the test mobile data sampling zone and the traffic model are not related.Secondly, the measurements are carried out for existing neighbours.

6. Based on CW measurements

Reliability can be low because usually the measurements do not reflect the traffic model. However, this source ofinformation can be very reliable for a subset of transmitters that was properly scanned. Carrying out CW meas-urements is expensive, which implies that often the collected information is partial or out of date.

7. Based on scan data drive tests

Highly reliable and an excellent source of information, but not usable in a radio planning tool because no informa-tion is available for mapping transmitters to the received signals at any pixel (x, y).

8. Upper bound interference matrix

The source of this type of interference matrix is not defined. It can be based on user experience. The informationcontained in this interference matrix is used as an upper limit, i.e., if this interference matrix indicates a certainlevel of interference, it should not be exceeded because other interference matrices show higher interference. Ifan upper bound interference matrix does not contain information about an entry, it is ignored.

9. Lower bound interference matrix

The source of this type of interference matrix is not defined. It can be based on user experience. The informationcontained in this interference matrix is used as a lower limit. This type of interference matrix can be very usefulbecause you can edit entries in this interference matrix, and be certain that the interference will be at least as highas the value you entered. This approach can be used when user experience shows a certain level of interferencewhich the radio network planning tool is unable to calculate.

7.2 Interference Matrices StorageThe interference matrices listed in this folder can be stored in the .atl file by embedding, or in external files, by externalising:

• Embedded interference matrices:

Advantages:

- Efficient and more flexible memory access and usage

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- Interference matrices are stored as binary format data, and can be (re)loaded to the RAM when needed (bythe AFP, for generating reports, or for exporting)

- Read/Write operations are quicker

Disadvantages:

- File size limit restricts the amount of information that can be stored in a .atl file.

• Externalised interference matrices:

Atoll can externalise interference matrices to one of the supported file formats. However, only the .clc file formatcan store complete information of an interference matrix. Please refer to the Technical Reference Guide for moreinformation on the different file formats.

Advantages:

- The size of the Atoll document is not affected by the size of the externalised interference matrices listed in theInterference Matrices folder.

Disadvantages:

- Read/Write operations take a bit longer with external files, therefore, once the interference matrix is loaded tothe RAM, it is kept loaded.

- File sharing between users is not possible.

You should externalise interference matrices if the .atl file size is close to the file size limit. It is, otherwise, recommendedto keep the interference matrices embedded.

7.3 Multiple File ImportMore than one interference matrix can be imported. If you have an interference matrix that covers a part of the network,and another that covers the entire network, and you want that the larger IM complete the smaller one, you must import thesmaller one before the larger one. So, when Atoll imports the smaller IM first, and the larger one afterwards, if an entryalready exists in the smaller IM, Atoll will ignore that entry in the larger IM.

It is also possible to select more than one file in the Open dialogue when importing interference matrices. In this case, filesare imported in the order in which they are selected.

7.4 Maximum Likelihood CombinationOne of the more advanced features of an AFP is to intelligently combine different interference matrices, and, in the caseof a frequency plan with interference, to determine which interference corresponds to which interference matrix.

Different types of interference matrices have different weak points. The maximum likelihood approach detects and avoidsthese weak points. Another important aspect of maximum likelihood combination is the capability to differentiate betweenno-interference and unknown-interference. Moreover, the maximum likelihood method keeps the information about thetype of the interference matrix, its quality indicators, and its scope.

The next two sections explain the maximum likelihood combination performed by the Atoll AFP Module. Before describingthe combination process, the scope and context of interference matrices is explained.

7.4.1 Scope and Context of Interference Matrices

7.4.1.1 Interference Matrix ContextThe context of an interference matrix refers to the following properties associated with each matrix:

1. Name (and comments, if any)

2. External file name (if the matrix in externalised)

3. Active or not

4. Type (one of the 9 types described in "Types of Supported Interference Matrices" on page 76)

5. Type-dependent quality indicators

The context of an interference matrix is mainly used to indicate the statistical quality if the interference matrix so that theAFP can weight the information read from the interference matrix accordingly.

Atoll can support a number of AFP tools. The interference matrix combination process, which is a part of the cost function,can be different in different AFP tools. The context of interference matrices allow a common representation and signifi-cance of the parameters influencing the combination process. These parameters are, therefore, described as a set of qual-ity indicators, with comprehensive units, such as the number of measurement days, standard deviation, calculationresolution, and whether the interference matrix is based on traffic or surface area.

The General tab of the Interference Matrix Properties dialog gives you access to the first three (see Figure 7.1: onpage 78).

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The Advanced tab lists the type and the quality indicators of the interference matrices (see Figure 7.2: on page 78).

Depending on the matrix type, the quality indicators available in the Advanced tab include:

1. For matrices based on path loss (propagation data) matrices

- The standard deviation- The resolution- Whether the interference information (probabilities) correspond to traffic or surface area

2. For matrices based on reselection statistics from the OMC

- The statistic duration- Whether the interference information (probabilities) correspond to traffic or surface area

3. For matrices based on handover statistics from the OMC

- The standard deviation, depending on the equipment quality and measurement post-processing- The average number of points collected in each matrix calculation point- The volume of information- Whether the interference information (probabilities) correspond to traffic or surface area

4. For matrices based on RXLEV statistics from the OMC

- The statistic duration- Whether the interference information (probabilities) correspond to traffic or surface area

Figure 7.1: Interference Matrix Properties Dialog - General Tab

Figure 7.2: Interference Matrix Properties Dialog - Advanced Tab

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5. For matrices based on test mobile data

- The standard deviation, depending on the equipment quality and measurement post-processing- The average number of points collected in each matrix calculation point

6. For matrices based on CW measurements


7. For matrices based on scan data drive tests


The context of an interference matrix is not included in the interference matrix files. That is why Atoll asks the user to setupthe type and quality indicators of the interference matrix manually.

7.4.1.2 Interference Matrix ScopeThe scope of an interference matrix is a mapping between a transmitter ID and the following information:

1. Transmitter name

2. BSIC (as was when IM statistics were gathered)

3. BCCH (as was when IM statistics were gathered)

4. % of victim coverage (an integer between 0 and 100)

5. % of interferer coverage (an integer between 0 and 100)

The most important information of the scope is contained in the columns "% of victim coverage" and "% of interferer cover-age". In order to understand their significance as well as their use, the following should be kept in mind:

• Interference matrices must provide interference information between each pair of subcell in the network. A largeamount of memory would be required for a simple sequential representation of the interference matrix, whichwould make it impossible to work with such interference matrices in large networks. Therefore, interferencematrices are represented as a set of entries for which interference exists. If an entry (i, j) does not exist in the set:

- Either j does not interfere i (no-interference),- Or the interference information is missing in the interference matrix because at least one of the two was out

of the scope of the interference matrix (unknown-interference).

In other words, the lack of information can be interpreted as either no or unknown interference.

• If there is only one interference matrix, it can be considered complete since it is the only source of interferenceinformation. In this case, there is no difference between no and unknown interference. If there is more than oneinterference matrix, the information missing in one matrix could be available in another. Therefore, it becomes veryimportant to distinguish between the two cases in order to intelligently combine different interference matrices.

Figure 7.3: Interference Matrix Scope

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The ideal method for differentiating between no-interference and unknown-interference cases would be to keep a matrixof values in memory, which depicts the reliability of each of the matrix entries, and thus, depicts the entries for which theinterference is "Unknown" as unreliable entries. It is not practically possible to implement such a method simply becausethis matrix of values will be too large to work with.

Therefore, Atoll includes a slightly restricted approach for storing the scope of interference matrices. Interference matricescontain two reliability indicators at transmitter level, i.e., the reliability when a transmitter is the victim, and the reliabilitywhen it is the interferer. This information is stored in the columns "% of victim coverage" and "% of interferer coverage".

The reliability of an entry (i, j) is:

VictimCoverage(Transmitter(i)) * InterfererCoverage(Transmitter(j))

This implementation is simple, compact, and sufficient for the most interference matrices.

Creation of the Interference Matrix Scope

The scope of an interference matrix is created by the tool that creates the interference matrix. If the interference matrix iscreated by Atoll, the AFP scope is used as an initial set of victims, which It corresponds to SEL + RING (see "Definition ofthe AFP Scope" on page 22). This means that even when only one transmitter is present inside the computation zone,many other transmitters may be taken into account in the set of victims. Atoll adds all potential interferers to this set, andcalculates the interference matrix. The interference matrix is accurate only between transmitters that are in the victim set.Inaccurate entries are removed, and the scope of the interference matrix becomes the victim set with 100% at both victimand interferer coverage.

Other software can be used to edit the interference matrix scope using the general API features, or by externalising theinterference matrix in the .clc format and editing it. The .clc format can store all the interference matrix information (seethe Technical Reference Guide for more information).

Two possibilities (examples) for editing the interference matrix information could be:

• An Addin that imports an interference matrix should should know its scope. For example, if it is an OMC addin,and the OMC covers 50 transmitters, the scope will contain 50 transmitters. Their indexes will be supplied by Atollonce added to the scope. The % of victim and interferer coverages should be 100%.

• When generating an interference matrix from CW measurements, there might be a few transmitters which werecorrectly scanned and others that were not. In this case, the correctly scanned transmtters would have good % ofvictim and interferer coverages, while the others would not.

Use of the BSIC and BCCH in the Scope

The BSIC and BCCH fields in the scope are used for the cases where the BSIC and BCCH allocation, during the periodwhen the interference matrix information was gathered, was different from the current BSIC and BCCH allocation.

7.4.1.3 Keeping the Scope and Context Up to DateWhen a .clc file (and its corresponding .dct) are imported, the transmitter indexes in the files can be arbitrary. In order toimprove access time, Atoll changes these indexes to the ADO record ID as index. When you rename or delete a transmit-ter, or when the ADO index is changed, the interference matrix is automatically updated, and saved when the Atoll docu-ment is saved.

Instead of updating the interference matrix every time a transmitter is renamed or deleted, Atoll stores the events inmemory, and updates the interference matrix only when it is used. It checks the ADO record ID’s and, if they have beenchanged, the changes are taken into account.

7.4.2 Interference Matrix Combination in Atoll AFP ModuleInterference matrices are combined considering the following criteria:

• The cost function does not change

Earlier, interference values were read from a single interference matrix. Now, they are read from more than oneinterference matrix.

• If the interference matrices are correctly managed in Atoll, no further parameterisation (weighting) is required.

Notes:

• The scopes of the interference matrices are automatically created when old .clc, .im0, .im1,or .im2 files are imported. The scope is created using the current BSIC and BCCHallocation, and finding the set of all victims and the set of all interferers.

• The interference matrix scope internally manages the transmitter ID’s. When exchanginginformation with a .clc file, these ID’s are visible to the user. They are arbitrary numbersused to index the interference matrix entries. Even if an addin is used to create theinterference matrix, the association of transmitter names to ID’s is carried out by Atoll. Theaddin will associate the interference information to pairs of transmitter ID’s.

• The .clc and .dct files have the same mapping of transmitter names to transmitter ID’s.

There are no restrictions on transmitter ID’s as long as they are unique integers under 231.

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The Interference Matrice tab (see Figure 7.4: on page 81) available in the Atoll AFP Module properties dialog lets you setup the interference matrix combination by defining its three weighting components.

The interference matrix combination is carried out as follows:

1. The Atoll AFP Module asks Atoll to load a subset of the active interference matrices of the document. This subsetis determined by comparing each interference matrix scope with the AFP scope. Only the interference matriceswhose scope intersects the AFP scope are loaded.

2. The Atoll AFP Module then reads the scope and context information of each loaded interference matrix.

At a given pixel, the interference, p(i, v, x), of subcell i (interferer) on subcell v (victim) for a given C/I level x, canbe read from more than one interference matrix.

3. The Atoll AFP Module combines all the values of p(i, v, x) by performing a weighted average. Therefore, itcalcu-lates as many weights as the number of p(i, v, x) entries for a pixel. These "reliability weights" are calculated bymultiplying the following three components, which are defined in the Interference Matrice tab of the Atoll AFPModule properties dialog:

a. Component quantifying the membership to the AFP scope:

VictimCoverage(Transmitter(v)) x InterfererCoverage(Transmitter(i))

For interference matrices based on OMC statistics, if the scope indicates that both i and v had the sameBCCH, the component will be 0.

b. Component depending on the interference matrix type.

c. Component depending on the interference matrix quality indicators (see "Reliability Calculation" on page 82)

7.5 Interference Matrix CalculationAtoll can calculate two types of interference matrices, and their related information such as scope and context.

1. Interference matrices calculates from path loss data:

The quality of the interference matrices depends upon the standard deviation of the propagation model for thecorresponding clutter classes. The interference matrices are calculated using the default calculation resolutiondefined in the Predictions tab of the Predictions folder’s properties dialog. You can either base the calculation onthe percentage of overlapped traffic or on the percentage of overlapped surface area.

2. Interference matrices calculated from test mobile data:

Note:

• In Atoll version 2.5.2, the AFP considered the first value of p(i, v, x). And in Atoll version2.6.0, the AFP worked with the highest value of p(i, v, x).

Figure 7.4: AFP Interference Matrices Parameters

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The victim and interferer scope is the transmitters included in the test mobile data path. The number of points pervictim is calculated and associated with the quality indicator related with the volume of information (see "ReliabilityCalculation" on page 82 for more details). A basic statistical analysis of the test mobile data measurements iscarried out in order to estimate the values of "% of victim coverage" and "% of interferer coverage" for each trans-mitter.

Reliability Calculation

Depending on the type of interference matrix, one of the following three equations is used to determine the third reliabilitycomponent:

1. Interference matrix based on propagation:

Where is the standard deviation of the propagation model, and r is the calculation resolution. A resolution of

50 m and a standard deviation of 7.5 dB gives a weight of 1.

2. Interference matrix based on measurements from the OMC performed during n days:

Which gives a weight of 1 for 8 days of measurements.

3. Interference matrix based on drive test analysis:

3 parameters determine the weight:

a. The standard deviation , which is assumed to be lower than the one of a propagation model.

b. The number of measurements considered at each calculation point, r

c. The number of calculation points per transmitter, n

75r 25+--------------- 7.5

--------

1 n+3

-----------------

1 n r 1++ 0.4

4 1+ ----------------------------------------------

82 AT271_ARG_E4 © Forsk 2008

Appendices

Chapter 8


Chapter 8: Appendices

8 Appendices

8.1 Appendix 1: Description of the AFP Cost Function

8.1.1 NotationsThe notations listed hereafter are used to describe the cost function:

• TRG denotes a group of TRXs.• # is used instead of “number of”. For example, # TRXi is the number of TRXs in TRGi.

• “” denotes the relation “if and only if”.

• denotes the size of any group g.

• ARFCN denotes the set of all the frequencies, and the set of all the subsets of frequencies.

• “TRGs” denote the set of all the TRGs.

• denotes the largest integer (x can be a real number).

• denotes the number of times a group is assigned to TRGi in the assignment A.

For example:

- When i is NH, g is a single member group containing one of the frequencies assigned at TRGi.

If |g| is not 1 or if g does not contain a frequency assigned at i, then .

- When i is BBH, can be either 0 or #TRXi.

g is the set of frequencies assigned to TRXs of TRGi. (|g| = # TRXi).

When we talk about “TRXs of i using g”, and in the case of BBH, then there are |g| such virtual TRXs, eachusing the entire group g and having a virtual MAIO [0, |g| - 1].

- When i is SFH, must be . g is the set of frequencies assigned to n TRXs of TRGi.

We assume all the groups assigned to TRGi to have the same length.

• TSi denotes the number of timeslots available for each TRX in TRGi.

• TLi is the traffic load of TRGi. This parameter may either be calculated during dimensioning or be user specified.

of a single TRX in TRGi divided by TSi

• TSUi refers to the downlink timeslot use ratio (due to DTX) at TRGi.

• CFi is the cost factor of TRGi (AFP Weight field).

• QMINi is the minimum required quality (in C/I) at TRGi.

• PMAXi is the percentage permitted to have quality lower than QMINi at TRGi.

• REQi corresponds to the required number of TRXs at TRGi.

A communication uses the group g in TRGi if its mobile allocation is g. The probability to be interfered is denoted by

(i’ is the TRX index). Different TRX indexes may have different MAIOs. is a function of the whole

frequency assignment. The precise definition of the term “to be interfered” is provided afterwards. The probability penalty

due to violating a separation constraint is . It is a function of the whole frequency assignment as well.

The term “Atom” will be used in the following context:

For two TRGs, i and k,

i and k are synchronised, have the same HSN, the same MAL length and the same hopping mode.

NH TRGs or BBH TRGs are always in separate atoms. If two TRGs interfere but are not in the same atom, these can betaken as unsynchronised. The quality of unsynchronised TRGs is a function of all possible frequency combinations. Forsynchronised TRGs, pairs of frequencies emitted at the same time are known.

8.1.2 Cost FunctionThe Atoll AFP cost function is a TRX based cost and not an interference matrix entry based cost. It counts the impairedtraffic of the network TRXs in weighted Erlangs.

The cost function is reported to the user during the AFP progress with the help of its 5 components: , ,

, and .

= + + + +

g

2ARFCN

x x

Ai g g 2ARFCN

Ai g 1=

Ai g 0=

Ai g

Ai g #TRXi=

Ai g #TRXi Ai g n=

TLi #Erlangs=

Pi i' g A Pi i' g A

Pi i' g A

ATOM i ATOM k

mis sep

comp corr dom

mis sep comp corr dom

© Forsk 2008 AT271_ARG_E4 85

AFP Reference Guide

where,

represents the missing TRX cost component

represents the separation component

represents the additional cost component (interference, cost of changing a TRX)

represents the corrupted TRX cost component

represents the out-of-domain frequency assignment cost component

In the above equations,

• i’ is the TRX index belonging to .

• is the number of missing TRXs for the subcell i.

• is the cost value for a missing TRX. This value can vary between 0 and 10. The default cost value is set to 1

and can be modified in the AFP module properties dialog.

• is the number of corrupted TRXs for the subcell i.

• is the cost value of a corrupted TRX. This value can vary between 0 and 10. The default cost value is set to 10

and can be modified in the AFP module properties dialog.

• is the number of TRXs, for the subcell i, having out-of-domain frequencies assigned.

• is the cost value of a TRX with out-of-domain frequencies assigned. This value can vary between 0 and 1. The

default cost value is set to 0.5 and can be modified in the AFP module properties dialog.

And, as mentioned earlier, a virtual TRX is considered in case of BBH.

If i’ is valid, the algorithm evaluates the cost of a valid TRX. This cost has two components, and

.

• is the separation violation probability penalty.

• is complementary probability penalty due to interference and the cost of modifying a TRX.

If the option “Take into account the cost of all the TRXs” available in the AFP module properties dialog is selected,then,

and

Note:

• Do not let this form of representation mask the fact that the cost function is a TRX basedcost function.

mis

sep

comp

corr

dom

mis MIS_TRXi TLi CFi TSi

i TRGs=

corr CORR_TRXi TLi CFi TSi

i TRGs=

dom DOM_TRXi TLi CFi TSii TRGs=

sep 'i i' g A

g 2ARFCN

i' TRXs of i using g

TLi CFi TSii TRGs=

comp ''i i' g A

g 2ARFCN

i' TRXs of i using g

TLi CFi TSii TRGs=

0 1 ... Ai g 1–

MIS_TRXi

MIS_TRXi MAX 0 REQi Ai g

g 2ARFCN

–=

CORR_TRXi

DOM_TRXi

'i i' g A

''i i' g A

'i i' g A

''i i' g A

'i i' g A P'i i' g A = ''i i' g A P''i i' g A =

86 AT271_ARG_E4 © Forsk 2008


Or if the option “Do not include the cost of TRXs having reached their quality target” available in the AFP module

properties dialog is selected, the algorithm compares with the quality target specified for i,

:

If ,

Then and .

Otherwise,

Both and will be equal 0.

is the same as (separation violation probability penalty) and the same as

(complementary probability penalty due to interference and the cost of modifying a TRX) in most cases. These areexplained in detail in the next sections.

8.1.3 Cost ComponentsSeparation violation and interference cost components are described hereafter. Parameters considered in the cost func-tion components can be fully controlled by the user. Some of these parameters are part of the general data model (qualityrequirements, percentage of interference allowed per subcell), while others (such as separation costs and diversity gains)can be managed through the properties dialog of the Atoll AFP module.

8.1.3.1 Separation Violation Cost ComponentThe separation violation cost component is evaluated for each TRX. Estimation is based on costs specified for the requiredseparations.

Let denote the required separation constraint between TRGi and TRGk. Let denote the user

defined separation penalty for a required separation “s” and actual separation “z”. is used instead of

as abbreviation.

is considered to be the effect of a separation violation on the th TRX of TRGi assigned the group g, caused by

the th TRX of TRGk assigned the group .

denotes the overall weight of the separation violation cost component. This value can be between 0 and 1, set to 1 by

default. It can be modified in the AFP module properties dialog.

represents the weight of the specific separation constraint between i and k. This specific weight depends on the type

of separation violation and follows the following priority rule:

1. Exceptional pairs

2. Co-transmitters

3. Co-site

4. Neighbours

For example, if a pair of subcells are co-site and neighbours at the same time, they will be considered as co-site because

higher priority. Hence, of these subcells will be the weight of co-site relations. If only a neighbour relation exists

between two subcells, then will be further weighted by the neighbour relation importance. The value of remains

between 0 and 1. The default weights of each type of separation are available in the Separation cost tab.

If

Then , which is same for all values of k.

If

Then

In the above equations, is the number of frames in the MAL g. .

P'i i' g A P''i i' g A +

PMAX

P'i i' g A P''i i' g A + PMAX

'i i' g A P'i i' g A = ''i i' g A P''i i' g A =

'i i' g A ''i i' g A

P'i i' g A 'i i' g A P''i i' g A ''i i' g A

Note:

• The AFP module properties dialog takes probability percentages as inputs while thisdocument deals in probability values.

SEP_CONSTRi k Costs z

SEPi k v

CostSEP_CONSTRi k z

i i'kgg'k' i'

k' g'

ik

ik

ik ik

ATOM i ATOM k

i i'kgg'k' ik

SEPi k f f'–

f gf' g'

g g'----------------------------------------------=

ATOM i ATOM k =

i i'kgg'k' ik

SEPi k g g'–

f_n 0 1 ... F_N 1–

F_N-------------------------------------------------------------------------------------=

F_N g F_N g g=

© Forsk 2008 AT271_ARG_E4 87

AFP Reference Guide

Let denote the instantaneous frame number from 0 to .

While modulo and is the frequency in g,

And modulo and is the frequency in g’.

In addition, frequencies belonging to a MAL with a low fractional load, and breaking a separation constraint, should not beweighted equally as in a non-hopping separation breaking case. Therefore, the cost is weighted by an interferer diversitygain.

The separation gain, denoted by is basically a function of the MAL length (and, of course, of the

hopping mode). With frequency hopping, the effects of DTX and traffic load become more significant (due to the consid-eration of the average case instead of the worst case). For this reason, it is possible to consider these effects in

through the relevant option available in the Advanced tab of the AFP module properties dialog.

Without this option, the is:

is the user defined interferer diversity gain (dB) for a given MAL length. It is used in definition as well.

On the other hand, if this option is selected, the becomes,

Where ,

And

More than one separation violations may exist for a TRX. Many “small” and have to be combined to form

one cost element, the . This is done through iterating over all violating assignments and by summing up an equiv-

alent to the probability of not being violated while considering each separation violation as an independent probabilityevent. This sum is naturally limited to 100% of the TRX traffic, and is given by,

In the above formula, if , then , so that interference with itself is not taken into account.

8.1.3.2 Interference Cost ComponentThe interference cost component is evaluated for each TRX. Its estimation is based on interference histograms calculatedfor pairs of subcells. In addition, it takes into account frequency and interferer diversity gains and models frequencyhopping and gain due to DTX.

When estimating , the following problems are encountered:

• The QMINi C/I quality indicator corresponds to the accumulated interference level of all interferers while the C/Iinterference histograms correspond to pair-wise interferences.

• Both QMINi and the histograms correspond to a single frequency. In case of a MAL containing more than one fre-quencies, interferences on several different frequencies of a MAL must be combined.

Note:

• Since , we shortly denote the two as .F_N g F_N g' = F_N

f_n F_N

f_n MAIOAi g i' + = F_N g th

f_n MAIOAk g' k' + = F_N g' th

Gi k g g' 1

100.1 SEP_GAIN i k g g'

--------------------------------------------------------------------=

SEP_GAIN i k g g'

SEP_GAIN i k g g'

SEP_GAIN i k g g'

SEP_GAIN i k g g' I_DIV g =

I_DIV g Pi i' g A

SEP_GAIN i k g g'

SEP_GAIN i k g g' I_DIV g 0.5 TSU_GAIN k min 10 4 2 I_DIV g + 2 ASYN_GAIN i k g' + 4

----------------------------------------------------------------------- +

+=

TSU_GAIN k log101

TLk TSUk------------------------------- =

ASYN_GAIN i k g' 0 if ATOM(i) = ATOM(k)

I_DIV( g' Otherwise=

Gi k g g' 'i i'kgg'

P'i i' g A

P'i i' g A

1 1 i i'kgg'k' Gi k g g' –

k TRGs

g' 2ARFCN

k' TRXs of k using g'

–

=

k i= k' i'

Note:

• Interference histograms are described in User Manual (GSM GPRS EGPRS projectmanagement, GSM GPRS EGPRS network optimisation, GSM GPRS EGPRS genericAFP management). Interference histograms can also be exported to files. For furtherdescription, refer to "Appendix 2: Interferences" on page 91.

P''i i' g A

88 AT271_ARG_E4 © Forsk 2008


This estimation, presented below, is the simplest possible as it solves the first problem by linear summation andtruncation at the value of 1 and it solves the second problem by averaging and adding the two diversity gains:

• , the frequency diversity gain, and

• , the interferer diversity gain.

Hereafter, denotes the global weight of interference cost component. This value can vary between 0 and 1 and is set

to 0.35 by default, which can be modified in the AFP module properties dialog.

Let be the number of frames in the MAL g. .

Let denote the instantaneous frame number from 0 to .

Let be the j’th MAIO of , where j is one of the TRXs.

The value of is one of

If TRGk is NH, then .

If TRGk is BBH, then .

As said earlier, in case of BBH, we consider virtual TRXs, the jth TRX has the MAIO j.

Let be the ith frequency in the group g.

Similar to the definition of , is defined as an interference event. is the effect interference on the

th TRX of TRGi assigned the group g, caused by the th TRX of TRGk assigned the group .

If

Then

Where

If

Then,

Since , these are both represented by .

Where,

,

,

modulo ,

modulo ,

Therefore, we have,

In the above formula, if , then , so that interference with itself is not taken into account.

The sum is limited to 100% of the TRX traffic. is quite similar to . The

only difference is the frequency diversity gain, , added to .

F_DIV g

I_DIV g

F_N g F_N g g=

f_n F_N

MAIOAk g' j Ak g' 0 1 ... Ak g' 1–

MAIOAk g' j 0 1 ... g'

MAIOAk g' j 0=

MAIOAk g' j j=

g'

gi

i i'kgg'k' 'i i'kgg'k' 'i i'kgg'k'

i' k' g'

ATOM i ATOM k

'i i'kgg'k'

Probabil ityCIik----- Q_UBi k f f'

g g'--------------------------------------------------------------------------------

f g f' g'=

Q_UBi k f f' QMINi f f'– ADJ_SUP INTERF_GAIN i k g g' +–=

ATOM i ATOM k =

F_N g F_N g' = F_N

i i'kgg'k'

ProbabilityCIik----- Q_UBi k f f'

F_N--------------------------------------------------------------------------------

f_n 0 1 ... F_N 1– =

f g=

f' g'=

f_n MAIOAi g i' + = F_N

f_n MAIOAk g' k' + = F_N

Q_UBi k f f' QMINi f f'– ADJ_SUP INTERF_GAIN i k g g' +–=

P''i i' g A 1 1 P'i i' g A – 1 i i'kgg'k'–

k TRGs

g' 2ARFCN

k' TRXs of k using g'

– P'i i' g A –=

i k= k' i'

INTERF_GAIN i k g g' SEP_GAIN i k g g'

F_DIV g SEP_GAIN i k g g'

© Forsk 2008 AT271_ARG_E4 89

AFP Reference Guide

8.1.4 I_DIV, F_DIV and Other Advanced Cost ParametersWhen combining interference effects (or separation violation effects) on different frequencies belonging to a MAL, thefollowing considerations should be taken into account:

1. Non-linearity of Frame Error Rate (FER) with respect to average C/I conditions and MAL length.

2. Interference Diversity Gain. This factor represents that the effect of average negative effects over user geographiclocation are directly proportional to the MAL length.

3. Frequency Diversity Gain. This factor models the gain due to diversity of multi-path effects and should be appliedto the interference cost component only.

4. The fact that long MALs with synthesized hopping permit discarding the worst case estimation and include a gaindue to DTX and low traffic load at the interferer end.

The Advanced properties tab shown in the figure below facilitates modelling these effects.

The Interference Diversity Gain table lists the values of I_DIV provided as a functions of MAL length. This gain is appliedto the interference cost component and to the separation constraint violation cost component. Therefore, it provides ameans to model the non-linear FER effects and interference diversity both. The default values in this table correspond to

the curve . This equation generates values somewhat lower than empirical best-found values (this is

because we prefer a slightly pessimistic cost function to be on the safe side).

The other table contains the F_DIV values, which are the same as the I_DIV values by default.

Figure 8.1: Atoll AFP Module Properties - Advanced Tab

y 2 log10 x =

90 AT271_ARG_E4 © Forsk 2008


8.2 Appendix 2: InterferencesIn the Technical Reference Guide, Chapter 3.8 (File Formats: Interference Histogram Formats), there is a detailed descrip-tion of the Atoll’s interference representation. The User Manual contains additional descriptions of interference usage:importing, calculating, keeping up-to-date etc. This appendix explains what is carried out at high level.

8.2.1 Using InterferencesIf interferences are to be taken into account by the AFP, they must be calculated or imported beforehand. In order to dothis, the user should previously decide to take interferences into account (enabling the loading of all the potential inter-ferers). Otherwise, Atoll does not allow performing their computation by disabling the histogram part in the correspondingdialog.

8.2.2 Cumulative Density Function of C/I LevelsFor each [interfered subcell, interfering subcell] pair, Atoll calculates a C/I value on each bin of the interfered subcell serv-ice area (as if the two subcells share the same channel). Then, Atoll integrates these C/I values to determine a C/I distri-bution and transforms this distribution function into a cumulative density function in the normal way.

In Atoll, both the IMco and IMadj are represented by this Cumulative Density function This implies that each query for the

probability to have C/I conditions worse than X dB requires a single memory access: the co-channel interference proba-bility at X dB. In order to deduce the adjacent interference probability value, Atoll looks up the cumulative density functionat the value corresponding to X - Y dB, Y dB being the adjacency suppression value. The following example may be helpfulin further clarifying this concept:

Example: Let [TX1, BCCH] and [TX2, BCCH] be the interfered and interfering subcells respectively. The service areas forboth have been defined by Best Server with 0 dB margin. The interference probability is stated in percentage of interferedarea.

In this case, we observe that the probability for C/I (BCCH of TX2 effecting the BCCH of TX1) being greater than 0 is 100%(which is normal because TX1 is the Best Server). The probability of having a C/I value at least equal to 31 dB is 31.1%.For a required C/I level of 12 dB on the BCCH of TX1, the interference probability is 6.5% (as this requirement is fulfilledwith a probability of 93.5%).

8.2.3 Precise Definition is defined to be the probability of a communication (call) occupying a timeslot in subcell v (victim) to have

C/I conditions of C_I with respect to a co-channel interference from the BCCH TRX of cell n (neighbour). We assume C_Ivalues to be discrete and in dB. CDF(Pci) is the cumulative density function of Pci:

Figure 8.2: The cumulative density of C/I levels between [TX1, BCCH] and [TX2, BCCH]

Note:

• The subcell power offset does not enter the calculation results in the .clc file. It is addedlater by the AFP interface. On the other hand, its influence on the subcell service zone istaken into account in the .clc file.

Pci v n C_I

CDF Pci v n C_I Pci v n x x C_I=

© Forsk 2008 AT271_ARG_E4 91

AFP Reference Guide

8.2.4 Precise Interference Distribution StrategyWhy does Atoll calculate and maintain precise interference distributions, while the most common solution (used by mostother tools) is rather to compress the information into two values: the co-channel and adjacent-channel interference prob-abilities?

The reason is simply that it,

• improves the AFP result,• introduces very little (or no) overhead, and• creates more generic interference information.

8.2.4.1 Direct Availability of Precise Interference Distribution to the AFPIn the presence of frequency hopping, and when one or more frequencies are common (or adjacent) in two interfering MALsequences, the hopping gain depends on following factors:

• the MAL length,• the traffic load on the interferer TRX,• DTX level, and• the number of common (and adjacent) frequencies in the two MALs.

All these factors cannot be pre-calculated since it is the AFP that determines the MAL length and the MAL frequencies.

8.2.4.2 Efficient Calculation and Storage of Interference DistributionIn the innermost loop of the calculation process Atoll increments a counter each time a C/I level has a certain value. In thecase of a two-entry IM, there are only two counters for each [interfered, interferer] pair. In the case of precise distributioninformation, there are about 40 counters per pair. In both cases, the number of operations is the same: one increment ofan integer value. Once Atoll finishes the counting for an [interfered, interferer] pair, it compresses the information from thecounters to a Cumulative Density Function (CDF) representation. In this way, access to interference probability at a certainlevel is instantaneous. Thus, the only overheads are the read / write times to the files and the memory occupation atrunning time. These two overheads are negligible and do not affect the calculations, the heaviest part of the task.

8.2.4.3 Robustness of the IMBy having precise C/I distributions calculated and exported, the user is free to change the following settings without theneed for recalculating their interference distributions:

1. Quality requirements of network elements (required C/I, % Probability Max, …),

2. C/I weighting (the interference levels above and below the C/I target),

3. Separation requirements and/or neighbour relations,

4. Hopping gain values, DTX activities, traffic load levels, HSNs, synchronisation information,

5. Any frequency assignment setting (MAL length directives, frequency domains, assignment strategies, number ofrequired TRXs, cost function parameters, …), or

6. Remove equipment

By not mixing any of the elements above, the interference information keeps its original probability units and is easier tocheck and validate. Therefore, the user spends less time on interference recalculations than in the case of a two-entrymatrix (where “everything” is included).

8.2.5 Traffic Load and Interference Information DiscriminationAtoll maintains the traffic load separate from the interference information. The reasons for implementing this strategy areexplained here.

Let us look at the possible alternatives to this strategy:

1. The mixed option: The interference information contains the traffic information as well. In this way, each IM entrywill contain the quantity of traffic interfered if a co-channel / adjacent channel reuse exists.

2. The separated option: The AFP has separate access to traffic load information and to interference probabilities(As in Atoll).

Knowing the difference between the two alternative solutions explains why the second strategy has been opted for for Atoll.However, in detail, this has been done because:

• Option 2 is a superset that contains option 1. But option 1, being a subset, does not contain option 2 (i.e. once theinformation are mixed they cannot be separated).

• It does not create any overhead (the size of the additional information is negligible compared to the size of the IM).• It helps keeping the unit definitions simpler.• It is facilitates merging IMs with different traffic units.• The traffic information can be used for weighting the separation violation component.• The traffic load can be used in deciding whether a TRX can be left uncreated.

92 AT271_ARG_E4 © Forsk 2008


For example, if there are too many TRXs at a site and the user wishes that the AFP remove one of them, in orderto be able to not violate site constraints, the AFP must know the traffic loads in order to choose a low load TRX tobe removed.

• The gain introduced by the traffic load of the interferer depends on the hopping mode and the MAL size. Incorpo-rating this gain in the IM (as a result of the mixed option) means that the IMs become hopping-mode and MAL-size dependent. This is a bad idea since the AFP should be able to change the MAL. And the user should be ableto change the hopping mode without recalculating the IM. In addition, an IM calculated externally to Atoll, with anon-hopping BCCH can be used for the hopping TCH.

A third option also exists. Though, this option is so practically useless due to its inefficiency. It consists in mixing IM andtraffic but still keeping the traffic in its isolated form. This is again a bad idea because of the unit definition and the varietyof IM sources. It involves less benefits than the option chosen in Atoll.

© Forsk 2008 AT271_ARG_E4 93

AFP Reference Guide

8.3 Appendix 3: BSIC AllocationThe soft and hard criteria of BSIC Allocation are described here. As explained earlier, not respecting the hard criterion isconsidered an error while not respecting the soft criterion just provokes a warning.

The hard criterion is easier to satisfy but must not be violated since it causes handover failures. It is based on the secondorder neighbour relation and BCCH co-channel reuse.

The soft criterion uses interference information as well and expands the BSIC reuse prohibition over adjacent-channelBCCH use. It aims at inducing a larger (BSIC, BCCH) reuse distance. When unable to satisfy this criterion, Atoll BSICallocation algorithm will use the interference and separation relations to choose the “least interfering” BSIC to assign.

8.3.1 DefinitionsHere,

• “iff” is used instead of “if and only if”.• “Pred” is used instead of predict.• Let Pred_Nei(X, Y) be True iff X is a neighbour of Y or Y is a neighbour of X.

• Let Pred_Nei_Of_Nei(X, Y) be true iff there exist Z such that Pred_Nei(X, Z) and Pred_Nei(Y, Z).• Let Pred_Co_BCCH(X, Y) be true iff X and Y both have the same BCCH.• Let Pred_Adj_BCCH(X, Y) be true iff X and Y both have adjacent BCCH frequencies.• Let Pred_Int(X, Y) be true iff X interferes with Y or Y interferes with X.

8.3.2 Hard CriterionProhibit using the same BSIC in both X and Y iff,

(Pred_Nei_Of_Nei(X, Y) OR Pred_Nei(X, Y)) AND Pred_Co_BCCH(X, Y)

8.3.3 Soft CriterionProhibit using the same BSIC in both X and Y iff,

(Pred_Nei_Of_Nei(X, Y) OR Pred_Int(X, Y) OR Pred_Nei(X, Y)) AND (Pred_Co_BCCH(X, Y) OR Pred_Adj_BCCH(X, Y))

8.3.4 BehaviourAs obvious, the soft constraint is much stronger and has a higher probability of not being respected.

For any criterion not respected, the AFP issues a warning message counting the number of times the AFP was blockeddue to each of the two criteria. The Consistency checking tool considers the cases where the hard criterion is not respectedas errors. The previous algorithm (version 2.2.1) had a weaker soft criterion and had a tendency of using fewer BSICs.

For a realistic test-bench network (using only one NCC), following BSIC usage results were obtained:

Note:

• For all X, Y in the network, if Pred_Nei(X, Y) then Pred_Nei(Y, X).

Old algorithm

(equal use of BSIC disabled)

Old algorithm

(equal use of BSIC enabled)

New algorithm

(equal use of BSIC disabled)

New algorithm

(equal use of BSIC enabled)

BSIC 20 204 36 74 49

BSIC 21 112 50 79 47

BSIC 22 52 45 76 39

BSIC 23 10 52 64 47

BSIC 24 1 52 39 44

BSIC 25 0 50 28 49

BSIC 26 0 48 16 52

BSIC 27 0 46 3 52

94 AT271_ARG_E4 © Forsk 2008


8.4 Appendix 4: Traffic Capture and Dimensioning

8.4.1 IntroductionThis appendix describes key GSM (and other TDMA based) network design processes in Atoll, namely Traffic Captureprocess and Network Dimensioning process. The purpose of this appendix is not to detail the algorithms and formulas onwhich these processes are based, but rather to describe their concepts and processing steps. A glossary of terms usedthroughout this document is provided in the beginning to familiarize the reader with terminology employed in Atoll and inthis document as well. It should be noted that the sequence in which these processes are explained is also, usually, thesequence of designing a GSM network. Though modifications (optimisation or otherwise) in a mature GSM network maynot necessarily follow this rule. The features described in this appendix are:

• Traffic Capture• Network Dimensioning (and Key Performance Indicator calculation)

Traffic Capture in Atoll is defined as the process of reading raw traffic data from the traffic maps and integrating them togenerate traffic demand for each subcell. In order to perform a Traffic Capture, Atoll collects traffic information (in the formof Services, Mobility types, Terminal types) from traffic maps and network parameters/criteria (HCS priorities, service zonemodel, HR/FR activity percentages, other compatibility criteria, etc.) from the traffic model. Then, it distributes this trafficaccording to the criteria over the network’s subcells, and generates and assigns the calculated traffic demand to eachsubcell. Traffic Demand is defined as the number of Circuit Switched/Packet Switched traffic Erlangs/kbps in a subcell.The results from this process are ready to be utilized in the next step.

Network Dimensioning is the process that determines the number of TRXs per subcell required to carry the trafficassigned to it while respecting the QoS/GoS criteria defined. The traffic captured by the network’s subcells in the previousstep is the main input to this process along with the Quality of Service (or Grade of Service for Circuit Switched traffic)criteria defined by the user. Assigning a large number of TRXs to a subcell may guarantee the QoS required but will makethe generation of a good frequency plan more difficult. This will also increase the infrastructure cost that depends directlyupon the quantity of equipment required. Therefore, network dimensioning is a more sophisticated process than a mereestimation. Additional outputs of this process are the Traffic Load values (used by the Automatic Frequency Planners) andthe Key Performance Indicators (KPIs).

8.4.2 Traffic Map GenerationTraffic map generation is the process of creating a geographic distribution of offered traffic demand based on user definedtraffic inputs. Atoll is capable of creating, editing, importing and exporting various types of traffic maps. Atoll is capable ofworking with raster and vector maps, and incorporates the function of spreading live traffic data (from the network) in theform of a traffic map.

8.4.3 Traffic Capture ProcessTraffic capture is the process of determining and accumulating served traffic onto specific network elements and bearers.To facilitate comprehension, we will divide the description of the entire process into three parts, the inputs, the calculationengine and the outputs.

8.4.3.1 InputsThe following inputs are required for performing a traffic capture:

• Defined traffic model data (Services, Mobility types, Terminal types)• Traffic map(s) (either internally generated, imported or edited)• Network elements (Transmitters, Subcells, HCS layers, Frequency domains, equipment, …)

The traffic model data contain the requirements for a certain class of traffic. Numerous classes of traffic can be createdthrough combinations of [Services, Mobility types, Terminal types]. For example, a Packet Switched service requiring acertain kbps data throughput, allowing a certain maximum number of simultaneous timeslots to be used, with a minimumblocking probability, together define a minimum Quality of Service criterion. When this service is accessed by a user withcertain mobility through a certain type of terminal device, this constitutes a particular class of traffic.

Traffic maps can comprise many such traffic classes with user densities for each geographically distributed over the entirenetwork or a part of it. Different traffic maps, raster, vector and live data, can be overlaid as shown in the figure below.During the traffic distribution, Atoll combines or integrates the traffic data read from these multiple layers of traffic maps togenerate the traffic per bin.

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The next section describes how these data, traffic information, compatibility criteria, and requirement criteria, are utilizedin distributing and assigning this traffic to the network’s sectors (subcells, to be precise).

8.4.3.2 The EngineThe Traffic Capture performs three principal tasks. First of all, it computes a Best Server per HCS layer prediction study(with the possibility to define an handover margin and a coverage reliability level at the boundaries) to define boundariesand overlaps between sectors corresponding to different layers and to generate an estimate timeslot capacity in kbps/timeslot per sector. You can choose whether the later be based on C or C/I and C/(I+N). Secondly, it divides the trafficinput from the maps between different HCS layers of the network and between sectors of the same layer complying withthe criteria defined in the data model. In the end, it integrates the traffic distributed to each subcell to generate the endresult: traffic demand per [service, subcell] pair in terms of Erlangs for CS traffic and in terms of kbps for PS traffic. Thistraffic demand provides Atoll with an estimate of average demand in terms of # TSL used.

These three steps are described one by one hereafter.

8.4.3.2.1 Traffic DistributionThe distribution of traffic can itself be divided into two parts, one that is performed between different HCS layers and onethat is performed between the sectors of the same layer. Here we will describe both respectively.

Inter-Layer Distribution

Once the Best Server per HCS layer prediction study has been performed in the background, Atoll proceeds to distributingthe traffic over the different HCS layers and between the subcells of each layer.

In Atoll, a user can define any number of HCS layers as required and assign priorities to them. A possible, rather probable,priority structure could be:

• Micro layer: assigned priority 3• Macro layer: assigned priority 2• Umbrella layer: assigned priority 1

Atoll starts by assigning traffic to the HCS layer with the highest priority and then moves down the priority scale. There aretwo levels of control for filtering the traffic for each layer:

• Global control• Local control

• Global Control

A user can define each HCS layer to have a certain priority in order to control its importance at the time of trafficdistribution. The priority parameter can hence be termed as one of the global control parameters that guide Atollto start with a certain HCS layer. Each HCS layer is assigned a maximum speed limit. Any user with mobility higherthan the maximum allowed on a certain layer cannot be allocated to it. Therefore, all traffic with speeds higher thanthat permissible on an HCS layer will not be assigned to it. Next, each layer can have a certain operatingfrequency. Although this parameter is managed at the TX level, a network can very well have, for example, a GSM900 layer and an 1800 layer. Only the traffic compatible with the operating frequency band of a layer will be distrib-uted over that layer. A network can also have, for example, a CS GSM layer and a PS EDGE layer. This technology

Figure 8.3: Traffic Maps Overlay

Live Traffic Data

Traffic Vector Map

Traffic Raster Map

Note:

• In Atoll, the priority levels increase directly as the integer assigned. This means that priority3 is higher than priority 2, which is higher than priority 1, and so on.

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compatibility criterion is also taken into account when distributing traffic over layers. This parameter is also at thelevel of transmitters in Atoll.

• Local Control

The local control parameters enable much finer tuning at the level of subcells. Each subcell in a network can beassigned a ‘Target Traffic Overflow’. This is the percentage of traffic that is allowed to overflow from this subcellto the lower priority layer beneath it. The figure below gives an idea of the effect of this parameter over traffic distri-bution.

In the example above, when the Target Traffic Overflow for the microcell layer is defined to be 0, the entire traffic(compatible to the micro layer, of course) covered by this cell will be carried by it. On the other hand, if there is apercentage of traffic allowed to overflow from the micro layer to the layer underneath (10% in this example), Atollwill be permitted in this case to assign this overflowing traffic to the macro layer. This parameter enables fine tuningof the network’s traffic distribution policy. This may be useful in order to avoid over-dimensioning the micro layer,or to avoid reaching the upper limit on the maximum number of TRXs that a sector can accommodate.

To be a bit more precise on the two compatibility criteria, i.e. the frequency band and technology, this compatibility compar-ison is in fact performed at the sector level. Atoll compares whether the traffic to be assigned is technologically compatiblewith the higher priority sector before handing it over to the lower priority one. For example, a user with a GSM terminalusing the 900MHz band cannot be assigned to a sector that operates on the 1800Mhz band. Similarly, a terminal access-ing a PS service using the EDGE technology cannot be allocated to a sector that can only perform CS functions.

Intra-Layer Distribution

This function enables the distribution of traffic between sectors of the same layer when there are more than one serversproviding coverage to that traffic. As, for example, in the figure below, there is an overlap between the coverage of A andB that corresponds to a certain HO margin (fixed by the user). The traffic under this overlapping region is covered by bothservers. Therefore, if the traffic complies with the compatibility criteria for both sectors, it will be equally distributed betweenthe two. Similarly, when there are more than two servers for traffic in a bin, it will be equally distributed among all the poten-tial servers of that bin.

8.4.3.2.2 Average Timeslot CapacityAtoll computes average TSL capacity for all sectors in terms of kbps for estimating the average TSL consumption relativeto the PS traffic. This capacity can either be based on the C level or interpolation between C/I and C/(I+N) for bins in thesector’s coverage area. Knowing the average kbps per TSL through this computation, and the kbps demand from the trafficassigned to a sector, Atoll is able to generate an estimate demand in terms of # TSL for PS traffic.

8.4.3.2.3 IntegrationAtoll integrates the demand in terms of # TSL from the above results to generate the resulting total demand per sector foreach service. This means that the CS traffic demand in Erlangs and PS traffic demand in kbps are converted into a totaldemand for each sector. This traffic demand per sector is later utilized when performing the network dimensioning process.

Figure 8.4: Traffiic Overflow

Figure 8.5: Intra-Layer Distribution

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8.4.3.3 OutputsThe outputs of this entire process are CS and PS traffic demands in Erlangs and kbps respectively, the average CS andPS traffic demand in terms of # TSL, and the average traffic demand in terms of # TSL. The Traffic Capture process gener-ates an item called ‘Traffic Capture X’, that is required as input to the dimensioning process.

Figure 8.6: Traffic Distribution in Atoll

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8.4.4 Network Dimensioning ProcessThe Network Dimensioning process is based on the output of a preceding traffic distribution. Once the traffic from the mapshas been distributed over the network following and respecting the criteria described earlier, it is possible to perform thedimensioning process for the network. Again, we will break the description into three parts to facilitate explanation andunderstanding.

8.4.4.1 InputsThe input to the dimensioning process is the output of the traffic distribution process described earlier. Once the traffic hasbeen distributed over the network’s layers and sectors, the dimensioning process can be launched. Apart from the trafficdemand, the dimensioning process also takes into account the minimum required QoS and GoS criteria defined for eachtype of service, the upper and lower limits on the # TSL for each service, and the upper limits on the number of TRXsupported by each sector.

8.4.4.2 DimensioningThe dimensioning engine in Atoll converts the traffic demand into the required # TSL, and eventually the required # TRX,following the QoS and GoS criteria. For example, for a CS service, let’s say voice, allowing a minimum GoS of 2%, thetraffic demand in Erlangs can easily be converted into # of TSL required to carry that traffic demand while respecting therequired GoS through the Erlang B and Erlang C formulas. The type of model, either Erlang B or Erlang C, can be selectedby the user.

The computation of # TSL required to carry a certain PS traffic demand is more complicated than the simple conversionprocess described above. PS traffic implies a more complex definition of Quality of Service than the simple Grade of Serv-ice of CS traffic. It implies, apart from a certain blocking probability, a certain data throughput (kbps) to be maintained witha maximum allowable delay. These parameters that indicate the PS traffic quality requirements are known as Key Perform-ance Indicators or KPIs.

8.4.4.3 OutputsTo abridge the numerous results generated at the end of a dimensioning process, we can say that the principal result isalways the # TRX required for each subcell, and eventually each sector. Another chief output of the dimensioning processis the Traffic Load. More specifically, the Atoll Network Dimensioning process provides the # TSL required for CS traffic,for PS traffic, and the KPIs and the Traffic Load for each subcell. The Traffic Load is defined as the ratio of traffic demandto the # TSL carrying that traffic. It is perhaps one of the most important outputs of the process as it is further utilized inthe Automatic Frequency Planning process. The consumption for a subcell can be extracted through multiplying the # TRXrequired by the Traffic Load and by the TSL multiplexing factor (8 for the GSM standard).

Atoll also incorporates an intelligent allocation methodology for assigning the CS and PS TSL inside a TRX. The user hasthe possibility to define the TSL allocation schemes for each type of TRX. This is known as timeslot Configuration.

Figure 8.7: Network Dimensioning Process

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Index

Index

Symbols% max interference 36, 51, 53, 68

AAdditional cost component 86

Adjacency suppression 38, 60

Adjacent channel protection level 38

Adjacent channel violation 54

Adjacent constraint 62

Adjacent-channel reuse violation 59

Advanced cost parameters 90

AFP 13

AFP performance indicators 38

AFP process in Atoll 19

AFP scope 22

AFP weight 22, 36, 37

AFP wizard 20

AMR 14

ARFCN 13, 37, 51, 61, 67

Assignment mode 36

Atoll AFP 67

Atoll data model 35

Atom 65, 85

Audit 59

Automatic constraint violation resolution 30

Automatic frequency planner 13

Automatic neighbour allocation 44

Average timeslot capacity 97

BBaseband hopping 66

BBH 14, 65, 85

BCCH 13, 36, 66, 76, 79, 93

BCCH co-channel reuse 94

Blocking rate 47

BSIC 13, 22, 38, 67, 76, 79, 94

BSIC allocation 66, 94

BSIC domain 67

Burst collision probability 49, 60

CC/I 14

C/I coverage prediction 70

C/I distribution 58

C/I threshold 36

C/I weighting 53

Calculation zone border effect 69

CDF 14, 91

Cell edge coverage reliability 35

Channel reuse 50

Close-to-threshold C/I conditions 53

Clutter weighting 43

Co-channel interference 91

Co-channel reuse violation 59

Co-channel violation 54

Collision probability 50, 66

Combination of separation violation and interference probabilities 48

Concentric Cells 36

Consistency check tool 59, 94

Constraints 35, 59

Corrupted TRX cost 51

Corrupted TRX cost component 86

Co-site 28, 38, 87

Cost 13, 48, 58, 61

Cost components 87

Cost distribution on frequencies 26

Cost function 13, 48, 85

Cost function parameters 52

Cost minimization 13

Cost of changing a TRX 52

Co-transmitter 28, 38, 87

Creating IMs based on traffic 44

CS 14, 43, 96

Cumulative density function of C/I levels 91

CW measurements 76

DDimensioning 13, 43, 47, 95, 99

DLPC 14, 36

Domain range effect 62

Domain use ratio 66

Downlink power control 36

Downlink power offset 36

DTX 14, 36, 57, 60, 88

Dual-band Cells 36

EEDGE 13

EGPRS 13

Embedded interference matrices 76

Erlang 26, 43, 48, 57, 70, 85, 96

Erlang B 99

Erlang C 99

Estimating frequency plan quality 57

Exceptional pairs 21, 28, 38, 87

Extending existing neighbour relations 45

Externalised interference matrices 77

FF_DIV 90

FAP 13

FER 14, 90

FH 14

FISFE 59

FN 14

FN offsets 15

FR 14

Fractional load 26, 49, 65, 88

Frame number 66, 88

Free MAL assignment 65

Freezing mechanism 37

Frequency assignment problem 13

Frequency band 37

Frequency distribution 61

Frequency diversity gain 89

Frequency domain 36, 37, 65

Frequency hopping 92

Frequency load 62

Frequency panning techniques 70

Frequency plan 39

Frequency plan optimisation 43

Frequency plan quality 57

Frequency planning 13, 36

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Frequency reuse 35

Frequency reuse ratio 66

Frozen cost 26

GGenerator initilialisation 24

Global cost 51

Global separation fitness expression 59

GoS 14, 95

GPRS 13, 38

Group constrained mode 36, 65

Group constrained subcells 51

GSM 13

HHandover 46, 66

Hard criterion 66, 94

HCS 14, 96

HCS layers 35, 76

Histogram 57

HO 14

HO margin 35

HO statistics 45

Hopping gain 65

Hopping mode 36, 37

HR 14, 43

HSN 22, 36, 51, 59, 65, 67, 85

HSN assignment 65

II_DIV 90

IM 13, 35, 43, 44, 61, 68, 92

Importing neighbour importance 45

Inner zone 36

Interfered Erlangs 49, 51

Interfered traffic 48, 53, 57

Interfered zones 57

Interference 31, 38, 51, 57, 68, 91

Interference calculation 68

Interference component 26

Interference cost 49, 61

Interference cost component 88

Interference distribution strategy 92

Interference histogram 88

Interference information discrimination 92

Interference matrices 23, 57, 75

Interference matrix combination 80

Interference matrix context 77

Interference matrix scope 79

Interference probability 48

Interference study quality criteria 69

Interference weight 52

Interferer diversity gain 88

Introduction to the AFP cost function 48

Kkbps 14, 43, 96

Key performance indicators 95

Key roles of subcells 36

KPI 14, 21, 43

LLocal domain restrictions 37

Lower bound interference matrix 76

MMAIO 22, 31, 37, 38, 51, 59, 65

MAIO allocation 66

MAL 14, 22, 36, 37, 38, 50, 51, 59, 65, 92

MAL length 67

MAL length determination 65

MAL size 62

Managing consistency in Atoll and the AFP 68

Manual frequency allocation for NH 31

Manual frequency allocation for SFH 31

Max MAL length 65, 66

Maximum likelihood combination 75, 77

Maximum MAL length 49

Maximum number of subcells 67

Maximum number of TRXs 48

Means to evaluate frequency plans 57

Minimum C/I 36, 49

Missing TRX cost 50

Missing TRX cost component 86

Mobility 35

Modifiable and non-modifiable costs 51

Modifiable cost 26

Modified TRX component 26

NNeighbour 28, 38, 59, 62, 87

Neighbour allocation 44, 68

Neighbour importance 38, 44

Neighbour relations 44

Neighbour separation violation 48

Network dimensioning 68

Network dimensioning process 99

NH 14, 65, 85

NH TRX 51

Non-frozen cost 51

Non-synchronous subcells 66

Number of different frequency domains 67

OOMC 38, 45, 76

Optimal dimensioning of an existing network 47

Optimising hopping gains 65

Out-of-domain frequency assignment cost 51

Out-of-domain frequency assignment cost component 86

PPair-wise interference matrices 57

Pair-wise violation 60

Partial sources of neighbour importance 46

Performance and memory issues in large GSM projects 70

Point analysis 60

Power offset 36, 60, 68

Predefined MAL assignment 65

Prediction studies 68

Probabilistic cost combination 50

Probability threshold 36

Propagation 35

PS 14, 43, 96

QQoS 14, 95

Quality indicator 62

Quality indicators 78

Quality target 36, 51, 53

Quality threshold 58

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Index

RRadio resource management 36

Rank 38

Raster traffic map 43

Reception threshold 36, 68

Required quality threshold 36

Required TRXs 51

RRM 14, 36, 38

RXLEV 76

SSafety margin 36, 53

Scan data drive tests 76

Scope and context of interference matrices 77

Second order neighbour relation 66

Separation component 86

Separation constraint 38, 62

Separation constraint violation 28

Separation cost 49

Separation fitness 59

Separation rule priority 38

Separation violation 48, 59, 60

Separation violation cost component 26, 39, 87

Separation weight 52

SeparationConstraints table 38

SeparationRules table 38

Service zone 36

Service zone of a subcell 68

SFH 14, 59, 65

SFH TRX 51

Soft criterion 66, 94

Spectrum 62

Spectrum administration 37

Staggered MAIO allocation 66

Standard deviation 35

Subcell 14, 36

Subcell audit 37

Subcell quality threshold. 58

Synchronous networks 65

Synchronous subcells 66

Synthesised hopping 62

TTarget computation time 24

TCH 14, 36, 66, 93

TCH_INNER 14, 36

TCH_OUTER 36

TDMA 14

Test mobile data 76

Thermal noise 36

Timeslot configuration 43

TL 14

TN offsets 15

Total cost 26, 39

Traffic capture 21, 43, 47, 95

Traffic capture process 95

Traffic distribution 96

Traffic environment 43

Traffic load 21, 36, 43, 57, 65, 68, 92, 99

Traffic map 43

Traffic model 43

Traffic overflow 35

Traffic overflow rate 36

Traffic weighting 58

Training sequence code 67

Transmitter 14

TRG 85

TRX 13, 15, 36, 85, 99

TRX based cost function 86

TRX based interference study 57

TRX cost 49

TRX rank 15, 38, 58

TSC 14, 67

TSL 13, 43, 96

TX 13

UUniform frequency usage distribution 61

Upper bound interference matrix 76

Usage distribution on frequencies 26

User profile 43

VVector traffic map 43

WWorst case combination 75

Worst case interference study 58

Worst interferer 58

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