njhx510d - radio resource management

Mason Communications Training: WCDMA Radio Planning CourseModule 5: Optimisation

Section 5.1: Radio Resource Management

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© Mason Communications Ltd 2001

WCDMA Radio Planning Course5 Optimisation5.1 Radio Resource Management

Mason Communications Training: WCDMA Radio Planning Course

Module 5 – Optimisation

Section 5.1 – Radio Resource Management



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Radio Resource Management

5.1.2© Mason Communications Ltd 2001

Where are We Now?Introduction

UMTS Overview

Access Technologies

WCDMA Introduction

Model Architecture

UMTS Standards

Mobile RadioChannel

Narrowband Channel

Wideband Channel

Local Mean Signal

Path Loss

Diversity

DesignElements

Basic Radio Principles

Antennas and Feeders

Interference

Matched Filters and

Rake Receivers

WCDMA Physical Layer

NetworkDesign

Operator’s Design Guides

The Planning Process

Polygons

Site Placement

Antenna Placement

Frequency Planning

Forward Capacity Planning

LinkBudgets

Conventional Optimisation

3G Optimisation

Course Overview

Optimisation

CourseWash Up


Where are We Now?

The Course Map shows which section we are now on.



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What is in This Section?

Power Control

Handover Control

Admission Control

Introduction to RRM

Load Control

Packet SchedulerPacket Scheduler

Packet SchedulerSummary

Optimisation


CourseWash Up

3G Optimisation




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Why is this Section Important to You?

• There are few parameters at the Operators disposal in order to deploy and create differentiation between other operator’s networks. Radio Resource Management is a set of tools and algorithms which the Operator can use to help Optimise his network

• In GSM the Radio Resource Management was a trivial task, and was embedded within Vendor Equipment. In UMTS Vendor Equipment will have default algorithms, but will need modifying to Optimise Performance.

Why is this Section Important to You?



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Where are We Now?

Power Control

Handover Control

Admission Control

Introduction to RRM

Load Control

Packet Scheduler


Optimisation


CourseWash Up

3G Optimisation




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Introduction to RRM

• Radio Resource Management (RRM) is responsible for Utilisation of the Air Interface Resources.

• RRM provides mechanisms to Manage the Air Interface resources. These mechanisms can be adjusted by the Operator in order to suit particular scenarios, and/or optimise his network.

• RRM provides the tools to allow Coverage, Capacity and Quality to be Optimised

NetworkNow

Quality

CapacityCoverage

Future Network



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Introduction to RRM

• A typical Operator RRM Optimisation Process is defined:

• An operator will carry out • Live and simulated

measurements on his network,

• Simulator test bed simulations (e.g. Dynamic Simulator)

• Analyse the results

• Propose changes in RRM parameters

Mason

Field measurements and actualSimulated Network Loading Testbed Simulations

Analysis

Change RRMParameters



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Introduction to RRM

• RRM can be divided into:• Handover• Power Control• Admission Control• Load Control• Packet Scheduling

Function

• RRM functions are carried out by different entities within the RNS as shown.

Mobile Station Base Station RNC

Power Control Power Control Power Control

Handover Control

Admission Control

Load Control

Packet Scheduler

Load Control



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Introduction to RRM

• RRM operates on Connection and Network/Cell based functions

• Admission Control, Load Control, and Packet Scheduler are Network based functions. These algorithms control the radio resources of a Cell at once

• Power Control and Handover Control are Radio Resource Connection (RRC) based functions, and operate on a per connection basis.

Power Control

Handover Control

Admission Control

Load Control

Packet Scheduler

Connection Orientated Functions

Network Orientated Functions



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Introduction to RRM

• Power Control maintains radio link level quality of a call through adjustment of the Uplink and Downlink powers. The aim of Power Control is to provide just enough power to maintain link quality, no more, no less power.

• Handover Control also maintains the radio link level quality by optimum cell selection, or combining in handovers.

• Admission Control decides whether a request to establish a connection is admitted into the Cell or not. Admission Control aims to ensure stability and high capacity in the cell.

• Load Control provides load information of the cells controlled by the RNC and provides information to the Admission Control and Packet Scheduler for control purposes. In overload scenarios, the Load Control carries out recovery actions through the functions of Admission Control, Power Control, and Packet Scheduler.

• Packet Scheduler schedules non Real Time radio access bearers. The Traffic load of the cell determines the scheduled transmission capacity.



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Where are We Now?

Power Control

Handover Control

Admission Control

Introduction to RRM

Load Control

Packet Scheduler


Optimisation


CourseWash Up

3G Optimisation




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Power Control

• Power Control contains the following entities:• Uplink (open loop) PC and Random Access procedure• Outer (open loop) PC (10-100Hz)• Fast (closed loop) PC (1500Hz)• PC for DL common physical channels

• Standards specify Fast PC steps 1500 times a second as:• +/-0.5dB steps• +/-1dB steps



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Power Control – Outer Loop

• Outer loop PC controls theEb/No set point.

• For Uplink the Outer loop PC is located in the RNC

• The Eb/No targets are sent from RNC to BS as shown

• For Downlink the Outer loop PC is located in the MS

• The Operator must set TargetEb/No’s based upon QoStargets (such as BER, FER), andEb/No dynamic range to cater for all speeds and channels

• Such Eb/No Targets can be derived from Link Level simulations and/or real surveys.

Macro diversityCombining

Outer LoopPower Control

DataOuter Loop PC Commands

RNC

Fast PC Commands

Eb/No Target set by Outer Loop PC



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Power Control – Outer Loop

• Table illustrates range of TargetEb/No’s to be expected for Voice AMR service withy QoS set by FER=1%.

• All possible Multipathenvironments and speeds results in a Eb/No Target Dynamic Range requirement of only 2-3dB.

• As Mobile approaches cell edgeEb/No Target ramps right up. This requires much greater dynamic range, typically 10dB.

• Different services may require different ranges, and dynamic ranges.

Multipath Channel Speed Average Eb/No TargetNon-fading any 5.3 dBITU Pedestrian A 3 km/h 5.9dB

ITU Pedestrian A 20 km/h 6.8 dB

ITU Pedestrian A 50 km/h 6.8 dB

ITU Pedestrian A 120 km/h 7.1 dB3-path equal powers 3 km/h 6.0 dB

3-path equal powers 20 km/h 6.4 dB



Time (order of seconds)

Targ

et E

b/N

o (d

B)

4

5

6

7

AMR Speech, FER = 1%. “WCDMA for UMTS” page 196.

Step Size = 0.125dB (very small!)



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Power Control – Fast Power Control

• Fast Power Control has been discussed in detail in section 4.1 (“Link Budgets”)

• Fast power control inherently helps to lower the Eb/No in a fading channel as shown left.

• Received Eb/No is kept stable butTx Power is peaky and results in Average Power Rise, which needs to be considered in planning.

• Fast PC occurs at 1500Hz

• Fast PC steps ±0.5dB or ±1dB (this results in negligible QuantisationNoise)

• Fast PC estimation and correction delay ~ 1 Slot (0.667ms)

Multipath ChannelWithout Fast

Power ControlWith Fast

Power ControlGain from Fast Power Control

ITU Pedestrian A 3km/h 11.3dB 5.5dB 5.8dBITU Vehicular 3 km/h 8.5dB 6.7dB 1.8dB

ITU Vehicular 50 km/h 6.8dB 7.3dB -0.5dB

Uplink Eb/No Values with and without Fast Power Control

“WCDMA for UMTS”, P.189Radio Channel Fading profile

-20

-15

-10

-5

0

5

10

15

20

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

Fast Power Control

-20

-15

-10

-5

0

5

10

15

20

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20



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Power Control – Fast Power Control

• Some Fast PC Considerations

• Power Control in SHO• Downlink PC Drifting

• Reduce dynamic range on Fast Power Control – but we need good dynamics for Fast PC to provide Eb/No Gain

• Power Drifting prevention algorithm (Nokia)• Reliability of Uplink Power Control Commands

• Data is Macro diversity combined in MS, Power control bits are not (Data gets SHO Gain, Control doesn’t!)

• Increase power of DL DPDCH bits

Data1 Data2 PilotTFCITPC

1 Slot = 0.667ms

Powe

r



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Where are We Now?

Power Control

Handover Control

Admission Control

Introduction to RRM

Load Control

Packet Scheduler


Optimisation


CourseWash Up

3G Optimisation




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Handover Control

• The performance benefits from SHO were discussed and presented during section 4.1 “Link Budgets”.

• Recap – There exists a number of Handover Types and strategies. There are:

• Soft Handovers• Soft (Cell to Cell)• Softer (Sector to Sector same

Cell)

• Hard Handover• Intra-frequency Hard

Handover• Inter-frequency Hard

Handover• Inter-System Hard Handover

Freq 1 Freq 1

Freq 1 Freq 2

WCDMA FDD GSM

Softer Handover Soft Handover

Intra -frequency Handover

Inter-frequency Handover

Inter-system Handover

Handover is a very important aspect of any mobile cellular system. In UMTS the optimisation of Handover is especially important as it not only allows the free movement of mobile terminals between cells, but also allows the Interference to be managed, which in turn allows capacity to be managed, and optimised.

The 3GPP Specifications specify parameters to be measured and reported. It is left to Equipment Vendors to define algorithms that use these parameters to make handover decisions and carry out the task. It will therefore be left to the Operator to then Optimise the performance of the default handover algorithms to suit specific scenarios in which the system is deployed.



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Handover Control – Soft Handover

• In GSM Hard Handover is used, together with a Hysteris margin.

• In the event that Cell 1 is fully loaded and Cell 2 isn’t fully loaded neighbour planning allows the mobile to remain connected to Cell 2.

• If this scenario occurs with UMTS Cell 1 will receive significantIntercell Interference.

• In UMTS if Cell 1 is fully loaded, under no circumstances should the mobile remain connected to Cell 1 as this will affect all other users connected to Cell 1.

• Admission Control is used to manage this scenario. For example another Mobile in Cell 1 could be handed off to another Cell to allow the Mobile to be connected to Cell 1.

Actual Cell Area Limits

GSM

UMTS

Cell 1 Cell 2

Cell 2Cell 1

ü

û

In GSM a Handover Hysteresis margin is used to avoid the “ping-pong” handover effect that would be generated if a Hysteresis margin had not been considered, since Best Server boundaries are usually ill defined due to uncorrelated log-normal variations in propagation loss due to terrain/clutter when the path losses to a mobile are roughly equal between two cells (the blurring of cell edge). If we use Hard Handover with Hysteresis with UMTS the mobile can be dragged into another cell (where that cell is a better candidate) and as a result cause excessive Intercell Interference. Soft Handover always allows the Minimum Tx Power from the Mobile and therefore counters this problem, albeit that an additional communication channel in the network (or more) is being consumed.

WCDMA Cell Breathing tends to provide some degree of Traffic Balancing in the above scenario. However the message this scenario conveys is the need for Admission Control to work closely with Handover Control such that the scenario where a Mobile connected to Cell 2 does not enter Cell 1’s coverage area as shown. UMTS Radio Resource Management must ensure that the Mobile always transmits with minimum power. In this case the Mobile service might have to be terminated, or other mobiles handed off to other cells.

This example also shows the need for Careful Neighbour Planning in UMTS to manage such handoffs efficiently, and in such a way as to minimise the impact to the overall Interference. The example also demonstrates that Large Cell Area overlap is unnecessary in UMTS. Cell Overlap is only needed to satisfy the SHO area.



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Handover Control – Soft Handover

• There exists an optimum Capacity/Cell as a function of SHO Margin

• This optimum will vary from cell to cell depending upon network parameters, spatial loading of users, and existing Interference

• Graph is purely illustrative to demonstrate that an optimum may exist

• SHO Optimisation allows the Operator to make best use of the UMTS network

Cell to Cell SHO Margin (dB)

Aver

age

Cell

Capa

city

(Mbp

s)

0 2 4 6 8 10 12 14

800

600

400

200

Too much SHO Margin –Consuming Capacity

Too little SHO Margin –Interference not

Optimally Managed

Optimum Operating Point

In WCDMA networks best spectral efficiency is achieved when a spectral frequency reuse factor of 1 is used. Hard Handover is not a viable option for WC DMA in this case because the resultant Intercell Interference severely limits system Capacity. In this case soft handover is used in which Macro Diversity combining is used to mitigate Fast Power Control variations, and provide link gain (thereby reducing the average power of a Mobile). This provides three key aspects to a UMTS network:

1. Eliminate the need for hysteresis margins at cell boundaries

2. Reduces the Intercell interference (by reducing Average Mobile Tx Power)

3. Reduces the average power rise (by mitigating Fast Power Control Variations)

By reducing Intercell Interference through Soft handover allows more capacity to be exploited. However, Soft Handover itself consumes capacity since two (or more) links from two (or more) Base Stations are supporting a soft handover connection. For capacity limited areas, the Optimisation process aims at providing enough Soft Handover Margin, and Control such that Capacity is maximised, but not to much such that Capacity is compromised. The actual Soft Handover margin will depend upon a number of factors, such as traffic loading, antenna Downtilts, antenna azimuth patterns, etc. (which all influence Interference and hence Capacity). It is envisaged that actual network loading statistics would be used in order to be able to optimise the SHO margins for different cells. Prior to network simulations using a planning tool (Dynamic or Static Simulations) will allow a degree of pre -optimisation of the network.



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Handover Control – Softer Handover

• Soft Handover requires that the Uplink received signals at each different receiving Base Station have to be despread to allow transmission across the fixed network. This looses Amplitude Information and therefore only allows Selection Combining at the RNC to be available.

• Softer Handover is essentially the same as Soft Handover.

• Advantage of Softer Handover is that the Maximal Combining can occur on both Uplink and Downlink, where Combining occurs at the Base Station for the Uplink.

RNC

The only difference between Soft and Softer Handover is in the manner the Uplink Signals are Combined. With Soft Handover different Base Station Cells receive the Mobile signal. The signals are combined in the RNC but need to be despread at the individual Base Stations before doing this. As a result we loose Amplitude Information on the RF Signal and can only be Selection Combined.

With Softer Handover advantage can be taken of the fact RF signals can be Maximally Combined and hence provide an improvement in Link Margin.

For both Soft and Softer Handover Maximal Combining is carried out on the Downlink at the Mobile Terminal.



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Handover Control – Soft/Softer Handover

AS_Th –AS_Th_Hyst

Cell 1 Connected Event 1A⇒ Add Cell 2

Event 1C ⇒Replace Cell 1 with Cell 3

Event 1B ⇒Remove Cell 3

CPICH 1

CPICH 2

CPICH 3

Time

MeasurementQuantity

∆T ∆T ∆T

As_Th +As_Th_Hyst

As_Rep_Hyst

Example Soft(er) Handover Algorithm shown (from 3GPP TR 25.922 – Radio Resource Management Strategies).

Example Soft Handover Algorithm. A describing example of a Soft Handover Algorithm presented in this slide which exploits reporting events 1A, 1B, and 1C described in 3GPP TS 25.331. It also exploits the Hysteresis mechanism and the Time to Trigger mechanism described in 3GPP TS 25.331. Any of the measurements quantities listed in 3GPP TS 25.331 can be considered. Other algorithms can be envisaged that use other reporting events described in 3GPP TS 25.331; also load control strategies can be considered for the active set update, since the soft handover algorithm is performed in the RNC. For the description of the Soft Handover algorithm presented in this slide the following parameters are needed:

- AS_Th: Threshold for macro diversity (reporting range);- AS_Th_Hyst: Hysteresis for the above threshold;- AS_Rep_Hyst: Replacement Hysteresis;- ∆T: Time to Trigger;

- AS_Max_Size: Maximum size of Active Set.

As described in the figure above:

- If Meas_Sign is below (Best_Ss - As_Th - As_Th_Hyst) for a period of ∆T remove Worst cell in the Active Set.- If Meas_Sign is greater than (Best_Ss - As_Th + As_Th_Hyst) for a period of ∆T and the Active Set is not full add Best cell outside the Active Set in the Active Set.- If Active Set is full and Best_Cand_Ss is greater than (Worst_Old_Ss + As_Rep_Hyst) for a period of ∆T add Best cell outside Active Set and Remove Worst cell in the Active Set.

Where:- Best_Ss :the best measured cell present in the Active Set;- Worst_Old_Ss: the worst measured cell present in the Active Set;- Best_Cand_Set:the best measured cell present in the monitored set.- Meas_Sign :the measured and filtered quantity.

.



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Handover Control – Hard Handover

• Inter-Frequency Hard Handover is used when Soft Handover is not viable, such as the case when a candidate Handover Cell on the same Carrier Frequency is fully loaded.

• Hysteresis Margins are used between Candidate Carriers in this case to avoid multiple Handover Transitions.

• Gaps in Transmission on the Physical Channel are required in order to make measurements of Candidate Carriers. (Compressed Mode).

Freq 1 Freq 2

Inter-frequency Hard Handover

Hard Handover should only be used when Soft Handover on the same Carrier is impractical. Admission and Load Control algorithms are also needed to invoke a Hard Handover decision, for example when a Mobile can not be soft handed over to another cell, because that cell is fully loaded.

There remains some issues in Release 99 of the UMTS specification for Inter-Frequency Hard Handover, such as limited Packet Switched services Hard Handover capabilities, particularly with Shared (BS Broadcast, or one to many) type Packet Services.



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• Intra-Frequency Hard Handover is often called Cell reselection.

• This special Hard Handover case can be used for Packet based services using the Random Access (RACH) or Forward Access (FACH), where cell reselection can be used between packet bursts.

Freq 1 Freq 1

Intra -frequency Hard Handover



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• Inter System Handover is a service concept within 3G.

• Dual Synthesiser radios required. Measurements must be made on GSM and UMTS networks. GSM1800/UMTS Handover requires the use of Compressed Mode measurements due to lack of isolation.

• GSM BSS unaffected by 3G to 2G Handovers for Circuit Switched services. Issues with GPRS however.

• 2G to 3G Handovers being addressed by 3GPP. Only exists for Circuit Switched services. Expected Software upgrades on BSS to achieve 2G to 3G Handovers.

WCDMA FDD GSM



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Where are We Now?

Power Control

Handover Control

Admission Control

Introduction to RRM

Load Control

Packet Scheduler


Optimisation


CourseWash Up

3G Optimisation




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Uplink noise Rise as a Function of Uplink Data Throughput

0

2

4

6

8

10

12

14

16

18

20

0 400 800 1200 1600

Throughput (kbps)

Noi

se R

ise

(dB

)Admission Control

• Cell Air Interface Load must not increase beyond the design or planned Maximum Capacity, otherwise Cell Range, and henceQoS targets will be jeopardised.

• Before a new connection is made the Admission Control must check that admission will not take capacity above planned maximum.

• Admission Control Algorithm estimates the incremental Noise Rise, ∆ I, that would result if a Mobile and its associated Incremental Load on the Cell , ∆L is admitted.

• Incremental Cell Load ∆I, must be estimated separately for Uplink and Downlink.

Maximum Planned

Noise Rise

∆∆ I

∆∆ L

The curve shown in this slide are based upon the Uplink Noise Rise for certain parameter, service and Intercell Interference conditions,i. The curve is from the same simulation example presented in section 4.1 (Link Budgets). Different parameters and Intercell Interference conditions would result in different Throughput values (x-axis) for the same Intracell Noise Rise.



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Uplink Noise Rise as function of Uplink data Throughput and Intercell Interference

0

1

2

3

4

5

6

7

8

9

10

0 500 1000 1500 2000 2500

Throughput (kbps)

Noi

se R

ise

(dB

)

10%

25%

50%

75%

90%

Admission Control

• Two methods for estimating ∆I are presented in “WCDMA for UMTS”, H. Holma.

• Wideband Power Load Estimation Based Admission Control

• Throughput Load Estimation Based Admission Control

The curves shown in this slide are based upon the Uplink Noise Rise given different Intercell Interference conditions,i. The curves are from the same simulation example presented in section 4.1 (Link Budgets).

Wideband Power Load Estimation Based Admission Control keeps the Coverage within Planned limits, regardless of Intercell Interference in that the Maximum Planned Noise Rise is maintained, and hence the Link Budget with respect to cell range. The Cell then has uncertain or variable Capacity due to variable Intercell Interference.

Throughput Load Estimation Based Admission Control keeps the Capacity within Planned limits, regardless of Intercell Interference in that the Maximum Planned Throughput is maintained. The cell has uncertain or variable Coverage due to variable Intercell Interference.



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Where are We Now?

Power Control

Handover Control

Admission Control

Introduction to RRM

Load Control

Packet Scheduler


Optimisation


CourseWash Up

3G Optimisation




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Load Control

• The Task of Load Control is to ensure that the network does not become overloaded or unstable. If the network is overloaded then Load Control returns the network to normal load in a controlled fashion.

• Admission Control and Packet Scheduler RRM Algorithms should manage the load. However, in the event Load exceeds a design limit Load Control is invoked to bring the network back to design limits.

Max Load Target

Real Time (Uncontrollable)

Traffic

Non-Real Time (Less Controllable)

Traffic

Under Control of the

Packet Scheduler

Under Control of the

Admission Control

Load Control provides load information of the cells controlled by the RNC and provides information to the Admission Control and Packet Scheduler for control purposes. In overload scenarios, the Load Control carries out recovery actions through the functions of Admission Control, Power Control, and Packet Scheduler.

There are a number of possible Load Control strategies or actions which can be used.

Downlink Fast Power Control (Deny Downlink Downlink Power-Up Commands from Mobile(s))

Uplink Fast Power Control (Reduce the Uplink Eb/No target used by the Uplink Fast Power Control)

Reduce throughput of Packet Switched Data

Hard Handover to another UMTS Carrier

Hard Handover to another System (GSM)

Reduce Information Rate of Real Time Users (e.g. 144kbps -> 64kbps)

Reduce Information Rate of Voice Users (through AMR Codec)

Terminate Calls in a controlled fashion



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Load Control

• Load Control Algorithm talks to Admission Control and Packet Scheduling Algorithms.

• Load Control acts as a Gatekeeper to ensure planned load is not exceeded given the independent processes of Admission Control and Packet Scheduler Algorithms.

Load ControlAlgorithm

AdmissionControl

Algorithm

Packet SchedulerAlgorithm

Load Status(from Measurement)

Load Change Information

Non Real Time Load

Information



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Where are We Now?

Power Control

Handover Control

Admission Control

Introduction to RRM

Load Control

Packet Scheduler


Optimisation


CourseWash Up

3G Optimisation




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Packet Scheduler – Packet Model

• Conversational and Streaming Classes of Traffic Transported using Dedicated Channels (i.e are Circuit Switched, such as LCD144)

• Background and Interactive Classes using Packet Delivery Channels. Real-Time Services can be delivered over Packet Channels, such as VoIP

• ETSI Web Model shown

• Packet Session Parameters vary enormously and UMTS provides 3 different Delivery Channels to support Packet Services

• Non-Real Time Packet Delivery actually can suffer significant errors, hence low Eb/No resulting in high capacity. As a result, retransmissions are needed at the expense of Time or latency.

Packet Service Session

Packet Call Reading

Time

PacketSize

PacketArrivalInterval

Packet Call and Reading Time Poisson Distributed in Time



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Packet Scheduler

• Packet Scheduler sits in the RNC and works behind the Load Control process as discussed in Load Control sub-section.

• Packet access uses the following Transport Channels:

• Common• Dedicated• Shared

PacketScheduler

LoadControl

Load Measurements (from Load Control)Packet Allocations (from Packet Scheduler)

RNC

MS to BS Links

Load ControlAt BS also



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Packet Scheduler – use of Common Channels

• Common Channels• FACH on Downlink, RACH on Uplink. • No feedback path and hence no Fast Power Control. This

degrades the Link Level performance with respect to Dedicated Channel (i.e. no Fast Power Control Gain)

• Only one or few RACH and FACH Channels available/sector• SHO not supported• Suited to the delivery of small, bursty quantities of data

(typically one web page, SMS type message, or text only email).



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Packet Scheduler – use of Common Channels

• Common Channels (cont’d)• CPCH option on Uplink. • Feedback path and hence Fast Power Control. This

improves the Link Level performance with respect to FACH and RACH Uplink Channels (i.e. Fast Power Control Gain)

• Many users share bandwidth in a Time Multiplex fashion (like a Downlink Shared Channel) – requires synchronisation?

• SHO not supported• Suited to the delivery of larger, but bursty data

sessions (Web Browsing, Interactive Gaming).



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Packet Scheduler – use of Dedicated Channels

• Dedicated Channels• DCH on Downlink, and Uplink. • Feedback path and hence Fast Power Control. This

improves the Link Level performance with respect to Common Channels (i.e. Fast Power Control Gain)

• Longer Connection Set-up, and OVSF Code resource on downlink must be allocated based upon max datarate. Can lead to inefficient consumption of the Downlink OVSF Code resources.

• SHO supported• Suited to the delivery of larger, less bursty data

sessions (ftp transfer)



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Packet Scheduler – use of Dedicated Channels

• Shared Channels• DSCH on Downlink only (Uplink could use DCH, RACH, or

CPCH?). N.B. CPCH is like a Shared Channel, but is Common by definition.

• Feedback path on Downlink and hence Fast Power Control. This improves the Link Level performance with respect to Common Channels (i.e. Fast Power Control Gain)

• One OVSF Code Resource on Downlink allocated but bandwidth shared between many other Packet users in a Time Multiplex.

• SHO not supported• Suited to the delivery of larger, more asymmetric but bursty

data sessions (Web Browsing, Interactive Gaming).• Can be used in conjunction with low data rate DCH to offer a

minimum guaranteed bitrate, and variable available bitrate.



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Packet Scheduler – Selection of Channel Type

• The specific Channel selection on both the Uplink and Downlink will be based upon:

• Service Delay Requirements

• Data Throughput• Loading of Channels• Radio Link Performance• Asymmetry• Traffic Packet Statistics

(Burstiness)• Traffic Volume

Dedicated Channels Shared ChannelsDCH FACH RACH CPCH DSCH

Uplink Yes No Yes Yes NoDownlink Yes Yes No No Yes

FPC Yes No No Yes YesSHO Yes No No No No

Data Suitability Large Small Small Medium MediumSuited for Busrty Data No Yes Yes Yes Yes

Common Channels

Modified from Holma, page 221, r.2001



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Packet Scheduler – Scheduling Algorithms

• Packet Scheduler makes optimal use of the available air interface capacity

• The optimum may be a mixture of :• Time Division Scheduling (High data rate for short time

period)• Code Division Scheduling (low data rate for long time

period)• Transmission Power Scheduling (data rate depends upon

distance to BS)

• The Optimisation is a complex task.



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Packet Scheduler – Time Division Scheduling

• One Packet user is served at a time

• All available capacity can be allocated to the user

• Advantages:• High data rates require low

Eb/No.• Low Interference• Hence High Throughput

• Disadvantages• Allocation Change amongst

users not instant• Burstiness traffic can lead

to high variation in Interference

Time

Bit Rate

User

5

User

4

User

3

User

2

User

1Different

OVSF Codes



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Packet Scheduler – Code Division Scheduling

• All packet users are served concurrently

• Capacity is divided amongst the users.

• Advantages:• Resources are in full

usage (more efficient code utilisation)

• Disadvantages• Low Datarates require

higher Eb/No• Hence Lower total

throughput

Time

Bit Rate

User 1

User 2

User 3

User 4User 5

Different OVSF Codes



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Packet Scheduler – Tx Power Based Scheduling

• Similar Downlink Power allocations

• Data rate depends on mobile location – High data rates for Mobiles close to BS, low data rates for Mobiles at cell edge

• Advantages:• Average Power per Bit is

minimised• Prevention of Power Peaking

with respect to Time Division Scheduling

• Disadvantages:

• Accurate prediction of power is required

• Distant users perceive poorQoS

384 864144kbps



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Summary

• 3GPP TR 25.922 provides views and thoughts on RRM Strategies for Load Control, Admission Control, Handover Control, and other features such as Code Resource Management (OVSF Code Usage and allocations).

• A lot of these functions are left to the Operator to discuss with the vendor on specifically how to change, and program such RRM algorithms.



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Where are We Now?

Power Control

Handover Control

Admission Control

Introduction to RRM

Load Control

Packet Scheduler

Summary

Optimisation


CourseWash Up

3G Optimisation




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Summary

• In this section on Radio Resource Management you have learnt

• The need for SHO – Intercell Interference management

• The need for Power Control• How Admission and Load Control can be used to

Optimise performance

• This section is important to you because• The Operator has control of a few parameters in the

Network. One of these is the RRM Algorithms and Functions. With careful planning and thought the RRM can be used to work to the benefit of the Operator



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The End of Radio Resource ManagementIntroduction Network

DesignDesign

Elements

Basic Radio Principles

Mobile RadioChannel

Optimisation

Narrowband Channel

Wideband Channel

Local Mean Signal

Path Loss

Diversity


UMTS Overview

Access Technologies

Model Architecture

UMTS Standards

WCDMA Introduction

Operator’s Design Guides

The Planning Process

Polygons

Site Placement

Antenna Placement

Frequency Planning

Forward Capacity Planning

LinkBudgets

Course Overview

Antennas and Feeders

WCDMA Physical Layer

Interference

Matched Filters and

Rake ReceiversConventional Optimisation

CourseWash Up

3G Optimisation

Any MoreQuestions?



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