cell planning principles

Cell Planning Principles

© AIRCOM International 2003 1

Copyright 2003 AIRCOM International Ltd All rights reserved AIRCOM Training is committed to providing our customers with quality instructor led Telecommunications Training. This documentation is protected by copyright. No part of the contents of this documentation may be reproduced in any form, or by any means, without the prior written consent of AIRCOM International. Document Number: P/TR/003/P013/1 This manual prepared by: AIRCOM International Grosvenor House 65-71 London Road Redhill, Surrey RH1 1LQ ENGLAND Telephone: +44 (0) 1737 775700 Support Hotline: +44 (0) 1737 775777 Fax: +44 (0) 1737 775770 Web: http://www.aircom.co.uk

CELL PLANNING PRINCIPLES


2 © AIRCOM International 2003



Contents

1 Cell Planning Principles: a Brief Introduction..................5 1.1 Introduction..........................................................................................................................5 1.2 Initial Scenario .....................................................................................................................6 1.3 Evolution of the Requirement: Coverage Enhancement......................................................7 1.4 Evolution of the Requirement: Capacity Enhancement ....................................................11 1.5 Evolution of Requirement: Coverage and Capacity .........................................................13 1.6 The Need for Frequency Planning. ....................................................................................14 1.7 Different Approaches for different environments..............................................................15

2 Link Budget for GSM...................................................19 2.1 Introduction........................................................................................................................19 2.2 Free Space Propagation Model ..........................................................................................20 2.3 Plane Earth Propagation Model .........................................................................................22 2.4 Cellular Radio Propagation Models ...................................................................................24 2.5 Okumura’s Measurements .................................................................................................25 2.6 The Hata Propagation Model.............................................................................................27 2.7 Diffraction Attenuation Models .........................................................................................30 2.8 CW Drive Testing ..............................................................................................................40 2.9 Propagation Model Tuning ................................................................................................46 2.10 Power Budgets ...................................................................................................................53

3 Frequency Planning....................................................73 3.1 Introduction........................................................................................................................73 3.2 Cellular Structures and Frequency Reuse Patterns ............................................................73 3.3 Interference Calculations ...................................................................................................76 3.4 Cell Splitting Techniques...................................................................................................77 3.5 GSM Frequency Patterns ...................................................................................................80 3.6 Self-Assessment Exercises.................................................................................................82

4 Traffic Analysis ...........................................................85 4.1 Introduction........................................................................................................................85 4.2 Traffic Measurements – Erlangs and Blocking..................................................................85 4.3 The Traffic Analysis Process .............................................................................................88 4.4 Using Demographic Data...................................................................................................89 4.5 Market Projections and Traffic Maps ................................................................................90 4.6 Roll-Out Strategy ...............................................................................................................93 4.7 Capturing Traffic and Assessing Resource Requirements.................................................95 4.8 Traffic Capturing Demonstration.......................................................................................97

5 Grid References and Bearings ....................................99 5.1 Grid References..................................................................................................................99 5.2 Bearings ...........................................................................................................................104 5.3 Self-Assessment Questions ..............................................................................................114

6 Base Station Positioning ........................................... 115 6.1 Introduction......................................................................................................................115 6.2 BTS Positioning for Different Environments ..................................................................115 6.3 The Site Acquisition Process ...........................................................................................118 6.4 Multilayer Cell Design.....................................................................................................122



6.5 Microcell Positioning.......................................................................................................123 6.6 Picocell Arrangements .....................................................................................................125 6.7 Resource Sharing .............................................................................................................125 6.8 Cell and Handover Admission Strategies ........................................................................127 6.9 Use of Repeaters ..............................................................................................................129 6.10 Self-Assessment Exercises...............................................................................................134

7 Base Station Engineering.......................................... 137 7.2 Estimation of Fresnel Zone Radius:.................................................................................143 7.3 Antenna Configurations ...................................................................................................143 7.4 Base Station Equipment ...................................................................................................150 7.5 Self-Assessment Exercises...............................................................................................163

Appendix A Model Tuning Demonstration Procedure..... 169

Appendix B Erlang B Tables ......................................... 175

Appendix C: Solutions to Questions............................... 179



1 Cell Planning Principles: a Brief Introduction

_____________________________________________________________________

1.1 Introduction

Imagine that we are set the task of establishing a GSM mobile communications network in a particular area. Our first task will be to establish a system that will provide coverage over a small geographic area (20 km2 perhaps). We are given the job of ensuring that the air interface operates adequately. This means that we are responsible for providing coverage and capacity to the customer. In order to design the network, we must make an initial estimate of the likely demand for the service that we are to provide. We will start by assuming a simple initial situation and use that as a platform on which to build our understanding of the essential tools that we need in order to design a progressively more demanding system. The more complicated systems will be designed in response to foreseen customer demand that will lead to the existing configuration becoming unsuitable. Examining these situations will lead to an assessment of the issues that need to be understood in order for performance to be improved in a logical, exact, scientific manner.

CellCell--Planning for GSM NetworksPlanning for GSM Networks

• Major Issues:

•Coverage

•Capacity

•Interference

•Cell Planning

•Environmental Aspects

Section 1 – Introduction to Cell Planning



1.2 Initial Scenario

An area of 20 km2 is defined. It is almost in a perfect circle with a radius of approximately 2.5 km. We are told it is estimated that 120 subscribers will be located within this area. The subscriber behaviour is such that the offered traffic is estimated to be 25 mE per subscriber during the busy hour. In designing a solution that will satisfy the demands of the user, we are very lucky that this is the sort of demand that GSM was almost designed to accommodate. The obvious solution would be to establish a single omni-directional site and allocate a single carrier. A range of 2.5 km is usually achievable from an omni-directional macro cell positioned above roof height. The carrier allocated would be capable of serving 7 simultaneous voice connections. From our Erlang B tables we can see that 7 simultaneous connections are sufficient to accommodate 3 Erlangs of traffic with a 2% blocking probability. Our estimated 120 subscribers will generate exactly 3 Erlangs of traffic in the busy hour if each one offers 25 mE (one fortieth of an Erlang) to the network. In this way we have what could be considered a perfect solution to the problem posed.

An Initial ChallengeAn Initial Challenge

• GSM Services are to be provided over a small area: 20

km2.

• Number of subscribers estimated to be 120.

• Average subscriber generates 25 mE of traffic in the

busy hour




An Initial ChallengeAn Initial Challenge

• Calculations:

•20 km 2: Circle approximately 2.5 km in

radius

•120 x 25 mE = 3 Erlangs (average

activity is 3 users: “peak” of 7 users).

•Single GSM carrier sufficient.

•Omni-directional (single cell) site would

be used.

2.5 km


1.3 Evolution of the Requirement: Coverage Enhancement

The traffic offered to a GSM network does not stay relatively constant for long. Indeed the initial scenario described is so simple to accommodate as to be remarkably convenient and unlikely to be encountered in practice. Suppose, for example, the coverage requirement increased beyond that normally possible from the omni-directional antenna used to date. What options are open to the planner to improve the coverage? We can go through a number of possible solutions:



Increasing the Coverage RangeIncreasing the Coverage Range

• Possible Methods:

•Increase Antenna Height

•Increase Antenna Gain

•Increase Cell Power

•Sectorise the Site

•Add Additional Sites


Increasing the mast height. As a general rule, increasing the mast height will reduce the path loss at a particular distance. The decrease in path loss is not, however, dramatic (a typical decrease would be 4 dB for doubling the height of the mast) but can lead to significant increases in the range (4 dB would represent a range increase from 2.5 km to about 3.2 km).

Predicting Effects: Increasing Antenna HeightPredicting Effects: Increasing Antenna Height

• Increasing Antenna Height reduces

path loss.

• Not dramatic: e.g. doubling mast

height can give 4 dB reduction in path

loss.

• 4 dB reduction in path loss can lead to

a 25% increase in range (approx 50%

increase in coverage area).


Increasing the gain of the antenna. Not all omni-directional antennas have the same gain. Examination of catalogues reveals that a variation from 10 dBi to 14 dBi is possible. If a 14 dBi antenna is used instead of a 10 dBi antenna, an increase in range is possible. However, this would not be achieved without a cost. A 14 dBi antenna would have a smaller vertical



beamwidth that could lead to problems closer to the mast. Careful, accurate consideration would have to be given to down-tilting the antenna beam.

Predicting Effects: Increasing Antenna GainPredicting Effects: Increasing Antenna Gain

• Omni-directional antennas can have

different gains (10 dBi to 14 dBi being

the commonly available range).

• Lower gain antennas will have a larger

vertical beamwidth.

• Down-tilting the antenna is a

technique used to ensure that there

are no coverage gaps and also to

restrict interference.

10 dBi antenna

14 dBi antenna

No downtilt

12° downtilt


Increasing the transmitter power. This will help coverage in the downlink only. Two-way communication is required. If the coverage problem is due to uplink constraints (and coverage problems usually are due to uplink constraints) then increasing the downlink power will do no good whatever. It is vital that the link is balanced (a topic dealt with later). Increasing the downlink power is often accompanied by introducing an extra (diversity antenna) at the base station.

Predicting Effects: Increasing Cell Tx PowerPredicting Effects: Increasing Cell Tx Power

• Communication must be two-way.

• Increasing the Cell Transmit power increases downlink coverage but does not affect uplink coverage.

• The link will become “unbalanced”.

• Balance can be restored by implementing diversity.

• 5 dB increase typical.A site implementing Space Diversity

Uplink Coverage

limitDownlink Coverage

limit




Sectorising the site. Instead of having an omni-directional antenna at the base station, it is possible to divide the coverage area up into (usually) three sectors. Because it has a narrower beamwidth, the sectored antenna will have a higher gain (about 6 dB higher). This would lead to the range of the cell increasing from its original value of 2.5 km to about 3.7 km. Sectorising will also raise the problem of a single carrier (often called a “single TRX”) no longer being sufficient. If 3 sectors are used, each would require a separate TRX. Coverage would be improved as a result, so would capacity – a factor considered in the next sub-section.

Predicting Effects: Sectorising the SitePredicting Effects: Sectorising the Site

• Instead of a single omni-directional antenna use 3 sectored antennas.

• Gains up to 18 dBi

• Requirement is for 3 TRXs as a minimum.

• Improvement in both coverage and capacity.

A base station employing sectored antennas.


Adding sites. This solution will almost certainly be effective – although sometime it leads to the result that the original site location is not appropriate. Adding a further site will almost certainly be the most expensive solution by far and is often seen as the “solution of last resort” by planners. As in the case of sectorisation, it will lead to the need for a different TRX frequency to be allocated so as to avoid interference problems. In general, this leads to the need for Frequency Planning to be done on the network. Frequency Planning is a key skill for the GSM Network Planner.



Predicting Effects: Adding an Extra SitePredicting Effects: Adding an Extra Site

• A single extra site will increase coverage in a particular direction.

• Very expensive.

• Separate carriers must be allocated to the new site (frequency planning) to avoid interference.

Interference Region


1.4 Evolution of the Requirement: Capacity Enhancement

It may be that, rather than coverage becoming a problem, the demand for voice connections becomes greater and the network cannot deliver a satisfactory quality of service (that is the blocking probability is seen to exceed 2% on a regular basis). To this end, a number of enhancements are considered:

Increasing the CapacityIncreasing the Capacity

• Possible Methods:

•Adding more carriers

•Sectorising the site




Adding additional carriers to the site. Two TRXs can be connected to the same omni-directional antenna. This will increase the number of simultaneous connections from 7 to 14 or 15. The number of Erlangs that this will accommodate will in fact more than double, due to an increase in trunking efficiency. The offered traffic that can be serviced will increase from 3 Erlangs to about 9 Erlangs, sufficient to accommodate the demand from approximately 360 “typical” subscribers.

Predicting Effects: Increasing TRXsPredicting Effects: Increasing TRXs

• 1 Carrier: 7 timeslots: 3 Erlangs: 120

subscribers

• 2 Carriers: 15 timeslots: 9 Erlangs 360

Subscribers

• Maximum for one cell is typically 6 carriers

(45 timeslots: 36 Erlangs 1440

subscribers).

• Maximum is influenced by network

allocation (e.g. 60 carriers occupies 12

MHz) and frequency re-use strategy.


Sectorising the site. As described when this method was put forward as a solution to the coverage problem, this entails replacing the omni-directional antenna by three sectored antennas. Each antenna would require its own TRX and therefore three carrier frequencies would have to be allocated to this site. In this way, each sector would be able to service 3 Erlangs of offered traffic resulting in a total of 9 Erlangs for the site. Note that this is the same as could be serviced by only 2 TRXs on an omni-directional antenna. However, the three-sectored solution will have the added benefit of increasing the coverage from the site as described in the previous sub-section.



Predicting Effects: Increasing TRXsPredicting Effects: Increasing TRXs

• Sectorising can lead to 3 separate

single-TRX cells each serving 3

Erlangs.

• This provides 9 Erlangs (the same as

with 2 TRXs on an omni site).

• Coverage will also be improved.

Approximate radiation patterns from sectored antennas.


1.5 Evolution of Requirement: Coverage and Capacity

Typically, the requirement or demand from the user will not vary by just increasing either traffic or coverage requirements but, more typically, both. In practice the above techniques will be refined and implemented in combination so as to achieve the desired effect. Throughout the process it is vital that quantitative analyses are made (that is, instead of simply saying that the performance will be improved we can say by how much (20%?... 50%?). We must be able to “quantify” any improvement so that alternative solutions can be compared and the best solution implemented. The following sections deal with specific issues that will provide us with techniques and tools to permit the analysis of situations in sufficient depth so that a high degree of confidence can be placed in the resulting predicted performance.



Network Evolution: Increasing Coverage and Network Evolution: Increasing Coverage and CapacityCapacity

• All previously-analysed methods may

be considered.

• Quantitative analysis required.

• e.g. coverage area increased by

100%; Capacity increased by 200%.


1.6 The Need for Frequency Planning. As mentioned when we placed an extra site as a possible solution to a coverage problem, if the same frequency is allocated to both the sites, there is an unusable region where the interference is too great. A typical requirement is that the wanted signal should be 12 dB above the interfering signal. Physically, this leads to a requirement that any interferer should be at least three times as far away as the source of the wanted signal (if all transmitters are transmitting at the same power through similar antennas). A network operator will be allocated many carriers (60 being a typical number). It is therefore possible to make sure that adjacent cells are not given the same frequency. However, there will be many more than 60 cells in a network and some cells will require more than one carrier. It is therefore necessary to re-use carriers within the same network. Frequency Planning aims to ensure that continuous coverage is provided over the required area without unacceptable interference occurring. This will entail adopting an appropriate frequency re-use strategy. Typically, a re-use factor of 12 has to be adopted so that, if 60 carriers are allocated, no more than 5 can be placed on any one cell. It should be noted that frequency planning is a highly-skilled job and that the figures quoted above are only approximate examples of what the outcome may be.



The Need for Frequency PlanningThe Need for Frequency Planning

• GSM network capacity is

eventually limited by inteference.

• Frequencies can only be re-used at

a far enough distance so as not to

exceed inteference limits.

• C/I of 12 dB typically required.

• Distance to interfering cell must be

3 times that to serving cell.


1.7 Different Approaches for different environments. Both cell configuration and density will depend upon the environment. Open rural areas will have a different requirement to dense, urban areas. Individual approaches need to be adopted for roads where the coverage pattern may need to be different from those provided by standard antennas. Additionally, the propagation model will be different in different environments such that the signal may attenuate more quickly in a dense urban environment than it does in a rural environ ment. This will lead to the need for different re-use factors in the two environments. The coverage versus capacity discussion will have different outcomes in different environments. This will impact on antenna heights and configuration. In suburban areas, building planning constraints are likely to prevent antennas from exceeding a certain height. This will impact on the number of cells required to cover a particular area.



Environmental AspectsEnvironmental Aspects

• Different Environments pose

different challenges.

• Rural environments have coverage

as a priority over capacity

• Capacity and Inteference issues

take priority in Dense Urban

environments.

• Path Loss Prediction difficult in a

Dense Urban environment.



• Planning constraints may limit

antenna heights, particularly in

suburban areas.

• Roads are sometimes covered

by antennas with a narrow

beam with special

arrangements made for

intersections.





• Small areas of high subscriber

density can be best served by a

low level antenna forming a

micro-cell.

• Office buildings are sometimes

served by indoor antennas that

form a pico-cell.




2 Link Budget for GSM

2.1 Introduction

Predicting the strength of a signal received by a mobile is not straightforward. Often the mobile receiver cannot see the base station and the signal strength is determined largely by reflection (also called “scattering”) and diffraction. The variety of possible environments encountered by the radio wave means that the distance between the base station and the mobile is not the only parameter that affects the path loss. A variety of possible methods exist that allow the engineer to predict the path loss with sufficient speed and accuracy. It is vital that a prediction method that engineers are confident in is adopted before the network is designed.

Why we need a Propagation ModelWhy we need a Propagation Model

• Mobile communication is made possible using multipath propagation

• The radio wave undergoes scattering, diffraction and attenuation

• Propagation model calculates the path loss

between transmitter and receiver

• Required for calculating power budgets

and system balance requirements

• Model used for setting up a network and subsequent optimisation

?

Section 2 – Link Budget for GSM



________________________________________________________________________________

2.2 Free Space Propagation Model

2.2.1 FREE SPACE RADIATED POWER

Ideal propagation implies radiating equally in all directions from the radiating source and propagating to an infinite distance with no degradation.

Free Space Radiated PowerFree Space Radiated Power

Power Pt (W)d

Surface area of sphere = 4πd2

• In free space the wave is not reflected or absorbed

• Attenuation is caused by spreading the power flux over greater areas

• Power Pt is transmitted equally in all directions

• Power flux Pd at distance d from antenna given by:

Pd = Pt / 4πd2 (W / m2)

Pd


However, if the radiating element is generating a fixed power flux and this power flux is spread over an ever-expanding sphere, the energy will be spread more thinly as the sphere expands. Therefore in any given direction the energy will diminish with distance, even in an ideal propagation environment. The measurable power at any point on this sphere is known as the power (or power flux density (Pd)) measured in Watts per square metre.

2.2.2 FREE SPACE RECEIVED POWER

Having identified the power flux density at any point of a given distance from the radiator, if a receive antenna is placed at this point, the power received by the antenna can be calculated. The amount of power ‘captured’ by the antenna at the required distance (d), is dependant upon the ‘effective aperture’ of the antenna and the power flux density at the receiving element. The effective aperture is dependant upon the wavelength of the received signal (i.e. the longer the wavelength, the greater the effective aperture required to capture the same power.



Free Space Received PowerFree Space Received Power

• Actual power received by antenna depends on:

• Aperture of receiving antenna (Ae)

• Wavelength of received signal (λ)

• Power flux density at receiving antenna (Pd)

• Effective area of an isotropic antenna is:

Ae = λ2 / 4π

Effective area Ae• Power received: Pr = Pd x Ae

= (Pt / 4πd2) x (λ2 / 4π)

= Pt x (λ / 4πd)2

Isotropic antenna


The formulas for calculating the effective antenna aperture and received power are shown above.

2.2.3 FREE SPACE PATH LOSS

Free Space Path LossFree Space Path Loss• Receive Power is given by the formula:

Pr = Pt x (λ / 4πd)2

• Expressing this formula in terms of dBs gives:

Pr = Pt − 20log10(4π) − 20log10(d) + 20log10(λ) dBm

• If path loss (LP) = Pt – Pr then:

LP = 20log10(4π) + 20log10(d) − 20log10(λ) dBm

• Substituting (λ = 0.3/f) and rationalising the equation produces the generic free space path loss formula:

LP = 32.5 + 20 log10(d) + 20 log10(f) dBm




Having determined formulas for the power at any point on the sphere of an isotropic radiator at a given distance and the received power for as given antenna aperture, basic path loss is simply the difference between the two. i.e. PL = PT - PR

________________________________________________________________________________

2.3 Plane Earth Propagation Model

The free-space propagation model does not consider the effects of propagating over ground. When a radio wave propagates over ground, some of the radio wave power will be directed into the ground. Some of this power will be reflected back up to the receive antenna. To determine the effects of the reflected power, the free-space propagation model is modified and referred to as the ‘Plain-Earth’ propagation model. This model better represents the true characteristics of radio wave propagation over ground. The Plane Earth model computes the received signal to be the sum of a direct signal and that reflected from a flat, smooth earth. The relevant input parameters include the antenna heights, the length of the path, the operating frequency and the reflection coefficient of the earth. This coefficient will vary according to the terrain type (e.g. water, desert, wet ground etc)

Plane Earth ModelPlane Earth Model

Tx Rx

Image Tx

Reflection at Earth’s surface

Signals at Rx may interfere constructively or destructively to different degrees

This depends on: Antenna heights (h1, h2)

Link distance d

Wavelength

Reflection coefficient of Earth




Plane Earth Model EquationPlane Earth Model Equation

• Calculations on the plane earth model lead to the following equation for path loss:

LPEL = 20 log (d2 / h1 h2) dB

LPEL = 40 log (d) - 20 log (h1) - 20 log (h2)

• d = path length in meters

• h1 and h2 are antenna heights

• Problems with using plane earth model in GSM:• Does not deal with multipath reflections

• Mobile height is constantly changing


For a perfectly reflecting earth, the path loss L is expressed by:

( ) ( ) ( )21 log20log20log40 hhdL −−= where d is the path length in metres and h1 and h2 are the antenna heights at the base station and the mobile.

Free Space Free Space vsvs Plain Earth PropagationPlain Earth Propagation

= Free Space Loss

= Plain Earth Loss




The plane earth model is not appropriate for mobile systems as it does not consider reflections from buildings, multiple propagation or diffraction effects. Further, if the mobile height changes (as it will in practice) then the predicted path loss will also change.

________________________________________________________________________________

2.4 Cellular Radio Propagation Models

The models described above are referred to as ‘theoretical’ as they are based on mathematical calculations only. Empirical models differ from theoretical models in that the formulas are determined from the analysis of actual measured practical data rather than theoretical mathematical models. The cellular radio propagation models described below all fall into the ‘empirical’ model type.

2.4.1 EMPIRICAL CELLULAR PROPAGATION MODELS

Empirical models are mathematical equations that are based on the result of measurements made in typical, realistic situations. In general, such models are “tuneable”, that is, they contain coefficients that can be altered to make the model agree with measurements made in the location in which the network is being planned.

Cellular Propagation ModelsCellular Propagation Models

• Models based on published data

• Main models available are:

• Okumura - Hata

• COST 231 - Hata

• COST 231 Walfisch - Ikegami

• Sakagami - Kuboi

• Different models are more appropriate depending on:• Location• Frequency range

• Clutter type


Typically, more than one model will be used in any given network in order to predict the changes in topography (land use; also known as “clutter category”). A few models are now widely used as they have been shown to produce reliable predictions in a wide variety of circumstances. Furthermore they produce predictions very rapidly. Remember that a prediction will be made over a grid that will have a resolution of, say, 20



metres. That means 2500 predictions must be made for every base station for every square kilometre. Speed of calculation of the propagation model is vital. Some “traditional” models (such as the Okumura-Hata) have been modified to extend their range of applicability. One very active group in this field has been the COST 231 project; a collaborative affair involving engineers and scientists from universities and industry throughout Europe.

2.5 Okumura’s Measurements

A lot of current mobile propagation models have at their heart the measurements made by a Japanese engineer named Okumura..

Okumura’s MeasurementsOkumura’s Measurements

• Okumura, a Japanese engineer, carried out extensive drive test measurements, with

a range of:

• clutter type

• frequency

• transmitter height

• transmitter power

• Main conclusion from Okumura field tests:

• Signal strength decreases at a much greater rate with distance than that predicted by free

space loss




•Typical curves for different base station antenna heights with fixed mobileheight (1.5m) and frequency (900 MHz)

•Field strength drops off more rapidly than free space line, particularly closerto the base station

Okumura’s ResultsOkumura’s Results

Fie

ld S

tren

gth

(dB

)Log Distance (km)

Free space loss

Increasing base station antenna height


From the graphs of lines of best fit for a number of situations it was possible to quantify the effect of link length and base station height on the received signal strength.



2.6 The Hata Propagation Model

Hata’s Propagation ModelHata’s Propagation Model

• Hata based the model on Okumura’s field test results

• Predicted various equations for path loss with different types of clutter

• Limitations on Hata model due to range of test results:

• Carrier Frequency: 150 MHz to 1500 MHz

• Distance from the base station (d): 1km to 20 km

• Height of base station antenna (hb): 30m to 200m

• Height of mobile antenna (hm): 1m to 10m


Using Okumura’s results, the Japanese engineer Hata created a number of representative mathematical models for each of the urban, suburban and open country environments.

Hata’s EquationsHata’s Equations

• Path loss for urban clutter:

Lp(urban) = 69.55 + 26.16 log(f) - 13.82 log(hb) - a(hm) + (44.9 - 6.55 log(hb)) log(d)

• Path loss for suburban clutter:

Lp(suburban) = Lp(urban) - 2log(f / 28)2 - 5.4

• Path loss for open country:

Lp(open country) = Lp(urban) - 4.78 log(f)2 + 18.33 log(f) - 40.94


The coefficients can generally be changed as part of a “tuning” process. It must be remembered that the model should be regarded as applicable only over the ranges for which measurements were made.



Limitations on Limitations on HataHata Model for GSMModel for GSM

• Maximum carrier frequency = 1500 MHz

• Not valid for 1800 MHz or 1900 MHz systems

• Assumes base station antenna is above surrounding clutter

• Not suitable for microcell planning where antenna is below roof height

hb

hm

d

microcell


The upper frequency limit of 1500 MHz with regard to the Okumura-Hata model posed a serious problem when GSM systems commenced operation in the 1800 MHz band. One of the major objectives of the COST 231 project was to establish an appropriate macrocell model, or models, for frequencies up to 2000 MHz.

2.6.1 THE COST 231-HATA MODEL

Cost 231 Cost 231 -- HataHata ModelModel

• COST : European Co-operation in the Field of Scientific and Technical Research

• COST 231 - Hata extends the Okumura-Hata model for medium to small cities to cover the 1500 to 2000 MHz band

• Path loss equation is:

Lp= 46.3 + 33.9 log(f) - 13.82 log(hb) - a(hm) + 44.9 -6.55 log(hb)log(d) + Cm

Cm = 3 dB for metropolitan centers

Cm = 0 dB for medium sized cities and suburban areas

• The model is not valid for hb <= hroof (i.e. base station below roof height) so it is not suitable for microcell planning




2.6.2 THE COST 231-WALFISCH-IKEGAMI PROPAGATION MODEL

COST 231 COST 231 WalfischWalfisch--Ikegami ModelIkegami Model

• Combination of theoretical models (Walfisch / Ikegami)

• Said to be a microcell model (but more realistically a small Macrocell model

• Model parameters include:

• Building separation (m)

• Average Building Height (m)

• Road width (m)

• Road angle of orientation (degress)


2.6.3 THE SAKEGAMI-KUBOI MODEL

SakagamiSakagami KuboiKuboi ModelModel• General model based on detailed analysis of Okumura’s results

• Valid over wide frequency range: 450 to 2200 MHz

• Processes a large number of parameters relating to the urban environment

• Claims validity for base antennas below roof top making it useful in planning

microcells

Tx

Ø

W




Sakagami Kuboi Formula

Sakagami Kuboi Formula

• Path loss in dB:Lp = 100 - 7.1 log(W) + 0.023 Ø + 1.4 log(hs) + 6.1 log<H> - 24.37-3.7(H / hb)2 log(hb) + 43.42 - 3.1

log(hb) log(d) + 20 log(f) + e[13 log(f)-3.23]

W = width of the road at the receiving point (5 - 50 m)Ø = orientation of road relative to base station direction

(0 to 90 degrees)

hs= height of the building on the base station side of the receiving point (20 - 100 m)

<H> = average height of the buildings near the receiving point (5 - 50 m)

H = average height of the buildings around the base station


The Sakagami -Kuboi formula is a level of sophistication above that of the Okumura-Hata or COST 231-Hata models. Its claim to be valid for base station heights below the building height makes it suitable for microcell and well as macrocells. However, it requires information regarding street width and orientation as well as building heights. This sort of information may not be readily obtainable for the mapping data to hand. Even if such data were available, the time taken to run the model may be prohibitive.

________________________________________________________________________________

2.7 Diffraction Attenuation Models

Terrain obstacles will sometime obstruct the line of sight (LOS) path between the base station and the mobile. The effect of an obstruction depends on: The amount by which it obstructs the line of sight path The distance from the obstruction to each end of the radio path The frequency of operation. These four parameters can be reduced to a single parameter by expressing the clearance in terms of the ‘Fresnel zone’ Radius.

2.7.1 FRESNEL ZONES

The Fresnel zone describes an ellipsoid in three dimensional space. If you add the distance to each end of the link from any point on the surface of this ellipsoid, the sum is half a wavelength more than the straight-line distance between the two ends.



The radius of this ellipsoid is referred to as the radius of the First Fresnel Zone.

Fresnel ZonesFresnel Zones

Tx Rx

Third Fresnel Zone

r1 0.6 r 1

Forbidden Region (0.6 r1)

First Fresnel Zone Second Fresnel Zone

First Fresnel Zone


• Path length of any wave reflected from a Fresnel zone surface is nλ/2 more than direct path:

a + b = d + n(λ/2)

• Radius of ellipsoid at d1 from Tx is given by:

Fresnel Zone DimensioningFresnel Zone Dimensioning

Tx Rx

d1 d2

d

R1a b

ddn λ21

1d R =

R1




First Fresnel Zone Radius CalculationFirst Fresnel Zone Radius Calculation• Normally only first Fresnel zone considered. Hence:

a + b = d + λ/2 and

• For macrocell planning d2 >> d1 and therefore d2 ˜ d. Hence:

• The site of the base station and antenna height should allow complete clearance of at least the first 100 metres of the first Fresnel zone

• For the 900 MHz band , λ ˜ 0.33m. Hence:

dd λ21

1d R =

λλ

11

1 d ddd

R =≈

m 5.7 33 0.33 100 R1 ==×≈


2.7.2 FIRST FRESNEL ZONE CLEARANCE

If the first Fresnel zone is clear of obstructions then the link can be regarded as if no obstructions existed. It is important to remember that the curvature of the earth must be considered when evaluating the degree of obstruction

First Fresnel Zone ClearanceFirst Fresnel Zone Clearance

• At 100 m from the base station, the first Fresnel zone radius is about 5.7 m for a distant receiver

• Using this figure, the required height of the antenna can be estimated

• Some compromise may be necessary in the clearance allowed

BTS

MS

100m5.7m

First Fresnel Zone




First Fresnel Zone Clearance


• Fresnel zone clearance is mainly used to calculate antenna heights for fixed line of sight microwave links

• The height is calculated to give 100% clearance with an Earth radius factor (k) of 4/3 and again for 60% clearance with k = 2/3. The greater of these two results is then used for the antenna height.

• It can be useful when placing a base station to consider Fresnel zone clearance using an average MS antenna height of 1.5m

BTS

First Fresnel zone clear of obstacles

MS


Atmospheric effects can lead to the curvature being either exaggerated or diminished. This is accounted for by applying a “k-factor” to the actual radius of 6373 km when determining the curvature effect. Typically, the whole of the first Fresnel zone would be expected to be obstruction -free for a k-factor of 1.33 and 60% free when the k-factor is 0.67.

2.7.3 SINGLE OBSTRUCTION DIFFRACTION FORMULA

If the clearance requirements are not met, then the amount of “diffraction loss” must be calculated. For a single obstruction (or ‘knife edge’) protruding into the first Fresnel zone, the diffraction loss can be calculated from the following formula:

Single KnifeSingle Knife--Edge Diffraction FormulaEdge Diffraction Formula

Fresnel diffraction parameter =

where λ = wavelength

21

21 )2( vddddh

λ+=

Section 1 - Propagation Models

h

d1d2



Diffraction Effects

Diffraction Effects


Single KnifeSingle Knife--Edge Diffraction FormulaEdge Diffraction Formula

The diffraction loss (L) is given by:

L = -20 log(x)

Where x = 1 for v < -0.8

x = 0.5 - 0.62v for -0.8 <= v < 0

x = 0.5exp(-0.95v) for 0 <= v < 1x = 0.4 – (0.1184-(0.38-0.1v)2)1/2 for 1 <= v <= 2.4

x = 0.255/v for 2.4 < = v




2.7.4 MULTIPLE KNIFE EDGE DIFFRACTION MODELS

However, if there is a series of obstacles in the radio path, the computation becomes extremely complex. A number of methods have been developed for approximating the total diffraction loss for multiple obstructions to the radio path. Each has advantages and disadvantages in certain circumstances and all those described here use the approach summing a number of individual diffraction losses.

Multiple Knife Edge Diffraction ModelsMultiple Knife Edge Diffraction Models

• Objects protruding into the first Fresnel zone will cause significant diffraction effects

• A variety of models are available to calculate diffraction loss or gain at the receiver due to a series of knife edges

• The commonly used knife edge models are:

• Bullington

• Epstein-Peterson

• Deygout

• Japanese Atlas




2.7.5 THE BULLINGTON DIFFRACTION MODEL

Bullington ModelBullington Model

• Defines a new effective knife edge obstacle at the point where the line-of-sight from the two antennas cross

• Advantage:• Simple method

• Disadvantage: • Significant obstacles may be ignored leading to an optimistic estimate of field strength

TxRx1 21 2

Equivalent knife edge


Burlington developed a diffraction model which was presented in 1947. It involves taking two diffracting knife edges and replacing them with a single equivalent knife edge. This process involves extending a line from one terminal through the peak of the first knife-edge. The process is then repeated from the second terminal through the peak of the second knife edge. Where these two extended lines intersect, an equivalent knife-edge is created. The diffraction effect is then calculated for the single equivalent obstacle rather than for the two separately. The Bullington model affords reasonable accuracy when the two obstacles are reasonably close together and a reasonable distance from the terminals. Otherwise significant inaccuracies can be introduced leading to underestimation of overall diffraction loss.

2.7.6 THE EPSTEIN-PETERSON DIFFRACTION MODEL

The Epstein-Petersen Model was introduced in 1953. This model estimates the total diffraction loss for a multiple-obstacle path by calculating individual losses fore each obstacle and adding these together to estimate the overall diffraction loss.



Epstein Epstein -- Peterson ModelPeterson Model

• This finds the total loss as the sum of the diffraction losses at each obstacle

• For obstacle 1, consider Rx to be at obstacle 2. Then for obstacle 2, consider Tx to be at 1 and Rx to be at 3 and so on.

Tx Rx1 2 31 32

Rx1

Tx1Rx2

Tx2

• Advantage: • does not ignore important obstacles as Bullington method may

• Disadvantages: • may overestimate path loss when the obstructions are close together


Referring to the above diagram, the process for calculating a single knife edge diffraction loss is as follows: Assume the Rx terminal is at the peak of the obstacle 2. Draw a new line of Sight (LOS) between the Tx terminal and the new Rx terminal. The diffraction loss of the obstacle 1 intrusion into this new LOS in then calculated. The next step is to shift the terminal positions one obstruction to the right. The Tx terminal is now deemed to be at the peak of obstacle 1 and the Rx terminal at the peak of obstacle 3. A new LOS is drawn between the two terminals. The diffraction loss of the obstacle 2 intrusion into this new LOS in then calculated. The next step is to shift the terminal positions one obstruction to the right again. The Tx terminal is now deemed to be at the peak of obstacle 2 and the Rx terminal at its actual position. A new LOS is drawn between the two terminals. The diffraction loss of the obstacle 3 intrusion into this new LOS in then calculated. The individual diffraction losses at each stage of calculation are then added together to produce the total estimated diffraction loss. This process can be repeated for any number of obstacles. The Epstein-Peterson Model provides a reasonable approximation provided the obstacles are well separated. In urban areas where intrusions are commonly close together, the accuracy of this model diminishes and tends to overestimate losses.



2.7.7 THE JAPANESE-ATLAS DIFFRACTION MODEL

This model was introduced by the Japanese Postal Service in 1957.

• Effective Tx position for each obstacle is found by extending the line to the previous obstacle back to meet the vertical line through the actual Tx

• Advantage:• gives improved results when the obstructions are closely spaced

• Disadvantage:• still suffers from underestimating the path loss• Non-reciprocal

Japanese Atlas ModelJapanese Atlas Model

TxRx

1 2 3

Loss for obstacle 1: Line from 2 to Tx – LOS Tx to 2

Tx1

Loss for obstacle 2: Line from 2 through 1 to Tx1 – LOS Tx1 to 3

Tx2

Loss for obstacle 3: Line from 3 through 2 to Tx2 – LOS Tx2 to Rx


The Japanese Atlas method is a variation on the Epstein-Petersen model whereby the contribution of obstacle 2 is determined not by assuming obstacle 1 to be the Tx terminal but as follows: The diffraction loss for the first obstacle is calculated as normal by extending a line from the peak of obstacle 2 back to the actual position of the Tx terminal and calculating the diffraction loss introduced by obstacle 1.

However, to calculate the diffraction loss of obstacle 2, a line joining the peaks of obstacles 1 and 2 is extended back towards the Tx terminal to a point where it crosses an imaginary line extending above the actual Tx terminal height. Where this imaginary line is crossed, a new virtual Tx source is established (T above). A new LOS is then drawn to the next obstacle (3 in this case) and the diffraction loss caused by obstacle 2 into this LOS is calculated. This second step is then repeated for each successive obstruction until all have been included. The individual diffraction losses are the added together to determine the overall loss. This method can produce more accurate results than the Epstein-Peterson model but must be treated with care as the results are non-reciprocal. This means that if the calculations are initiated from the Rx terminal, the results will be different.



2.7.8 THE DEYGOUT DIFFRACTION MODEL

• This calculates a V parameter for each obstacle• Obstacle with highest value of V is the ‘main obstacle’• Loss for this edge is calculated• Loss over next most significant obstacle is then found and added to loss and so on

• Advantages: • Accurate when there is a clearly dominant edge• For three or four obstructions, Deygout gives the best results of any of the

approximate methods• Disadvantages:

• Where there is no dominant edge, Deygout tends to overestimate the loss• Does not work well when there are two similar height edges such as ends of a building

DeygoutDeygout ModelModel

Tx Rx11 2

main edge

3


2.7.9 SELECTING A SUITABLE MODEL

Which Model to Use?Which Model to Use?

• Cell planners using various planning

tools have their favourite models

• No one model is accurate in

every situation

• Before using a model to predict

coverage it must be verified by drive testing

• Model must be tuned or calibrated according to the local situation

Asset’s model is based on COST 231-Hata and is tuned by varying a combination of parameters k1 - k7




SummarySummary

• Need for propagation models: predictions, power budgets, optimisation• Theoretical Propagation Models:

• Free Space Model, Plain Earth Model

• Empirical Propagation Models: • Okumura’s results, Hata model, COST 231 Hata, Sakagami - Kuboi,

• Diffraction Models • Fresnel zones

• Diffraction Formula• Diffraction Models:

• Epstein - Peterson, Bullington, Japanese Atlas, Deygout


2.8 CW Drive Testing ________________________________________________________________________________ The propagation models described in the previous section are ‘generic’ for a particular notional environment. That is to say, only one model is defined for each environment type (e.g. urban, sub-urban, rural etc). Clearly, each physical urban environment will be different, i.e. different countries, different cities, different urban densities and building types etc. Therefore, it is necessary to carry out measurements of the physical environment in order to adjust the ‘generic’ propagation model to be more representative of the local physical environment. This is the purpose of ‘CW drive testing’. CW drive testing involves covering an extensive part of the proposed coverage area measuring the signal strength received from individual BTSs. For this purpose a narrow-band unmodulated carrier wave (CW) signal is used. Hence the term ‘CW’ drive testing. ________________________________________________________________________________

2.8.1 THE TRANSMITTER

It is usually necessary to establish a temporary transmitter in order to conduct a drive-test. The transmitter could utilise its own mobile mast or, alternatively, make use of existing buildings. It is, of course, vital that either the transmitter is battery powered or there is ready access to a mains power supply.



• Temporary Transmitter Arrangement:

• Roof top or crane mounted

• Access to AC power source

• Low gain omni-directional antenna

Temporary mastBATTERY

RADIOTRANSMITTER

Drive Test Drive Test -- TransmitterTransmitter


________________________________________________________________________________

2.8.2 THE RECEIVER

The equipment must be capable of recording both the signal strength and the location of the mobile at the measurement instant. This is so that the measurement can be compared with the prediction for the signal strength at that position. The measurement equipment must include a sensitive, narrow band, receiver; usually including a spectrum analyser. The location information is provided by a GPS receiver. As a considerable distance may be travelled between one GPS reading and the next, the position information may be supported by speed and direction information provided by in-car equipment.



GPSReceiver

Wheel pulser

PC

PositionalInformation

DirectionalInformation

SpeedInformation

C W Analysis C W Analysis -- ReceiverReceiver

RadioReceiver Disk

Storage

Gyro


________________________________________________________________________________

2.8.3 CW MEASUREMENT PROCESS

CW Test ProcessCW Test Process

• Drive testing should be performed on radial and circumferential routes

• Radial routes show variationin signal strength with distance

from base station

• Circumferential routes provide predictions for signal strength in

different directions from the base station




It is important that as much variety as possible is incorporated into the measurements. It is not very useful if the mobile is just moved in a circle at a constant distance from the base station as no data would be gathered regarding the variation of signal strength with distance from the mobile. Similarly moving the mobile along one radial line from the base station would render the results likely to be unrepresentative due to some particular characteristic of the terrain in the direction chosen.

CW Analysis CW Analysis -- Transmitter SitingTransmitter Siting• Select sites which are good representatives of your network

• Use a range of antenna heights

• Ensure there are no immediate obstructions near the test transmitter

• Do not place the test transmitter on a building having long roof

Long roof obstructs transmission in this direction


• Test drive in the main vertical lobe of the omni antenna - low gain antenna -large main lobe - consistent good coverage over wide area

• Do not test drive in the shadow regions

• Take panoramic photographs around the test site to relate measurements to actual ground features

CW Analysis CW Analysis -- Drive TestingDrive Testing

X

Omni antenna




• Cover all clutter types equally throughout the test

• Be aware of man-made features such as bridges or tunnels

Most models assume a mobile height of 1.5m, bridges can affect the actual height above

ground:

Clutter and ManClutter and Man--made Featuresmade Features

Actual position of mobile

Model assumes mobile is here

Bridge

Ground level - given by map data


When comparing results with the model it is important that the validity of any assumptions made by the model is maintained. One of these assumptions will concern the gain of the antenna. It is therefore very important that the mobile remains within the main lobe of the base station antenna. This entails ensuring that the mobile does not get too close to the antenna such that it is “under” the main lobe. Further, it is essential that, when the positional information gathered is translated onto a map of the test route, the mobile is calculated to be where it actually is. This may sound obvious but there are situations where discrepancies can occur. One such situation is when the mobile is on a bridge over a valley. The model may well assume that the mobile is on the valley floor when, in fact, it would be many metres above this point. An additional case to be avoided is placing the mobile in a tunnel when the mapping data would lead to the assumption that it was on the land surface vertically above.



CW Measurement EquipmentCW Measurement Equipment

• Measurements should be distance based• Take readings no closer than 0.38 wavelengths apart.

• Equipment can be:• Distance triggered

• Time triggered

• GPS outputs position every second.• Position interpolation is required for each measurement

• Test mobile measurements are NOT suitable• Fluctuating power levels (TCH carriers)

• Minimum 2dB steps

• 200kHz channel bandwidth


Measurements should be taken at regular intervals. If the equipment is distance-triggered, care must be taken to ensure that th e speed of the drive test vehicle is not so large that the equipment cannot complete a measurement before the next trigger pulse arrives. If the equipment is time triggered, a slow moving vehicle will produce the desired small distances between measuremen ts. In this situation, the speed of the vehicle should be maintained constant. It is tempting to economize on the measurement equipment by using a test mobile instead of a professional measuring receiver. Test mobile receivers are inadequate for a number of reasons: They record signal levels to the nearest 2 dB. They are wideband (200 kHz) devices and hence not sufficiently sensitive. Power levels fluctuate on a live traffic carrier



Summary Summary –– CW Drive TestingCW Drive Testing

• Purpose of CW Drive Testing

• CW Drive Test Equipment

• The Drive Testing Process

• The Practicalities of CW Drive Testing

Wheel pulser

PC

GPSReceiver

PositionalInformation

DirectionalInformation

SpeedInformation

RadioReceiver Disk

Storage

Gyro


2.9 Propagation Model Tuning ________________________________________________________________________________

The measurements obtained from the CW drive testing are compared with those predicted by the theoretical model. Where discrepancies exist, the parameters of the theoretical model are modified until the mathematical model becomes the closest approximation to the measured data. This modified mathematical propagation model is then generally used for all planning purposes in a particular environment (urban, rural etc). This modification process is known as ‘model tuning’ or ‘model calibration’. This allows the coefficients of the various terms contained in the model to be altered so as to produce a “best-fit” curve to the measured data. The equation for this curve is then used as the propagation model.



Purpose of Model TuningPurpose of Model Tuning

• The theoretical propagation model is ‘generic’

• The physical environment will vary

• The generic model is compared to CW measurements

• Where differences exist, the theoretical model is modified to reflect the physical environment.

• The modification process is known as model ‘tuning’ or ‘calibration’


________________________________________________________________________________

2.9.1 ANALYSIS OF A THEORETICAL PROPAGATION MODEL

In order to describe how a theoretical mathematical propagation model can be ‘tuned’ is if first necessary to examine the components of the formula than describes the propagation model.

A Mathematical Propagation ModelA Mathematical Propagation Model

• A ‘modified’ path loss model based on the COST-Hata 321 model:

Ploss = k1 + k2(log(d)) + k3(HMS) + k4 log(HMS)

+ k5 log(Heff) + k6 log (Heff) + k7 + Closs

Where d = distance from MS to BTS

HMS = MS antenna height

Heff = BTS effective antenna height




The above equation is an adaptation of the COST 231-Hata propagation model. It can be seen that the equation comprises the following components: The effective heights of the MS and BTS antennas The distance between the MS and BTS A number of variables known as ‘k’ factors. The factors can be modified in order to ‘tune’ the model to become a more accurate representation of the chosen environment. Each time the value of a factor is changed, the model has to be re-analysed to determine whether or not the mathematical model is more closely aligned with the measured CW data. The model is deemed to be tuned when the mathematical model is most closely aligned with the measured data.

Propagation Model ‘K’ FactorsPropagation Model ‘K’ Factors

• k1/k2 – attenuation intercept and slope

• k3 – mobile antenna height correction factor

• k4 – mobile antenna height multiplying factor

• k5 – BTS antenna height multiplying factor

• k6 – Hata multiplying factor

• k7 - diffraction loss (model-dependant)

• Closs – Clutter attenuation adjustment


___



_____________________________________________________________________________ 2.9.2 THE MODEL TUNING PROCESS

2.9.2.1 MODEL TUNING PROCESS OVERVIEW

Model Tuning ProcessModel Tuning Process

• Different approaches possible

• Trial and error process

• Some planning tools have automated process

• Optimise ‘k’ values in sequence to:

• minimise mean error value

• minimise standard deviation value


Because all the factors are inter-related, a number of different approaches can be taken to the tuning process. However, there are essentially two criteria by which the effectiveness of the tuning process can be gauged: Minimised mean error value Minimised standard deviation (SD) value



2.9.2.2 EXAMPLE TUNING PROCESS

Example Model Tuning Process (1)Example Model Tuning Process (1)

CW Data ApplyFilters

Slope/Intercept Correction

DiffractionCorrection

Eff Antenna HeightCorrection

Final Slope Correction?

YESFinish

NO

Start

Prediction Model

Clutter OffsetCorrections

Analyse


The above diagram shows one approach to the model tuning process. This outline process includes the following steps: STEP 1 Import the captured CW drive test data. STEP 2 Analyse the CW data. Filter out any erroneous or unwanted measurements. STEP 3 Apply the filtered data to the mathematical propagation algorithm by: Selecting the propagation model to be used Setting the default K parameter values Analysing the data

STEP 4 Optimise K parameters STEP 5 Make any clutter offset corrections. Clutter offsets allow the user to tune the model to particular types of clutter. In the Standard Macrocell model positive clutter offsets add additional path loss to areas of clutter. Offsets can be set individually on each clutter type. A negative offset would reduce the path loss over the chosen clutter type.



The following flow chart illustrates the steps that take place in optimising the K parameters (Step 4 above):

Example Model Tuning Process (2)Example Model Tuning Process (2)

Start Analyse

Adjust diffraction (k7)

Select Diffraction Algorithm

Analyse SDminimum?

NO

YESMean Errorminimum?

NO

Adjust Slope (k1)

Adjust Intercept (k2)

Analyse

SDminimum?

NO YES

YES

Analyse

Analyse

SDminimum?

NO YES

SLOPE/INTERCEPT CORRECTION

DIFFRACTION CORRECTION

Adjust Eff Heights (k3-k6)

NO

YES

Analyse

EFFECTIVE ANTENNA HEIGHT

CORRECTION

Analyse

Mean Errorminimum?

NO

Adjust Slope (k1)

Finish

FINAL SLOPECORRECTION

SDminimum?

YES


The K value tuning process can be divided into four parts: Slope/Intercept Correction Diffraction Correction Effective Antenna Height Correction Final Slope Correction

2.9.2.3 Slope/Intercept Correction

Initial analysis of the data will indicate a mean error. The K1 parameter should be adjusted by a value equal to the current mean value to reduce it to zero. For example, if the mean value is -8.5, the K1 value should be set to 8.5 to compensate. This should reduce the mean value to 0. Further adjustment may be necessary on a trial-and-error basis to achieve the goal. The K2 value should now be adjusted to minimise the initial SD value. This is an interactive process and it will be found that if an increase in K2 reduces the SD, further increases will eventually result in the SD beginning to increase again at some point. Hence, adjustment of the K2 value will follow the characteristic shown in the diagram below and should be adjusted to achieve the minimum SD value.



Standard Deviation (SD) ‘k’ Value OptimisationStandard Deviation (SD) ‘k’ Value Optimisation

‘k’ Value

Mea

n D

evia

tion

Val

ue

Optimum value


2.9.2.4 Diffraction Correction

This process is initiated by selecting a diffraction model and analyzing the data to assess the effect on the SD. The model that produces the lowest SD should be retained. The K7 parameter should now be adjusted using the same interactive process described in 3.3.2.1 above to minimise the SD.

2.9.2.5 Effective Antenna Height Correction

This process involves using the same iterative process described above but using parameters K3-K6. Note that id the antenna height of the MS is deemed to be fixed, K3 and K4 can be ignored.

2.9.2.6 Final Slope Correction

The final stage is to return to the K1 parameter and make any further adjustments to minimise the mean error value.

2.9.3 PRACTICAL MODEL TUNING DEMONSTRATION

This is a practical demonstration of tuning a propagation model using the AIRCOM ASSET tool. The procedures used are described in Appendix A to these course notes



2.10 Power Budgets ________________________________________________________________________________

One essential part of the system planning procedure is to establish the signal strength that a mobile will receive in a particular area and, further, to ensure that wherever coverage is provided on the “downlink” (from the base station to the mobile) then system balance is maintained by engineering the sites so that there is sufficient signal power received on the uplink.

• Calculations to allow for losses and gains in signal strength to ensure level is

acceptable throughout service area

• Minimum level must be greater than sensitivity of mobile, with a margin for fading

and penetration loss

• Decibel calculations allow simple tracking of losses and gains

• Power input to mobile = Tx output - Losses + Gains

Power BudgetsPower Budgets

TRX

Radio Path

Feeder


When assessing downlink coverage, it is important that due attention is paid to the threshold level (or “sensitivity”) of the mobile. This is the minimum signal level for which a service of acceptable quality will be provided. In practice, the signal strength will suffer fades due to multipath propagation. A margin should be allowed for this fading. Further, the propagation model will predict the signal strength in the street rather than inside buildings. If coverage is to be provided within buildings, an additional “penetration loss” must be accounted for. These margins will be added to the path loss and other losses to give a total loss. The antennas will provide some gain to offset against this. A net loss can then be calculated as the difference between the total losses and the total gains. This loss is subtracted from the transmit power to give an estimate of the power level received at any point.



________________________________________________________________________________

2.10.1 REVIEW OF DECIBEL SCALE

Review of Decibel ScaleReview of Decibel Scale

• Logarithmic scale for comparing power levels

• Gain = Pout / Pin as a ratio

• In decibels: Gain = 10 log (Pout / Pin )

• Using logarithms allows a sequence of gains and losses to be found by adding and subtracting decibel values rather than multiplying and dividing

• Decibel scale can be used to measure an actual power level by using a reference level

• Power in dBm is compared to a power of 1 milliwatt (1 mW = 1/1000 W)• Example, convert 2 watts to dBm :

P = 10 log ( 2 W / 1 mW) = 10 log (2000 / 1 ) = 10 x 3.3 = 33 dBm

• Note: 1 mW = 0 dBm (since log(1) = 0)


The use of the decibel scale allows the result of combining losses and gains within a system to be determined by means of addition and subtraction rather than multiplication and division. A gain or a loss is expressed in decibels (dB) in accordance with the equation given in the above slide. It is possible to express an absolute power, rather than a gain, using the decibel scale by adopting 1 milliwatt as a reference power. The absolute power is then quoted in dBm, the “m” referring to a milliwatt. Certain commonly-encountered gains and losses are tabulated below.

Gain as a ratio Gain in dB (= 10 log10[gain as ratio])

2 3 dB 4 6 dB 10 10 dB 50 17 dB 100 20 dB 1000 30 dB 0.5 (a loss of a factor of 2) -3 dB 0.1 (a loss of a factor of 10) -10 dB



Power in milliwatts Power in dBm

(= 10 log10[power in mW]) 2 3 dBm 10 mW 10 dBm 100 mW 20 dBm 1000 mW 30 dBm 20 W = 20000 mW 43 dBm 1 µW -30 dBm 1 nW -60 dBm 1 pW -90 dBm

________________________________________________________________________________

2.10.2 ANTENNA GAIN

Antenna GainAntenna Gain

• Antenna gain is quoted relative to an isotropic radiator

• Units : dBi

• Gain is achieved because the output power is concentrated into a smaller region

Isotropic pattern

Omni-directional dipole pattern

Typical antenna gains

Omni: 8 to 12 dBi

Sector: 10 to 18 dBi


Antenna gains are also quoted using a decibel scale. The gain of an antenna refers to its ability to concentrate the radiated energy into a narrow beam rather than spread it equally in all directions. A theoretical antenna (known as an “isotropic radiator”), that radiates power equally in all directions, is usually chosen as a reference against the field strength produced by a practical antenna. In order to make it clear that an isotropic antenna has been adopted as a reference, the gain is quoted using the unit dBi (‘i’ being for isotropic).

________________________________________________________________________________



2.10.3 THE DOWNLINK POWER BUDGET

Downlink Power BudgetDownlink Power Budget

BTS Tx Output Power

CombinerLoss

Duplex FilterLoss

Feeder Loss

Antenna Gain

Path LossMS Antenna Gain

Feeder Loss

Input to mobile

PoBS

Lc

Ld

Lfb

Gab

Lp

Gam

Lfm

PinMS

PinMS = PoBS - Lc - Ld - Lfb + Gab - Lp + Gam - Lfm


The above diagram highlights the contributing factors to gains and losses as the signal progresses from the Base Transceiver Station (BTS) to the mobile. A base station will probably transmit more than one carrier. These will share a common antenna. The combiner involved will introduce some loss. Additionally, in order to be able to use the same antenna for transmitting and receiving, it is necessary to use a device known as a duplexer. The duplexer will provide isolation between the transmitter and the receiver to prevent interference between the transmit and receive signals. In providing this isolation, it will inevitably insert a small loss into the wanted signal path. In calculating the received signal power it is simply necessary to insert the appropriate numbers into the equation. This is demonstrated in the following slides.



Downlink Power Budget AnalysisDownlink Power Budget Analysis

• Power input to the mobile (dBm):


PoBS = Power output from BTS TRX dBm

Lc = BTS combiner loss dBLd = BTS duplex filter loss dB

Lfb = BTS Feeder loss dB

Gab = BTS antenna gain dBiLp = Path loss dB

Gam = Mobile antenna gain dBi

Lfm = Mobile station feeder loss dB


Downlink Power Budget Downlink Power Budget -- ExampleExample

• A class 4 mobile has a sensitivity of -102 dBm. Allowing a margin for fading, we take the minimum signal strength at the cell boundary as - 90 dBm. This is to be 10 km from the base station.

• Find the BTS output power, PoBS , required given the following data:BTS combiner loss Lc = 6 dB

BTS duplex filter loss Ld = 1 dB

BTS feeder loss L fb = 7 dB

Omni antenna gain Gab = 12 dB

Hata path loss for 10 km Lp = 132 dB

Mobile antenna gain Gam = 0 dBiMobile station feeder loss L fm = 0 dBi




Downlink Power Budget Downlink Power Budget -- SolutionSolution

Downlink power budget equation:


-90 = PoBS - 6 - 1 -7 + 12 -132 + 0 - 0

-90 = PoBS - 134

PoBS = 44 dBm


________________________________________________________________________________

2.10.4 THE UPLINK POWER BUDGET

Uplink Power BudgetUplink Power Budget

BTS Rx

Duplex FilterLoss

Feeder Loss

Antenna Gain

Path Loss

MS Antenna Gain

Feeder Loss

Output from mobile

PinBS

Ld

Lfb

Gab

Lp

Gam

Lfm

PoMS

Diversity Gain

GdBS

PinBS = PoMS - Lfm + Gam - Lp + GdBS + Gab - Lfb - Ld

Input to BTS Rx




The uplink power budget has two distinct differences when compared with the budget for the downlink. There is no combiner in the base station on the downlink path, hence no combiner loss Two receive antennas are often used at the base station (this is not feasible on the downlink as it is not possible to provide more than one antenna at the mobile). This provides, what is known as a “diversity gain” due to the fact that, if the signal received from one antenna suffers a severe fade, the signal at the second antenna is unlikely to suffer from a fade. Thus the uplink has the advantage of no combiner loss and diversity gain. Additionally, the receiver in the base station is more sensitive than the receiver in the mobile. These three factors help compensate for the lower transmit power available on the uplink.

Uplink Power Budget Uplink Power Budget -- ExampleExample

• Using the data given earlier for downlink, find the input power to the base station if:

• Output power of mobile PoMS= 33 dBm (2 W class 4 mobile)• Diversity reception gain at base station GdBS= 5 dB

• Solution:PinBS = 33 - 0 + 0 - 132 + 5 + 12 - 7 - 1 = -90 dBm




________________________________________________________________________________

2.10.5 OTHER POWER BUDGET FACTORS

Other Power Budget FactorsOther Power Budget Factors

• Building/Vehicle Penetration Loss

• Body Loss

• Antenna Orientation Loss

• Polarisation Loss

• Additional Fast Fade Loss

• Interference Degradation Loss


2.10.5.1 BUILDING PENETRATION LOSS

Building Penetration LossBuilding Penetration Loss

• Defined as the difference between measurements taken on a specific building floor and measurements taken externally at street level.

• Losses dependant upon:• Type of outside wall construction (brick, glass, thickness etc)• Floor elevation• Propagation environment near the building• Orientation of building with respect to BTS antenna




Building Penetration LossBuilding Penetration Loss

• ETSI GSM 03.03 recommends :• mean values of

• Urban: 15-18dB• Rural 10dB

• Standard deviation values of:• 9-11dB

• Varies with frequency used

17-9th

--8th

19-7th

-156th

20245th

-274th

20373rd

-392nd

22421st

-31Ground

2240Basement

Building 2Building 1

BPL (dB)Floor


2.10.5.2 VEHICLE PENETRATION LOSS

Vehicle Penetration LossVehicle Penetration Loss

• Defined as the difference between measurements taken inside and outside of a stationary vehicle

• Losses dependant upon:• Materials used for the vehicle construction• Thickness of vehicle skin

• Typical values 10-15dB




2.10.5.3 BODY ABSORPTION LOSS

Body Absorption LossBody Absorption Loss

• Two Types:• Body loss: • Body proximity loss

• Losses dependant upon:• Proximity of body• Direction of LoS• Antenna type• Frequency in use

• Typical values 2-6dB


________________________________________________________________________________

2.10.6 COVERAGE LOCATION PROBABILITIES

Coverage Location ProbabilitiesCoverage Location Probabilities

• Defined as the probability of an acceptable signal being received by an MS at any point in the cell coverage area

• This probability is determined from the characteristics of slow-fade margin applied in the power budget

• Two probabilities used:

• Point Location Probability (cell boundary)

• Area Location Probability (within cell coverage area)




Point Point vsvs Area Location ProbabilitiesArea Location Probabilities

Point location probability

Area location probability


Coverage Location ProbabilitiesCoverage Location Probabilities

Slow Fade Margin vs Location Probability

-15

-10

-5

0

5

10

15

0 10 20 30 40 50 60 70 80 90 100

Location Probability (%)

Slo

w F

ade

Mar

gin

(dB

)




Point Location ProbabilityPoint Location Probability

• Defined as the reception probability at a location on a cell boundary• Higher slow fade margin improves probability• Higher slow fade margin reduces cell coverage for the same EIRP.• Calculated from the mean (µ) and standard deviation (s) values of

the received signal strength:

ex

xP σ

µ

σπ22)( 2

22

1 −

=

where: Px = location probability

x = signal level

s = standard deviation of x

µ = mean value of x


Point Location ProbabilityPoint Location Probability

location probability of 50% (0dB fade margin)



Increasing the fade margin allowance will decrease the available power budget and therefore decrease the cell radius (r)

r




Area Location ProbabilityArea Location Probability

• Defined as the probability of receiving a call at any location within the cell coverage

• Accounts for degradation of signal strength as distance from BTS increases• Measured as the ‘useful area’ within cell coverage for a specific probability of

reception• Calculated from the mean (µ) and standard deviation (s) values of the

received signal strength:

=

+−+

++

baberfe b

abaerfAuseful

11212

)(121

where: Auseful = useful service area within a circle of radius R

erf = error function

a = point probability value

b = propagation slope characteristic


Point / Area Slow Fade MarginsPoint / Area Slow Fade Margins

14.7412.6210.5418.6116.2813.9699

12.3810.538.7216.4314.3812.3298

10.879.197.5515.0513.1711.2897

9.738.186.6714.0112.2510.596

8.87.365.9513.1611.519.8795

5.564.483.4310.258.977.6990

1.550.90.286.735.895.0580

-1.41-1.76-2.084.23.673.1570

-4.01-4.11-4.182.031.771.5260

-6.51-6.39-6.2500050

-9.09-8.77-8.43-2.03-1.77-1.5240

-11.99-11.46-10.92-4.2-3.67-3.1530

-15.59-14.85-14.14-6.73-5.89-5.0520

-21.12-20.19-19.34-10.25-8.97-7.6910

876876

Area Location ProbabilityPoint Location Probability

Standard Deviation (s ) dBLocation

Probability(%)


________________________________________________________________________________



2.10.7 LINK BUDGET TYPES AND THRESHOLDS

Link Budget Types / ThresholdsLink Budget Types / Thresholds

• Link Budget Types:• Outdoor• Indoor• In-building• In-car

• Thresholds:• Outdoor (-92 dBm)• Good In-building (-70 dBm)• Average in-building (-78 dBm)• Good in-car (-85 dBm)• Marginal in-car (-88dBm)


________________________________________________________________________________

2.10.8 SYSTEM BALANCE

System BalanceSystem Balance

• Power budget calculations show the maximum distance of the mobile from the base station at which uplink and downlink can be maintained

• In a balanced system, the boundary for uplink and downlink must be the same

• An unbalanced system would drop many calls in the fringe region

Uplink limitDownlink limit

Unbalanced system


Balanced system




There is little point in being able to communicate in one direction only on a mobile telephone system. The coverage area, and hence the maximum path loss tolerated, should be the same for the uplink and the downlink. If this is the case the system is said to be “balanced”. By considering the asymmetries between the uplink and the downlink it is possible to derive an equation that will allow the required base station transmit power to be calculated in terms of the mobile transmit power, the combiner loss, the diversity gain and the threshold levels of the base station and mobile receivers.

Conditions for System BalanceConditions for System Balance

• The conditions for system balance depend on the asymmetries between the uplink and downlink power budgets

• The asymmetries are:• Maximum output power from MS and

BTS are not the same• MS has less sensitive receiver than BTS

• Diversity reception can be used at the BTS but not at the MS

• Combiner loss occurs at the BTS on the downlink only


When making modifications to a network design, it is important to consider the impact on the system balance of any changes. For example, if it is required to increase coverage, simply increasing the BTS transmit power will not help as it will upset the system balance. However, utilising a higher gain antenna will provide increased coverage whilst maintaining balance. Similarly, adjusting the tilt of the antenna will affect coverage without upsetting the system balance.



System Balance EquationSystem Balance Equation

• Power budget equations:Downlink: P inMS = PoBS - Lc - Ld - Lfb + Gab - Lp + Gam - Lfm

Uplink: P inBS = PoMS - Lfm + Gam - Lp + GdBS + Gab - Lfb - Ld

• When the mobile is at the extreme boundary of the cell:PinMS= P refMS

P inBS = PrefBS

These are the reference sensitivities of the MS and BTS The output levels PoBS and PoMS are the maximum allowed values

• If the boundaries for uplink and downlink are the same, the path loss Lp will be the same in each direction

• Subtracting the uplink equation from the downlink gives the system balance equation:

PoBS = PoMS + Lc + GdBS + ( PrefMS - PrefBS )


Field Implications of System BalanceField Implications of System Balance

• When changing cell size to alter coverage, consider whether the change will affect the system balance, for example:

• Increasing BTS Tx power (PoBS ) to increase coverage would upset the balance

• Ways of altering coverage without affecting balance include:

• Decreasing BTS Tx power - the BSS can force the MS to use dynamic output power control (adjusting PoMS to maintain balance)

• Altering the gain of the base station antenna - Gab is a symmetrical term in the power budgets

• Antenna down tilting changes coverage area without affecting balance




System Balance ExampleSystem Balance Example

• A downlink power budget calculation leads to a requirement that:

PoBS + Gab = 56 dBm

• Find PoBS using the system balance equation, with the following data:

GdBS = 3dB , Lc = 6 dB , PrefBS = -105 dBm , PrefMS = -102 dBmPoMS = 33 dBm ( GSM Class 4 mobile)

• Solution:

PoBS = 33 + 6 + 3 + ( -102 - (-105 )) = 45 dBm• This is the maximum value for PoBS as balance can be maintained with reduced power

• The downlink power budget now gives the antenna gain as 11 dBi

• If the antenna gain is greater than 11 dBi, it can be down tilted to adjust coverage.


As an example consider the case where a downlink power budget is conducted using the following figures

Minimum mobile receive power -90 dBm Maximum Path loss 131 dB Feeder Loss 8 dB Combiner Loss 6 dB Duplexer Loss 1 dB Mobile antenna gain 0 dB Mobile feeder loss 0 dB

Using the equation

dBm 560013181690

GLLLLLPGP

LGLGLLLPP

amfmpfbdcinMSaboBS

fmampabfbdcoBSinMS

=−+++++−=

−+++++=+

−+−+−−−=

Notice that, as no information is given regarding the base station antenna gain, it is possible only to state the sum of the transmit power and the gain. We are now required to determine conditions for system balance using the following additional information.



Diversity Gain 3 dB Receive threshold for mobile -90 dBm Receive threshold for base station -93 dBm Mobile transmit power 33 dBm

Now we can determine a required figure for the base station transmit power.

dBm 4593903633

)P(PGLPP refBSrefMSdBScoMSoBS

=+−++=

−+++=

This value is the maximum possible value for base station transmit power at which system balance can be maintained. It is possible to maintain balance at lower power levels by relying on the power control features within the mobile station. However, if this value was adopted, it is simple to calculate the required antenna gain to be 11 dBi. If a transmit power of 45 dBm is adopted and an antenna of higher gain is used, coverage can be restricted to the nominal value of 131 dB path loss by means of controlling the tilt of the antenna.

SummarySummary• Review of decibel scale: dB (gain or loss), dBm (absolute measure of

power input or output), dBi (antenna gain)

• Uplink and downlink power budget calculations: equations tracking gains and losses in up or downlink directions, final results for power inputs in dBm

• Other power budget factors including:

• Slow fade margin, building penetration, body losses etc

• Concept of system balance: cell boundary for uplink and downlink power budgets should be the same

• Calculations for system balance: equations relating asymmetric terms in power budgets

• Practical implications: ways of altering coverage without upsetting system balance




2.10.9 SELF-ASSESSMENT EXERCISES

A particular radio link has a path loss of 146 dB. In one direction the sensitivity of the receiver is –102 dBm. The receiving antenna has a gain of 2 dBi and the transmitting antenna has a gain of 17 dBi. Miscellaneous feeder, combiner and filter losses amount to 7 dB. Determine the required transmitter power.

Answer:

2. In a GSM system, the mobile terminal receiver has a sensitivity of –102 dBm and the Base Station receiver has a sensitivity of –105 dBm. The uplink generates an additional space diversity gain of 2 dB. The downlink suffers from a combiner loss of 4 dB. If the maximum mobile terminal transmit power is 33 dBm, what must the downlink transmit power be to maintain balance?

Answer



3 Frequency Planning ____________________________________________________________________

3.1 Introduction

In this section the following aspects of frequency planning will be covered:

• Cellular structures and frequency reuse patterns • Interference calculations • Cell splitting • Practical frequency planning • Multiple reuse patterns

____________________________________________________________________

3.2 Cellular Structures and Frequency Reuse Patterns

Cellular StructureCellular Structure

• Cellular radio systems divided into small cells

• Each cell surrounds a fixed radio site (BTS)

• Hexagon shape used for convenience - tessellates to cover large area

• Real pattern rather different - use planning tools

Hexagons for planning Ideal Coverage Reality

Section 3 – Frequency Planning



Frequency ReFrequency Re--use use

• Cellular structure allows carrier frequencies to be re-used

• High frequency re-use:

• Short distance between same carriers

• High traffic capacity

• Low C/I ratio (i.e. worse interference)

• Frequency planning involves a compromise between requirements for capacity and interference

• Digital systems like GSM can cope with lower values of C/I than analog systems (20dB analogue compared to 12dB digital)


Simple frequency plans assume a homogeneous distribution of carriers and equal sized cells. We can use this to give an estimate of the interference that is likely.

7 Cell Cluster7 Cell Cluster

• Simple pattern - interlock 7 cell cluster to cover area

• Same number of carriers in each cell

• Re-use same carriers in corresponding cells, A, B etc.

AB

CD

E

FG

AB

CD

AF

G

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

B

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

D

A

C

D

E

F

G

B

C FA

B G


E



Frequency ReFrequency Re--use Distanceuse Distance• Around each cell, there are 6 cells in adjacent clusters using the same

carriers

• These cells will cause mutual co-channel interference

AB

CD

E

FG

AB

CD

AF

G

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

B

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

D

A

C

D

E

F

G

B

C FA

B G

• The C/I due to these cells can be found from the re-use distance, D

• D can be calculated from the geometry of the clusters as:

R 73D =R = radius of cell to a corner

R


Finding the re-use distance is the first step towards estimating the interference in the plan.

General ReGeneral Re--use Patterns use Patterns • For a frequency re-use pattern based on clusters of N sites, each of cell radius R,

the re-use distance, D is:

N 3RD =

• Typical cluster sizes are:3, 4, 7, 12, 21

• Larger cluster sizes give better C/I ratios

• However, smaller cluster sizes give higher traffic capacity per cell - more carriers available in each cell




____________________________________________________________________

3.3 Interference Calculations

Estimating C/I for ReEstimating C/I for Re--use Patternsuse Patterns

• To estimate C/I we assume:• Each base station radiating the same power• Homogeneous propagation throughout the service area

• Propagation follows a 1/Rx law (x is the propagation co-efficient)

• Re-use distance, D, is large compared with cell radius, R

Serving cell 6 nearest interfering cells

D

• On the edge of the serving cell:

xR1

C =

= xD

16I

=

x

RD

61

log 10 I/C

( )

=

63N

log 10 I/Cx

3N R D =


If xRC 1= and xD

I 6=

Then x

xx

x

x

RDD

RD

RIC

=

==

61

61

6

1

However, NRD 3=

Therefore, ( )

633

61

xxN

RNR

IC

=

=

Note the assumption that D >> R. This is more appropriate for large clusters. The value of x will depend on the local radio propagation properties, but 3.5 is generally a good estimate. The higher the value of x the better the C/I.



C/I for Typical Cluster SizesC/I for Typical Cluster Sizes

• Analog systems require a minimum C/I of about 20 dB

• Digital systems can cope with C/I as low as 9 dB

( )

=

63N

log 10 I/Cx

• Estimates of C/I in dB, using the equation:


28.2123.7119.2110.2121

23.3419.4515.567.7812

20.8517.2713.686.539

18.6615.3612.055.447

13.811.18.413.014

11.38.926.531.763Clu

ster Size N

43.532

Propagation Coefficient x

____________________________________________________________________

3.4 Cell Splitting Techniques

Cell Splitting Cell Splitting • Initial network based on omni-directional antenna sites

• To increase capacity, split each cell into 3 using sectored antennas

Original omni site

New tri-sectored

site


Our estimates of interference have assumed a simple pattern of omni sites. Realistic plans will have sites spilt into sectors. Different methods of achieving a split are shown here.



Further Splitting

Further Splitting• As the network grows, capacity can be further increased by another

3 way split as shown

Rotate original antennas through 30o

Add new sites as shown

New siteOld site rotated

New cell


1:4 Cell Split1:4 Cell Split

• Alternative way of further splitting the cells• No re-alignment of antennas needed

• Increases traffic capacity, frequency re-use and number of sites by a factor of 4


By reducing mutual interference effects, sectoring cells reduces the overall interference in the network.



Effect of Cell Splitting on InterferenceEffect of Cell Splitting on Interference

• Directional pattern of sectored antennas reduces response to interference

• Increases C/I significantly• Allows greater frequency re-use, i.e. smaller

cells

• If cells A and B use the same carrier:• B will cause co-channel interference in A• A will cause very little co-channel

interference in B

• Interference is no longer mutual

A

B


Transition ZonesTransition Zones

• Problems may occur at the boundaries between high and low traffic areas

• Large cells in rural areas will use higher power - can cause interference with smaller urban cells nearby

• Requires careful frequency planning -possibly reserve carriers for use in such transition zones

• Alternatively, hierarchy of cells (e.g. overlay / underlay) may be used

Large rural cells

Small urban cells


Transition Zone



3.5 GSM Frequency Patterns

Simple frequency plans for sectored networks are the 3/9 and 4/12 patterns. Again these assume a regular distribution of carriers and equal sized cells.

GSM Frequency PatternsGSM Frequency Patterns

• Two common re-use patterns in GSM are 3/9 and 4/12

• 3/9 consists of 3 sites, each of which has been tri-sectored giving a cluster of 9 cells

Frequencies are assigned in sequence to the cells A1 - C3

3/9 Frequency Group in ASSET


A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3

272625242322212019

181716151413121110

987654321

C3B3A3C2B2A2C1B1A1

Interference in the 3/9 PatternInterference in the 3/9 Pattern

• 3/9 pattern allows frequencies to be allocated so no physically adjacent cells use the same frequency

• C/I is about 9 dB, which is the minimum specified for GSM with frequency hopping

• Cells A1 and C3 are physically adjacent and are allocated adjacent carriers

• On the boundary of A1 and C3:C/A = 0 dB

• GSM specifies a minimum C/A of -9 dB


A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3



4/12 Re4/12 Re--use Patternuse Pattern

• 4 sites, each tri-sectored to give a 12 cell cluster

• Numbering of D cells allows carriers to be allocated so that no adjacent carriers are used in physically adjacent cells

Frequencies are assigned in sequence to the cells A1 - D3

4/12 Frequency Group in ASSET


A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

363534333231302928272625

242322212019181716151413

121110987654321

D3C3B3A3D2C2B2A2D1C1B1A1

Interference in the 4/12 PatternInterference in the 4/12 Pattern

• 4/12 pattern has no physically adjacent cells with co-channel or adjacent channel carriers

• C/I is about 12 dB

• This is adequate in GSM without frequency hopping

• C/A is higher than in 3/9 pattern

• Traffic capacity is lower than 3/9 as there are fewer carriers per cell


A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3



3.6 Self-Assessment Exercises

3.6.1 FREQUENCY RE-USE CLUSTER SIZES

The number of hexagon cells in a cluster, which can be repeated to form a frequency re-use pattern can be found from the formula:

22 jiji ++ where i and j and integers. The table gives the numbers produced by this formula for small values of i and j.

0 1 2 3 4 5 0 0 1 4 9 16 25 1 1 3 7 13 21 31 2 4 7 12 19 28 39 3 9 13 19 27 37 49 4 16 21 28 37 48 61 5 25 31 39 49 61 75

Which cluster sizes are typically used in GSM group frequency planning? For: An analogue mobile system A digital mobile system Choose a suitable cluster size (giving a reasonable compromise between frequency re-use and interference) and calculate the corresponding re-use distance. Take the radius of a cell to be 10 km and the propagation coefficient as 3.5.

3.6.2 FREQUENCY PLANNING ADJUSTMENTS

In part of a network using a 4/12 frequency re-use pattern as shown below, one B1 cell is particularly heavily loaded with traffic. The cells adjacent to it, B2 and B3 are lightly loaded, each with a spare carrier.

i / j



A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3 A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

Carriers are assigned to the cells as follows:

A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D31 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 17 18 19 20 21 22 23 2425 26 27 28 29 30 31 32 33 34 35 36

Make a case for or against moving a carrier from either the B2 cell or the B3 cell into the B1 cell. Note: assume the re-use pattern continues beyond the cells explicitly shown in the diagram.

Heavily loaded cell

Lightly loaded cells



4 Traffic Analysis ________________________________________________________________________________

4.1 Introduction The traffic analysis process invo lves collating data regarding the location and numbers of potential customers and combining this information with a marketing forecast that will estimate the likely usage of the services offered to such potential customers. The usage is estimated from projections for both market penetration (what percentage of the population will become customers?) and the service usage per individual subscriber. One significant contributor to these inputs is the demographics of a country. ________________________________________________________________________________

4.2 Traffic Measurements – Erlangs and Blocking

• Unit of traffic measurement: erlang (E)

• Traffic in erlangs is the number of call-hours per hour:

A = C T / 3600

A = Traffic in ErlangC = number of calls during the hourT = mean holding time per call in seconds

• One channel in continuous use is carrying a traffic of 1 erlang

• Typical traffic per subscriber during the busy hour is 25 mE which corresponds to a mean call holding time of 90 s

Traffic MeasurementTraffic Measurement

Section 4 – Traffic Analysis

Another traffic unit, used mostly in the USA, is the Call Centum Second (CCS): 1 CCS = 100 call seconds per hour 1 Erlang = 3600 call seconds per hour 1 Erlang = 36 CCS



BlockingBlocking

Offered Traffic : Total traffic offered to channel by all users

Carried Traffic : Traffic successfully carried by the channel

Blocked Traffic: Traffic which is blocked at call setup

Call Setup

ProcessOffered Traffic

Blocked Traffic

Carried Traffic

Offered Traffic = Carried Traffic + Blocked Traffic


Grade of Service (Grade of Service (GoSGoS))

• Typical Grade of Service is 0.02 (2%)

• Grade of Service is also called blocking probability or loss probability

• Grade of Service is the fraction of incoming calls (offered traffic) allowed to beblocked due to congestion in the channel

Offered Traffic

Blocked Traffic

Carried Traffic

A

A x GoS

A x (1 - GoS)Call Setup

Process


A good grade of service is a low value. This implies low channel utilization. If a poorer grade of service is accepted, more traffic can be offered to the same number of traffic channels.



Erlang Models of TrafficErlang Models of Traffic• Two commonly used models are Erlang B and Erlang C

• Erlang B - blocked calls are lost or cleared

• Erlang C - calls that cannot be handled are put in a queue until a channelbecomes available

A A(1-GoS)

A (GoS)

QueueErlang B

Erlang C

• GSM uses the Erlang B model not Erlang C


For GSM we are concerned with circuit switched voice traffic which must be handled in real time. Thus the Erlang B model with no queuing is appropriate.

Erlang B CalculationsErlang B Calculations

• Tables based on the Erlang B model allow calculations to be maderelating:

• Offered traffic• Grade of Service• Number of channels

• Structure of Erlang B table:

• Example: at 2% blocking (0.02 GoS), 2 traffic channels can carry 0.22347 erlangs of traffic

0.01 0.02 0.03

12

3

.01010 .02041 .03093

.15259 .22347 .28155

.45549 .60221 .71513

Grade of Service

n

Offered trafficNumber of channels


________________________________________________________________________________



4.3 The Traffic Analysis Process

What is Traffic Analysis?What is Traffic Analysis?

• By traffic analysis we mean:• Examining the demographic spread within a country• Identifying subscriber distribution from market projections

• Calculating the traffic offered to the network per subscriber

• Creating a traffic ‘map’ describing the spread of traffic in the network

• Marketing or engineering?• Data about demographic trends and subscribers’ potential use of the network comes from

marketing surveys

• Engineers need traffic maps to:Carry out network dimensioning

Carry out a first pass network capacity analysis of the nominal plan

Simulate the performance of the final network plan


Traffic Analysis ProcessTraffic Analysis Process

Calculate distribution of subscribers

Demographic Data

Business Data

Marketing

Offered Traffic Map per Service

Service Definitions

Market P

enetrat

ion

Service Usage Per Subscriber

Offered Services


________________________________________________________________________________



4.4 Using Demographic Data

DemographicsDemographics

• Demography is the study of population in a country

• This can be our first step into our analysis of traffic in the network

• The demographic data describing a country can typically be purchased from:• National Statistics Office• GIS data suppliers

• Marketing organisations

• It is usually based upon census data• Most EU countries have a census every 10 years, most scheduled for

2000/2001

• This is updated yearly based on births/deaths /immigration


Resolution of Demographic DataResolution of Demographic Data

• It is possible purchase demographic data describing a number of sizes of areas:

• Postcode/Zip

• Municipality/Commune (NUTS 5 - about 98 000 throughout EU)• Electoral Areas

• Regions/Provinces

• Telephone Code Areas

• Nomenclature of Territorial Units (NUTS) is an EU wide classification for categorisingthe size of administrative areas, up to national level (NUTS 1)

• Typically we would use commune level data initially, some operators take this analysis to a household level




Using Demographic DataUsing Demographic Data

• Typically people analysedemographic data using a GIS

• Creating a traffic map requires the number of subscribers per commune

• Not just people who live there - include commuters etc.

• May need separate daytime and evening analysis to account for the movement of subscribers to suburban areas in the evening

• Business data can be acquired over administrative regions


It is important to gather details not just of people’s residences but also their working locations. The location of peak demand will move over a 24-hour, weekly and annual cycle. Further, the fact that people may live a considerable distance from their places of work may lead to considerable demand from areas in between the residential and industrial/business centres during the peak travel times.

________________________________________________________________________________

4.5 Market Projections and Traffic Maps

Market Projections Market Projections

• Market Penetration

• Number of subscribers per head of population/business employee• % penetration for different target groups

• Service Offerings

• What types of services will be offered• What data rates and quality of service (QoS) these will require

• Service usage per subscriber

• For circuit switched services in Erlangs or calls per busy hour• For packet switched services in Mb/h or sessions per busy hour




It should be noted that the demand of a subscriber to digital services is best measured by the amount of data transferred rather than by the length of time that the subscriber was connected to the network. Some packet based services will be offered on an “always on” basis.

Subscriber DistributionsSubscriber Distributions

• We can calculate the number of subscribers in an area from the market penetration and the demographic/ business data we are using

• However, this will just give us a table of geographical areas with the number of subscribers

• We must take different land usage categories (clutter) within each geographical area into account to create a subscriber map suitable for network capacity analysis or simulation

Very HighHighMediumLow

Subscriber Density

Commune Border

Spread by boundary

Spread by Boundary and Clutter

Town Clutter

Clutter Types


Once the number of likely subscribers within a particular geographical region has been identified, it is important to realise that the demand will not be distributed evenly throughout the commune area. Within a commune border, there is likely to be open areas from which little demand can be expected. The different types of land usage must be considered within the area.



Traffic Maps

Traffic Maps

• If we then apply the service usage per subscriber then we can create a traffic map for each service

• This can then be imported into the planning tool or used for network dimensioning


The likely traffic from each different land usage (or “clutter”) category can be combined with a data base that divides the entire network coverage area into different categories. It is then possible to use a computer to spread the traffic over the network and produce a traffic map. This traffic map will be a key factor in deciding on the roll-out strategy. In the more advanced systems, certain new services will initially be available only in a restricted area. A further use of the traffic map is that it allows decisions to be made regarding where new services should be targeted in order to maximise revenue for a minimum investment.



________________________________________________________________________________

4.6 Roll-Out Strategy

Target Rollout AreasTarget Rollout Areas

• Typically a licence is issued subject to a population coverage requirement

• We can use the demographic data to calculate which towns or regions we must cover to meet these conditions

• Deciding the target regions is a major strategic decision to be taken at board level


Target CoverageTarget Coverage

• The environment that a user is in forces a change in the required coverage levels due to building penetration and model accuracy

• We also need the service availability required

• We can determine what these coverage levels are by using the link budget

• But we need to know where to target coverage to these levels




Specifying Coverage Areas Specifying Coverage Areas --Coverage PolygonsCoverage Polygons

• Coverage polygons can be used to describe the areas to be covered to a certain level

• To give guidance to planners• To provide the basis for acceptance

testing for turnkey/outsourced planning

• Just because the clutter type suggests a certain type of land usage does not mean that it exists there

• Coverage polygons should not be generated purely from clutter data

Dense UrbanUrbanSuburban


Specifying Coverage Areas Specifying Coverage Areas -- RoadsRoads

• Road and Rail does not lend itself to coverage polygons

• Dense urban, urban and suburban coverage levels will typically form concentric rings around a town, and do not overlap between towns

• Roads linking towns should not be used as Polygons as it may result in very long and spindly shapes which overlap each other

• A better way to specify road coverage is to produce a list or schedule of roads to be covered.


The spreading of traffic is normally undertaken on a “subscribers per unit area” basis. That approach makes the use of polygons that are assumed to enclose a certain amount of subscribers appropriate. However, when roads and railway lines are expected to contain significant numbers of subscribers, describing the density in terms of subscribers per kilometre rather than per square kilometre is more appropriate. The activity is known as spreading traffic “along a vector” rather than over an area.



________________________________________________________________________________

4.7 Capturing Traffic and Assessing Resource Requirements

Capturing TrafficCapturing Traffic

• Each cell will be the “best server” for a particular area.

• “Best server” means that it will deliver the largest signal at a particular point.

• By overlaying the “Best Server” information on top of the traffic map it is possible to estimate how much traffic a cell will “capture”.

• This can identify overloaded cells and provide information regarding resource requirements.


Providing the ServiceProviding the Service

• Once the likely amount of traffic per cell has been established, it is possible to decide on the number of channels (timeslots in GSM, a nominal provision in UMTS) that should be made available.

• The traffic forecast is in Erlangs. If a traffic of 3 Erlangs is forecast then, on average, 3 channels will be in use.

• However, simply providing 3 channels will not be sufficient as the users do not co-ordinate their demands but, rather, make them randomly.





• The random manner in which users access and use the service usually follows what is known as a “Poisson” distribution.

• This allows the number of channels required to be predicted for a given “blocking ratio” or “grade of service”.

• A “blocking ratio” of 2% means that 2% of calls made will not be able to access a channel because they will all be in use.

Call setup

processOffered Traffic

Blocked Traffic

Carried Traffic

100 %

2 %

98 %



• Example:Blocking ratio = 2% Offered Traffic = 3 Erlangs Number of channels required = 7

• Trunking Efficiency: measure of usage of the channels

• In the example: Trunking Efficiency = 3 / 7 = 43%• Trunking Efficiency increases with the number of trunks (channels)

• Number of channels found using Erlang B tables or calculator

• Examples for 2% blocking:10 channels required for 5 Erlangs30 channels required for 22 Erlangs

50 channels required for 40 Erlangs




SummarySummary• The Meaning of Traffic Analysis: marketing data, services required by users,

traffic offered, traffic map

• The Traffic Analysis Process: offered traffic map for each service, service definitions

• Demographics and Business Data: sources of statistics, resolution of data, interpretation of data

• Market Projections: market penetration, service offerings, service usage

• Target Coverage: specifying coverage areas, capturing traffic

• Providing the Service: Erlang B model, blocking, grade of service, channels required


4.8 Traffic Capturing Demonstration Analysing the traffic captured by cells.



5 Grid References and Bearings

5.1 Grid References

A grid reference defines the position of a site on the Earth’s surface. There exist two major methods of defining the grid reference:

• Latitude-Longitude • Easting-Northing

5.1.1 LONGITUDE-LATITUDE

Lines of Longitude. The Earth can be pictured as being divided into segments by lines of longitude that run from pole to pole. One of these lines is taken as a reference point. It is the line that runs through Greenwich, London, England. Other lines of longitude are described as being so many degrees east or west of Greenwich. Lines of Latitude. Lines of latitude form parallel hoops with the largest of these lines (or “hoops”) being known as the equator. Other lines are parallel to the equator and are defined by the angle between this line and the equator that would be measured from the centre of the earth. Lines of latitude are therefore referred to as being so many degrees north (or south) of the equator.

Lines of Longitude and LatitudeLines of Longitude and Latitude

Lines of Longitude

Lines of Latitude

Section 5 – Grid References and Bearings



Lines of Longitude viewed from North PoleLines of Longitude viewed from North Pole

30° west of Greenwich

Greenwich Meridian


The gap between lines of latitude can be calculated in a straightforward manner. The circumference of the earth is 40,000 km. If the earth is thought of as a circle of 360 degrees, each degree will represent a physical distance of 111 km. Thus, the lines of latitude 10° north and 30° north will be 2220 km apart. As the lines are parallel this distance is constant.

Lines of LatitudeLines of Latitude

30° North of the Equator

Equator30°




The Distance Between Lines of LatitudeThe Distance Between Lines of Latitude


Equator30°

Circumference of the Earth ~ 40000 km

1 degree latitude represents 40000÷360 = 111 km

30 degrees represents 3330 km


Lines of longitude are not parallel. They converge at the north and south poles. The distance between to given lines varies. It is a maximum at the equator where each degree east or west again represents approximately 111 km. This distance will decrease as the latitude increases north or south of the equator. The distance between two lines of longitude of

difference α at a latitude θ north (or south) of the equator would be given by θα cos111 ×× kilometres. Thus the distance between the lines 20° east of Greenwich

and 50° east of Greenwich would be 3330 km at the equator but only 1665 km at 60° north.

The Distance Between Lines of LongitudeThe Distance Between Lines of Longitude

θ×α× cos111

Distance between lines of longitude here......

will be less than the distance here.

General formula for distance between two

lines of difference a degrees longitude is

Where θ is the latitude value.




Specifying Positions.Specifying Positions.

This position is:

20° E, 30° N.

20° east of Greenwich

Greenwich Meridian


Equator


Specifying a position in longitude and latitude. A location on the earth’s surface can be specified by quoting the longitude and latitude. The convention is to specify the longitude followed by the latitude. 40° east and 25° north would specify a particular point. As the position has to be specified as a pair of numbers, they are often referred to as “coordinates”. In order to define a point with sufficient accuracy, the degree is broken down into minutes (60 minutes make a degree) and seconds (60 seconds make 1 minute). One second represents a distance of approximately 31 metres. As an alternative to quoting the position in terms of degrees, minutes and seconds, it is possible to simply state the number of degrees as a decimal number: “decimal lat-long”. Thus 3°24’16” would be equivalent to 3.4044°.



Degrees, Minutes and Seconds.Degrees, Minutes and Seconds.

60 minutes make 1 degree.

60 seconds make 1 minute.

Degrees, minutes and seconds are often

specified as a decimal number of degrees.

“Lat-Long”

38°12’42”E, 17°27’24”N

“Decimal Lat-Long”

38.2117°E, 17.4567°N


5.1.2 EASTING-NORTHING

For areas that do not represent a large fraction of the earth’s surface, it is possible to represent a grid position by specifying its distance east and north from a particular point. The values are usually quoted in terms of a six or seven figure number. The least significant digit represents a distance of 1 metre. A typical position would then be specified as 342789E 876347N which would be interpreted as 342.789 km east and 876.347 km north of the chosen reference point.

Grid ReferenceGrid Reference

Small (<1000 km x 1000 km) can be

represented on a flat surface with

acceptably low levels of distortion.

Place positions can then be

represented by a number of metres

East and North of a particular

reference point: “Eastings and

Northings”.

Reference Point

Metres east:the “easting”.

Metres north:the “northing”.




5.2 Bearings

A bearing is another word for direction. By convention bearings are expressed as a number of degrees “east of north”. Therefore, a bearing of 000° is due north, 090° is due east, 180° is due south and 270° is due west. Notice that it is also conventional to state the number of degrees using three digits, starting with a zero if necessary. Bearings can be specified more accurately by dividing a degree into minutes and seconds or, alternatively, specifying the number of degrees in decimal form.

5.2.1 MAKING CALCULATIONS USING LATITUDE AND LONGITUDE COORDINATES AND BEARINGS.

It is possible to make a number of calculations using the coordinate position of a point and/or the bearing. You can:

• Calculate the distance between two points by using the coordinates of the two points;

• Calculate the bearing from one point to another by using their coordinates;

• Calculate the coordinates of a point having been given its bearing and distance from

a point whose coordinates are known. Two points of convention that is important to adhere to when making the calculations: degrees south of the equator are regarded as negative; degrees west of Greenwich are regarded as negative.

Calculating distances. This is easiest to do if we are given the coordinates of the two points in easting and northing form. We are being given enough information to calculate the lengths of the sides of a right-angled triangle from which we can calculate the length of the straight line joining them together. To calculate the lengths of the sides of the right angled triangle we have to subtract the “eastings” and “northings” from each other as shown in the example.



Calculating DistanceCalculating Distance

If coordinates are given in grid reference form, the distance between two points can be calculated using Pythagoras Theorem:

167823E 216953N

1248 m east

2763 m north

169071E 219716N

303227631248

27362169532197161248167823169071

22 =+

=−=−

In the example given, the two points are 3032 m apart.


When the coordinates are given in degrees of longitude and latitude the process is similar but the differences in degrees have to be converted to a distance (it is best to convert to decimal degrees if minutes and seconds are given). In terms of the difference in latitude, the process is straightforward with each degree representing approximately 111 km. However, the distance represented by a difference in longitude depends on the latitude. The cosine of the number of degrees north or south of the equator is the relevant parameter. The value of latitude will be different for the two points in question, a fact that causes further complications. In fact, to do this accurately requires an understanding of three dimensional geometry that is beyond the scope of this course. However, for situations where a relatively small portion of the earth’s surface is being considered (distances less than about 1000 km), taking the average value of latitude will produce results of acceptable accuracy.

Calculating DistanceCalculating Distance

If coordinates are given in lat-long form, it is first necessary to convert to decimal form. When calculating the distance east, it is necessary to consider the longitude.

29°18’37”E 65 °27’12”N

96.65 km east

83.47 km north

31°22’14”E 66°12’19”N

7.12765.9647.83

47.83111752.0752.04533.652053.66

4533.65"12'27652053.66"19'126665.9665cos1110603.2

0603.23103.293706.313103.29"37'1829

3706.31"14'2231

22 =×

=×=−=°=°=°××=−=°

=°

In the example given, the two points are 127.7 km apart.




Calculating the bearing from one point to another. In order to calculate the bearing from one point to another, the same triangle as that constructed to calculate distance must be used. The bearing is given by the arctangent of the appropriate angle. If the bearing is clearly greater than 180°, it is usually more convenient to work out the bearing “east of south” rather than “east of north” and add 180° to convert. The bearing from “A to B” will be 180° different when compared with the bearing from “B to A”.

Calculating BearingsCalculating BearingsIf coordinates are given in grid reference form, the bearing of one point from another is determined using trigonometry.

167823E 216953N

1248 m east

2763 m north

169071E 219716N

In the example given, the bearing shown is equal to 24.3°. The bearing in the reverse direction would be 180+24.3 = 204.3°.

1248 m east

2763 m north

θ ( ) °==θ − 3.2427631248tan 1


Calculating the position of a second point. Suppose you are told to calculate the coordinates of a point 10 km away at a bearing of 48° from a point whose coordinates you know. The distance north travelled will be 10cos48° km and the distance east travelled will be 10sin48° km. Converting these figures to an increase in latitude is simply achieved by dividing the distance in kilometres by 111. The increase in longitude is determined by dividing the distance by 111cosθ where θ is the latitude of the point.



Calculating Position of Second PointCalculating Position of Second Point

If coordinates of a reference point are given, together with the bearing and distance to a second point, it is possible to determine the coordinates of the second point

30°00’00”E 65 °00’00”N100 km east

150 k

m

???

In the example given, the coordinates of the second point would be 32.055°E, 61.035°N

40°055.265cos11142.9642.9640sin150

035.11119.114

9.11440cos150

=°÷=°=÷=°

Increase in latitude

Increase in longitude


The Site Location ProcessThe Site Location Process

• The process of actually implementing a site can be simplified to:

• Place the site of a 2-dimensional map.

• Ascertain the longitude and latitude of the position.

• Locate this position in the field using a GPS receiver.




The Site Location ProcessThe Site Location ProcessThe GPS receiver must be programmed with the same ellipsoid and datum as the map data.Errors of 1 kilometre can occur if this isn’t done.

Map Data•Ellipsoid 1

•Datum A

GPS Receiver

•Ellipsoid 2•Datum B


Why does this matter?Why does this matter?

The fact is that, although coordinates in latitude and longitude give the impression of being fixed, the exact coordinates of a particular location will depend on the ellipsoid and datum used.

30°00’00”E 65°00’00”Nusing to datum 1

30°00’00”E 65°00’00”NUsing datum 2




Why does this matter?Why does this matter?

If you are not careful, these errors can lead to sites being located incorrectly.

30°00’00”E 65°00’00”Nusing to datum 1

30°00’00”E 65°00’00”NUsing datum 2


Finding where you are: Ellipsoids, Finding where you are: Ellipsoids, DatumsDatums and Projectionsand Projections

• All the information on coordinates given so far have made two assumptions:

• The earth is smooth

• The earth is spherical

• Unfortunately, the earth is not smooth or perfectly spherical.

• A closer approximation is an ellipsoid.


Sphere

Ellipsoid



DatumsDatums

• Once the best ellipsoid has been identified, it is necessary to define a “datum”.

• Best Ellipsoid shown by the yellow grid

• The datum can be thought of as a place where the actual earth and the ellipsoid touch.

• Actual earth shown by the solid blue object

• The datum serves to locate the ellipsoid in three-dimensional space.


ProjectionsProjections

• There is yet another issue: that of ensuring the paper maps and scanned backdrops are consistent with the Ellipsoid and Datum.

• 2-dimensional maps of a 3-dimensional earth are produced using Projections.

• You use maps and backdrops to ensure for example that the site is located sensibly (on the shore of a lake rather than in the middle of the lake, for example).





• Any attempt at replicating a curved earth on a flat piece of paper will result in distortions such as:

• Conformality (scale differences)

• Distance

• Direction

• Scale• Area

• Some projections minimise distortions in some of these properties at the expense of maximising errors in others

• Some projections are attempts to only moderately distort all of these properties



• The two major forms of projection are Cylindrical and Conical.

• Cylindrical Projections: resulting from projecting a spherical surface onto a cylinder before unwrapping and flattening out the cylinder to give Cartesian coordinates.

• Mercator projection

• Conic Projections: resulting from projecting a spherical surface onto a cone.

• Lambert Conformal Conic projection




The UTM ProjectionThe UTM Projection

• The most popular projection is the Universal Transverse Mercator (or UTM).

• Globe is subdivided into narrow longitude zones, which are projected onto a Transverse Mercator projection

• The word “Transverse” suggests that the cylinder goes from “East to West”



• The projection must be carried out in a section at a time. Only the part of the earth’s surface that is nearly touching the cylinder will have low levels of distortion.

• However, the scale is not constant, distance become exaggerated as you move north and south from the equator.

• The lines of longitude are parallel on the projection whereas in reality they meet at the poles.





The projection is defined into 120 zones, each covering an interval of 6 degrees longitude. There are separate zones for north and south of the equator

1N 2N 3N 4N 5N 6N 7N

1S 2S 3S 4S 5S 6S 7S

The origin for grid references is then at the bottom left hand corner of each zone.

The references are in units of metres.

Origin for zone 4N

Origin for zone 2S


Consistency is VitalConsistency is Vital

The Scanned Map and/or Air Photo backdrop must be consistent (same projection, ellipsoid and datum) with the digital terrain map (DTM).

Otherwise:

• Heights on the DTM will be incorrect.

• Road vectors on the DTM will not coincide with the map or air photo.




Consistency is VitalConsistency is Vital

The GPS must use the same Ellipsoid and Datum as the Digital Terrain Map.

Otherwise:

• “Field” locations will not be the same as the “Map” locations.


5.3 Self-Assessment Questions

1. Calculate the distance between the points A and B given their coordinates.

A. 36.5382°E 47.3421°N B. 37.1486°E 46.7593°N

2. A point C has the latitude-longitude coordinates 23.2186°E 19.4783°N. Point D is 86 km from point C at a bearing of 041°. Determine the coordinates of point D.

3. What problems would occur if the Digital Map data used in planning and the GPS receiver used in the field had different Ellipsoids and/or Datums?

4. What problems would occur if the scanned map backdrop and the digital terrain map used different projections?



6 Base Station Positioning ____________________________________________________________________

6.1 Introduction

In this section the following topics are covered:

• BTS positioning for different environments • Microcell positioning • Picocell arrangements • Multi-layer cell design • Use of Repeaters

____________________________________________________________________

6.2 BTS Positioning for Different Environments

• Initial grid of cells produced by planning process

• Actual base station positions used depend on many factors such as:

• planning permission

• site availability• site surveys

• power wayleaves

• Nominal plan should take into account:• traffic distribution

• transport routes

• topography

Nominal PlanNominal Plan

Section 6 – Base Station Positioning



Base Stations in Rural AreasBase Stations in Rural Areas

• Low traffic capacity required

• Large cell radius

• Aim for complete coverage on 900 MHz (macrocells)

• Concentrate 1800 MHz coverage on areas of higher population and transport routes

• Macrocells may be omni or tri-sectored - standard frequency plans, such as 4/12


BTS Positioning BTS Positioning -- Topographic EffectsTopographic Effects

• Hilly regions may have dead spots and shadow areas

• The effects of different site placement and antenna heights

• Low antenna on top of hill is generally preferable to a high one at the base

Antenna on top of hillAntenna at the base of the hill

25m height

50m height

100m height

10m height 25m height




BTS Positioning BTS Positioning -- Water Surface EffectsWater Surface Effects

• Water surfaces act almost as plane Earth reflectors with very low path loss

• This can result in interference between widely spaced cells across bays or river estuaries

• may require directional or down tilted antennas to reduce interference

• The extra coverage may be useful to serve ferry routes and shipping lanes

• Similar problems may occur over very flat land

Coverage from similar sites -extended coverage across sea


BTS Positioning BTS Positioning -- Traffic RoutesTraffic Routes• Require continuous coverage along main road and rail

routes

• Dead spots in hilly areas can be filled in by directional microcells Directional antennas to

fill in coverage along road

• Cells boundaries and Location Area boundaries should avoid traffic routes

• This would cause unnecessary handovers and location updates as users travel along the route

Road along cell boundaries - frequent handovers

Road crosses edges of cells - not along boundaries




BTS Positioning BTS Positioning -- Urban SitesUrban Sites

• High traffic capacity - smaller cells

• Propagation strongly affected by clutter detail - height and type of buildings

• Cell hierarchy:

• Macrocells (umbrella cells) above roof height to cover wide areas

• Microcells below roof height - localised cover for traffic hot spots

900 MHzmacrocell

1800 MHzmicrocell

overlay

underlay


6.3 The Site Acquisition Process

Define Search AreasDefine Search Areas

• The sites in a nominal plan are only imaginary.

• To become a real network, physical sites are required.

• A suitable physical site must be found for each nominal site.

• A suitable physical site must among other things:• Give adequate radio coverage.

• Have connectivity into the transmission network.• Be aesthetically and politically acceptable to the local community.

• Have power nearby, good access and a co-operative owner.

• A survey of each nominal site is normally carried out to identify possible site options which meet the above criteria.




Define Search AreasDefine Search Areas

• Guidelines given to the surveyor should be based on the appropriate radio coverage required from the site.

• The guideline is given in the form of a search area, such as:• Radius from the nominal site.

• One or more polygons following height contours.

Or


It is desirable for a surveyor to be provided with as wide a range of acceptable alternatives as possible. In the situation described in the diagram, it has been determined that the site could be located either in the service area or, alternatively, overlooking the area from a surrounding hillside.

Identify Site OptionsIdentify Site Options

• Surveyor visits each search area and identifies potential site options.

• The first sites to be considered should be • Existing radio sites.

• Sites offered from major site owners (MSOs) e.g. utilities and railways.

• All options should meet certain criteria to ensure that they are:• Technically acceptable.

• Buildable

• A good idea to consult with the planning/zoning authority during the survey.

• Good training of surveyors will save time later in the building process.




Identify Site Options

Identify Site Options

• The surveyor will prepare a report listing the options.

• Report will include:• Accurate grid reference.

• Accurate height of structures or available antenna windows.

• Photographs of the site.

• 360º panoramic photos from site or if obstructed from nearby location/structure.

A

D

C B


Site SelectionSite Selection

• Normally a desk study.

• Evaluate radio coverage and transmission.

• Quickly eliminate unsuitable options.

• Rank the remaining sites in order of preference.

• Nominate a preferred option and possibly a backup option.

A3rd

D1st

C2ndB - Unsuitable




Site AcquisitionSite Acquisition

• Run more than one site simultaneously.

• Negotiate with site owners.

• Prepare drawings.

• Draw up leases.

• Apply for planning permissions.

• Apply for power wayleaves.

• As soon as one option is ready to proceed:• Sign the lease• Abandon the alternatives• Enter site into building program.


Detailed Site DesignDetailed Site Design

• Prior to starting construction work, a detailed site design is required.

• This includes• Antenna and feeder requirements.

• Antenna azimuths and tilts.• Equipment capacity requirements

• Cannot be completed in isolation. Must take into account other sites.

60º

60º

180º180º

300º

300º

Ant 1

Ant 2Ant 5

Ant 4

Ant 6

Ant 3


Providing coverage over a large area will necessitate accurate configuration of a large number of sites simultaneously. It is not possible to state the ideal configuration of any one site in isolation. The network of sites must work together in harmony to produce the desired results.



____________________________________________________________________

6.4 Multilayer Cell Design

MultiMulti--layer Cell Design layer Cell Design

• Network design considerations:• Microcell positioning

• Radio resource management (channels/frequencies)• Call and handover admission

• Use test cells to determine suitable microcell positions:

Macrocell BTS

Test microcell

Mobile measures power levels of neighbour cells including test microcell

Dummy BCCH


A hierarchical GSM network can have macrocells providing continuous coverage, with microcells to serve hot spots of high traffic density (e.g. near a railway station) and to fill in coverage for regions of shadow from the main macrocell (e.g. street ‘canyons’ in cities). Problems with microcell use include the complex radio propagation environment, which is difficult to model and dealing with frequent handovers for fast moving mobiles. Important considerations for network designers are:

• Detecting hot spots and determining the best size and position for a microcell. • Resource management between the network layers – channel allocation and

frequency planning. • Call admission and handover strategies between the layers.



MultiMulti--layer Spectrum Allocationlayer Spectrum AllocationMethods are:

• Orthogonal sharing - generally used

• Spectrum sharing - isolated microcells

• Dynamic Channel Allocation - picocells

Orthogonal sharing

Spectrum sharing for an isolated microcellusing carrier 1 inside a macrocell using carrier 4

F2

F1


6.5 Microcell Positioning

Positions for microcells may be determined by setting up test microcells which transmit a dummy BCCH channel so that mobiles in neighbouring cells will make signal level measurements. Access is barred to the microcell so that actual handover is not attempted. Reports can then be analysed to determine how often mobiles would have accessed the dummy microcell.

MicrocellsMicrocells

• Coverage over a small area - typical range of a few hundred metres - power output ~ 250 mW = 24dBm

• Mounted below roof top

• Energy contained within streets by ‘canyon’ effect

• Lower power - less interference - shorter re-use distance

> 2m

> 5m

Directional antennas Omni antenna

Coverage patterns confined to streets by ‘canyon’ effect




Microcell PositioningMicrocell Positioning

• Important considerations when placing microcells:• location in street - effect of reflections in nearby streets

• distance above street and below roof top

• type of antenna - omni, sectored • antenna parameters - gain, beamwidth, polarisation

• orientation and tilt of antenna

• Examples:• directional antennas for long road

• directional antenna down tilted for in-building coverage

• omni-directional antenna for open spaces and cross-roads


InIn--Building CoverageBuilding Coverage• Path losses for signal from outside building:

External path loss (not necessarily direct path)

Penetration loss at external wall

Reflections at walls, floors, ceilingsPenetration through walls etc.

BTS antenna

Losses depend on building materials and thickness, angles of incidence, number of floors, walls etc. Each loss term may be several dB




____________________________________________________________________

6.6 Picocell Arrangements

PicocellsPicocells• Microcell base stations sited inside buildings

• Antennas may be:• omni directional - ceiling mounted• directional panel array - wall mounted

• Propagation within a building is very complex

• To achieve a more consistent coverage, distributed antennas may be used:

• antennas in different parts of building connected to same TRX via splitters / combiners

• active repeater amplifiers may be used to overcome feeder losses

• leaky feeders (radiating coaxial cable) can give very uniform coverage

TRX

Splitters / combiners

Ceiling mounted omni antenna

Distributed antennas


6.7 Resource Sharing

Methods of allocating spectrum to the layers are:

• Orthogonal sharing – each layer uses its own frequencies. This may lead to poor trunking efficiency

• Spectrum sharing – same frequencies are used by macrocells and microcells, relying on base station power control to reduce interference

• Dynamic Channel Allocation (DCA) – use same frequencies but not at the same time. The system intelligently allocates frequencies in order to minimise interference based on current activity.

6.7.1 COMPARISON OF ORTHOGONAL AND SPECTRUM SHARING Simulations show that the cross layer interference caused by spectrum sharing leads to reduced overall capacity. The conclusion is that the simpler strategy of orthogonal sharing is the better one. Spectrum sharing may be suitable for isolated microcells. The interference from co-channel macrocells is small as a mobile using the microcell will generally be in line of sight of the microcell base station but not of the distant macrocells. Frequency must be selected to avoid co- and adjacent channel interference:



In the example, carriers 2, 6, 7, 10, 11 and 12 are used in physically adjacent cells; carriers 3 and 5 are adjacent channels to 4 (used in the macrocell). Of the remaining carriers (1, 8 and 9), carrier 1 gives the greatest re-use distance.

6.7.1.1 Dynamic Channel Allocation

DCA may be suitable for indoor picocells. Channels from a fixed set of available frequencies can be allocated dynamically based on current interference levels from surrounding cells. DCA allows a microcell / picocell layer to be introduced without reorganising the existing macrocell frequency plan.



6.8 Cell and Handover Admission Strategies

Call and Handover AdmissionCall and Handover Admission

• Generally allocate:• slow moving handsets to microcells• fast moving handsets to macrocells

• In-car mobiles would move rapidly through microcells - causing many unnecessary handovers

• Pedestrians are generally at street level, in LOS with microcell base station - do not change cell often


Two mobile behaviours should be distinguished:

• Slow moving or static (pedestrians) • Fast moving (motorists)

Fast moving mobiles are better handled by macrocells. Slow moving mobiles may be handled by microcells with overflow to macrocell if required.

6.8.1.1 Reversible and Non-reversible Systems In a non-reversible system, once a mobile has been handed over from a microcell to a macrocell, no handover is allowed back to the microcell layer. In reversible systems, handover and hand back between macro and micro cell layers are allowed as required. Simulations of the two systems have shown that reversible systems lead to more handovers causing extra signalling traffic without substantial benefit to the overall system performance.



Reversible or NonReversible or Non--ReversibleReversible• Reversible system:

Macrocell layer

Microcell layer

Macrocell layer

Microcell layer

• Non-reversible system:

Mobile can be handed back and forth between layers

Once in macrocell layer, mobile cannot be handed back


6.8.1.2 Estimation of the Mobile’s Speed

The speed of the mobile can be estimated by measuring the dwell time, i.e. the time the mobile spends in a particular cell. Various strategies are possible for handing over to the same layer or up/down to a different layer by comparing the dwell time with one or more threshold values. Speed estimation can be used to alter the handover margin algorithm used to determine the power level at which a handover is required. This can reduce unnecessary handovers for fast moving mobiles.



Speed Sensitive HandoverSpeed Sensitive Handover• One possible handover strategy based on dwell time measurement

(three layer system)

Macrocell layer

Microcell layers

Dw

ell t

ime

t2

t1High speed (short dwell time) -hand to higher layer

High speed - hand upMedium speed (dwell time between thresholds) - hand over on same layer

Low speed (long dwell time) -hand to lower layer

Low speed - hand down

Medium speed -hand over

• Simulations show this strategy has fewer handovers than one based on a single dwell time threshold value


6.8.2 CELL SELECTION ALGORITHM

In GSM Phase 2, the cell selection algorithm uses a parameter C2, which includes a temporary offset value if the speed of the mobile (measured by a timer) is greater than a certain threshold value as it enters the cell. This is covered in Section 6: Network Operations. This ensures that a fast moving mobile will not select the microcell but will stay on in the macrocell.

Further reading: Multitier Cell Design, Xavier Lagrange, IEEE Communications Magazine, August 1997. (calab.kaist.ac.kr/research/sig_network/old/papers/MultitierCellDesign.pdf)

____________________________________________________________________

6.9 Use of Repeaters

Establishing a new site can be very expensive. Providing coverage where there is currently a “hole” can be more economically achieved by using a repeater. This is particularly true where the level of offered traffic is low. A repeater operates by using a high gain antenna (usually a Yagi or a parabolic dish) to receive the signal radiated by the BTS, amplifying it and re-radiating it. In this way, the power density in the region of the repeater is increased and coverage can be maintained. The repeater acts in both directions, amplifying uplink signals before transmitting them towards the BTS.



Cell RepeatersCell Repeaters• Repeaters allow coverage to be extended into

‘blackspots’ such as tunnels or cuttings or inside office buildings

• A repeater consists of two antennas back to back with amplifiers in each direction:

Repeaters by Allgon

Typical gain: 50 - 90 dBDirectional antenna towards base station

Directional or omni antenna as appropriate towards users

• Repeater passes on same frequency it receives

• Response may be: • band selective• channel selective

Band pass filter

Amplifier


As an example, consider the situation where coverage from the BTS can be maintained within a region where the path loss is less than 153 dB. Suppose that, due to obstructing terrain features, the loss at a particular point (at mobile height) is 163 dB. Placing a repeater can provide gain in three distinct ways:

• The repeater antenna is elevated to have line of sight to the BTS • The repeater antenna has a higher gain than the mobile antenna • The signal received will be amplified before it is retransmitted.

Using RepeatersUsing Repeaters

• Coverage from a BTS can be achieved only if the pathloss is below a certain maximum level

• A repeater may provide a more economic method of providing coverage in areas where the pathloss to the BTS is above this maximum

Repeater can provide coverage in area of high pathloss to BTS.




Repeater ConstructionRepeater Construction

• A repeater consists of:

• A Yagi or parabolic antenna• A high gain amplifier

• A sectored antenna similar to that used on the BTS.


Repeater AnalysisRepeater Analysis

• Gain is provided in three ways:• Repeater antenna is elevated above the height of a typical mobile

• Repeater antenna has higher gain than a mobile antenna

• The repeater is “active”, that is it contains an amplifier.

• Typical values• Elevation gives a 15 dB gain.• Yagi will have a 20 dBi gain.

• Amplifier will have a 65 dB gain.

• Total Gain: 100 dB

• Thus if pathloss was 10 dB bigger than maximum tolerated, coverage will be provided in areas where pathloss to repeater antenna is less than 90 dB.


Typical values would be:

• The elevation of the repeater antenna would increase the signal strength by 15 dB. • The antenna gain would be 20 dBi, • The gain of the repeater amplifier would be 65 dB.



This gives a total gain of 100 dB. This means that mobiles within a region such that the path loss to the repeater was less than 90 dB would receive a service. The coverage provided by repeaters is often very small and they are generally used to fill in gaps that would otherwise be very expensive to fill. The gain of the amplifier is limited by the need to avoid a positive feedback loop developing. The repeater is receiving, amplifying and retransmitting at the same frequency. The coupling loss between the two antennas must be greater than the gain of the amplifier by a suitable margin (typically 20 dB).

Repeater Design ConsiderationsRepeater Design Considerations

• The gain of the amplifier is limited by the need to avoid positive feedback (“singing”).

• If the amplifier has a gain of 70 dB, the antennas would need to be provided with typically 90 dB of isolation.

Positive feedback


Adding a Repeater Adding a Repeater

Asset screens showing the effect of adding a repeater:

Coverage restricted to a valley

Coverage needed at this end of valley

BTS site

Repeater added here

Extended coverage produced by repeater

A repeater is suitable here as the traffic loading on the cell is low in this rural area.




Some Considerations with Repeaters: A repeater extends coverage range but does not add capacity. They should not be added to carriers, which are heavily loaded. Repeaters amplify and pass on everything they receive – noise as well as wanted signals. Feedback can cause a repeater to oscillate. If several repeaters are in a chain, they will all then oscillate, which makes troubleshooting difficult.

SummarySummary• BTS positioning problems in specific types of location: rural areas,

topographical effects, water surfaces, traffic routes

• Microcell positioning: urban areas, location and type of microcell antennas

• Picocell arrangements: in-building coverage, losses, types of antenna, distributed antennas

• Multi-layer cell design: determining best positions for microcells, resource sharing methods, call admission and handover strategies


.




The following activities involve some general considerations of base station positioning in various situations and an exercise in selecting a suitable microcell carrier for spectrum sharing.

6.10.1 BASE STATION POSITIONING

Describe some of the considerations a planner should take into account when placing a base station in the following locations: On the bank of a wide river In a hilly countryside region To provide coverage for a road through hilly countryside In a long straight road in town At a cross roads in town To provide coverage for an office block



6.10.2 SPECTRUM SHARING IN A MICROCELL

A network uses a standard 4/12 frequency plan as shown. Carriers are allocated to the groups in the usual way. The planner needs to place a microcell in the B1 cell marked. Suggest a carrier that could be used in this microcell

6.10.3 REPEATER POSITIONING

The path loss from a particular region to the best serving BTS is 161 dB, 8 dB above the maximum level. It is decided to use a repeater to provide coverage for this region. A 22 dBi antenna is used to transmit and receive to and from the BTS. The signal strength at the repeater antenna is 15 dB above what it would be at the height of a typical mobile receiver. The maximum isolation that can be obtained between the two antennas is 78 dB and an isolation margin of 14 dB is to be provided. Deduce the maximum gain amplifier that can be used and hence determine the maximum path loss from the repeater that can be tolerated by mobile terminals assuming that the same antenna is used at both the BTS and the repeater. Solution. If the maximum isolation between antennas is 78 dB and a margin of 14 dB is to be provided, the maximum gain amplifier will be 64 dB. Thus the total gain is 15 + 22 + 64 = 101 dB. As the path loss was originally 8 dB too high, a maximum path loss from the repeater of 93 dB can be tolerated.

Microcell needed here



7 Base Station Engineering ____________________________________________________________________

We will now examine the issues of:

• Site suitability • Radio property testing • Antenna configurations • Base station equipment • Electrical Considerations • Choice of Configuration

____________________________________________________________________

7.1.1 SITE SUITABILITY

Site SuitabilitySite Suitability

• Nominal plan gives ideal pattern of cells

• Actual cell sites must meet various requirements as seen previously

• Engineering requirements include:

• suitable radio properties (propagation, interference etc.)

• clearance of nearby obstacles for radio signal

• space for equipment

• power supplies - main and back up• transmission links

Section 7 – Base Station Engineering



Site FacilitiesSite Facilities• The site must have space for the antenna mast/tower and

the cabinets or building required to house the BTS equipment

• The ground should be structurally suitable for a tower or mast to be built

• Mains power supply should be available or able to be provided

• Back up power must be made available, such as:• batteries

• diesel generator - space, fuel supply and noise problems may be an issue

• fuel cells - being considered - efficient, environmentally friendly


TransmissionTransmission• The base station must be connected to the rest of the network

• Connection is via E1 (European) or T1 (American) hierarchy PCM system

• Physical link may be:• copper (symmetrical pair or co-axial) cable

• optical fibre• microwave

• satellite link (rare)

• Link planning may be required, including:• network topologies• link budgets

• surveys




__________________________________________________________________ 7.1.1.1 Radio Property Testing

Radio MeasurementsRadio Measurements

• Measurement of the radio properties of the site include:

• Propagation - this would have already been done in drive testing the area to tune the propagation model - further measurements for verification may be needed

• Time dispersion tests - to check the effect of multipath propagation on C/R values

• Interference - particularly from sources outside the network -frequency planning should already have given acceptable C/I and C/A values within the network


The C/R value is the ratio of the power in the direct path (Pd) compared to the power in the reflected path (Pr) and is expressed as: Carrier to Reflection ratio ( C/R ) = 10 log (Pd / Pr) GSM recommends C/R should be 9 dB or greater.



Time Dispersion TestsTime Dispersion Tests

• Transmitter sends pulse at appropriate frequency (e.g. 900 MHz)

• Receiver picks up pulse and any echoes

• Display shows the strength and time delay of the echoes

• Problem results would contain strong echoes with long time delays -equalisation can be used to deal with short delays

Main pulse

Echoes

Time delays Time (µs)

Rx

Lev

el (

dB

m)


Interference TestsInterference Tests

Frequency

900 MHz band 1800 MHz band

f 1 f2

f1 + f22f1 - f 2 2f2 - f1

f1 + f2 - f2= f1

f1 + f2 - f1= f2

2f1 2f2

3rd order products are equalto or close to the carriers in use

Carriers

2nd order products

3rd order products

• Use spectrum analyser in ‘off - air’ monitoring mode• Check for radio activity from other operators in the area,

especially when sites are co-located with those of other operators

• Tests should check for:• direct interference• intermodulation products - particularly third order products


7.1.2 INTERMODULATION INTERFERENCE

Intermodulation products arise from mixing of frequencies in a non-linear system. The order of a product is the total number of frequencies involved in its production. Two frequencies f1 and f2 can produce second order products: 2f1, 2f2, f1 + f2, f1 – f2 and third order products: 3f1, 2f1 + f2, 2f1 – f2, 2f2 + f1, 2f2 – f1, 3f2, f1 +f2 – f1 (= f2), f2 + f1 – f2 (= f1).



If f1 and f2 are in the 900 MHz band, most of the second order products will be in the 1800 MHz band, but many of the third order products are also in the 900 MHz band and cause interference problems.

7.1.2.1 Calculating Intermodulation Power Levels

In the case of signals radiated by a particular base station, the strength of these intermodulation frequencies can be estimated using data for the amplifiers causing the non-linear distortion. The important values are the gain, G dB, of the amplifier and a parameter known as the third order intercept point (IP3) measured in dBm. The power (PIMD) of the third order intermodulation products of two frequencies each input to the amplifier with power Pin is given by:

3inIMD IP 2P 3G 3P −+= Example: For a particular amplifier, G = 51 dB, IP3 = 47 dBm and two frequencies are input with powers of -8 dBm. Calculate the power of the third order intermodulation products produced by this amplifier. PIMD = 3 x 51 + 3 x (-8) – 2 x 47 = 26 dBm The power levels of the intermodulation frequencies at any point can then be estimated using the same propagation models and power budgets that are used for the main carriers. If carriers are in use at the frequencies of these intermodulation products, the resulting C/I ratio can be found. This must be sufficiently large to allow the carriers to be used.

7.1.2.2 Reducing Intermodulation Distortion

The non-linear amplification, which generates the products, should be minimised in the design and manufacture of the equipment. The non-linear effects can be reduced by running the system with lower than normal input power, or equivalently using a higher gain amplifier to produce the same output power.

Frequency hopping can reduce the interference effects caused by intermodulation frequencies. Non-linear effects produced by poor connectors or equipment operated out of specification should be checked and corrected.





• The site of the base station and antenna height should allow complete clearance of at least the first 100 metres of the first Fresnel zone

• At 100 m from the base station, the first Fresnel zone radius is about 5.7 m for a distant receiver

• Using this figure, the required height of the antenna can be estimated

• The antenna height should not affect the coverage and interference predictions already made

• Some compromise may be necessary in the clearance allowed

BTS

MS

100m5.7m

First Fresnel Zone


• Path length of any wave reflected from a Fresnel zone surface is nλ/2 more than direct path:

a + b = d + n(λ/2)

• Radius of ellipsoid at d1 from Tx is given by:

Fresnel Zone DimensioningFresnel Zone Dimensioning

Tx Rx

d1 d2

d

R1a b

ddn λ21

1d R =

R1




7.2 Estimation of Fresnel Zone Radius:

The first Fresnel zone is an ellipsoid with foci at the transmitter and receiver. The distances a and b to the surface of the ellipsoid are such that:

2dba

λ+=+

The distance d from a macrocell base station to the mobile receivers will typically be several kilometres, which is large compared to the distance d1 = 100 m.

Thus 2d d ≈ and the equation for the radius becomes: λ=

λ≈ 1

11 d

ddd

F

For the 900 MHz band m 0.33 ≈λ , m 5.7 33 0.33 100 F1 ==×≈

____________________________________________________________________

7.3 Antenna Configurations

AntennasAntennas• Isotropic Radiator:

• Theoretical form of antenna• Equal radiation in all directions

• Used as the basis against which practical antenna gains are measured

• Half Wave Dipole:• Physically half the radiated wavelength• Radiation pattern is confined to ‘doughnut’ shape

• Gain is 2.14 dBi

• Antenna manufacturers often quote gains relative to dipole in dBd

• Gains used in power budget calculations must be in dBi

Gain in dBi = Gain in dBd + 2.14




Radiation PatternsRadiation Patterns• Antenna radiation pattern (polar diagram) shows antenna gain against

angular direction

• Pattern is actually 3 dimensional - generally show horizontal (azimuth or H plane) and vertical (elevation or E plane) plots

H plane E plane


Antenna GainAntenna Gain• Gain varies with angle as shown by the radiation pattern

• Manufacturers’ quoted gain is the maximum value in the main lobe(boresight) direction

Isotropic

Dipole

Practical antenna

Gain dBi

Gain dBd

2.14 dBi

Boresight

E plane (vertical) patterns for different antennas




BeamwidthBeamwidth

• Antenna beamwidth is defined by the points on the radiation pattern at which the radiated power falls to half the maximum value (- 3dB from boresight)

Gain = max

Gain = max - 3dB

Gain = max - 3dB

Beam width is quoted for vertical and horizontal pattern


Transmission and ReceptionTransmission and Reception• Theorem of Reciprocity states that the gain of an antenna is the same

whether it being used to transmit or receive a signal

• Power received by an antenna depends on its effective aperture (Ae)

Pr = S x Ae

Pr = received power (W) S = power density (W/m2)

• Gain, G and effective aperture are related by the equation:

e2 A?p4

G =

• Differences between Tx and Rx antennas:• Tx uses higher power levels than Rx and requires higher rated components

• Reflections of radio signals will have different effects on Rx and Tx antennas




OmniOmni--directional Antennasdirectional Antennas

• Designed to give complete 360o coverage around the base station

• H plane pattern is circular

• E plane pattern is generally narrow with some side lobes

• Typical gain: 6 - 12 dBi

• Construction: collinear array of dipoles arranged vertically - signal supplied to all dipoles in phase

Commercially availableomni antennas

3 m typical length for 900 MHz

TRX

dipoles

feeder cable

collinear array

housing


Sector AntennasSector Antennas• Designed to give give coverage within a restricted

angle

• Horizontal beamwidth, typically 60o - 90o

• Used in sectored cells e.g. when an omni cell is tri-sectored

• Typical gain: 10 - 18 dBi

• Construction: omni-directional collinear array with corner reflector to direct the beam

corner reflector

collinear array

Commercially available sector antennas




Antenna TiltAntenna Tilt• Down tilt of antennas often used to:

• reduce interference• adjust cell size

• direct coverage e.g. into a building

• Mechanical tilt:• set by operator

• distorts azimuth (H plane) radiation pattern

• Electrical tilt:• set by manufacturer• reduces radiation H plane pattern equally in all

directions, without distortion

Omni-directional antenna with electrical down tilt


Examples of Antenna TiltExamples of Antenna Tilt

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

No Tilt Mechanical Downtilt

Electrical Downtilt

Electrical Downtilt +

Mechanical Uptilt




Distributed Antenna SystemsDistributed Antenna Systems• In buildings, more uniform coverage may be achieved by having several picocell

antennas fed by the same TRX

• Extreme form of distributed antenna is the leaky feeder:• Coaxial cable with slots in outer conductor to allow r.f. energy to ‘leak out’

• Arrangement of slots depends on operating frequency

TRX

Possible layout of leaky feeders in a

building

construction

radiation pattern

• Applications : • underground railways• mines• tunnels

• Disadvantages : • high cost• no antenna gain


Antenna SeparationAntenna Separation• Physical separation isolates antennas, reducing:

• interference• intermodulation products

• Typical separation provides 30 -40 dB isolation

• Vertical separation is more effective than horizontal

• Physical separation required depends on:• wavelength - longer λ, greater separation• antenna gain

• beamwidth

• Typical separation used:• vertical ~ 0.2 metres or more• horizontal ~ several metres




Diversity ReceptionDiversity Reception• To overcome effects of multipath fading - receive signal with two

independent antennas

• Two forms of diversity reception:

polarisation diversity

10 λ

Two collinear array antennas separated by 10λ (3 m in GSM 900)

Single antenna with dipoles at 45 0

Dual polarised PCS-1900 base station array by ERA Technologies

space diversity


7.3.1 DIVERSITY RECEPTION

Diversity reception uses a second receiving antenna, which receives a signal that is independent of the first antenna. This independence is achieved either by separating the signals in space (space diversity) or by receiving two independent polarisation components of the signal (polarisation diversity). As the signals are independent, it is unlikely they will both experience fading at the same time. The signals can be combined to produce a diversity gain of about 3 – 5 dB.

7.3.1.1 Space Diversity

Two antennas are mounted sufficiently far apart that they receive independent signals. The separation should be at least 10 wavelengths, which for the 900 MHz GSM band is 3.3 metres and for the 1800 MHz band, half this value

10λ



7.3.1.2 Polarisation Diversity

The polarisation of the radio signal changes due to multiple scattering and atmospheric effects. The many signals incident at the antenna have a wide range of planes of polarisation. Diversity gain can be achieved by mounting antennas in pairs at 45o either side of the vertical so that two independent polarisation components are received. The antennas are placed at 45o rather than horizontal and vertical, as the purely horizontal polarisation component is very small close to the ground. Advantages of polarisation diversity: Similar gain to space diversity (3 – 5 dB) Smaller antenna arrangement – mount on mast rather than tower Less environmental impact – easier planning permission Most systems make widespread use of space diversity, but polarisation diversity is increasing in popularity.

____________________________________________________________________

7.4 Base Station Equipment

7.4.1 USING ANTENNA COMBINERS

Why Use Combiners?Why Use Combiners?

• To reduce the number of antennas at the BTS.

• Advantages:• More aesthetically pleasing

• Reduces wind and weight loading

• Reduces leasing charges

• Disadvantages:• Insertion loss

• Why not connect TRXs directly to antenna?• Changes impedance matching

• Causes feedback between transmitters

TRX 1

TRX 2

TRX 3

TRX 4

Combiner




It is generally the case that operators seek to minimise the number of antennas installed at a BTS. This is for several reasons: More elements are less aesthetically appealing – less likely to acquire planning permission Introduces higher weight and wind loading – heavier mast/tower required or lower positioning Reduces leasing charges which are often charged per antenna element. Antennas combiners are used to enable multiple transmitters to use a common antenna in order to reduce the number of installed elements. It is not possible to simply connect transmitter outputs to a single antenna element for the following reasons: Change in 50 ohm matched impedance caused by multiple transmitters cables connected in parallel. Power would be fed back from one transmitter to another. For these reasons, combiners are used to combine the outputs of multiple antennas to a single antenna element.

Antenna Combiner ConsiderationsAntenna Combiner Considerations

• Combiners allow several TRXs to share one transmit antenna

• Main considerations when using combiners are:• power levels to be handled

• minimising losses

• isolation between carriers• linearity to avoid intermodulation distortion

• Two main types of combiner in use:• hybrid combiner

• cavity filter combiner

TRX 1

TRX 2

TRX 3

TRX 4

Combiner




7.4.2 HYBRID COMBINERS

Hybrid combiners are passive devices i.e. they have no active components in them. They are designed to combine the outputs from two transmitters into a single output whilst retaining adequate separation between the two inputs to avoid power reflections.

Hybrid CombinerHybrid Combiner• Passive device with two inputs, two outputs

• Can combine two input signals• One output must be terminated by a matched

impedance - typically 50Ω load with heatsink for cooling

• Half total input power is lost to the load - combiner loss is at least 3dB

• Typical loss is about 3.3 dB

Load

Output to antennaInput from TRX 1

Input from TRX 2

Commercial hybrid combiner (Microlab/FXR)

90 mm

Hybrid

Combiner

Terminating loads


Hybrid Combiner StacksHybrid Combiner Stacks• To combine more than two inputs, several combiners must be stacked

• Each level introduces a 3 dB loss - gives inadequate output when many signals to be combined

Hybrid

Combiner

Load

Output to antenna

Input from TRX 1

Input from TRX 2

Hybrid

Combiner

Hybrid

Combiner

Input from TRX 3

Input from TRX 4Load

Load 3 dB loss

3 dB loss

3 dB loss

Combined loss is 6 dB for each TRX

• Hybrid combiners are cost effective for cells with few TRXs

• They have a wide bandwidth - used in frequency hopping




7.4.3 CAVITY FILTER COMBINERS

Cavity filters have an advantage over hybrid filters in that multiple devices can be connected in parallel to an antenna without increasing the overall insertion loss.

Cavity FiltersCavity Filters

• Tuned cavity acts as band pass filter

• Centre frequency of pass band depends on the dimensions of the cavity

• Tuned by adjusting a plunger on the cavity - may be servo motor operated to automatically follow the tuning of the TRX

• Generally supplied as a block of several cavities

Block of 5 cavity filters by RFS Ltd.

Tunable band pass cavity filter by K&L

Cavity filters by Aerial Facilities Ltd.


Cavity Filter CombinerCavity Filter Combiner• Cavity filters can be used to combine several frequencies:

• Outputs of filters are directly connected together• band pass filters isolate the different frequency outputs

• connection harness and stub must be correctly matched to the wavelength to reduce losses

Input from TRX 1

Input from TRX 2

Input from TRX 3

Connectionharness

Matching stub

• Losses:• Typically 2 - 5 dB per cavity• No addition of losses when

more signals are combined

• More expensive than hybrid combiners but give low loss when many frequencies are combined

f1

f2

f3




Combiners for Combiners for BasebandBaseband HoppingHopping• The baseband signal is fed to one of several TRXs in turn by a switch

• The TRX outputs must be combined to be fed to the antenna• The combiner must be able to handle a wide bandwidth of signals

• This can be achieved using either:• hybrid combiners - several stages causing large loss

• cavity filters - one associated with each TRX - maximum loss ~ 5 dB

TRX

TRXBasebandData Signal

TRX

Antenna

Switch controller

Cavity filter method is preferred as it gives lower loss


Combiners for Synthesiser HoppingCombiners for Synthesiser Hopping

• A single channel using synthesiser hopping has only one TRX output and would not require a combiner

• If several channels are to be combined and fed to one antenna, the combiner must have a wide bandwidth to deal with the range of frequencies from the synthesiser

• Hybrid combiners must be used in this case

Tuning controller

BasebandData Signal 1 TRX 1

BasebandData Signal 2 TRX 2

HybridCombiner

Load

Antenna




Antenna Multicoupler

Antenna Multicoupler• Required to couple the receiving antennas - main (A) and diversity

(B) to the TRXs

• Power from each antenna is split and amplified

• Identical pairs of outputs are available for each TRX

• Multicoupler produces no overall gain or loss - neutral

Multicoupler

Rx A Rx B

Rx A outputs

Rx B outputs

TRX 1

TRX 2

Further TRXs

Commercial multicoupler


Antenna DuplexerAntenna Duplexer

• With diversity reception, a cell would require 3 antennas - transmit (Tx), main receive (Rx A), diversity receive (Rx B)

• Duplexer (duplex filter) can reduce this to 2 antennas by combining Tx with one Rx

• Duplexer consists of two band pass filters - one tuned to the uplink frequency (Rx) and one tuned to the downlink (Tx)

• Isolation between Tx and Rx typically 50 - 80 dB

• Power loss < 1 dB

Rx Tx

FuFd

Tx / RxAntenna

Duplexer

TRX

Duplex filter by AMP Ltd




Duplexer with Space DiversityDuplexer with Space Diversity

Using a duplexer on a tri-sectored site can reduce the number of separate antennas on the tower from 9 to 6

Tx

Tx

Tx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Tx/Rx

Tx/Rx

Tx/Rx

Without duplexer - separate Tx and Rx antennas

With duplexer - common Tx/Rx antennas


Duplexer with Polarisation DiversityDuplexer with Polarisation Diversity

Using a duplexer can reduce the number of separate antennas from 6 to 3 - a mast could be used rather than a tower

2 Rx

2 Rx

2 Rx

Tx

Tx

TxTx Rx A + Rx B

Separation of about 2λfor isolation

Without duplexer:

Tx/Rx

Tx/RxTx/Rx

With duplexer:

Tx + Rx A Rx B




Losses in Feeders and ConnectorsLosses in Feeders and Connectors• Long feeder cables from antenna to base station equipment

can cause considerable power loss

• Typical loss in co-axial cable: 3 -10 dB per 100 m • Loss increases with frequency:

• 1800 MHz can have 4 - 10 dB greater loss than 900 MHz

• Loss depends on quality of cable:• Cheap cable may give 20 dB per 100m

• Very expensive cable can have:• 1 dB / 100m for 900 MHz• 3 dB / 100m for 1800 MHz

• Connectors between duplexers, combiners, couplers and so on should produce no more than 0.2 dB loss


_____________________________________________________________



7.4.4 ELECTRICAL CONSIDERATIONS

Base Station Grounding SystemsBase Station Grounding Systems• Efficient grounding required for protection

against lightning strikes:• strike energy must be dissipated across

wide area• local ground potential should not rise and

cause equipment damage

• Grounding also needed for efficient RF operation of antenna

• BTS equipment grounding:• A.C power - separate grounding for each

phase (3 phase systems)

• D.C. power grounding - taken separately to ground or possibly combined with lightning protection above ground

Feeder cable outer conductor bonded to tower at top and bottom - using feeder grounding kit

Earth bar bonded to feeder

Separate grounding for D.C. power, A.C. power etc.

Earth ringsElectrodes driven into ground

Enhanced soil conductivity

Conducting concrete

Underground connection of earthing systems to produce equipotential


Lightning Protection Lightning Protection • Lightning protection finial at top of tower

or building - rod or spiked sphere -provides 45o protection zone

• Connection to ground via flat copper strap - required on towers as well as buildings

• Conductor thickness should increase nearer ground if several routes are combined

• Path of conductor must always be downwards - never turn back up

45o protection zone provided by finial

Lightning protection finial

Conductor turns back -

lightning won’t !


____________________________________________________________________



7.4.5 CONFIGURATION SELECTION

Selecting an Appropriate Configuration When deciding on the configuration of a site, the network planner can choose a site that falls in one of the following four categories: § Omni-directional § Omni-directional with diversity § Sectored § Sectored with diversity

Selecting the Correct ConfigurationSelecting the Correct Configuration

There are four major categories of site:

OmniRx

Rx

Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/RxTx/Rx

Tx/Rx

Tx/RxTx/Rx

Omni with diversity

Sectored

Sectored with diversity


The choice made will affect the coverage and capacity achievable from that site. As an example, consider a typical link budget for a GSM 1800 mobile channel;

Base Station Transmit Power

43 dBm

Receiver Sensitivity -95 dBm

Feeder Loss 5.0 dB Combiner Loss 6.0 dB Mobile Antenna Gain 0.0 dBi Allowable link loss 127 dB

Now, if the antenna is an omni-directional antenna, a gain of 13 dBi can be assumed, whereas 18 dBi is more likely if the antenna is sectored. That means that the maximum path loss for an omni-directional site is 140 dB whereas 145 dB can be tolerated on a sectored site.



Estimating the Affect on Cell RangeEstimating the Affect on Cell Range

• The choice of configuration will affect capacity and coverage.

• A sectored antenna will have about 5 dB more gain than an omni antenna (18 dBi compared with 13 dBi).

• Maximum Path Loss• Omni site: 140 dB

• Sectored site: 145 dB (Link loss 127 dB in both cases)

• Maximum Range• Omni site: 1.22 km

• Sectored site: 1.69 km

• (assuming path loss model L = 137 + 35 log [R] )


If an urban path loss model of L = 137 + 35 log(R) is taken to be appropriate then the path losses can be translated into a cell range.

Path Loss Cell Range 140 dB 1.22 km 145 dB 1.69 km

Calculating the Area of CoverageCalculating the Area of Coverage• Maximum Range

• Omni site: 1.22 km

• Sectored site: 1.69 km

• (assuming path loss model L = 137 + 35 log [R] )

1.22 km

Area = 4.0 km2

1.69 km

Area = 5.6 km2




An omni-directional site would cover an area of 4.0 km2. The sectored site would cover an area of approximately 5.6 km2. However, the sectored site would consist of three cells, each cell covering 1.9 km2. Therefore the sectored configuration would not only cover a greater range but also be able to serve an area of greater user density. Omni-directional sites are cheaper to provision and would be used when they can meet the demands for coverage and anticipated traffic.

Estimating the Affect on CapacityEstimating the Affect on Capacity

• Sectored site will have approximately 3 times the capacity of an omni-directional site (assuming the same number of carriers).

• Sectored site will accommodate a traffic density more than twice that of an omni-directional site.

1.22 km

Area = 4.0 km2

1.69 km

Area = 5.6 km2

1.69 km


Deciding whether to use DiversityDeciding whether to use Diversity

• Diversity is used when necessary to balance the system.

• It helps the uplink but not the downlink.

• Diversity allows the BTS to operate at higher power whilst maintaining link balance.

• Hence it allows greater coverage to be achieved.


Unbalanced system


Balanced system




Remember that link balance can be maintained when the base station transmit power is lower as the mobile power can be reduced using the power control system. The decision whether or not to provide uplink diversity is connected with the issue of link balancing. In the above situation it may well be that the uplink would not be able to operate over the allowable link loss of 127 dB without diversity. Suppose that the maximum link loss that the uplink could tolerate was 125 dB without diversity. A diversity gain of 2 dB would restore link balance. If diversity was not employed, the base station transmit power would have to be reduced to 41 dBm and the allowable link loss would be 125 dB. A 2 dB reduction in path loss corresponds to the range altering by a factor of approximately 0.88. Therefore, the new ranges would be:

Cell Configuration Range without Diversity

Omni-directional 1.07 km Sectored 1.49 km

Summarising, using diversity allows link balance to be maintained whilst increasing the base station transmit power. If coverage can be provided on the downlink using a low transmit power, then diversity is not required.

Selecting the Correct Configuration Selecting the Correct Configuration -- SummarySummary

Sectored site; diversityMaximum Coverage, high capacity requirements

Sectored site; no diversityLarger Coverage Region, high capacity requirements

Omni site; diversityLarge Coverage Region, low capacity requirements

Omni site; no diversitySmall Coverage Region, low capacity requirements.





7.5.1 INTERMODULATION PRODUCTS

At a base station two GSM carriers are used, ARFCN 30 and 35. What are the actual frequencies of these carriers? Calculate the second order intermodulation frequencies. Will any of these frequencies interfere with DCS 1800 carriers? Calculate the third order intermodulation frequencies that overlap with the 900 MHz band. Non-linear distortion producing the intermodulation products is produced by amplifying equipment of overall gain 20 dB and third order intercept point 35 dBm. If the carriers are input to the system at a power level of 5 dBm, what will be the power of the third order intermodulation products?



7.5.2 ANTENNA PATTERNS

The H plane patterns shown below are for antennas of beam width 16, 26, 60 and 86 degrees and gains of 11, 13, 15 and 18 dBd (not in that order). Suggest a possible beamwidth and gain for each antenna.



7.5.3 BASE STATION EQUIPMENT – POWER LOSS CALCULATION

Calculate the power in dBm supplied to the antenna from one TRX in this system:

TRX output power: 5 W Hybrid combiner loss: 3.2 dB Duplexer insertion loss: 1 dB Cable loss at 900 MHz: 6 dB per 100m Height of tower: 20m Length of feeder from equipment to tower base: 10m Allowance for bends and cable routing: 5m Loss per connector: 0.1 dB

TRX Hybrid Combiner

TRX

TRX

TRX

Hybrid Combiner

Hybrid Combiner Duplexer Feeder cable



7.5.4 CHOICE OF CELL CONFIGURATION

Coverage is to be provided over a small area such that the range from the proposed transmitter site is approximately 100 metres. Each cell can be allocated two carriers that can then serve 15 traffic channels (timeslots). Suggest appropriate cell configurations (including BTS Tx power) if the offered traffic is expected to be: 4 Erlangs 12 Erlangs Assume that the maximum path loss at the cell edge is 102 dB. Additional information:

Omni antenna gain 12 dBi Sectored antenna gain 17 dBi Feeder and Combiner Losses 8 dB Mobile Threshold -90 dBm

Link balance can be maintained on a particular cell if the BTS transmit power is no more than 8 dB higher than the mobile transmit power. If uplink diversity is used, the BTS power can be 10 dB higher than the mobile transmit power. Determine the maximum coverage range from the cell with and without diversity given the following information:



7.5.5 EFFECTS OF DIVERSITY

Link balance can be maintained on a particular cell if the BTS transmit power is no more than 8 dB higher than the mobile transmit power. If uplink diversity is used, the BTS power can be 10 dB higher than the mobile transmit power. Determine the maximum coverage range from the cell with and without diversity given the following information:

Mobile Transmit Power 33 dBm Path Loss Model L = 137 + 35 log (R)

R = 10(L-137)/35 Mobile Threshold -92 dBm Combiner and Feeder Losses 8 dB Antenna Gain 18 dBi



Appendix A Model Tuning Demonstration Procedure

Model Calibration ExerciseModel Calibration Exercise

• In this exercise you will calibrate an empirical propagation model at 900 MHz.

• Whilst the results will vary with frequency, the calibration porcess remains the same

• Procedure:• Start Enterprise

• Log into the database• Enter User Id and Password using values provided by the trainer• Start the Project.

Firstly, we have to check that a propagation model exists. In the tools menu, click on “Propagation Model Editor”. The “900 MHz” model should already exist. Ensure that all categories on the Clutter tab are set to zero; Diffraction is set to “Epstein-Peterson”; Effective Antenna Height is set to “relative”. Finally click on the Path Loss tab and set the values to correspond with those given on the slide.

Create a Propagation ModelCreate a Propagation Model

• Add a new propagation model.• Type - Standard macrocell• Name 900MHz

• Set up a propagation model with the default parameters.

Parameter SettingModel Type Standard MacrocellFrequency 900

Mobile Rx Height 1.5Effective Earth Radius 8491.2

K1 135K2 38K3 -2.55K4 0K5 -13.82K6 -6.55K7 0.7

Eff. Ant. Height RelativeDiffraction Epstein Peterson

Merge knife edges 0

g



Load a CW Measurement FileLoad a CW Measurement File

• Open the CW measurement analysis window.

• Use the Add button to load the CW file.

• Use the options button to check the CW measurement options.• Model

20m resolution.

900 MHz prediction model.

• FilterDeselect all clutter types.

Radius 0 » 100000m.

Signal -110dBm » -40dBm.Visibility: Check both boxes.

• DisplayCheck the “Overall Summary” and “Clutter Summary” boxes.

The “CW Measurement Analysis” window is found under the Tools menu. Having selected this option follow the steps below: 1. Click on “Add” to load the CW file. It will be necessary to change the “file type” to “Signia” in order to see the required file: “cw.hd”. Open this file (its name should now appear in the CW Measurements Analysis window). 2. Select ‘Options’ and complete the following:

a. Model: • Set the map data resolution to an appropriate value (20m – 50m generally). • Ensure the prediction model is set to GSM 900.

b. Filter:: • Set radius values to Min=0 and Max = 100000. • Set Signal values to Min =-110 and Max = -40. • Visibility – check LOS and NLOS boxes • Ensure all clutter types are deselected.

3. Select ‘Analyse’ and complete the following

a. Ensure Display Mode is set to ‘LL’ b. Ensure ‘Overall Summary’ and ‘Clutter Summary’ boxes are ticked.

Note that you may not get as many clutter categories reported on as shown in the slide above. They may all have more than 100 readings in which case the next slide can be ignored.



Perform a Preliminary Analysis (2)Perform a Preliminary Analysis (2)

• Open the “CW measurement options” window. Highlight all the invalid clutter types on the “Filter” tab.

• These clutter types will be excluded from further analysis.

• The final propagation model will not be valid for these clutter types.

• This is one reason why careful selection of the drive route is important.

• Perform the analysis a second time to check that only valid clutter types remain.


• Use the “Graph” button to plot:• Received Level vs log(distance)

• Error vs log(distance)

• These can be used to spot potential problems with CW measurement files.

• The example here shows a potential problem possibly caused by collecting data in underpasses and road cuttings. Such measurements should be removed prior to calibration.

Examining the report we can see that the Mean and Standard Deviation of the error is reported. The objective of a tuning exercise is to reduce the mean to zero and make the Standard Deviation as small as possible. Note that, if the mean is zero, the standard deviation of the error will equal the rms error.



The table below is used to test the effectiveness of modifying the K values. The closer the ‘Mean Error’ and ‘Std.Dev.Err’ are to zero, the more accurately the model will represent real-world propagation characteristics.


• Use of the ‘Analyse’ button will produce a table showing the following information:

0.81959.114.3-11.02763urban

0.52756.69.6-7.01646suburban

0.22831.912.6-12.419denseforest

0.81396.811.1-8.8659openland

Corr. Coeff.Std.Dev. ErrorRMS ErrorMean ErrorNum. BinsClutter:

0.80408.312.5-9.45087GSM 900 URBAN MODEL

Corr. Coeff.Std.Dev. ErrorRMS ErrorMean ErrorNum. BinModel

• The two key parameters are ‘Mean Error’ and ‘St.Dev.Error

• The aim of propagation model tuning is to reduce these two values to the minimum possible

• This will result in a propagation model which matched the real-world environment as closely as possible

k1 is simply an offset, so reducing the mean error to zero is a trivial matter. Do this by altering k1 by an amount equal to the mean error reported. Check that the error is now zero.

Model Calibration (1)Model Calibration (1)

• The propagation model can now be calibrated.

• Mostly a trial and error process.• Change one model parameter at a time.

• Re-analyse the modified propagation model and see if the model improves ordeteriorates.

• Repeat the previous two steps until the error has been minimised for that parameter.

• Moving on to another parameter.• Changing one parameter might affect the optimum value of another parameter

so when all parameters have been calibrated the process might need repeating until convergence has been reached.



Now we must try and reduce the standard deviation by tuning the other parameters. k2 affects the slope of the graph with distance. At first it is set to 38. Vary this between 38 and 58 to see that the SD reaches a minimum. Notice that when k2 has been changed, the mean error is no longer zero. For this reason, adjusting the mean error is usually one of the last operations. Examining the other terms; k3 and k4 govern the affect of mobile height which was kept constant for the measurements shown here and are therefore not tuneable. The process would involve tuning k5 then k6 followed by k2 and so on until the standard deviation is minimised. It is possible, however, to tune the parameter k7. This is a factor that reduces the diffraction loss predicted. This can be appropriate when the field strength in the shadow of an obstacle is enhanced by either reflections or diffraction around the side of the obstacle.



Appendix B Erlang B Tables

n Grade of Service n

0.00001 0.00005 0.0001 0.0005 0.001 0.002 0.003 0.004 0.005 0.006 1 .00001 .00005 .00010 .00050 .00100 .00200 .00301 .00402 .00503 .00604 1 2 .00448 .01005 .01425 .03213 .04576 .06534 .08064 .09373 .10540 .11608 2 3 .03980 .06849 .08683 .15170 .19384 .24872 .28851 .32099 .34900 .37395 3 4 .12855 .19554 .23471 .36236 .43927 .53503 .60209 .65568 .70120 .74124 4 5 .27584 .38851 .45195 .64857 .76212 .89986 .99446 1.0692 1.1320 1.1870 5 6 .47596 .63923 .72826 .99567 1.1459 1.3252 1.4468 1.5421 1.6218 1.6912 6 7 .72378 .93919 1.0541 1.3922 1.5786 1.7984 1.9463 2.0614 2.1575 2.2408 7 8 1.0133 1.2816 1.4219 1.8298 2.0513 2.3106 2.4837 2.6181 2.7299 2.8266 8 9 1.3391 1.6595 1.8256 2.3016 2.5575 2.8549 3.0526 3.2057 3.3326 3.4422 9

10 1.6970 2.0689 2.2601 2.8028 3.0920 3.4265 3.6480 3.8190 3.9607 4.0829 10 11 2.0849 2.5059 2.7216 3.3294 3.6511 4.0215 4.2661 4.4545 4.6104 4.7447 11 12 2.4958 2.9671 3.2072 3.8781 4.2314 4.6368 4.9038 5.1092 5.2789 5.4250 12 13 2.9294 3.4500 3.7136 4.4465 4.8306 5.2700 5.5588 5.7807 5.9638 6.1214 13 14 3.3834 3.9523 4.2388 5.0324 5.4464 5.9190 6.2291 6.4670 6.6632 6.8320 14 15 3.8559 4.4721 4.7812 5.6339 6.0772 6.5822 6.9130 7.1665 7.3755 7.5552 15 16 4.3453 5.0079 5.3390 6.2496 6.7215 7.2582 7.6091 7.8780 8.0995 8.2898 16 17 4.8502 5.5583 5.9110 6.8782 7.3781 7.9457 8.3164 8.6003 8.8340 9.0347 17 18 5.3693 6.1220 6.4959 7.5186 8.0459 8.6437 9.0339 9.3324 9.5780 9.7889 18 19 5.9016 6.6980 7.0927 8.1698 8.7239 9.3515 9.7606 10.073 10.331 10.552 19 20 6.4460 7.2854 7.7005 8.8310 9.4115 10.068 10.496 10.823 11.092 11.322 20 21 7.0017 7.8834 8.3186 9.5014 10.108 10.793 11.239 11.580 11.860 12.100 21 22 7.5680 8.4926 8.9462 10.180 10.812 11.525 11.989 12.344 12.635 12.885 22 23 8.1443 9.1095 9.5826 10.868 11.524 12.265 12.746 13.114 13.416 13.676 23 24 8.7298 9.7351 10.227 11.562 12.243 13.011 13.510 13.891 14.204 14.472 24 25 9.3240 10.369 10.880 12.264 12.969 13.763 14.279 14.673 14.997 15.274 25 26 9.9265 11.010 11.540 12.972 13.701 14.522 15.054 15.461 15.795 16.081 26 27 10.537 11.659 12.207 13.686 14.439 15.285 15.835 16.254 16.598 16.893 27 28 11.154 12.314 12.880 14.406 15.182 16.054 16.620 17.051 17.406 17.709 28 29 11.779 12.976 13.560 15.132 15.930 16.828 17.410 17.853 18.218 18.530 29 30 12.417 13.644 14.246 15.863 16.684 17.606 18.204 18.660 19.034 19.355 30 31 13.054 14.318 14.937 16.599 17.442 18.389 19.002 19.470 19.854 20.183 31 32 13.697 14.998 15.633 17.340 18.205 19.176 19.805 20.284 20.678 21.015 32 33 14.346 15.682 16.335 18.085 18.972 19.966 20.611 21.102 21.505 21.850 33 34 15.001 16.372 17.041 18.835 19.743 20.761 21.421 21.923 22.336 22.689 34 35 15.660 17.067 17.752 19.589 20.517 21.559 22.234 22.748 23.169 23.531 35 36 16.325 17.766 18.468 20.347 21.296 22.361 23.050 23.575 24.006 24.376 36 37 16.995 18.470 19.188 21.108 22.078 23.166 23.870 24.406 24.846 25.223 37 38 17.669 19.178 19.911 21.873 22.864 23.974 24.692 25.240 25.689 26.074 38 39 18.348 19.890 20.640 22.642 23.652 24.785 25.518 26.076 26.534 26.926 39 40 19.031 20.606 21.372 23.414 24.444 25.599 26.346 26.915 27.382 27.782 40 41 19.718 21.326 22.107 24.189 25.239 26.416 27.177 27.756 28.232 28.640 41 42 20.409 22.049 22.846 24.967 26.037 27.235 28.010 28.600 29.085 29.500 42 43 21.104 22.776 23.587 25.748 26.837 28.057 28.846 29.447 29.940 30.362 43 44 21.803 23.507 24.333 26.532 27.641 28.882 29.684 30.295 30.797 31.227 44 45 22.505 24.240 25.081 27.319 28.447 29.708 30.525 31.146 31.656 32.093 45 46 23.211 24.977 25.833 28.109 29.255 30.538 31.367 31.999 32.517 32.962 46 47 23.921 25.717 26.587 28.901 30.066 31.369 32.212 32.854 33.381 33.832 47 48 24.633 26.460 27.344 29.696 30.879 32.203 33.059 33.711 34.246 34.704 48 49 25.349 27.206 28.104 30.493 31.694 33.039 33.908 34.570 35.113 35.578 49 50 26.067 27.954 28.867 31.292 32.512 33.876 34.759 35.431 35.982 36.454 50 51 26.789 28.706 29.632 32.094 33.332 34.716 35.611 36.293 36.852 37.331 51 0.00001 0.00005 0.0001 0.0005 0.001 0.002 0.003 0.004 0.005 0.006




0.007 0.008 0.009 0.01 0.02 0.03 0.05 0.1 0.2 0.4 1 .00705 .00806 .00908 .01010 .02041 .03093 .05263 .11111 .25000 .66667 1 2 .12600 .13532 .14416 .15259 .22347 .28155 .38132 .59543 1.0000 2.0000 2 3 .39664 .41757 .43711 .45549 .60221 .71513 .89940 1.2708 1.9299 3.4798 3 4 .77729 .81029 .84085 .86942 1.0923 1.2589 1.5246 2.0454 2.9452 5.0210 4 5 1.2362 1.2810 1.3223 1.3608 1.6571 1.8752 2.2185 2.8811 4.0104 6.5955 5 6 1.7531 1.8093 1.8610 1.9090 2.2759 2.5431 2.9603 3.7584 5.1086 8.1907 6 7 2.3149 2.3820 2.4437 2.5009 2.9354 3.2497 3.7378 4.6662 6.2302 9.7998 7 8 2.9125 2.9902 3.0615 3.1276 3.6271 3.9865 4.5430 5.5971 7.3692 11.419 8 9 3.5395 3.6274 3.7080 3.7825 4.3447 4.7479 5.3702 6.5464 8.5217 13.045 9

10 4.1911 4.2889 4.3784 4.4612 5.0840 5.5294 6.2157 7.5106 9.6850 14.677 10 11 4.8637 4.9709 5.0691 5.1599 5.8415 6.3280 7.0764 8.4871 10.857 16.314 11 12 5.5543 5.6708 5.7774 5.8760 6.6147 7.1410 7.9501 9.4740 12.036 17.954 12 13 6.2607 6.3863 6.5011 6.6072 7.4015 7.9667 8.8349 10.470 13.222 19.598 13 14 6.9811 7.1155 7.2382 7.3517 8.2003 8.8035 9.7295 11.473 14.413 21.243 14 15 7.7139 7.8568 7.9874 8.1080 9.0096 9.6500 10.633 12.484 15.608 22.891 15 16 8.4579 8.6092 8.7474 8.8750 9.8284 10.505 11.544 13.500 16.807 24.541 16 17 9.2119 9.3714 9.5171 9.6516 10.656 11.368 12.461 14.522 18.010 26.192 17 18 9.9751 10.143 10.296 10.437 11.491 12.238 13.385 15.548 19.216 27.844 18 19 10.747 10.922 11.082 11.230 12.333 13.115 14.315 16.579 20.424 29.498 19 20 11.526 11.709 11.876 12.031 13.182 13.997 15.249 17.613 21.635 31.152 20 21 12.312 12.503 12.677 12.838 14.036 14.885 16.189 18.651 22.848 32.808 21 22 13.105 13.303 13.484 13.651 14.896 15.778 17.132 19.692 24.064 34.464 22 23 13.904 14.110 14.297 14.470 15.761 16.675 18.080 20.737 25.281 36.121 23 24 14.709 14.922 15.116 15.295 16.631 17.577 19.031 21.784 26.499 37.779 24 25 15.519 15.739 15.939 16.125 17.505 18.483 19.985 22.833 27.720 39.437 25 26 16.334 16.561 16.768 16.959 18.383 19.392 20.943 23.885 28.941 41.096 26 27 17.153 17.387 17.601 17.797 19.265 20.305 21.904 24.939 30.164 42.755 27 28 17.977 18.218 18.438 18.640 20.150 21.221 22.867 25.995 31.388 44.414 28 29 18.805 19.053 19.279 19.487 21.039 22.140 23.833 27.053 32.614 46.074 29 30 19.637 19.891 20.123 20.337 21.932 23.062 24.802 28.113 33.840 47.735 30 31 20.473 20.734 20.972 21.191 22.827 23.987 25.773 29.174 35.067 49.395 31 32 21.312 21.580 21.823 22.048 23.725 24.914 26.746 30.237 36.295 51.056 32 33 22.155 22.429 22.678 22.909 24.626 25.844 27.721 31.301 37.524 52.718 33 34 23.001 23.281 23.536 23.772 25.529 26.776 28.698 32.367 38.754 54.379 34 35 23.849 24.136 24.397 24.638 26.435 27.711 29.677 33.434 39.985 56.041 35 36 24.701 24.994 25.261 25.507 27.343 28.647 30.657 34.503 41.216 57.703 36 37 25.556 25.854 26.127 26.378 28.254 29.585 31.640 35.572 42.448 59.365 37 38 26.413 26.718 26.996 27.252 29.166 30.526 32.624 36.643 43.680 61.028 38 39 27.272 27.583 27.867 28.129 30.081 31.468 33.609 37.715 44.913 62.690 39 40 28.134 28.451 28.741 29.007 30.997 32.412 34.596 38.787 46.147 64.353 40 41 28.999 29.322 29.616 29.888 31.916 33.357 35.584 39.861 47.381 66.016 41 42 29.866 30.194 30.494 30.771 32.836 34.305 36.574 40.936 48.616 67.679 42 43 30.734 31.069 31.374 31.656 33.758 35.253 37.565 42.011 49.851 69.342 43 44 31.605 31.946 32.256 32.543 34.682 36.203 38.557 43.088 51.086 71.006 44 45 32.478 32.824 33.140 33.432 35.607 37.155 39.550 44.165 52.322 72.669 45 46 33.353 33.705 34.026 34.322 36.534 38.108 40.545 45.243 53.559 74.333 46 47 34.230 34.587 34.913 35.215 37.462 39.062 41.540 46.322 54.796 75.997 47 48 35.108 35.471 35.803 36.109 38.392 40.018 42.537 47.401 56.033 77.660 48 49 35.988 36.357 36.694 37.004 39.323 40.975 43.534 48.481 57.270 79.324 49 50 36.870 37.245 37.586 37.901 40.255 41.933 44.533 49.562 58.508 80.988 50 51 37.754 38.134 38.480 38.800 41.189 42.892 45.533 50.644 59.746 82.652 51 0.007 0.008 0.009 0.01 0.02 0.03 0.05 0.1 0.2 0.4




0.00001 0.00005 0.0001 0.0005 0.001 0.002 0.003 0.004 0.005 0.006 51 26.789 28.706 29.632 32.094 33.332 34.716 35.611 36.293 36.852 37.331 51 52 27.513 29.459 30.400 32.898 34.153 35.558 36.466 37.157 37.724 38.211 52 53 28.241 30.216 31.170 33.704 34.977 36.401 37.322 38.023 38.598 39.091 53 54 28.971 30.975 31.942 34.512 35.803 37.247 38.180 38.891 39.474 39.973 54 55 29.703 31.736 32.717 35.322 36.631 38.094 39.040 39.760 40.351 40.857 55 56 30.438 32.500 33.494 36.134 37.460 38.942 39.901 40.630 41.229 41.742 56 57 31.176 33.266 34.273 36.948 38.291 39.793 40.763 41.502 42.109 42.629 57 58 31.916 34.034 35.055 37.764 39.124 40.645 41.628 42.376 42.990 43.516 58 59 32.659 34.804 35.838 38.581 39.959 41.498 42.493 43.251 43.873 44.406 59 60 33.404 35.577 36.623 39.401 40.795 42.353 43.360 44.127 44.757 45.296 60 61 34.151 36.351 37.411 40.222 41.633 43.210 44.229 45.005 45.642 46.188 61 62 34.900 37.127 38.200 41.045 42.472 44.068 45.099 45.884 46.528 47.081 62 63 35.651 37.906 38.991 41.869 43.313 44.927 45.970 46.764 47.416 47.975 63 64 36.405 38.686 39.784 42.695 44.156 45.788 46.843 47.646 48.305 48.870 64 65 37.160 39.468 40.579 43.523 45.000 46.650 47.716 48.528 49.195 49.766 65 66 37.918 40.252 41.375 44.352 45.845 47.513 48.591 49.412 50.086 50.664 66 67 38.677 41.038 42.173 45.183 46.692 48.378 49.467 50.297 50.978 51.562 67 68 39.439 41.825 42.973 46.015 47.540 49.243 50.345 51.183 51.872 52.462 68 69 40.202 42.615 43.775 46.848 48.389 50.110 51.223 52.071 52.766 53.362 69 70 40.967 43.405 44.578 47.683 49.239 50.979 52.103 52.959 53.662 54.264 70 71 41.734 44.198 45.382 48.519 50.091 51.848 52.984 53.848 54.558 55.166 71 72 42.502 44.992 46.188 49.357 50.944 52.718 53.865 54.739 55.455 56.070 72 73 43.273 45.787 46.996 50.195 51.799 53.590 54.748 55.630 56.354 56.974 73 74 44.045 46.585 47.805 51.035 52.654 54.463 55.632 56.522 57.253 57.880 74 75 44.818 47.383 48.615 51.877 53.511 55.337 56.517 57.415 58.153 58.786 75 76 45.593 48.183 49.427 52.719 54.369 56.211 57.402 58.310 59.054 59.693 76 77 46.370 48.985 50.240 53.563 55.227 57.087 58.289 59.205 59.956 60.601 77 78 47.149 49.787 51.054 54.408 56.087 57.964 59.177 60.101 60.859 61.510 78 79 47.928 50.592 51.870 55.254 56.948 58.842 60.065 60.998 61.763 62.419 79 80 48.710 51.397 52.687 56.101 57.810 59.720 60.955 61.895 62.668 63.330 80 81 49.492 52.204 53.506 56.949 58.673 60.600 61.845 62.794 63.573 64.241 81 82 50.277 53.012 54.325 57.798 59.537 61.480 62.737 63.693 64.479 65.153 82 83 51.062 53.822 55.146 58.649 60.403 62.362 63.629 64.594 65.386 66.065 83 84 51.849 54.633 55.968 59.500 61.269 63.244 64.522 65.495 66.294 66.979 84 85 52.637 55.445 56.791 60.352 62.135 64.127 65.415 66.396 67.202 67.893 85 86 53.427 56.258 57.615 61.206 63.003 65.011 66.310 67.299 68.111 68.808 86 87 54.218 57.072 58.441 62.060 63.872 65.897 67.205 68.202 69.021 69.724 87 88 55.010 57.887 59.267 62.915 64.742 66.782 68.101 69.106 69.932 70.640 88 89 55.804 58.704 60.095 63.772 65.612 67.669 68.998 70.011 70.843 71.557 89 90 56.598 59.526 60.923 64.629 66.484 68.556 69.896 70.917 71.755 72.474 90 91 57.394 60.344 61.753 65.487 67.356 69.444 70.794 71.823 72.668 73.393 91 92 58.192 61.164 62.584 66.346 68.229 70.333 71.693 72.730 73.581 74.311 92 93 58.990 61.985 63.416 67.206 69.103 71.222 72.593 73.637 74.495 75.231 93 94 59.789 62.807 64.248 68.067 69.978 72.113 73.493 74.545 75.410 76.151 94 95 60.590 63.630 65.082 68.928 70.853 73.004 74.394 75.454 76.325 77.072 95 96 61.392 64.454 65.917 69.791 71.729 73.896 75.296 76.364 77.241 77.993 96 97 62.194 65.279 66.752 70.654 72.606 74.788 76.199 77.274 78.157 78.915 97 98 62.998 66.105 67.589 71.518 73.484 75.681 77.102 78.185 79.074 79.837 98 99 63.803 66.932 68.426 72.383 74.363 76.575 78.006 79.096 79.992 80.760 99

100 64.609 67.760 69.265 73.248 75.242 77.469 78.910 80.008 80.910 81.684 100 101 65.416 68.589 70.104 74.115 76.122 78.364 79.815 80.920 81.829 82.608 101

0.00001 0.00005 0.0001 0.0005 0.001 0.003 0.004 0.005 0.006




0.007 0.008 0.009 0.01 0.02 0.03 0.05 0.1 0.2 0.4 51 37.754 38.134 38.480 38.800 41.189 42.892 45.533 50.644 59.746 82.652 51 52 38.639 39.024 39.376 39.700 42.124 43.852 46.533 51.726 60.985 84.317 52 53 39.526 39.916 40.273 40.602 43.060 44.813 47.534 52.808 62.224 85.981 53 54 40.414 40.810 41.171 41.505 43.997 45.776 48.536 53.891 63.463 87.645 54 55 41.303 41.705 42.071 42.409 44.936 46.739 49.539 54.975 64.702 89.310 55 56 42.194 42.601 42.972 43.315 45.875 47.703 50.543 56.059 65.942 90.974 56 57 43.087 43.499 43.875 44.222 46.816 48.669 51.548 57.144 67.181 92.639 57 58 43.980 44.398 44.778 45.130 47.758 49.635 52.553 58.229 68.421 94.303 58 59 44.875 45.298 45.683 46.039 48.700 50.602 53.559 59.315 69.662 95.968 59 60 45.771 46.199 46.589 46.950 49.644 51.570 54.566 60.401 70.902 97.633 60 61 46.669 47.102 47.497 47.861 50.589 52.539 55.573 61.488 72.143 99.297 61 62 47.567 48.005 48.405 48.774 51.534 53.508 56.581 62.575 73.384 100.96 62 63 48.467 48.910 49.314 49.688 52.481 54.478 57.590 63.663 74.625 102.63 63 64 49.368 49.816 50.225 50.603 53.428 55.450 58.599 64.750 75.866 104.29 64 65 50.270 50.723 51.137 51.518 54.376 56.421 59.609 65.839 77.108 105.96 65 66 51.173 51.631 52.049 52.435 55.325 57.394 60.619 66.927 78.350 107.62 66 67 52.077 52.540 52.963 53.353 56.275 58.367 61.630 68.016 79.592 109.29 67 68 52.982 53.450 53.877 54.272 57.226 59.341 62.642 69.106 80.834 110.95 68 69 53.888 54.361 54.793 55.191 58.177 60.316 63.654 70.196 82.076 112.62 69 70 54.795 55.273 55.709 56.112 59.129 61.291 64.667 71.286 83.318 114.28 70 71 55.703 56.186 56.626 57.033 60.082 62.267 65.680 72.376 84.561 115.95 71 72 56.612 57.099 57.545 57.956 61.036 63.244 66.694 73.467 85.803 117.61 72 73 57.522 58.014 58.464 58.879 61.990 64.221 67.708 74.558 87.046 119.28 73 74 58.432 58.930 59.384 59.803 62.945 65.199 68.723 75.649 88.289 120.94 74 75 59.344 59.846 60.304 60.728 63.900 66.177 69.738 76.741 89.532 122.61 75 76 60.256 60.763 61.226 61.653 64.857 67.156 70.753 77.833 90.776 124.27 76 77 61.169 61.681 62.148 62.579 65.814 68.136 71.769 78.925 92.019 125.94 77 78 62.083 62.600 63.071 63.506 66.771 69.116 72.786 80.018 93.262 127.61 78 79 62.998 63.519 63.995 64.434 67.729 70.096 73.803 81.110 94.506 129.27 79 80 63.914 64.439 64.919 65.363 68.688 71.077 74.820 82.203 95.750 130.94 80 81 64.830 65.360 65.845 66.292 69.647 72.059 75.838 83.297 96.993 132.60 81 82 65.747 66.282 66.771 67.222 70.607 73.041 76.856 84.390 98.237 134.27 82 83 66.665 67.204 67.697 68.152 71.568 74.024 77.874 85.484 99.481 135.93 83 84 67.583 68.128 68.625 69.084 72.529 75.007 78.893 86.578 100.73 137.60 84 85 68.503 69.051 69.553 70.016 73.490 75.990 79.912 87.672 101.97 139.26 85 86 69.423 69.976 70.481 70.948 74.452 76.974 80.932 88.767 103.21 140.93 86 87 70.343 70.901 71.410 71.881 75.415 77.959 81.952 89.861 104.46 142.60 87 88 71.264 71.827 72.340 72.815 76.378 78.944 82.972 90.956 105.70 144.26 88 89 72.186 72.753 73.271 73.749 77.342 79.929 83.993 92.051 106.95 145.93 89 90 73.109 73.680 74.202 74.684 78.306 80.915 85.014 93.146 108.19 147.59 90 91 74.032 74.608 75.134 75.620 79.271 81.901 86.035 94.242 109.44 149.26 91 92 74.956 75.536 76.066 76.556 80.236 82.888 87.057 95.338 110.68 150.92 92 93 75.880 76.465 76.999 77.493 81.201 83.875 88.079 96.434 111.93 152.59 93 94 76.805 77.394 77.932 78.430 82.167 84.862 89.101 97.530 113.17 154.26 94 95 77.731 78.324 78.866 79.368 83.134 85.850 90.123 98.626 114.42 155.92 95 96 78.657 79.255 79.801 80.306 84.100 86.838 91.146 99.722 115.66 157.59 96 97 79.584 80.186 80.736 81.245 85.068 87.826 92.169 100.82 116.91 159.25 97 98 80.511 81.117 81.672 82.184 86.035 88.815 93.193 101.92 118.15 160.92 98 99 81.439 82.050 82.608 83.124 87.003 89.804 94.216 103.01 119.40 162.59 99

100 82.367 82.982 83.545 84.064 87.972 90.794 95.240 104.11 120.64 164.25 100 101 83.296 83.916 84.482 85.005 88.941 91.784 96.265 105.21 121.89 165.92 101

0.007 0.008 0.009 0.01 0.02 0.03 0.05 0.1 0.2 0.4



Appendix C: Solutions to Questions

Section 2: Power Budgets 1.

Summing the losses: 146 + 7 = 153 dB Summing the gains: 17 + 2 = 19 dBi Net loss = 153-19 = 134 dB Required Tx Power = -102 + 134 = 32 dBm

2.

Notice that all the differences are “in favour” of the uplink. Hence the downlink will require a bigger transmit power Difference in sensitivity = 3 dB Diversity gain = 2 dB Combiner loss = 4 dB Total of above = 9 dB Required downlink transmit power = 33 + 9 = 42 dBm.

SECTION 3 Exercise 3.1 - Frequency Re-use Cluster Sizes (a) Typical GSM frequency re-use cluster sizes are: 3, 4, 7, 9, 12 e.g. 3/9, 4/12 patterns. (b) i) analogue system requires a minimum C/I of about 20 dB. From the table in the notes, when x = 3.5, a cluster size of 12 gives C/I of 19.45dB. Re-use distance, km606x1012x310N3RD ==== ii) Digital systems can cope with C/I of about 9 dB. From table, cluster size of 3 gives C/I of 8.9 dB. Re-use distance, km303x103x310N3RD ====



Exercise 3.2 - Frequency Planning Adjustments Consider the change in C/A and C/I caused by moving either carrier. B2 carriers are adjacent to A2 and C2 carriers – both of which border on the B1 cell. B3 carriers are adjacent to A3 and C3 carriers – only C3 borders on the B1 cell. Thus from the decrease in C/A, B3 is a better prospect. Both moves will place a carrier (either B2 or B3) closer to another of the same group – either the B2 to the north west (west of A1) or B3 to the north east (east of D3). (These are not shown explicitly on the diagram.) These will cause similar decreases in C/I. On balance the B3 move is better although it will cause increased interference.

SECTION 5 Section 5 Latitude, Longitude and Grid References 1. Calculate the distance between the points A and B given their coordinates.

A. 36.5382°E 47.3421°N B. 37.1486°E 46.7593°N

Distance is represented by 0.5828 degrees north-south and 0.6104 degrees east-west. Each degree north-south represents 111 km. 0.5828 degrees represents 64.7 km. Each degree east-west represents 111 x cos 47 = 75.7 km. 0.6104 degrees represents 46.2 km.

By Pythagoras; distance = 5.792.467.64 22 =+ km. 2. A point C has the latitude- longitude coordinates 23.2186°E 19.4783°N. Point D is 86 km from

point C at a bearing of 041°. Determine the coordinates of point D.

Distance east-west of Point D from Point C is 86 sin 41 = 56.42 km. 1 degree represents 111 x cos 19.48 = 104.6 km. 56.42 km represents 0.5392 degrees. 23.2186 + 0.5392 =23.7578 degrees. Distance north-south of point D is 86 cos 41 = 64.91 km. 1 degree represents 111 km. 64.91 km represents 0.5847 degrees. 19.4783 + 0.5847 = 20.0630 degrees. New coordinates are: 20.0630°N 23.7578°E



3. What problems would occur if the Digital Map data used in planning and the GPS receiver used in the field had different Ellipsoids and/or Datums?

The location in the field would not correspond with that expected from planning on the map data. The results could include specified locations being interpreted in the field as in the middle of roads etc. Additionally, rural sites may be located at positions with different heights from those expected.

4. What problems would occur if the scanned map backdrop and the digital terrain map used

different projections?

Different projections will result in heights and road vectors not corresponding between the DTM and the scanned map. Also, clutter categories on the DTM will not correspond with the correct locations on the scanned map.

SECTION 6 Exercise 6.1 - Base Station Positioning

. 1. On the bank of a wide river Path loss across water much lower than land. Directional or down tilted antenna may be needed to confine coverage to one bank Effect could be used to provide coverage for ferry passengers

2. In a hilly countryside region Dead spots and shadow regions BTS on top of hill generally better Reflections from hills may cause time dispersion problems

3. To provide coverage for a road through hilly countryside Need to fill in gaps caused by shadow areas Directional antennas (microcells) ‘back to back’ along road

4. In a long straight road in town Microcells below building height Directional antennas Use canyon effect Possible reflections into side streets Adjust power to avoid overlapping coverage at junctions causing handovers Macro/micro cell handover strategies for vehicular and pedestrian users



5. At a cross roads in town

Omni antenna near centre of cross roads Do not use overlapping directional antennas - handovers

6. To provide coverage for an office block Down tilt outdoor antennas for in-building coverage Extra path losses in building Use picocells inside building – distributed antenna, leaky feeder

cell planning principles

Technology