gsm training 2[1]

GSM SystemsGSM Systems

RF Network Design RF Network Design

IntroductionIntroduction

The high level life cycle of the RF network planning process can be The high level life cycle of the RF network planning process can be summarised as follows :summarised as follows :--

• To help the operator to identify their RF design requirement

• Optional

• Discuss and agree RF

• Issuing of search ring• Cand. assessment• Site survey, design, approval

• Drive test (optional)

Comparative Analysis

Site Realisation

Slide No.2

• Discuss and agree RF design parameters, assumptions and objectives with the customer

• Coverage requirement• Traffic requirement• Various level of design (ROM to detail RF design)

• Drive test (optional)

• Frequency plan• Neighbour list• RF OMC data• Optimisation

RF Design requirement

RF Design

RF Design Implementation

Comparative AnalysisComparative Analysis

This is an optional stepThis is an optional step

This is intended to :This is intended to :--

• Help an existing operator in building/expanding their network

• Help a new operator in identifying their RF network requirement, e.g.

where their network should be built

Slide No.3

For the comparative analysis, we would need to :For the comparative analysis, we would need to :--

• Identify all network that are competitors to the customer

• Design drive routes that take in the high density traffic areas of interest

• Include areas where the customer has no or poor service and the

competitors have service

Comparative AnalysisComparative Analysis

The result of the analysis should include :The result of the analysis should include :--

For an existing operatorFor an existing operator

• All problems encountered in the customer’s network

• All areas where the customer has no service and a competitor does

• Recommendations for solving any coverage and quality problems

Slide No.4

For a new operatorFor a new operator

• Strengths and weaknesses in the competitors network

• Problem encountered in the competitors network

RF Network Design InputsRF Network Design Inputs

The RF design inputs can be divided into :The RF design inputs can be divided into :--

• Coverage requirements

– Target coverage areas

– Service types for the target coverage areas. These should be marked

geographically

– Coverage area probability

– Penetration Loss of buildings and in-cars

Slide No.5

– Penetration Loss of buildings and in-cars

• Capacity requirements

– Erlang per subscriber during the busy hour

– Quality of service for the air interface, in terms GoS

– Network capacity

• Growth plan - Coverage and Capacity

RF Network Design InputsRF Network Design Inputs

• Available spectrum and frequency usage restriction, if any

• List of available, existing and/or friendly sites that should be included in

the RF design

• Limitation of the quantity of sites and radios, if any

• Quality of Network (C/I values)

Slide No.6

• Related network features (FH, DTX, etc.)

RF Network DesignRF Network Design

There are 2 parts to the RF network design to meet the :There are 2 parts to the RF network design to meet the :--

• Capacity requirement

• Coverage requirement

For the RF Coverage DesignFor the RF Coverage Design

Digitised

DatabasesCW Drive Customer

Slide No.7

RF

Coverage

Design

Link

BudgetPropagation

Model

DatabasesCW Drive Testing

Customer Requirements

CW Drive TestingCW Drive Testing

CW drive test can be used for the following purposes :CW drive test can be used for the following purposes :--

• Propagation model tuning

• Assessment of the suitability of candidate sites, from both coverage and interference aspect

CW drive test process can be broken down to :CW drive test process can be broken down to :--

Test • Equipment required • Power setting

Slide No.8

Test Preparation

Propagation

Test

Data

Processing

• Equipment required

• BTS antenna selection

• Channel selection

• Power setting

• Drive route planning

• Test site selection

• Transmitter setup

• Receiver setup

• Drive test

• Transmitter dismantle

• Measurement averaging

• Report generation

CW Drive Testing CW Drive Testing -- Test PreparationTest Preparation

The test equipment required for the CW drive testing :The test equipment required for the CW drive testing :--

• Receiver with fast scanner

– Example : HP7475A, EXP2000 (LCC) etc.

– The receiver scanner rate should conform to the Lee Criteria of 36 to

50 sample per 40 wavelength

• CW Transmitter

Slide No.9

– Example : Gator Transmitter (BVS), LMW Series Transmitter (CHASE),

TX-1500 (LCC) etc.

• Base Station test antenna

– DB806Y (Decibel-GSM900), 7640 (Jaybeam-GSM1800) etc.

• Accessories

– Including flexible coaxial cable/jumper, Power meter, extended power

cord, GPS, compass, altimeter


Base Station Antenna SelectionBase Station Antenna Selection

• The selection depends on the purpose of the test

• For propagation model tuning, an omni-directional antenna is preferred

• For candidate site testing or verification, the choice of antenna depends

on the type of BTS site that the test is trying to simulate.

– For Omni BTS :

Slide No.10

– For Omni BTS : – Omni antennas with similar vertical beamwidth

– For sectorised BTS– Utilising the same type of antenna is preferred– Omni antenna can also be used, together with the special feature in the

post processing software like CMA (LCC) where different antenna

pattern can be masked on over the measurement data from an omni antenna


Test Site SelectionTest Site Selection

• For propagation model tuning, the test sites should be selected so that :-

– They are distributed within the clutter under study

– The height of the test site should be representative or typical for the

specific clutter

– Preferably not in hilly areas

Slide No.11

• For candidate site testing/verification, the actual candidate site

configuration (height, location) should be used.

• For proposed greenfield sites, a “cherry-picker” will be used.


Frequency Channel SelectionFrequency Channel Selection

• The necessary number of channels need to be identified from the

channels available

– With input from the customer

• The channels used should be free from occupation

– From the guard bands

Slide No.12

– From the guard bands

– Other free channels according to the up-to-date frequency plan

• The channels selected will need to be verified by conducting a pre-test

drive

– It should always precede the actual CW drive test to verify the exact

free frequency to be used

– It should cover the same route of the actual propagation test

– A field strength plot is generated on the collected data to confirm the

channel suitability


Transmit Power SettingTransmit Power Setting

• For propagation model tuning, the maximum transmit power is used

• For candidate site testing, the transmit power of the test transmitter is

determined using the actual BTS link budget to simulate the coverage

• On sites with existing antenna system, it is recommended that the

Slide No.13

• On sites with existing antenna system, it is recommended that the

transmit power to be reduced to avoid interference or inter-modulation to

other networks.

• The amount of reduction is subject to the possibility if separating the test

antenna from the existing antennas


Drive Route DeterminationDrive Route Determination

• The drive route of the data collection is planned prior to the drive test

using a detail road map

– Eliminate duplicate route to reduce the testing time

• For propagation model tuning, each clutter is tested individually and the

drive route for each test site is planned to map the clutter under-study for

the respective sites.

Slide No.14

the respective sites.

• It is important to collect a statistically significant amount of data, typically

a minimum of 300 to 400 data points are required for each clutter

category

• The data should be evenly distributed with respect to distance from the

transmitter

• In practice, the actual drive route will be modified according to the latest

development which was not shown on the map. The actual drive route

taken should be marked on a map for record purposes

CW Drive Testing CW Drive Testing -- Propagation TestPropagation Test

Transmitter Equipment SetupTransmitter Equipment Setup

• Test antenna location

– Free from any nearby obstacle, to ensure free propagation in both

horizontal and vertical dimension

– For sites with existing antennas, precaution should be taken to avoid

possible interference and/or inter-modulation

• Transmitter installation

Slide No.15

• Transmitter installation

• A complete set of 360º photographs of the test location (at the test height) and the antenna setup should be taken for record


Scanning Receiver Setup Scanning Receiver Setup -- HP 7475A Receiver ExampleHP 7475A Receiver Example

HP 7475A ReceiverHP 7475A Receiver

Slide No.16


Scanning Receiver SetupScanning Receiver Setup

• The scanning rate of the receiver should always be set to allow at least

36 sample per 40 wavelength to average out the Rayleigh Fading effect.

For example: scanning rate = 100 sample/s

test frequency = 1800 MHz

therefore, to achieve 36 sample/40 wavelength, the max. speed is =

Slide No.17

• It is recommended that :-

– Beside scanning the test channel, the neighbouring cells is also

monitored. This information can be used to check the coverage overlap

and potential interference

– Check the field strength reading close to the test antenna before

starting the test, it should approach the scanning receiver saturation

hkmsm36/100

0.166740/67.66/52.18 ==

×


Drive TestDrive Test

• Initiate a file to record the measurement with an agreed naming

convention

• Maintain the drive test vehicle speed according to the pre-set scanning

rate

• Follow the pre-plan drive route as closely as possible

• Insert marker wherever necessary during the test to indicate special

Slide No.18

• Insert marker wherever necessary during the test to indicate special

locations such as perceived hot spot, potential interferer etc.

• Monitor the GPS signal and field strength level throughout the test, any

extraordinary reading should be inspected before resuming the test

Dismantling EquipmentDismantling Equipment

• It is recommended to re-confirm the transmit power (as the pre-set value)

before dismantling the transmitter setup

Measurement Data ProcessingMeasurement Data Processing

Data AveragingData Averaging

• This can be done during the drive testing or during the data processing

stage, depending on the scanner receiver and the associated post-

processing software

• The bin size of the distance averaging depends on the size of the human

made structure in the test environment

Slide No.19

Report GenerationReport Generation

• For propagation model tuning, the measurement data is exported into the

planning tool (e.g. Asset)

• Plots can also be generated using the processing tool or using MapInfo

• During the export of the measurement data, it is important to take care of

the coordinate system used, a conversion is necessary if different

coordinate systems are used

Propagation ModelPropagation Model

COST 231 COST 231 -- Hata propagation modelHata propagation model

Lu (dB) = 46.3 + 33.9 log(f) Lu (dB) = 46.3 + 33.9 log(f) -- 13.82 log(Hb) 13.82 log(Hb) -- a(Hm) + [44.9 a(Hm) + [44.9 -- 6.55 log(Hb)] log(d) + Cm6.55 log(Hb)] log(d) + Cm

wherea(Hm) = [1.1*log(f) - 0.7]*Hm - [1.56*log(f) -0.8]

For medium sized city, suburban centres with moderate tree densityCm = 0 dB

Slide No.20

Cm = 0 dB

For metropolitan centresCm = 3 dB

The propagation model applies with condition :The propagation model applies with condition :--

• Frequency of operation (f) : 1500 - 2000 MHz• Base station height (Hb) : 30 - 200 m• Mobile height (Hm) : 1 - 10 m• Distance (d) : 1 - 20 km


Hata ModelHata Model

Lu (dB) = 69.55 + 26.16 log(f) Lu (dB) = 69.55 + 26.16 log(f) -- 13.82 log(Hb) 13.82 log(Hb) -- a(Hm) + [44.9 a(Hm) + [44.9 -- 6.55 log(Hb)] log(d)6.55 log(Hb)] log(d)

For medium-small city

a(Hm) = [1.1 log(f) -0.7] Hm - [1.56 log(f) -0.8]

For large city

Slide No.21

a(Hm) = 8.29 [log(1.54 Hm)]2 - 1.1 for f <= 200 MHza(Hm) = 3.2 [log(11.75 Hm)]2 - 4.97 for f >= 400 MHz

For Suburban

Lsu (dB) = Lu Lsu (dB) = Lu -- 2 [log(f/28)]2 [log(f/28)]22 -- 5.45.4

For Rural (Quasi-open)

Lrqo (dB) = Lu Lrqo (dB) = Lu -- 4.78 [log(f)]4.78 [log(f)]22 + 18.33 log(f) + 18.33 log(f) -- 35.9435.94

For Rural (Open area)

Lrqo (dB) = Lu Lrqo (dB) = Lu -- 4.78 [log(f)]4.78 [log(f)]22 + 18.33 log(f) + 18.33 log(f) -- 40.9440.94


Hata ModelHata Model

The propagation model applies with condition :The propagation model applies with condition :--

• Frequency of operation (f) : 150 - 1000 MHz

• Base station height (Hb) : 30 - 200 m

• Mobile height (Hm) : 1 - 10 m

• Distance (d) : 1 - 20 km

Slide No.22


Standard Macrocell Model for AssetStandard Macrocell Model for Asset

Lp (dB) = K1 + K2 log(d) + K3 Hm + K4 log(Hm) + K5 log(Heff) Lp (dB) = K1 + K2 log(d) + K3 Hm + K4 log(Hm) + K5 log(Heff) + K6 log(Heff) log(d) + K7 Diffraction + Clutter factor+ K6 log(Heff) log(d) + K7 Diffraction + Clutter factor

where Lp, Diffraction, Clutter factor are in dBd, Hm, Heff are in m

• It is based on the Okumura-Hata empirical model, with a number of

Slide No.23

• It is based on the Okumura-Hata empirical model, with a number of additional features to enhance its flexibility

• Known to be valid for frequencies from 150MHz to 2GHz

• Applies in condition :-

– Base station height : 30 - 200 m– Mobile height : 1 - 10 m– Distance : 1 - 20 km

• An optional second intercept and slope (K1, K2) for the creation of a two-piece model with the slope changing at the specified breakpoint distance.

Link BudgetLink Budget

Link Budget Element of a GSM NetworkLink Budget Element of a GSM Network

BTS Antenna Gain Max. Path Loss Fade Margin

LNA

(optional) Penetration Loss

Slide No.24

Feeder Loss

Diversity

Gain

BTS Receiver

Sensitivity

ACE

Loss

BTS Transmit

Power

MS Antenna Gain,

Body and Cable Loss

Mobile Transmit

Power

Mobile Receiver

Sensitivity


BTS Transmit PowerBTS Transmit Power• Maximum transmit power• GSM900 and 1800 networks use radios with 46dBm maximum transmit

power

ACE LossACE Loss• Includes all diplexers, combiners and connectors.• Depends on the ACE configuration• The ACE configuration depends on the number of TRXs and combiners

Slide No.25

• The ACE configuration depends on the number of TRXs and combiners used

No ofTRXs

Network ACE Configuration Downlink ACELoss (dB)

1 or 2 GSM900 2 antennas per cell, diplexer 1.0

1 or 2 GSM1800 2 antennas per cell, diplexer 1.23 or 4 GSM900 2 antennas per cell, diplexer + hybrid combiner 4.43 or 4 GSM1800 2 antennas per cell, diplexer + hybrid combiner 4.4


Mobile Receiver SensitivityMobile Receiver Sensitivity

• The sensitivity of GSM900 and GSM1800 mobile = -102 dBm

• The following should be noted :-

– The sensitivity level is not sufficient to achieve

RXQUAL of 4 without frequency hoppingRXQUAL of 5 with frequency hopping

Slide No.26

• A mobile receiver that moves at 50km/h averages the fading, but a static one will be under more severe fading influences. Therefore :-

– If the quality of a static mobile needs to be considered, then a quality margin of approximately 4 - 5 dB is used

– The mobile sensitivity would be -97 or -98 dBm


Mobile Transmit PowerMobile Transmit Power

• GSM900 : Typical mobile class 4 (2W)

• GSM1800 : Typical mobile class 1 (1W)

Class GSM 900 (Watt/dBm) GSM 1800 (Watt/dBm)1 - 1 / 302 8 / 39 0.25 / 243 5 / 37 4 / 36

Slide No.27

LNA (Optional)LNA (Optional)

• To improve the performance of the uplink

• Should be located close to the antenna to :-

– Improve the system noise figure– Compensate the feeder losses

4 2 / 33 -5 0.8 / 29 -

Achieves quality impovement and cell expansion by improving Achieves quality impovement and cell expansion by improving receive sensitivity at the antennareceive sensitivity at the antenna

The Mast Head Amplifier is installed in the receive path, close to the The Mast Head Amplifier is installed in the receive path, close to the antennaantenna

It compensates for the cable loss between antenna and BTS, for the It compensates for the cable loss between antenna and BTS, for the uplink path, allowing higher BTS transmit powers while retaining uplink path, allowing higher BTS transmit powers while retaining path balance.path balance.

Mast Head AmplifierMast Head Amplifier

Slide No.28

path balance.path balance.

Only effective in uplinkOnly effective in uplink--limited cellslimited cells


Diversity GainDiversity Gain

• Two common techniques used :-

– Space– Polarisation

• Reduce the effect of multipath fading on the uplink

• Common value of 3 to 4.5 dB being used

Slide No.29

BTS Receiver SensitivityBTS Receiver Sensitivity

• Depends on the type of propagation environment model used, most commonly used TU50 model

• BTS2000 :-

– Receiver Sensitivity for GSM900 = -107 dBm– Receiver Sensitivity for GSM1800 = -108 dBm


Feeder LossFeeder Loss

• Depends on the feeder type and feeder length

• The selection of the feeder type would depends on the feeder length, I.e. to try to limit to feeder loss to 2 - 3 dB.

BTS Antenna GainBTS Antenna Gain

• Antenna gain has a direct relationship to the cell size

Slide No.30

• The selection of the antenna type depends on :-

– The morphology classes of the targeted area and coverage requirements

– Zoning and Local authority regulations/limitations

• Common antenna types used :-

– 65º, 90º, omni-directional antennas with different gains


Slow Fading MarginSlow Fading Margin

• To reserve extra signal power to overcome potential slow fading.

• Depends on the requirement of coverage probability and the standard deviation of the fading

• A design can take into consideration :-

– both outdoor and in-building coverage, which utilises a combined standard deviation for indoor and outdoor (Default value = 9dB)

– Only outdoor coverage (Default vendor value = 7dB)

Slide No.31

– Only outdoor coverage (Default vendor value = 7dB)

– Pathloss slope used, 45dB/dec (Dense Urban), 42dB/dec (Urban), 38dB/dec (Suburban) and 33dB/dec (Rural)

Combined (outdoor &indoor) slow fade margin

(dB)

Outdoor slow fade margin(dB)

Cell AreaCoverageProbability(%) DU U SU RU DU U SU RU

85 2 3 3 4 1 1 2 290 5 6 6 6 3 3 4 495 9 9 9 10 6 6 7 7


Penetration LossPenetration Loss

• Penetration loss depends on the building structure and material

• Penetration loss is included for in-building link budget

• Typical value used for Asia-Pacific environment (if country specific information is not available) :-

– Dense Urban : 20 dB– Urban : 18 dB

Slide No.32

– Urban : 18 dB– Suburban : 15 dB– Rural : 9 dB

Body LossBody Loss

• Typical value of 2dB body loss is used

MS Antenna GainMS Antenna Gain

• A typical mobile antenna gain of 2.2 dBi is used


Link Budget Example (GSM900)Link Budget Example (GSM900)

UPLINK DOWNLINKMS Transmit Power 33 dBm BTS Transmit Power 46 dBmCable Loss 0 dB ACE Loss ZMS Antenna Gain 2.2 dBi Feeder Loss 2 dBBody Loss 2 dB LNA Gain 0 dBPenetration Loss W BTS Antenna Gain 18 dBiSlow Fade Margin X Max. Path Loss Y

Slide No.33

Slow Fade Margin X Max. Path Loss YMax. Path Loss Y Slow Fade Margin XBTS Antenna Gain 18 dBi Penetration Loss WLNA Gain 0 dB Body Loss 2 dBFeeder Loss 2 dB MS Antenna Gain 2.2 dBiACE Loss 0 dB Cable Loss 0 dBDiversity Gain 4 dB Diversity Gain 0 dBBTS Receiver Sensitivity -107 dBm MS Receiver Sensitivity -102 dBm

AntennaAntenna

Antenna SelectionAntenna Selection

• Gain

• Beamwidths in horizontal and vertical radiated planes

• VSWR

• Frequency range

• Nominal impedance

Slide No.34

• Radiated pattern (beamshape) in horizontal and vertical planes

• Downtilt available (electrical, mechanical)

• Polarisation

• Connector types (DIN, N)

• Height, weight, windload and physical dimensions

AntennaAntenna

The antenna selection processThe antenna selection process

• Identify system specifications such as polarisation, impedance and bandwidth

• Select the azimuth or horizontal plane pattern to obtain the needed coverage

• Select the elevation or vertical plane pattern to be as narrow as possible,

Slide No.35

• Select the elevation or vertical plane pattern to be as narrow as possible, consistent with practical limitations of size, weight and cost

• Check other parameters such as cost, power rating, size, weight, mounting capabilities, wind loading, connector types, aesthetics and reliability to ensure that they meet system requirements

AntennaAntenna

System SpecificationSystem Specification

• Impedance and frequency bandwidth is normally associated with the communication system used

• The polarisation would depends on if polarisation diversity is used

Horizontal Plane PatternHorizontal Plane Pattern

• Three categories for the horizontal plane pattern :-

Slide No.36

– Omnidirectional– Sectored (directional)– Narrow beam (highly directional)

Elevation Plane PatternElevation Plane Pattern

• Choosing the antenna with the smallest elevation plane beamwidth will give maximum gain. However, beamwidth and size are inversely related

• Electrical down tilt

• Null filling

AntennaAntenna

ExampleExample

• 90º vs 60º horizontal beamwidth

– Bore sight gain vs performance at sector cross over– Indoor : 90º antenna gives a more circular coverage

• Vertical Beamwidth

– Wider vertical beamwidth, better RF performance in rolling terrain

• Excessive Multipath Environment

Slide No.37

• Excessive Multipath Environment

– Reduce horizontal and vertical beamwidth

• Long Bridge over Water

– Very high gain antennas with extremely narrow beamwidth

Receive DiversityReceive Diversity

Diversity schemes provide two or more inputs at the receiver so that Diversity schemes provide two or more inputs at the receiver so that the fading phenomena among the inputs are less correlatedthe fading phenomena among the inputs are less correlated

Types of Receive Antenna DiversityTypes of Receive Antenna Diversity

• Space diversity• Polarisation diversity

Space DiversitySpace Diversity

• Two receive antenna separated physically by a distance, d• The separation, d, varies with the antenna height

Slide No.38

• The separation, d, varies with the antenna height

where h = antenna heightd = antenna separation distanceρ = correlation coefficient of 2 signals received

• For practical limitation, the diversity antenna distance for :-

– GSM900 : approximately 3 m– GSM1800 : approximately 1.5 m

)f( ,d

hρηη ==

Nominal RF DesignNominal RF Design

Link Budget

Maximum

path loss

Propagation

model

Site radius

Nominal RF

Design (coverage)

Coverage

requirements

• Recalculate the site

radius using the

Traffic requirements

Slide No.39

Typical site configuration

(coverage)

Nominal site

count

Coverage site count

• Transmit Power

• Antenna configuration

(type, height, azimuth)

• Site type (sector, omni)

Traffic

requirements

• Standard hexagon site

layout

• Friendly, candidate sites

• Initial site survey inputs

Traffic site

count

Traffic > Cov.

Cov. > Traffic

radius using the

number of sites from

the traffic requirement

• Repeat the nominal

RF design


Calculation of cell radiusCalculation of cell radius

• A typical cell radius is calculated for each clutter environment

• This cell radius is used as a guide for the site distance in the respective clutter environment

• The actual site distance could varies due to local terrain

Inputs for the cell radius calculation :Inputs for the cell radius calculation :--

• Maximum pathloss (from the link budget)

Slide No.40

• Maximum pathloss (from the link budget)

• Typical site configuration (for each clutter environment)

• Propagation model

Example (GSM1800) :Example (GSM1800) :--

• Maximum Pathloss = 138 dB

• Typical Site Configuration (Urban)

– Antenna Height = 30 m– EiRP = 56 dBm

• Standard COST231 model

• Mobile Height = 1.5 m

Nominal RF Design Nominal RF Design

COST231COST231--Hata model (Urban)Hata model (Urban)

Lu (dB) = 46.3 + 33.9 log(f) Lu (dB) = 46.3 + 33.9 log(f) -- 13.82 log(Hb) 13.82 log(Hb) -- a(Hm) + [44.9 a(Hm) + [44.9 -- 6.55 log(Hb)] log(d)6.55 log(Hb)] log(d)

a(Hm) = 0.0432a(Hm) = 0.0432

Rearranging the equation and substituting the value given :-

35.22 Log(d) = 136.24 - 0.0432 - 138

d = 0.889 km

Slide No.41

• The cell radius is calculated without using any terrain/clutter information

– A margin is taken to take into consideration of diffraction and implementation margin

– A clutter offset (for each clutter type) can be applied

• In a standard 3 sector hexagon site configuration, the relationship between the cell radius and site distance is :-

Site Distance = 1.5 x Maximum Cell Radius


There are different level of nominal RF design :There are different level of nominal RF design :--

• Only using the cell radius/site distance calculated and placing ideal hexagon cell layout

• Using the combination of the calculated cell radius and the existing/friendly sites from the customer

Slide No.42


The site distance also depends on the required capacityThe site distance also depends on the required capacity

• In most mobile network, the traffic density is highest within the CBD area and major routes/intersections

• The cell radius would need to be reduce in this area to meet the traffic requirements

If the total sites for the traffic requirement is more than the sites If the total sites for the traffic requirement is more than the sites

Slide No.43

If the total sites for the traffic requirement is more than the sites If the total sites for the traffic requirement is more than the sites required for coverage, the nominal RF design is repeated using the required for coverage, the nominal RF design is repeated using the number of sites from the traffic requirementnumber of sites from the traffic requirement

• Recalculating the cell radius for the high traffic density areas

• The calculation steps are :-

– Calculate the area to be covered per site

– Calculate the maximum cell radius

– Calculate the site distance

Site RealisationSite Realisation

vendor

Add sites to

survey schedule

Site Survey

RF Design

Site Identification

process

vendor

Cust / vendor

vendor

Objective

Link objective to sites

Prioritise objective

vendor

Slide No.44

Planning

meeting

Cust / vendor

No

Yes

Site Package

forwarded to Cust

Implementation

Other sites available for objective ?

No

Yes

Rejected

Accepted

vendor

Cust / vendor

High priority objectives with

linked sites

Prioritise sites


Release of Search Ring

Suitable Candidates?

Candidates Approved?

Arranged Caravan

All parties agreed at

Caravan

Produce Final RF Design

Caravan next candidate

Next candidate

Problem identifying candidate

Exhausted candidates

Y

N

Y Y

NN

N

N

Slide No.45

Exhausted candidates

Additional sites required

Cell split required

Candidate approved?

Driveby, RF suggest possible

alternative

Discuss alternative with

customer

Issue design change

Y

Y

YY

N

NN

YN


Search Ring FormSearch Ring Form

• Site ID

• Site Name

• Latitude/Longitude

• Project name

• Issue Number and date

• Ground height

Slide No.46

• Clutter environment

• Preliminary configuration

• Number of sector

• Azimuth

• Antenna type

• Antenna height

• Search ring radius

• Search ring objective

• Attachment

• Location map

• Approvals


Candidate Assessment ReportCandidate Assessment Report

• Includes all suitable candidates for the search ring

• For each candidates :-

– Location (latitude/longitude)

– Location map showing the relative location of the candidates and also

the search ring

– Candidate information (height, owner etc)

Slide No.47

– Candidate information (height, owner etc)

– Photographs (360º set, rooftop, access, building)

– Possible antenna mounting position

– Possible base station equipment location

– Information for any existing antennas

– Planning reports/comments (restrictions, possibilities of approval etc.)


Final RF Configuration FormFinal RF Configuration Form

• Base Station configuration

– Azimuth

– Antenna height

– Antenna type

– Down tilt

– Antenna location

Slide No.48

– Antenna location

– Feeder type and length

– BTS type

– Transmit power

– Transceiver configuration


The suitability of a candidate site is determine based on the coverage The suitability of a candidate site is determine based on the coverage that the candidate will provide (against the design coverage) and the that the candidate will provide (against the design coverage) and the interference that the candidate site will causeinterference that the candidate site will cause

• Antenna selection

– Type : omni, directional (options of various beamwidth)– Type : Cross-polarised, vertical polarised– Downtilt : fixed, variable– Gain (low, medium, high)

Slide No.49

– Gain (low, medium, high)

• Antenna installation

– Clear of any local clutters, obstructions

– d ≥ 2D2/λ, where D is the maximum antenna dimension

– Obstacles within the surrounding region can dramatically distort RF radiation pattern

– Position antenna such that at least the main lobe is un-obstructed

– 1:3 rule of thumb for antenna height vs distance to roof top parapet


• Antenna installation

– Omni-directional antenna

– Normally mounted at the highest point possible– If it is side mounted, the antenna pattern will be distorted due to tower RF

wave reflection and shadowing

– Directional antenna

– For the new cross-polarised antenna, all the 3 antennas can be mounted on a single pole

Slide No.50

– For the new cross-polarised antenna, all the 3 antennas can be mounted on a single pole

– Wall Mounting

– Ideal perpendicular to wall surface– Avoid metal building structural objects

– Corner Mounting

– Maximum 15º from perpendicular direction to avoid distortion


• Collocating with other antennas

– Spurious emission

– Cause rx desensitization (noise floor increase)– Level should be 10dB below thermal noise floor

– IMP3

– Cause by rx LNA non-linearity– IMP3 level 10dB below thermal noise floor

Slide No.51

– Receiver overload

– Total received power drive amplifier into non-linear gain region– Total rx power 5dB below 1dB compression point of rx amplifier

– Use vertical separation if possible (provide better decoupling)


• Antenna downtilt

θ = arctan(h/2R) + BWv/2 (equation 1)θ = 180 - 2* arctan(R/h) (equation 2)

where R = cell radiush = antenna heightBWv = antenna vertical beamwidth

Slide No.52

R

desired

R

Interfering

Arctan(h/2R)

R

desired

Arctan(h/R)


• Antenna downtilt reduces the interference to neighbouring cells and enhance the weak spots in the cell

• Equation 1 is used to control extreme interference, reduces the interference at the neighbouring cell (d=2R) by 3dB

• Equation 2 is used to improve interference, preserving the coverage at the edge of the cell (d=R)

• RF feeder run :-

Slide No.53

• RF feeder run :-

– Proposed route– Feeder length– Feeder type

Traffic EngineeringTraffic Engineering

Spectrum Available

Reuse factor

Traffic Requirement

Slide No.54

Maximum number of TRX per cell

No of TCH available

Traffic offered

Requirement

Subscriber supported

Channel loading


Traffic RequirementTraffic Requirement

The Erlang per subscriber (during busy hour) is given by :The Erlang per subscriber (during busy hour) is given by :--

where BHCA = Busy hour call attemptAverage call holding time = Duration of time (s) for an average call

3600

)(/

stimeholdingcallAverageBHCAsubErlang

×=

Slide No.55

Average call holding time = Duration of time (s) for an average call

Grade of Service (GoS)Grade of Service (GoS)

• GoS is expressed as the percentage of call attempts that are blocked during peak traffic

• Most cellular systems are designed to a blocking rate of 1% to 5% during busy hour

• Outside busy hour, the blocking rate is much lower


Frequency ReuseFrequency Reuse

• In designing a frequency reuse plan, it is necessary to develop a regular pattern on which to assign frequencies

• The hexagon is chosen because it most closely approximated the coverage produced by an omni or sector site

• Common reuse factor : 4/12, 7/21

Slide No.56


Distance to Cell Radius and C/IDistance to Cell Radius and C/I• The reuse cluster size, N and the D/R ratio are related by :-

where D is the distance separation between cell centers and R is the cell radius

• As N decreases, the D/R ratio becomes smaller and the C/I ratio goes

NR

D3=

Slide No.57

• As N decreases, the D/R ratio becomes smaller and the C/I ratio goes down, interference increases

• As the number of sector increases, the number of potential interferers decreases. For example, using a 3 sector configuration reduces the number of first tier interferers from 6 to 2

• In GSM conventional frequency planning, the 4/12 reuse pattern is typical. Using the inverse 3.5 exponent law, a mean C/I ratio of ~18dB would be found at the edge of the cell

• Advance frequency planning techniques further reduces the reuse factor


Example :Example :--

• Available spectrum = 10 MHz– Available channels : 48 channels

Design 1

• Proposed Reuse factor = 4/12

– Channels required per TRX layer : 12– Number of TRX : 4

Slide No.58

– Number of TRX : 4

Design 2

• Proposed reuse factor for BCCH = 4/12

• Proposed reuse factor for remaining TRX = 3/9

• Number of channels for BCCH layer = 12

• Remaining channels = 36

• Number of channels for non-BCCH layer = 9

• Number of non-BCCH layers = 4

• Total number of TRX = 5


Channel LoadingChannel Loading

• As the number of TRX increases, the control channels required increases accordingly

• The following channel loading is used for conventional GSM network

• For services such as cell broadcast, additional control channels might be required

Number of TRX Control Channels Number of TCH

Slide No.59

Number of TRX Control Channels Number of TCH1 Combined BCCH/SDCCH 72 Combined BCCH/SDCCH 153 1 BCCH, 1 SDCCH 22

4 1 BCCH, 1 SDCCH 305 1 BCCH, 2 SDCCH 376 1 BCCH, 2 SDCCH 457 1 BCCH, 3 SDCCH 528 1 BCCH, 3 SDCCH 60


After determining the number of TCH available and the traffic After determining the number of TCH available and the traffic requirements, the traffic offered is calculated using the Erlang B tablerequirements, the traffic offered is calculated using the Erlang B table

• For example, for a 2% GoS and 3 TRX configuration, the traffic offered is 14.9 Erlang

• If the traffic per subscriber is 35mE/subscriber, then the total subscribers supported per sector = 425

Slide No.60

For a uniform traffic distribution network, the number of sites required For a uniform traffic distribution network, the number of sites required for the traffic requirement is :for the traffic requirement is :--

siteper supportedSubscriber

rs subscribeTotal sitesTotal =


Erlang B TableErlang B Table

N 1% 1.20% 1.50% 2% 3% 5% 7% 10% 15% 20% 30% 40% 50%

1 0.01 0.01 0.02 0.02 0.03 0.05 0.1 0.11 0.18 0.25 0.43 0.67 1

2 0.15 0.17 0.19 0.22 0.28 0.38 0.5 0.6 0.8 1 1.45 2 2.73

3 0.46 0.49 0.54 0.6 0.72 0.9 1.1 1.27 1.6 1.93 2.63 3.48 4.59

4 0.87 0.92 0.99 1.09 1.26 1.52 1.8 2.05 2.5 2.95 3.89 5.02 6.5

5 1.36 1.43 1.52 1.66 1.88 2.22 2.5 2.88 3.45 4.01 5.19 6.6 8.44

6 1.91 2 2.11 2.28 2.54 2.96 3.3 3.76 4.44 5.11 6.51 8.19 10.4

7 2.5 2.6 2.74 2.94 3.25 3.74 4.1 4.67 5.46 6.23 7.86 9.8 12.4

8 3.13 3.25 3.4 3.63 3.99 4.54 5 5.6 6.5 7.37 9.21 11.4 14.3

9 3.78 3.92 4.09 4.34 4.75 5.37 5.9 6.55 7.55 8.52 10.6 13 16.3

Slide No.61

9 3.78 3.92 4.09 4.34 4.75 5.37 5.9 6.55 7.55 8.52 10.6 13 16.3

10 4.46 4.61 4.81 5.08 5.53 6.22 6.8 7.51 8.62 9.68 12 14.7 18.3

11 5.16 5.32 5.54 5.84 6.33 7.08 7.7 8.49 9.69 10.9 13.3 16.3 20.3

12 5.88 6.05 6.29 6.61 7.14 7.95 8.6 9.47 10.8 12 14.7 18 22.2

13 6.61 6.8 7.05 7.4 7.97 8.83 9.5 10.5 11.9 13.2 16.1 19.6 24.2

14 7.35 7.56 7.82 8.2 8.8 9.73 10.5 11.5 13 14.4 17.5 21.2 26.2

15 8.11 8.33 8.61 9.01 9.65 10.6 11.4 12.5 14.1 15.6 18.9 22.9 28.2

16 8.88 9.11 9.41 9.83 10.5 11.5 12.4 13.5 15.2 16.8 20.3 24.5 30.2

17 9.65 9.89 10.2 10.7 11.4 12.5 13.4 14.5 16.3 18 21.7 26.2 32.2

18 10.4 10.7 11 11.5 12.2 13.4 14.3 15.5 17.4 19.2 23.1 27.8 34.2

19 11.2 11.5 11.8 12.3 13.1 14.3 15.3 16.6 18.5 20.4 24.5 29.5 36.2

20 12 12.3 12.7 13.2 14.0 15.2 16.3 17.6 19.6 21.6 25.9 31.2 38.2

21 12.8 13.1 13.5 14 14.9 16.2 17.3 18.7 20.8 22.8 27.3 32.8 40.2

22 13.7 14 14.3 14.9 15.8 17.1 18.2 19.7 21.9 24.1 28.7 34.5 42.1

23 14.5 14.8 15.2 15.8 16.7 18.1 19.2 20.7 23 25.3 30.1 36.1 44.1

Traffic Engineering Traffic Engineering -- ExampleExample

NORTH

(40%)

Traffic distributionGiven

• Supporting up to 10,000 startup sub

• GOS : 2% (0.02)

• Traffic/subs : 25 mErlang(0.025 Erlang)

Slide No.62

(40%)

SOUTH

(60%)

Solutions

A = function(GOS, #TCH) - refer Erlang B table

B = A x # Sector

Radio Network Capacity = B/Erlang per Sub

Traffic Engineering Traffic Engineering -- ExampleExample

BTS Count with Respective TRX Configuration For Traffic Regions

Region Clutter BTS

Configuration

No of

BTS

Radio Network

Capacity

Capacity

Forecast

1 North DenseUrban

1/1/1 4

Urban 1/1/1 6 4,351 4,000

Suburban 1/1 3

Slide No.63

Suburban 1/1 3

Rural 1 1

2 South Dense

Urban

1/1/1 5

Urban 1/1/1 10 5,998 6,000

Suburban 1/1 2

Rural 1 2

Total 33 10,349 10,000


If a traffic map is provided, the traffic engineering is done together If a traffic map is provided, the traffic engineering is done together with the coverage designwith the coverage design

After the individual sites are located, the estimated number of After the individual sites are located, the estimated number of subscribers in each sector is calculated by :subscribers in each sector is calculated by :--

• Calculating the physical area covered by each sector

• Multiply it by the average subscriber density per unit area in that region

• The overlap areas between the sectors should be included in each sector

Slide No.64

• The overlap areas between the sectors should be included in each sector because either sector is theoretically capable of serving the area

The number of channels required is then determined by :The number of channels required is then determined by :--

• Calculating the total Erlangs by multiplying the area covered by the average load generated per subscriber during busy hour

• Determine the required number of TCH and then the required number of TRXs

• If the number of TRXs required exceeded the number of TRXs supported by the available spectrum, additional sites will be required

gsm training 2[1]

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