Gsm Training 2[1]
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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
CW Drive Testing CW Drive Testing -- Test PreparationTest Preparation
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
CW Drive Testing CW Drive Testing -- Test PreparationTest Preparation
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.
CW Drive Testing CW Drive Testing -- Test PreparationTest Preparation
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
CW Drive Testing CW Drive Testing -- Test PreparationTest Preparation
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
CW Drive Testing CW Drive Testing -- Test PreparationTest Preparation
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
CW Drive Testing CW Drive Testing -- Propagation TestPropagation Test
Scanning Receiver Setup Scanning Receiver Setup -- HP 7475A Receiver ExampleHP 7475A Receiver Example
HP 7475A ReceiverHP 7475A Receiver
Slide No.16
CW Drive Testing CW Drive Testing -- Propagation TestPropagation Test
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 ==
×
CW Drive Testing CW Drive Testing -- Propagation TestPropagation Test
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
Propagation ModelPropagation Model
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
Propagation ModelPropagation Model
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
Propagation ModelPropagation Model
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
Link BudgetLink Budget
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
Link BudgetLink Budget
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
Link BudgetLink Budget
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
Link BudgetLink Budget
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
Link BudgetLink Budget
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
Link BudgetLink Budget
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
Link BudgetLink Budget
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 BudgetLink Budget
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
Nominal RF DesignNominal 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
Nominal RF DesignNominal RF Design
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
Nominal RF DesignNominal RF Design
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
Site RealisationSite Realisation
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
Site RealisationSite Realisation
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
Site RealisationSite Realisation
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.)
Site RealisationSite Realisation
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
Site RealisationSite Realisation
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
Site RealisationSite Realisation
• 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
Site RealisationSite Realisation
• 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)
Site RealisationSite Realisation
• 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)
Site RealisationSite Realisation
• 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 EngineeringTraffic Engineering
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
Traffic EngineeringTraffic Engineering
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
Traffic EngineeringTraffic Engineering
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
Traffic EngineeringTraffic Engineering
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
Traffic EngineeringTraffic Engineering
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
Traffic EngineeringTraffic Engineering
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 =
Traffic EngineeringTraffic Engineering
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
Traffic EngineeringTraffic Engineering
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