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GSM : RF Planning and Engineering.
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RF Planning AspectsIn RF planning we are concerned with planning of radio
network.
Broadly this implies-
Deciding number and location of BTS/BSC.
Deciding the Radio Parameters.
Transmission link for backhaul connectivity.
It becomes more important as it is an ongoing process,so as to cater the varying traffic and coverage requirements.
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GSM Cell Planning Requirement
Provision of required Capacity
Optimum use of the available frequency spectrum
Minimum number of cell sites
Provision of easy and smooth expansion of the network in future
Provision of adequate Coverage of the given area,for a minimum specified level of interference
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Coverage and traffic Analysis
Nominal cell planning Survey
System design
Implementation
System Tuning
Cell Planning Process
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Initial Cell Planning
Objective: Creating a Nominal Cell Plan
Calculating number of sites and distributionrequired to meet coverage requirement.
Calculating number of sites and distributionrequired to meet capacity requirement.
Assessment of available site locations.
Locating the nominal sites.
Making coverage predictions.
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Detailed Cell Planning
Obtain Digitised Terrain Maps (DTMs)
Prepare link budgets
Make use of a Planning Tool.
Get Coverage Plots.
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A Typical Coverage Plot
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Traffic offered from each configuration
Required input data:
Traffic per subscriber : e.g. 25 mE/sub.
GoS (Grade of Service) e.g. 2% at air interface.
number of TCHs available for each carrier configuration, forexample:
7 TCHs for 1 carrier configuration
14
TCHs for 2 carrier configuration 22 TCHs for3 carrier configuration
1. Calculating Number of Sites - Capacity
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Excerpts from Erlang B Table
No.ofTrunks
Grade of Service
0.01% 0.10 0.50% 1.00% 2.00% 4.00% 5.00%
1. 0.0001 0.001 0.005 0.0101 0.0204 0.0417 0.0526
2. 0.0142 0.0458 0.1054 0.1526 0.2235 0.3333 0.3813
3. 0.0868 0.1938 0.349 0.4555 0.6022 0.812 0.8994
4. 0.2347 0.4393 0.7012 0.8694 1.0923 1.3994 1.5246
5. 0.452 0.7621 1.132 1.3608 1.6571 2.0573 2.2185
6. 0.7282 1.1459 1.6218 1.909 2.2759 2.7649 2.9603
7. 1.0541 1.5786 2.1575 2.5009 2.9354 3.5095 3.7378
8. 1.4219 2.0513 2.7299 3.1276 3.6271 4.283 4.543
9. 1.8256 2.5575 3.3326 3.7825 4.3447 5.0796 5.3702
10. 2.2601 3.092 3.9607 4.4612 5.084 5.8954 6.2157
11. 2.7216 3.8511 4.6104 5.1599 5.8415 6.7272 7.0764
12. 3.2069 4.2314 5.2789 5.876 6.6147 7.5827 7.9501
13. 3.7133 4.8305 5.9638 6.6072 7.4015 8.43 8.934914. 4.2387 5.4464 6.6632 7.3517 8.2003 9.2977 9.7295
15. 4.7811 6.0772 7.4755 8.108 9.0096 10.175 10.6327
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Capacity Considerations - I
1
1
1
1
2
88 Access Channels
1--Signaling7- Voice
With 2 % GoS
2.94 E
2.94E/25mE=120 Subs
120 Subs/Sectorv 3 = 360 Subscribers
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1
1
1
8 Access Channels1--Signaling
7- Voice
4
2
4
32 Access Chls3
--Signaling29- Voice
16 Access Chls2Signaling14- Voice
120v 3 = 360 Subs 840v 3 = 2520 Subs330v 3 = 1000Subs
Capacity Considerations - II
4
22
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2. Calculating Number of Sites - Coverage
Steps:
Step 1: Analyse Coverage Distribution Step 2: Link Budget Analysis - MAPL
Step 3: Cell range calculation
Step 4: Estimate number of sites
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R
R
Estimating Number of Sites
Rough cell coverage area calculation For an omni site: or a sectorised site:
Cell coverage area =(3/2)*3 *R2 Cell coverage area = (9/8)* 3 * R2= 1.95* R2
R = cell radius. R = cell radius.
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Estimate the Number of Sites
Calculate number of sites for each area classification, e.g. coverage area per site -
Total Coverage area
no. of sites required for coverage in urban area
Total Coverage AreaCoverage area per site
=
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Link Budget Analysis
BTS Antenna
GainPath Loss Fade Margin
Feeder Loss
Diversity
ai
B
Receiver
e sitivity
CO
Loss
B
ra smit
Power
Penetration Loss
M A te a ai ,
Bo y a Cable
Loss
Mobile
ra smit
Power
Mobile
Receiver
e sitivity
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Types of Coverage
Indoor Coverage : RSS -65 dBm
In-Car Coverage : RSS -75 dBmOutdoor Coverage: RSS -85 dBm
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Coverage Model
SIGNAL LEVEL MEASURED AT STREETCOVERAGE
SHOULD BE BETTER THAN -65 dBmINDOOR
SHOULD BE BETTER THAN -75 dBmINCAR
SHOULD BE BETTER THAN -85 dBm IN 90%
OF TOTAL COVERAGE AREAOUTDOOR
SIGNAL LEVEL FOR 95% OF THE TIME FOR THE COVERAGE
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Coverage Predictions
Required input data: Site locations (longitude, latitude)
Propagation Modelof the planning network
e.g. GSM900 or GSM1800
Antenna design height, tilt
direction
type, pattern
EiRP (effective isotropic radiated power), based on theweaker link (UL or DL) from the link budgetcalculation
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Okumara Model
The Okumara tests are valid for: 150-2000 Mhz
1-100 Kms
BTS heights of30 -100 meters
MS antenna height , typically 1.5 m (1-10m) The results of Okumara tests were graphically represented
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Step 3: Analyse Traffic Distribution
15 %
10 %
20 %8 %
30 %12 %
5 %
9400 Subscribers25 mErl per subscriber
Total 235 Erlang
Determine traffic
in each area type.
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Surveys
Radio survey (Area visits)
Site surveys
Simulation of surveyed site alternatives Joint site surveys with civil works engineers
Site survey reports
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Site Survey
Important topics to consider during evaluation: Coverage objectives (site locations)
Antenna Mounting (obstructions, etc)
Feeder Length (feeder cable loss)
Equipment room (size and location) Cable ducts / Antenna masts (construction)
Transmission Links (Microwave, fixed line)
Construction Cost (alternative solutions)
Relationship to other sites (handover, etc)
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Joint Survey
In principle this is done after the site candidate is finalised In some cases the joint survey is carried out in before the
site survey in order accommodate some sites
The joint survey team should consist of people responsible
for different tasks e.g. radio-planning
construction/civil work (CW)
site-acquisition
transmission
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Frequency Planning Aspects
A1 1 1 D1 A2 2 2 D2 A3 3 3 D3
1 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 17 18 19 20 21 22 23 24
25 26
27 28
293
03
13
233 34 3
536
A1
A2
A3 1
2
3
D1
D2
D3 1
2
3
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General Considerations - TRX Requirement
Traffic Requirements ( Erlangs)
Grade of service required
Typical Cell Model
Number of carriers from Traffic requirements Control Channel Determination
Equipment Configuration
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Capacity Planning- TCH Cha els Requireme t
RF Carriers Needed depend upon:
Number of Subscribers to be served
Average traffic per subscriber
Grade of service
200 Sub
200 Subscribers
GoS = 2%
25mE Traffic per
200 v 25 mE = 5.0 E
At2% GoS
10 TCH Required
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Control Channel Configuration
1. Combined Time Slot: (TS0 of BCCH Carrier)
1 BCCH + 3 CCCH + 4 SDCCH
2. Non Combined Time Slot :
( 1 BCCH + 9 CCCH ) in one time slot (TS 0)
8
SDCCH in one time slot ( any time slot )
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3
0
Other Related Planning Aspects
Dimensioning of BTS equipment
Dimensioning of BSC
Dimensioning E1s needed.
Drive test after commissioning Optimization.
Traffic Monitoring.
Plan for expansion.
These aspects are beyond the scope of this presentation
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Optimizatio of
mobileN
etwork
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Optimizatio of mobile Network
What is Optimizatio :-In a GSM network subscriber may face any unwanted situations likecall drop, one way talk, echo, access failure, mute etc due tointerference and inaccurate parameter definitions & that may cause
subscriber dissatisfaction.To overcome these situations optimization of GSM network isrequired. So the optimization is a process for improvement of bothquality and coverage of GSM network by performing drive test,considering network statistical reports generated by OSS ,customerfeedbacks etc
Drive testing involves driving in a vehicle and collecting network databy making a lot of calls & using these data for planning andoptimization tools to generate useful plots such as serving cellscoverage plots, Quality plots etc to monitor the health of the network.
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I puts for optimizatio
How it can be decided that whether any area needs optimization or not?For that few inputs are considers like :-1) QOS Parameters:- QOS Parameters are the quality indicators of the Network.like Call Success rate, Call Drop Rate, Handover success rate, Call These parameters
have to be continually monitored on cell, site, BSC and Network basis. If anyabnormality is observed or if any deterioration is seen in any of the parametersoptimization process has to be initiated.2) OMC alarms:- Any problem in the Network results in a alarm at the OMC.Whenever an alarm is observed at the OMC it must be carefully analyzed to determineif there is a network problem and if it is required to initiate optimization process.3) Routi e Drive Testi g:- coverage plots, Quality plots generated from drive test may
4) Customer fee back:- These information are used to target areas requiring optimizationand to verify coverage against the RF design.
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How to perform Optimizatio of
GS
M etwork
For optimization of GSM networkDrive test are performed & Reportsgenerated by making lot of calls during drive test & OSS reports areloaded to optimization tools like Netact Planner,TEMS, Planet to
generate useful reports & plots from which problem in GSM networkmay analyzed.Equipme t Necessary for Drive testing are
Vehicle Drive test mobile phone (e.g.Ericcson TEMS) External vehicle mounted GPS
Laptop with drive test software and GPS connection capability.
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How to perform Optimizatio of
GSM etworkcall trace tool However one powerful tool provided by all
operators is the call trace tool. This feature enables us toput a trace on a call and collect all data related to the call
Since in call trace we can accumulate data for call beingmade throughout the cell it includes the indoor calls alsoand hence gives us the correct picture regarding the
performance of the cell.Protocol a alyzer may also be used to analyze the C7 and
LAPD signaling messages between the MSC, BSC and theBTS ,these are used to analyze problems which mayoriginate either in the Radio part or the MSC e.g. paging
problems.
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Optimizatio Solutio s
Once the problem has been analyzed a solution has to be provided. Common solution to problems are1) Database Parameter Cha ges
Many problems can be solved by changing some database parameters like Handover parameters andthresholds, Maximum transmit power of BTS, Paging parameters, SDCCH Parameters,
2) A te a OptiimiizatiioThis includes changing of anteena tilts, orientations, positions. Sometimes the antenna may also be
changed.3) Freque cy Cha ges
Frequency changes help us to control the interference in the network.However one should be careful when doing these changes so that this changes do not affect the other sites
adversely. If there are a lot of changes it is advisable to change the whole frequency plan. A carefulstudy of cell coverage area and server area helps in making those changes.
4) Neiighbor A iitiio A Deletio
Many problems arise due to wrong neighbor definitions or missing neighbors. Neighbor definitions mustbe reviewed on a regular basis. Statistics and drive tests provide good inputs for this purpose.
5) Formatiio OfNew Locatiio AreasSometimes to solve paging load problems it might be required to for new location areas.
6) A itio of ew cell sitesSometimes to solve coverage hole problems we need to add more site (normally micro or pico cells)
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THANKS.