Gsm Plg & ion

8/6/2019 Gsm Plg & ion

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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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3

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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8

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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10

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.

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