GSM Optimization

Optimization: Introduction

Optimization: Optimization: IntroductionIntroduction


CCoontentsntents

Global indicatorsGlobal indicators Typical Radio Network ProblemTypical Radio Network Problem

Coverage ProblemCoverage Problem Interference problemInterference problem Unbalanced power budget Unbalanced power budget

problemproblem Congestion problemCongestion problem

Problems and responsible Problems and responsible partiesparties


GlobalGlobal Indicators Indicators

4 stages of a call establishment, 4 stages of a call establishment, 2 stages (1&2) for location 2 stages (1&2) for location update :update :

1.1. Radio link establishment Phase Radio link establishment Phase

2.2. SDCCH Phase SDCCH Phase

then only then only ““Circuit Switch callCircuit Switch call””

3.3. TCH assignment Phase TCH assignment Phase

4.4. Alerting/Connect Phase Alerting/Connect Phase


GlobalGlobal IndicatorsIndicators

MS BTS BSC MSC

(RACH)

CHANNEL REQUESTCHANNEL REQUIRED

CHANNEL ACTIVATION (SDCCH)

CHANNEL ACTIVATION ACK

IMMEDIATE ASSIGN COMMEND

(AGCH)

IMMEDIATE ASSIGN

(SDCCH)

SABM (L3 info)

(SDCCH)

UA (L3 info)

ESTABLISH IND (L3 info) CR (Connection Request: L3INFO)

CC (Connection Complete)

AUTHENTICATION REQUEST

AUTHENTICATION RESPONSE

CIPHERING MODE COMMAND

CIPHERING MODE COMPLETE

SETUP

CALL PROCEEDING

LOCATION UPDATE REQUEST (IN CASE OF LU)

LOCATION UPDATE ACCEPT (IN CASE OF LU)

TMSI REALLOCATION COMPLETE (IN CASE OF LU)

ASSIGNMENT REQUESTPHYSICAL CONTEXT REQUEST

PHYSICAL CONTEXT CONFIRM

CHANNEL ACTIVATION (TCH) TCH allocation

CHANNEL ALLOCATION ACK.

(SDCCH)

ASSIGNMENT COMMEND

SABM

UA (L3 info)TCHESTABLISH INDICATION

ASSIGNMENT COMPLETE

ASSIGNMENT COMPLETE

ALERTING

CONNECT

CONNECT ACK.

CONVERSATION

Mobile Originated Call (MOC)

1. 1. Radio Link Radio Link EstablishmenEstablishment Phaset Phase

2. 2. SDCCH PhaseSDCCH Phase

3. 3. TCH Assignment TCH Assignment PhasePhase

4. 4. Alert and Connect Alert and Connect PhasePhase


GlobalGlobal Indicators Indicators HandoverHandover : Intracell HO : Intracell HO

MS BTS BSC MSC

Measurement ReportMEASUREMENT RESULT

PHYSICAL CONTEXT REQUEST (old channel)

PHYSICAL CONTEXT CONFIRM (old channel)

CHANNEL ACTIVATION (new channel)

(SDCCH)

SABM (L3 info)

(SDCCH)

UA (L3 info)

ESTABLISH IND (new channel)

CHANNEL ACTIVATION ACK (new channel)

ASSIGNMENT COMMEND (old channel)ASSIGNMENT CMD

ASSIGNMENT CMP ESTABLISH COMPLETE (new channel)

HANDOVER PERFORMED

RF CHANNEL RELEASE (old channel)

RF CHANNEL RELEASE ACK (old channel)


GlobalGlobal Indicators Indicators HandoverHandover : Internal HO : Internal HO

MSServing

CellBSC MSC

Meas. Report

MEASUREMENT RESULT

HANDOVER COMMAND

HANDOVER ACCESS

CHANNEL ACTIVATION

SABM (L3 info)

UA (L3 info)

HANDOVER PERFORMED

TargetCell

CHANNEL ACTIVATION ACK.

HO CMD

HANDOVER DETECTION

PHYSICAL INFORMATION

ESTABLISH INDICATION

HANDOVER COMPLETE HO CMP


GlobalGlobal Indicators Indicators HandoverHandover : External HO : External HO

MS Serving Cell MSCBSC

MEAS_REPORTMEAS_RESULT

HO_COMMAND

HO_ACCESS

SABM (L3 info)

UA (L3 info)

Target Cell

HO_REQUIRED

HO_DETECTION

ESTABLISH_INDICATION

HO_COMPLETE

Release of TCH

BSC MS

CR (HO_REQUEST)

CC CHANNEL_ACTIVATION

CHANNEL_ACT_ACKHO_REQUEST_ACK

(HO_COMMAND)

HO_ACCESSHO_DETECTION

PHYSICAL_INFO

HO_COMPLETE

CLEAR_COMMANDCause: HO_SUCCESSFUL


GlobalGlobal Indicators IndicatorsImportant indicators :Important indicators :

SDCCH CongestionSDCCH Congestion SDCCH Assignment FailureSDCCH Assignment Failure SDCCH DropSDCCH Drop TCH Assignment FailureTCH Assignment Failure Call DropCall Drop Call Setup SuccessCall Setup Success Call SuccessCall Success Outgoing HandoverOutgoing Handover Incoming HandoverIncoming Handover Handover Causes Distribution Handover Causes Distribution

(Better/Level/Quality/MCHO/...)(Better/Level/Quality/MCHO/...)


GlobalGlobal Indicators Indicators SDCCH SDCCH CongestionCongestion : :

MS BTS BSC

(RACH)



(AGCH)

IMM. ASS. REJECT (OPTION)

NO FREE SDCCH !!!

MS will try to request again for a certain of MS will try to request again for a certain of timestimes

If still failures, it willIf still failures, it will Wait for a certain of time without Wait for a certain of time without

reception of immediate_assign reception of immediate_assign messagemessage

Try an automatic cell_reselection in Try an automatic cell_reselection in case of LU (no impact for subscriber)case of LU (no impact for subscriber)

Notify a network error for call Notify a network error for call establishment (call setup failure for establishment (call setup failure for subscriber)subscriber)


GlobalGlobal Indicators Indicators SDCCH SDCCH CongestionCongestion : Main causes : Main causes

Too much SDCCH Too much SDCCH ““normalnormal”” traffic for traffic for cell SDCCH designcell SDCCH design

Logical cell design, extra TRX, new siteLogical cell design, extra TRX, new site ““Common Transport EffectCommon Transport Effect””

Difficult to avoid for small cellsDifficult to avoid for small cells LA border at crowded areaLA border at crowded area

Abnormal SDCCH trafficAbnormal SDCCH traffic ““phantomphantom”” channel requests channel requests Inadequate LAC design, causing too Inadequate LAC design, causing too

much LUmuch LU Redesign LACRedesign LAC

Problem with neighbor cells belong to Problem with neighbor cells belong to other LACother LAC


GlobalGlobal Indicators Indicators SDCCH SDCCH RF FailureRF Failure : main causes : main causes

Real radio problemsReal radio problems Unbalanced power budgetUnbalanced power budget Bad coverageBad coverage InterferenceInterference

In case of radio failure, MS will retry as in case In case of radio failure, MS will retry as in case of SDCCH congestionof SDCCH congestion

MS BTS BSC MSC

(RACH)


CHANNEL ACTIVATION (SDCCH)

CHANNEL ACTIVATION ACK


(AGCH)

IMMEDIATE ASSIGN

??? no message from MS


GlobalGlobal Indicators Indicators SDCCH SDCCH RF FailureRF Failure : main causes : main causes

““Phantom/Ghost/Spurious/Phantom/Ghost/Spurious/Dummy...RACHDummy...RACH””

Channel request received but not sent : 3 Channel request received but not sent : 3 causescauses

1.1. Noise decodingNoise decoding

2.2. Reception of channel request sent to Reception of channel request sent to a neighbor cella neighbor cell

3.3. Reception of HO_ACCESS sent to a Reception of HO_ACCESS sent to a neighbor cellneighbor cell


GlobalGlobal Indicators Indicators SDCCH RF Failure : main causes : SDCCH RF Failure : main causes : Phantom RACHPhantom RACH

1.1. Noise decodingNoise decoding GSM 05.05: GSM 05.05: ““0.02% of RACH Frame can 0.02% of RACH Frame can

be decoded without error without real be decoded without error without real input signalinput signal”” (this extra-load has no (this extra-load has no impact for the system)impact for the system)

BCCH not combined: 156 phantom BCCH not combined: 156 phantom RACCH/hour (or about 0.08 Erlang RACCH/hour (or about 0.08 Erlang SDCCH)SDCCH)

BCCH combined: 83 phantom RACH/hourBCCH combined: 83 phantom RACH/hour During period with low real traffic (night), During period with low real traffic (night),

high rate of phantom RACHhigh rate of phantom RACH No impact for subscriberNo impact for subscriber But impact on indicator SDCCH RF access But impact on indicator SDCCH RF access

failurefailure



2.2. Channel request sent to neighbor cellChannel request sent to neighbor cell

Subscriber is not impacted ( the real Subscriber is not impacted ( the real transaction is performed elsewhere)transaction is performed elsewhere)

But SDCCH RF access failure is impactedBut SDCCH RF access failure is impacted

Usual radio planning rules are sufficient Usual radio planning rules are sufficient to avoid the trouble (BSIC and BCCH to avoid the trouble (BSIC and BCCH frequency plan)frequency plan)



3.3. Channel request due to handoverChannel request due to handover During HO, first message sent to target During HO, first message sent to target

cell is HO access which is an access burst cell is HO access which is an access burst like channel_requestlike channel_request

If received on BCCH, can be understood If received on BCCH, can be understood as a channel-requestas a channel-request

This case is the most dangerousThis case is the most dangerous MS is sending usually a sequence of HO MS is sending usually a sequence of HO

Access message, every frame !!Access message, every frame !! In some cases, this can create phantom In some cases, this can create phantom

RACH if the frequency of TCH is co- or RACH if the frequency of TCH is co- or adjacent to one of the interfered BCCHadjacent to one of the interfered BCCH

Can block very easily SDCCHCan block very easily SDCCH


GlobalGlobal Indicators Indicators SDCCH SDCCH DropDrop : :

Loss of connection during SDCCH phase = Loss of connection during SDCCH phase = SDCCH DropSDCCH Drop

3 causes of SDCCH drop3 causes of SDCCH drop Radio problems when connected on Radio problems when connected on

SDCCHSDCCH BSS problems (Transcoder and Internal BSS problems (Transcoder and Internal

BSS problems)BSS problems) Call lost during an SDCCH HO Call lost during an SDCCH HO

(handover failure without reversion to (handover failure without reversion to old channel)old channel)

BTS BSC

CONNECTION FAILURE INDICATION(cause : radio link failure)

Radio connection loss

CLEAR REQUEST(cause : radio interface failure)

MSCMS


GlobalGlobal Indicators Indicators TCHTCH assign failureassign failure : Congestion : Congestion

4 sub causes of congestion4 sub causes of congestion

AA: Queuing is not allowed: Queuing is not allowed BB: Queue is full: Queue is full CC: T11 expired: T11 expired DD: RTCH requests is de-queued due to : RTCH requests is de-queued due to

a high priority (i.e. emergency call) a high priority (i.e. emergency call) request to be queuedrequest to be queued

BTS BSC

no RTCH available on request cellASSIGNMENT FAILURE

cause No Radio Resources Available

MS

ASSIGNMNET REQUEST

MSC


GlobalGlobal Indicators Indicators TCHTCH assign failureassign failure : Radio : Radio

MS BTS BSC MSC





(SDCCH)

ASSIGNMENT COMMEND

TCHRadio Problem

ASSIGNMENT FAILURERadio interface failure


GlobalGlobal Indicators Indicators TCHTCH assign failureassign failure : BSS : BSS

MS BTS BSC MSC





(SDCCH)

ASSIGNMENT COMMEND

BSS Problem


GlobalGlobal Indicators Indicators TCHTCH DropDrop : Radio : Radio

MS BTS BSC

CONNECTION FAILURE INDICATION(cause : radio link failure)

Radio Problem

CLEAR REQUEST(cause : radio interface failure)

MSC

Alerting Connection Phase or Communication : at any time


GlobalGlobal Indicators Indicators TCHTCH DropDrop : BSS : BSS

Transcoder reported problemTranscoder reported problem

AAbisbis transmission Problem: Microwave, transmission Problem: Microwave, Microwave antenna, fixed line problems.Microwave antenna, fixed line problems.

Problem on TC boards (hardware problem)Problem on TC boards (hardware problem)

MS BTS BSC

CONNECTION FAILURE INDICATION(Remote transcoder failure)

Radio Problem

CLEAR REQUEST(Equipment failure)

MSC



GlobalGlobal Indicators Indicators TCHTCH DropDrop : BSS : BSS

Other BSS problem (excluding TC)Other BSS problem (excluding TC) Hardware or software failures of BSC/BTSHardware or software failures of BSC/BTS

MS BTS BSC

BSS problemCLEAR REQUESTO&M intervention

Radio interface failure

MSC



GlobalGlobal Indicators Indicators TCHTCH DropDrop : Handover : Handover

Call drop during handoverCall drop during handover

MS BTS BSC

HO failure without reversion CLEAR REQUESTRadio interface message failure

MSC



GlobalGlobal Indicators Indicators Intracell HO Intracell HO FailuresFailures

CongestionCongestion Reversion to Old Channel (ROC)Reversion to Old Channel (ROC) Drop RadioDrop Radio BSS problemBSS problem


GlobalGlobal Indicators Indicators Intracell HO Failures Intracell HO Failures : Congestion: Congestion

MSServing

BTSBSC MSC

Measurement ReportMEASUREMENT RESULT

No Free TCH/SDCCH

Intracell HO Failures Intracell HO Failures : Drop: Drop

MS BTS BSC MSC

ASSIGNMENT CMDASSIGNMENT COMMAND (old channel)

Release of old and new channels


GlobalGlobal Indicators Indicators Intracell HO Failures Intracell HO Failures : : Reversion to Old ChannelReversion to Old Channel

ServingBTS

ServingBSC MSC

SABM (new channel)

UA (new channel)

ESTABLISH IND (new channel)

ASSIGNMENT COMMEND (old channel)ASSIGNMENT CMD

ESTABLISH INDICATION (old channel)

RF CHANNEL RELEASE (old channel)

RF CHANNEL RELEASE ACK (old channel)

MS

XSABM (new channel)

UA (new channel)X

SABM (old channel)

UA (old channel)

ASSIGNMENT FAIL ASSIGNMNENT FAILURE


GlobalGlobal Indicators Indicators Internal HO FailuresInternal HO Failures : : Reversion to Old ChannelReversion to Old Channel

ServingCell

BSC MSC

HANDOVER COMMAND

HANDOVER ACCESS

SABM (L3 info)

UA (L3 info)

TargetCell

HO CMD

HANDOVER DETECTION

PHYSICAL INFORMATION


HANDOVER COMPLETE

MS

X

SABM

UM

HO FAILURE


HO FAILURE

Release of new channel


GlobalGlobal Indicators Indicators Internal HO FailuresInternal HO Failures : : DropDrop

MSServing

CellBSC MSC

Meas. Report

MEASUREMENT RESULT

HANDOVER COMMAND

CHANNEL ACTIVATION

Clear_request

TargetCell

CHANNEL ACTIVATION ACK.

HO CMD

Clear_command

Release of old and new TCH


GlobalGlobal Indicators Indicators External HO FailuresExternal HO Failures : Congestion : Congestion



HO_REQUIRED_REJECT

Target Cell

HO_REQUIRED

BSC MS

CR (HO_REQUEST)

HO_FAILURECause: no radio resource available

External HO FailuresExternal HO Failures : A int. : A int. CongestionCongestionMS Serving Cell MSCBSC


HO_REQUIRED_REJECT

Target Cell

HO_REQUIRED

BSC MS

CR (HO_REQUEST)

HO_FAILURECause: terrestrial circuit already allocatedRequested trerestrial resource unavailableBSS not equipped


GlobalGlobal Indicators Indicators External HO FailuresExternal HO Failures : Reversion to Old Channel : Reversion to Old Channel



HO_COMMAND

HO_ACCESS

Target Cell

HO_REQUIRED

Release connection

BSC MS

CR (HO_REQUEST)



(HO_COMMAND)

CLEAR_COMMAND

XHO_ACCESS

XSABM

UAESTABLISH_INDICATION

HO_FAILURE(reversion to pld channel)

Radio interface fail:Reversion to old channel


GlobalGlobal Indicators Indicators External HO FailuresExternal HO Failures : Drop : Drop



HO_COMMAND

HO_ACCESS

Target Cell

HO_REQUIRED

Release connection

BSC MS

CR (HO_REQUEST)



(HO_COMMAND)

CLEAR_COMMAND

XHO_ACCESS

X

Radio interface fail

SABMX

SABMX

SABMX


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : SDCCH Congestion RateSDCCH Congestion Rate

DefinitionDefinition: Rate of SDCCH not allocated : Rate of SDCCH not allocated during radio link establishment procedure during radio link establishment procedure due to congestion on Air interfacedue to congestion on Air interface

CommentComment: Check SDCCH Erlang : if not : Check SDCCH Erlang : if not critical, SDCCH availability/allocation critical, SDCCH availability/allocation problem, or HO access on a nearby cell problem, or HO access on a nearby cell side effect or interference on the carrier side effect or interference on the carrier handling SDCCH (the last 2 can lead to handling SDCCH (the last 2 can lead to high rate if Phantom RACHhigh rate if Phantom RACH


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : SDCCH Assign Failure RateSDCCH Assign Failure Rate

DefinitionDefinition: Rate of SDCCH seizure failed : Rate of SDCCH seizure failed (BSS problem, radio access problem) (BSS problem, radio access problem) during radio link establishment procedure during radio link establishment procedure over the total amount of SDCCH seizure over the total amount of SDCCH seizure requests during radio link establishment requests during radio link establishment procedureprocedure


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : SDCCH Drop RateSDCCH Drop Rate

DefinitionDefinition: Rate of dropped SDCCH : Rate of dropped SDCCH (SDCCH is established for any (SDCCH is established for any transaction OC, TC, LU, ...)transaction OC, TC, LU, ...)

CommentComment: Drop radio + Drop HO + : Drop radio + Drop HO + Drop BSSDrop BSS


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : TCH Assign Failure/Congestion RateTCH Assign Failure/Congestion Rate

DefinitionDefinition: : TCH Assign Failure RateTCH Assign Failure Rate: Rate of RTCH : Rate of RTCH

seizure failed (BSS problem, radio access seizure failed (BSS problem, radio access problem) during normal assignment problem) during normal assignment procedure over the total amount or RTCH procedure over the total amount or RTCH request for normal assignment procedurerequest for normal assignment procedure

TCH Assign Congestion RateTCH Assign Congestion Rate: Rate of : Rate of RTCH not allocated during normal RTCH not allocated during normal assignment due to congestion on Air assignment due to congestion on Air interfaceinterface


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : Call Drop Rate Call Drop Rate

DefinitionDefinition: Rate of dropped calls over the : Rate of dropped calls over the total amount of calls with a successful endtotal amount of calls with a successful end

CommentComment: : Drop BSS + Drop radio + Drop HODrop BSS + Drop radio + Drop HO TCH drop occurring after successful TCH drop occurring after successful

assignment but before speech connection assignment but before speech connection are considered as call drop even if from are considered as call drop even if from customercustomer’’s point of view it is a call setup s point of view it is a call setup failurefailure


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : Call Setup Success Rate Call Setup Success Rate

DefinitionDefinition: Rate of calls going until TCH : Rate of calls going until TCH successful assignment, that is not interrupted successful assignment, that is not interrupted by SDCCH drop neither by assignment by SDCCH drop neither by assignment failuresfailures

CommentComment: : Subscriber : call not established at the Subscriber : call not established at the

first attemptfirst attempt


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : Call Success Rate (BSS view) Call Success Rate (BSS view)

DefinitionDefinition: Rate of calls going until normal : Rate of calls going until normal release, that is not interrupted by SDCCH release, that is not interrupted by SDCCH drop neither by assignment failures and drop neither by assignment failures and neither by CALL DROPneither by CALL DROP

CommentComment: : 1 call success =1 call success =

1 call successfully established1 call successfully established Without any call dropWithout any call drop


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : Outgoing Handover Success Rate Outgoing Handover Success Rate

DefinitionDefinition: Rate of outgoing external and : Rate of outgoing external and internal intercell TCH and SDCCH handover internal intercell TCH and SDCCH handover successes over the total amount of outgoing successes over the total amount of outgoing external and internal intercell TCH and external and internal intercell TCH and SDCCH handover requiredSDCCH handover required


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : Incoming Handover Success Rate Incoming Handover Success Rate

DefinitionDefinition: Rate of incoming external and : Rate of incoming external and internal intercell TCH and SDCCH handover internal intercell TCH and SDCCH handover successes over the total amount of outgoing successes over the total amount of outgoing external and internal intercell TCH and external and internal intercell TCH and SDCCH handover requestsSDCCH handover requests


GlobalGlobal Indicators IndicatorsImportant indicators : Important indicators : Handover Cause DistributionHandover Cause Distribution

DefinitionDefinition: Distribution of Handover requests by : Distribution of Handover requests by cause: UL Qual, UL Lev, DL Qual, DL Lev, Better cause: UL Qual, UL Lev, DL Qual, DL Lev, Better Cell, UL Interference, DL Interference, Cell, UL Interference, DL Interference, Interband, Micro cells HO, Concentric cell Interband, Micro cells HO, Concentric cell causescauses


Typical Typical Radio ProblemsRadio Problems

i.i. Coverage ProblemCoverage Problem

ii.ii. Interference problemInterference problem

iii.iii. Unbalanced power Unbalanced power budget problembudget problem

iv.iv. Congestion problemCongestion problem


Typical Typical Radio ProblemsRadio Problems

Several sources of information Several sources of information for optimizationfor optimization

QoS indicatorsQoS indicators Coverage predictionsCoverage predictions Customer complaintsCustomer complaints Drive testsDrive tests AAbisbis/A traces/A traces Other teams information (NSS Other teams information (NSS

statistics)statistics)


i. Coveragei. Coverage Problem Problem

Bad coverageBad coverage : :

A network facing coverage problems A network facing coverage problems has has badbad RxLevRxLev. RxQual can be bad . RxQual can be bad at the same time.at the same time.

Sometimes the RxLev can look OK on Sometimes the RxLev can look OK on the street (i.e. from drivetest) but the street (i.e. from drivetest) but coverage inside the buildings can coverage inside the buildings can be poor due to building losses. be poor due to building losses. Building losses can range from 10 Building losses can range from 10 to 30 dB or more.to 30 dB or more.


i. Coveragei. Coverage Problem Problem Indications :Indications :

Customers complain about dropped Customers complain about dropped calls and/or calls and/or ““No NetworkNo Network””

OMC QoS indicatorsOMC QoS indicators– TCH failure rateTCH failure rate– Call drop rateCall drop rate– Low proportion of better cell HOLow proportion of better cell HO– High rate of DL & UL Level HO High rate of DL & UL Level HO

(possibly also DL/UL quality HO)(possibly also DL/UL quality HO) A interface indicatorsA interface indicators

– High rate of Clear Request message, High rate of Clear Request message, cause radio interface failurecause radio interface failure

Drive TestDrive Test– Poor RxLev ( < -95 dBm)Poor RxLev ( < -95 dBm)


i. Coveragei. Coverage Problem Problem Investigation and Optimization :Investigation and Optimization :

If actual coverage is not the one If actual coverage is not the one predicted by planning toolpredicted by planning tool

– Check antenna system (azimuth, Check antenna system (azimuth, crossed sector?)crossed sector?)

– Check prediction in the tool (EIRP, Check prediction in the tool (EIRP, Clutter Type, Obstructing building?). Clutter Type, Obstructing building?). Most of the time the prediction will be Most of the time the prediction will be incorrect, as it is only a computer incorrect, as it is only a computer simulationsimulation

– Increase or decrease antenna down-tiltIncrease or decrease antenna down-tilt– Check BTS output power set in the Check BTS output power set in the

OMC-R (BS_TXPWR_MAX: should OMC-R (BS_TXPWR_MAX: should always be set at 0)always be set at 0)



Investigation and Optimization :Investigation and Optimization : If actual coverage OK compared to If actual coverage OK compared to

predicted onespredicted ones– Improve coverage by adding Macro Improve coverage by adding Macro

site, Microcell site (Border or Shadow site, Microcell site (Border or Shadow areas), or IBC site (In-building areas), or IBC site (In-building coverage).coverage).

– Use parameter setting ex. Bi-layer Use parameter setting ex. Bi-layer Handover.Handover.



Example on thresholds : Example on thresholds :

From Drive test or AFrom Drive test or Abisbis InterfaceInterface

RxLev RxLev < < -95 dBm-95 dBm

andand RxQual RxQual > > 44


ii. Interferenceii. Interference Problem Problem

Interference : Interference :

A network facing A network facing interferences problems interferences problems presents presents goodgood RxLevRxLev and and bad bad RxQualRxQual in the same in the same time on some areas.time on some areas.


ii. Interferenceii. Interference Problem Problem Indications :Indications :

Customers complain about bad speech Customers complain about bad speech quality (noisy calls) and/or call dropsquality (noisy calls) and/or call drops

OMC QoS indicatorsOMC QoS indicators– SDCCH/TCH DropSDCCH/TCH Drop– Low proportion of better cell HOLow proportion of better cell HO– High rate of DL/UL quality HO and High rate of DL/UL quality HO and

interference HOinterference HO– Low HO success rateLow HO success rate

A interface indicatorsA interface indicators– High rate of Clear Request message, High rate of Clear Request message,

cause radio interface failurecause radio interface failure Drive TestDrive Test

– RxQual > 4 with RxLev > -85 dBmRxQual > 4 with RxLev > -85 dBm


ii. Interferenceii. Interference Problem ProblemTypical causes :Typical causes :

GSM interferencesGSM interferences Co-channelCo-channel adjacentadjacent

Non GSM InterferenceNon GSM Interference Other Mobile NetworkOther Mobile Network Other RF sourcesOther RF sources



Co-channel interference :Co-channel interference : C/I = Carrier-to-interference C/I = Carrier-to-interference

ratioratio +12 dB is taken into account +12 dB is taken into account

for Alcatel ( +9 dB according for Alcatel ( +9 dB according to GSM standard) (i.e. to GSM standard) (i.e. interference can be 9 interference can be 9 12 12 dB weaker than serving cell dB weaker than serving cell to cause poor RxQual).to cause poor RxQual).

Level

Frequencyf(cell1)=f(cell2)

+12 dB



Co-channel interference :Co-channel interference : IndicationsIndications

Downlink and/or Uplink InterferenceDownlink and/or Uplink Interference High rate of quality handover, call drop, High rate of quality handover, call drop,

and call setup failureand call setup failure

InvestigationInvestigation Drive test analysisDrive test analysis Lumpini: Co-channel checkingLumpini: Co-channel checking Check prediction to verify which cell Check prediction to verify which cell

could be causing the interferencecould be causing the interference Frequency plan C/I < 12 dBFrequency plan C/I < 12 dB



Co-channel interference :Co-channel interference : OptimizationOptimization

Antenna optimizationAntenna optimization Change frequencyChange frequency Reduce BTS power (not an option in TA Reduce BTS power (not an option in TA

Orange network)Orange network) Concentric cellConcentric cell


ii. Interferenceii. Interference Problem ProblemCo-channel interference: Optimization: Co-channel interference: Optimization: Concentric cellConcentric cell

ConceptConcept Conclusion from Alcatel Conclusion from Alcatel trial on Orangetrial on Orange’’s network s network (Suburban area)(Suburban area)

Concentric cell is difficult to Concentric cell is difficult to optimize, and hence is optimize, and hence is rarely used in the network rarely used in the network today.today.


ii. Interferenceii. Interference Problem ProblemAdjacent channel interference :Adjacent channel interference : C/A = Carrier-to-adjacent ratioC/A = Carrier-to-adjacent ratio -6 dB is taken into account for Alcatel ( --6 dB is taken into account for Alcatel ( -

9 dB according to GSM standard).9 dB according to GSM standard).Level

Frequencyf(cell2)=f(cell1)+1

-6 dB

f(cell1) f(cell2)

E.g.f(cell1)= Ch.573f(cell2)= Ch.574


ii. Interferenceii. Interference Problem ProblemAdjacent channel interference :Adjacent channel interference : IndicationsIndications

Downlink and/or Uplink InterferenceDownlink and/or Uplink Interference High rate of quality handover, call drop, and High rate of quality handover, call drop, and

call failurecall failure InvestigationInvestigation

Adjacent HO statistics (if they are defined Adjacent HO statistics (if they are defined as neighbors). If they often handover, then as neighbors). If they often handover, then adjacent channel interference could be a adjacent channel interference could be a problem.problem.

Drive test analysisDrive test analysis Lumpini: Adjacent channel checkingLumpini: Adjacent channel checking Cell coverage predictionCell coverage prediction Frequency plan C/I < -6 dBFrequency plan C/I < -6 dB



Adjacent channel interference :Adjacent channel interference : OptimizationOptimization

Antenna optimizationAntenna optimization Change frequencyChange frequency Reduce BTS power (not an option in TA Reduce BTS power (not an option in TA

Orange network)Orange network) Concentric cellConcentric cell


ii. Interferenceii. Interference Problem ProblemInterference : Forced Directed RetryInterference : Forced Directed Retry

MS should connect to Cell_A, but MS should connect to Cell_A, but no TCH available.no TCH available.

MS connects to Cell_B with forced MS connects to Cell_B with forced directed retrydirected retry

MS is emitting at high level (due to MS is emitting at high level (due to long distance from Cell_B)long distance from Cell_B)

UL interference for Cell_CUL interference for Cell_C Cell_B is emitting at high level (if Cell_B is emitting at high level (if

DL PC is being used)DL PC is being used) DL interference at Cell_CDL interference at Cell_C

MS is serving on the 2MS is serving on the 2ndnd or 3 or 3rdrd best best server: increases chances of server: increases chances of interference problem (poor C/I & interference problem (poor C/I & C/A as C/A as ““CC”” is lower) is lower)

Cell_B: Ch.573

Cell_C: Ch.572

Cell_A: Ch.569



Non GSM interference :Non GSM interference :

Other mobile networkOther mobile network Inter-modulation with GSM BTS/MS Inter-modulation with GSM BTS/MS

receiverreceiver Other RF interferersOther RF interferers

RadarRadar Shop anti-theft mechanismShop anti-theft mechanism Medical devicesMedical devices Other man-made radio transmissionOther man-made radio transmission Illegal usage of GSM frequencies (e.g. Illegal usage of GSM frequencies (e.g.

illegal imported devices, illegal usage illegal imported devices, illegal usage of other organization, ...)of other organization, ...)

......


iii. Unbalance power budgetiii. Unbalance power budget ProblemProblem

A cell facing unbalanced power budget A cell facing unbalanced power budget problems presents a too high path-loss problems presents a too high path-loss difference between UL and DL (often DL>UL)difference between UL and DL (often DL>UL)

Lower Rx diversity gain of cross polarized Lower Rx diversity gain of cross polarized antenna in rural area compared to dense antenna in rural area compared to dense areaarea

Crossed feedersCrossed feeders Traffic not directly in boresight of antenna, Traffic not directly in boresight of antenna,

where cross-polar discrimination is lowerwhere cross-polar discrimination is lower Loose connectorsLoose connectors Faulty antenna, feeder, TMAFaulty antenna, feeder, TMA Rule : try to have delta as small as possible Rule : try to have delta as small as possible

to avoid access network possible only in 1 to avoid access network possible only in 1 direction (usually BTS->MS : OK and MS-direction (usually BTS->MS : OK and MS->BTS : NOK), i.e. uplink limited>BTS : NOK), i.e. uplink limited


Indicators :Indicators : OMC QoS indicatorsOMC QoS indicators

– High ratio of Uplink level Handover causeHigh ratio of Uplink level Handover cause– Low incoming HO success rateLow incoming HO success rate– DL level looks OK for HO, but UL is too DL level looks OK for HO, but UL is too

weak when HO is attemptedweak when HO is attempted– Degradation of TCH failures and OC call Degradation of TCH failures and OC call

drop indicatorsdrop indicators A interface indicatorsA interface indicators

– High rate of Clear Request message, High rate of Clear Request message, cause radio interface failurecause radio interface failure

O&M AlarmsO&M Alarms– Voltage Standing Wave Ratio (VSWR)Voltage Standing Wave Ratio (VSWR)– TMATMA



Investigation :Investigation : AAbisbis monitoring: monitoring:

– ABS(delta Path loss) > 10ABS(delta Path loss) > 10» Check if problem is occurring for 1 Check if problem is occurring for 1

TRX or all.TRX or all.– ABS(delta path loss) = ABS(UL Path loss ABS(delta path loss) = ABS(UL Path loss

–– DL Path loss) DL Path loss)– UL Path loss = MS transmitted power UL Path loss = MS transmitted power ––

measured received UL levelmeasured received UL level– DL Path loss = BTS transmitted power DL Path loss = BTS transmitted power ––

combiner loss combiner loss –– measured received DL measured received DL levellevel

– Large difference between uplink and Large difference between uplink and downlink level triggered HO.downlink level triggered HO.

Use PM observation counter (in OMC-R)Use PM observation counter (in OMC-R)– RT11RT11



Optimization : This equipment Optimization : This equipment should be checkedshould be checked

TRX types (MP, HP)TRX types (MP, HP) Antennas or common RF Antennas or common RF

components, TMA (common to all components, TMA (common to all TRX of the BTS)TRX of the BTS)

TRX RF cables, LNATRX RF cables, LNA



iv. TCH congestioniv. TCH congestion ProblemProblem

TCH Congestion : TCH Congestion :

TCH Congestion rate (TCH TCH Congestion rate (TCH Assignment Phase) is too Assignment Phase) is too high (more than 2%)high (more than 2%)

Rule : try to meet the offered Rule : try to meet the offered traffic (asked by users) by traffic (asked by users) by providing the right number of providing the right number of resources (TRX extension)resources (TRX extension)



Indications :Indications : Customers complain about Customers complain about ““Network Network

busybusy”” OMC QoS indicatorsOMC QoS indicators

– High High ““TCH Congestion rateTCH Congestion rate””, , ““RTCH RTCH Assignment fail-CongestionAssignment fail-Congestion””

– Low Low ““incoming Intra/Inter BSC HO success incoming Intra/Inter BSC HO success raterate”” (no TCH available) (no TCH available)

– High High ““Directed Retry rate or Congestion Directed Retry rate or Congestion Relief (Motorola)Relief (Motorola)”” if activated if activated

A interface indicators: A interface indicators: ““BSS Congestion BSS Congestion failure in OCfailure in OC””

– High rate of Assignment Failure message, High rate of Assignment Failure message, No radio resource availableNo radio resource available

Drive TestDrive Test– Handover to better cell is slow, or never Handover to better cell is slow, or never

occursoccurs



Optimization :Optimization :

Special events :Special events :– Foreseeable: football match, Foreseeable: football match,

important meeting, Exhibition, important meeting, Exhibition, etc.etc.

» Add some extra TRXsAdd some extra TRXs» Add special mobile BTSs (Cell Add special mobile BTSs (Cell

on Wheel)on Wheel)» Activate HR (may not always Activate HR (may not always

be possible due to BSC be possible due to BSC capacity limitations)capacity limitations)

– Not foreseeable: car crash on the Not foreseeable: car crash on the highwayhighway




Daily periodic problems : At busy Daily periodic problems : At busy hour:hour:

– Hardware solution :Hardware solution :» Add TRX(s)Add TRX(s)» Concentric cellConcentric cell» New siteNew site» Optimize cell boundaries (i.e. Optimize cell boundaries (i.e.

antenna optimization) to antenna optimization) to share traffic with surrounding share traffic with surrounding cellscells




Daily periodic problems : At busy Daily periodic problems : At busy hour:hour:

– Software solution :Software solution :» Directed RetryDirected Retry» Traffic HandoverTraffic Handover» Half Rate (Alcatel)Half Rate (Alcatel)» Congestion Relief (Motorola)Congestion Relief (Motorola)» Flow control (Motorola)Flow control (Motorola)


Problems Problems and responsible and responsible partiesparties

Coverage problem :Coverage problem : If the measured RxLev does not If the measured RxLev does not

match the predictionmatch the prediction– Check the prediction, check Check the prediction, check

panoramic pictures for obstructionspanoramic pictures for obstructions– Field Operation team to check Field Operation team to check

physical configuration (tilt, physical configuration (tilt, azimuth, antenna height...). Also azimuth, antenna height...). Also check for faults in the antenna check for faults in the antenna system (VSWR, sweep antennas, system (VSWR, sweep antennas, DTF test, etc.)DTF test, etc.)

– If Field Operation find no problem, If Field Operation find no problem, antenna optimization antenna optimization maymay be be required (if necessary)required (if necessary)



Coverage problem :Coverage problem :

If the field reality match the If the field reality match the predictionprediction

– RF team to add new sites (tri-RF team to add new sites (tri-sector, micro cellular, indoor sector, micro cellular, indoor cells) to improve poor/no cells) to improve poor/no coverage area (Optimizer coverage area (Optimizer requests for some new sites to RF requests for some new sites to RF team regarding to the drive test team regarding to the drive test result)result)


Interference problem :Interference problem : Optimization team to identify the Optimization team to identify the

interference source and request interference source and request Spectrum Management team to Spectrum Management team to correct it in case of internal source correct it in case of internal source (new frequency planning...)(new frequency planning...)

Unbalanced power budget Unbalanced power budget problem :problem :

Field Operation team to check the Field Operation team to check the impacted BTS (Antenna, TMA, RF impacted BTS (Antenna, TMA, RF cables, LNA, diversity system...) cables, LNA, diversity system...) according to request from Optimizer.according to request from Optimizer.



TCH Congestion problem :TCH Congestion problem :

Regional RF to request TRX Regional RF to request TRX expansion.expansion.


GSM Optimization

Documents

global indicatorsimportant

ta orange

radio link

dlul quality

radio interface

global indicators

daily periodic

alerting connection