2G RF Network Optimization Cases_3
66
2G RF Optimization 2G RF Network Optimization Cases Lampiran 5
-
Upload
ashu-kunwar -
Category
Documents
-
view
190 -
download
50
description
optimization
Transcript of 2G RF Network Optimization Cases_3
-
OutlineProblems SysmtomsCoverage AnalysisDrop Call Analysis Call Setup AnalysisHandover AnalysisSpeech Quality AnalysisInterference ReductionParameter Optim
-
How to improve the network?AlternativesAnalyzing ProgramsStatus of the NetworkDecide further Analysis ProgramCoverageDropped CallsCall Setup SuccessHandover Perf.Speech QualityGeneral CheckConcept for Optimisation *[email protected]
-
Problem Symptoms*[email protected]
No service
No coverage
No System AvailabilityNetwork Element FailuresTransmission Network Failures
Low call setup success rate
RF NetworkNo coverageInterferenceBlockingFixed Network BSS, SSSBlockingOverloadOther
High call drop rate
RF Network
No coverage
Interference
Handover failure
Fixed Network BSS, SSS
Network Element Failure
Transmission Failures
Other networksMobile terminal
Poor speech quality
RF Network
No coverage
Interference
Poor handover performanceFixed Network BSS, SSS
Network element failure
Transmission network failure
Other networksMobile Phone
2G RF Optimization
Coverage Analysis
-
Page - * Shadowed Antenna Antenna Direction Antenna Height / down tilt Output Power Missing Neighbor Relation Site Location Faulty Hardware e.g. antenna Cell is downSignal Strength Case Possible Reasons [email protected]
-
Page - *Shadowed AntennaFaulty HardwareHeight/down TiltOutput PowerVisit siteCheck antenna installationIs there a better antenna position at same site?Add reduce down tilt? Can antenna be placed lower or higher to give better coverage? Check output powerParametersBSPWRT - NON BCCH FREQBSPWRB - BCCH FREQSite LocationPossible to move site?New antenna location at same site? Is it necessary to expand and build a new site? Check alarm & BTS Error logVisit site
AnalysisMissing NeighborIs the call dragged?Is low SS due to missing neighbor relations Signal Strength [email protected]
-
Page - * Change parameter BSPWR , BSPWRT. Add neighbor relation. Physical changes: Antenna direction Antenna height, tilt or position New site as last option. Signal Strength Case Possible [email protected]
-
Page - * Shadowed Antenna Antenna Direction Antenna Height / down tilt Output Power Missing Neighbor Relation Site Location Faulty Hardware e.g. antenna Cell is downSignal Strength Case Possible Reasons [email protected]
-
Page - *Shadowed AntennaFaulty HardwareHeight/down TiltOutput PowerVisit siteCheck antenna installationIs there a better antenna position at same site?Add reduce down tilt? Can antenna be placed lower or higher to give better coverage? Check output powerParametersBSPWRT - NON BCCH FREQBSPWRB - BCCH FREQSite LocationPossible to move site?New antenna location at same site? Is it necessary to expand and build a new site? Check alarm & BTS Error logVisit site
AnalysisMissing NeighborIs the call dragged?Is low SS due to missing neighbor relations Signal Strength [email protected]
-
Page - * Change parameter BSPWR , BSPWRT. Add neighbor relation. Physical changes: Antenna direction Antenna height, tilt or position New site as last option. Signal Strength Case Possible [email protected]
2G RF Optimization
Drop Call Analysis
-
Dropped Call AnalysisHow to measure drive testsrepeated call setups (preferred)continuous callsOMC measurementsReasons for dropped callslack of coverageinterference problemshandover problemslack of synchronisation in networkproblems with other parts of the network*[email protected]
-
Overview cont.TCH Drop Excessive Timing AdvanceLow Signal StrengthBad QualitySudden LossOther reason
TxNDROP (x=F for full rate, x=H for half rate) total number of dropped TCH connections incremented when theres abnormally terminated connections
-
Dropped Call - Low Signal StrengthDropped calls due to low signal strength can occur in downlink (DL), uplink (UL) or bothlink (BL)
Reasons :Isolated siteAntenna/Feeders too much downtilt, incorrect orientation, hidden antenna, faulty antenna/feedersOutput power incorrect power settingsBSC Exchange property improper LOWSSUL/DL settingsUnforseen subscriber behaviour use MS in lifts, car parkMissing NRELObstacles building, hills, tunnel etc.*[email protected]
-
Low SS troubleshootingCheck power settings (BSPWRB, BSPWRT), power balanceCheck neighbour relationsuse site position on map and manually determine neighbourfind suitable neighbourconsistency check to find missing relationsBTS error log check for any hardware faults indicating high VSWRPerform drivetestCheck for missing neighbours, swapped feeders, probable obstacles
-
Low SS troubleshooting cont.LOWSSUL & LOWSSDL settingsThe settings of LOWSSUL/DL influences the counter step If LOWSSDL & LOWSSUL have same value, than STS would probably indicate most of the low SS drop is on the UL. Recommend to have LOWSSDL > LOWSSUL because MS&BTS sensitivity different and SS on UL&DL are different
-
Dropped Call Bad QualityDropped calls due to bad quality can occur in downlink (DL), uplink (UL) or bothlink (BL)Reasons :Frequency plan adjacent and co-channel interferenceNo dominant server low SSMissing NREL MS is not able to connect to strongest serverHardware problems antennas, feeders, connectorsEnvironment near open waterExternal other networks, microwave links, illegal transmitters*[email protected]
-
Bad Quality troubleshooting cont.Perform drivetest can locate interferer by halting the effected cell & performing freq. scanning to locate the interfering cell. can also use spectrum analyser check for missing NREL QLIMUL & QLIMDL ensure correct settings. Recommended QLIMUL/DL = 55 for hopping and QLIMUL/DL = 45 for non-hoppingReduce interference if cant change freq, then consider downtilt/power down interfererUse features IHO,DTX, Frequency hopping, MS/BTS Power Control*[email protected]
-
Dropped Call Sudden LossValid when none of the first 3 types of droppped calls (i.e. excessive TA, low SS, BQ) are indicated and locating procedure indicates missing measurement results from MS
-
Sudden Loss Probable ReasonEnvironment sudden drop in SS, such as when subscribers enter into building, lift, tunnel etc.Battery MS battery finishes during conversation, or battery being pulled outBTS/MS hardware faultTransmission fault synchronization/ABIS link faultInterference very sudden and severe occurrence of interference or bad quality*[email protected]
-
Sudden Loss troubleshootingRLINKT & RLINKUP check is correct settings. Consider increasing for certain scenariosCheck synchronization and link faultsCheck BTS error logCheck if its related to human behaviour
-
Dropped Call Other reasonsTCH drops due to other reason than low SS, bad quality, excessive TA and sudden loss. Reasons :No specific counters reasons for it occuring are subjectiveHardware faults BTS or MSTransmission/link problemsMaintainence work affecting network serviceInterference severe interference problems
-
Other reasons - troubleshootingCheck BTS error log any HW faultsCheck with O&M transmission problems, maintainence work during the effected time periodCheck if indicating uplink interference in cellCheck object type help find faulty devices
2G RF Optimization
Call Setup Analysis
-
BTSMSRACH(1)RACH (2)RACHAGCHE.g: MAXRETR = 2MAXRETRSlotted ALOHA mechanism: Several users may attempt to access channel simultaneouslyin case of collision new attempts are madeMAXRETR: Maximum no. of retries allowed*[email protected]
-
Page - *Call Setup Failure Analysis- Possible reasons with rankingLow Signal StrengthInterferenceHigh Congestion on SDCCH High Congestion on TCHTransmission FaultFaulty TRU/Hardware Central Processor OverloadSoftware File CongestionCell is not defined in [email protected]
-
Page - *Call Setup Failure Analysis- Possible solutionsLow signal strength Signal strength analysis.Interference Interference analysis.High Congestion on SDCCH:Define more SDCCHs. Activate adaptive configuration of logical channel feature and immediate assignment to TCH.High Congestion on TCH:Add capacity/Tune coverage array.Activate assignment to worse cell.
-
Page - *Failed Call Setup (Blocked Call) ExampleMultiple Channel Requests.Successful Random Access after the third try. Congestion in [email protected]
2G RF Optimization
Handover Analysis
-
Handover Performance AnalysisWhen moving from one cell to another (neighbour cells) handovers are necessary*[email protected]
-
Handover ParametersObjectives:mobile should be connected to the bestcellavoid unnecessary handoversConsequencegood speech qualityless dropped calls*[email protected]
-
Consequence of Missing NeighboursDefined neighboursServerMissing neighbourInterfererCell dragging*[email protected]
-
Consequence of Many Neighbour DefinitionsOnly about 100 measurement samples are possible during one measurement period for all defined neighbour cells
(Rec. GSM 0508)Problem:Sites with too large coverage area*[email protected]
Number of BCCH carriers
Number of samples per
In BCCH Allocation
Carrier in SACCH multiframe
32
34
16
67
10
1011
8
1213
:
:
-
Handover ParametersFine-tuning of handover parametersMoving cell boundaries in order to Enhance success rate for critical handoversMinimise local interference at the cell edgeTraffic load sharing between cellsCompared to other opimisation measures improvement potential is limitedAffected byMeasurement averagingPower control parametersNeighbours should in generalbe mutual*[email protected]
-
0637Intracell HOdue to QualityNo handoveraction due toquality or levelIntercell HOdue to qualityIntercell HOdue to levelHandover CriteriaHandover Region (due to quality and level)*[email protected]
-
Handover Decision*[email protected]
Sheet1
Handover TypesDecision Criteria
Intercell HO1. RXQUAL_XX > L_RXQUAL_XX_H
due to Quality2. RXLEV_XX < L_RXLEV_XX_IH
3. XX_TXPWR = Min (XX_TXPWR_Max,P)
HO due to Level1. RXLEV_XX > L_RXLEV_XX_H
2. XX_TXPWR = Min(XX_TXPWR_Max,P)
HO due to Distance1. MS_BS_DIST > MS_Range_Max
HO due to1. RXLEV_NCELL(n) > RXLEV_MIN(n)
Power Budget+ Max (0,MS_TXPWR_MAX(n)-P)
2. PBGT(n) > HO_MARGIN(n)
Intracell HO1. RXQUAL_XX > L_RXQUAL_XX_H
due to Quality2. RXLEV_XX > L_RXLEV_XX_IH
Sheet2
Sheet3
-
L_Rx_Qual_XX_HL_Rx_Lev_XX_IHL_Rx_Lev_XX_HIntracell HOdue to QualityIntracell HandoverCheck for simultaneous occurrence of:Poor quality (high Rx_Qual)Sufficient signal level L_Rx_Lev_XX_IH
-
Rx_LevDriven routeHO_Threshold_LevServerneighbourHOMARGINMinHOReqIntLevel HandoversAdjacent cell not stronger than current cell + HO marginServing cell has insufficient coverageemergency handover to cell with better coverage*[email protected]
-
Page - *INPUTLarge area DTSpecific area DTPost-ProcessingAnalysisLook for: Repeated handover (Ping Pong)Repeated Intra-cell handoverHandover failure, Unrealistic handoverHandover Case [email protected]
-
Page - *Repeated Handover (Ping Pong)- [email protected]
-
Page - *Repeated Handover (Ping Pong) - Possible Reason 1Merry-go-round Handover, Offset > Hysterisis [email protected]
-
Page - *Repeated Handover (Ping Pong) - Possible Reason 2Offset only in one direction e.g A-B for Inter BSC relationCELL ACELL BA -> B OFFSET = -5dBBSC 2BSC 1No B -> A [email protected]
-
Page - *Repeated Handover (Ping Pong) Other Possible ReasonsNo dominant serverLocating penalty settingsToo small hysterisis [email protected]
-
Page - *Antenna direction
Antenna Tilts
Plan for new site
Change Locating Parameter e.g. KHYST or LHYSTRepeated Handover (Ping Pong) Possible Solutions [email protected]
-
Page - *Change Parameter, KHYST or LHYSTHysterisisCELL ACELL BHandover From A to BRepeated Handover (Ping Pong) Possible Solution [email protected]
-
Page - *Check layer 3 message Handover command BSC correct?Check reason for handover SS, RXQUALTarget cell?Handover Case Handover [email protected]
-
Page - *Duplicates of BSIC BCCH combinations in neighboring list610_31610_31610_12606_33608_32608_32Serving cellNeighbor cell 1RoadNeighbor cell 2Handover command?Handover Reversion Common Reason [email protected]
-
Page - *Uplink interference in target cellDownlink interference at MSSolutionsInterference Investigation Statistics ScanningHandover Reversion Other [email protected]
-
Page - *Possible ReasonsWrong intra-cell handover settings External Uplink InterferencePossible SolutionsConsider to change parameters: SSOFFSETUL, SSOFFSETDL QOFFSETUL, QOFFSETDLA wrong setting of parameters will cause unnecessary IHOTurn off Intra-cell Handover?Handover Case Repeated Intra-cell [email protected]
-
Page - *Handover Case Unrealistic [email protected]
-
Page - *Possible ReasonsWrong locating settings, in Serving or Target cellNote: Could be on purpose e.g. Dual Band network with HCS
Solution Fix locating settings e.g. MSRXSUFF, BSRXSUFF
Unrealistic Handover Reason & [email protected]
2G RF Optimization
Speech Quality Analisys
-
Speech Quality AnalysisParametersRxQualFrame Erasure Rate (FER)Speech Quality Index (SQI)MeasurementsDrive testpreferably continuous callOMC statisticsCause for poor qualitylow signal strength (coverage relatedinterferencelow signal strength and interferenceCauses of interferenceco-channel interferenceadjacent channel interferenceintermodulationmainly on one link onlymultipath interferenceInterfering cell of base station within GSM - networkBase station within GSM Network
-
Downlink Interference MeasurementTypical requirementspeech: RxQual 4data: RxQual 3With frequency hopping: RxQual not a valid parameter*[email protected]
BER %
RxQual
0.0 - 0.2
0
0.2 - 0.4
1
0.4 - 0.8
2
0.8 - 1.6
3
1.6 - 3.2
4
3.2 - 6.4
5
6.4 - 12.8
6
> 12.8
7
-
Frequency ChangesSometimes necessary to minimise interferenceAs network reaches capacity limit this becomes difficultOther frequencies may be affected by the changeCan be done at either interfering cell or victim cellChoice: Whichever happens to be easier to changeExisting plan may be entered into planning tool as constraintssearch for optimum frequency allocation for a given cellAt a certain point the whole network e.g. in a city may have to be re-planned*[email protected]
-
Effectiveness depends on TCH traffic loadBCCH / TCH sub-bands are mixedCould be used as a temporary measurewhile traffic load is lowFrequency ChangesBCCH/TCH swappingMethod sometimes used: Alternate between clusters*[email protected]
-
f9f9f9BSIC OptimisationBase Station Identity CodesUsed by the MS to distinguish between cellsusing the same frequencyCo-Channel cells must have different BSICs*[email protected]
-
Location Area CodesPurposeidentify location areain incoming call is paged to all BTSs within LALarge location areaadvantage: less location updates (reduced SDCCH load)disadvantage: more paging trafficBoundaries should not cross high traffic areasCell reselection across LA boundariesParameter Cell_Reselect_Hysteresis (typ. 4 dB) used to avoid unnecessary signalling due to ping-pong cell reselections*[email protected]
-
Power Control*[email protected]
-
Page - *
INPUTLarge area DTIdentify areas with Rxqual > 5 Identify source using Map and STSNew drive test around problem area?
Specific area DTPost-ProcessingAnalysisInterference Case [email protected]
-
Page - *BCCH 590BCCH 590High siteBCCH 590BCCH 590BCCH 595BCCH 600CASE 1CASE 2Types of Interference Co - Channel interference Adjacent [email protected]
-
Page - * Poor frequency plan No dominant cell --> low C/I ---> increased Rxqual Frequency Hopping is off External interference e.g. jammerExample of high Rxqual due to low Signal Strength Interference Case Possible [email protected]
-
Page - *Interference Case Possible solutionsEnable Frequency Hopping or add frequencies to Hopping group.Enable BTS Power Control, MS power control and make it less aggressive.Change frequency of interferer or interfered cell: Possible to find new frequency by using TEMS Scanning.Down tilt or change antenna of interferer.Redo frequency plan.Add new [email protected]
2G RF Optimization
Cell Parameter Optim
-
Cell Parameter OptimisationDefault parameter sets:Standard setting suitable for most casesStarting point for possible optimisation, howevermore relevant after other optimisation activitiesDifferent parameter standards may be used for different area typesBTS typesetc.Dangermany parameters easy to lose overviewinconsistenciesdeterioration of quality*[email protected]
**When a call is abnormally disconnected, a check is made in the Assignment/Handover function so see any of the urgency state existed. If more than one type of urgency is indicated in locating, then the following in order of highest priority is used to determine type of urgency state : 1) Excessive Timing Advance2) Low Signal Strength3) Bad quality4) Sudden loss
Counter TFNDROP gives the total number of dropped TCH connections. Counter is step either in two conditions :When BSC sends CLEAR REQUEST to MSC and MSC then sends CLEAR COMMAN to BSCOrb)MSC sends CLEAR COMMAND and cause value is neither for Call Control or Handover Succesful*Other related counters are TFDISSSx= TFDISSS1, TFDISSS2, TFDISSS3, TFDISSS4, TFDISSS5 (depending on MS classs)
*Check power settings are defined properly. Also can check power balance to see if system is UL/DL limited.Check neighbour relations define suitable relations by looking at site position on map, RNO feature (NCS/NOX), consistency check can be carried out to find missing neighbour relations (defined as single).
Check error logs for any hardware faults indication such as high VSWR which could limit output power.
*By default LOWSSDL & LOWSSUL are set to -104dBm. As we know that MS and RBS sensitivity is different. RBS sensitivity is around 110dBm and MS is 104dBm. If LOWSSUL/DL are set to 104dBm, then most drops will fall in the low signal strength uplink category first.
*If RxQual UL> BADQUL, counter TFDISQAUL will be steppedIf RxQual DL> BADQDL, counter TFDISQADL will be steppedIf RxQual UL> BADQUL and RxQual DL> BADQDL, then counter TFDISQABL is step
*Drivetest can be carried out to determine the source of the interferer. One method is to hald the effected cell and perform frequency scanning to locate the interfering cell. The source of the interference and the channel that is causing interference can be found by using a spectrum analyser along with a directional antenna.Important to set the correct settings for QLIMUL/DL which determines the condition for bad quality urgency handover. Recommended value for QLIMUL/DL = 55 for hopping channels and 45 for non-hopping channels.If the source of the interference is known, and it isnt possible to change the frequency to a cleaner one, than can consider down tilting or reducing the output power of the interferer.Features such as Intra Cell Handover, DTX, frequency hopping, MS/BTS Power Control can be implemented to reduce the interference in the network.
*Sudden loss of connection is valid if none of the first three drop calls (excessive TA, low SS and Bad Quality) is indicated and also the locating procedure indicates missing measurement results from the MS.
*One of the reasons for sudden loss is due to the rapid decrease in SS when subscribers enter a building, lift or tunnel where there isnt coverage. It could also be due to hardware faults and unstable transmission links. Other reasons would be interference problems or MS battery runs out during conversation.*Check the radio link time-out value, and if for scenarios like for a tunnel, see if its possible to retain the call by setting a longer RLINKT RLINKUP.Check the synchronization and ABIS link faults. Check the location fot the drops. If it is related to human behaviour, than there is nothing much that can be done.Check BTS error log for any hardware faults that could cause drop calls.
*If the cell suffers from dropped calls besides the reasons low SS, bad quality and excessive timing advance the dropped calls will be counted as other reasons. That is that the counters for SS, quality and timing advance are notincremented and only the CNDROP, TFNDROP or THNDROP are stepped.
*Check BTS error log for hardware faults. Ask O&M personnel whether there were any work being carried out during the effected period. Since severe interference could also cause drops due to other reasons, then it would be useful to check the ICM and also RxQual distribution using MRR. Useful also to check object type MOTS, which is based on drop on TS to find faulty devices.To check drop on TS can use formule TS_DR = (CONNERCNT/CONCNT)*100%*
