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Ps irat(u2g) optimization

Ps irat(u2g) optimization. INTRODUCTION. PS IRAT (UMTS to GSM ) Success Rate

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Ps irat(u2g) optimization

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  1. Ps irat(u2g) optimization

  2. INTRODUCTION PS IRAT (UMTS to GSM ) Success Rate The KPI defines the success rate for PS Inter RAT cell change attempts for UE on dedicated channel. During Inter-RATCC from UTRAN to GPRS, UE on DCH, the Handover evaluation function triggers this function to indicate that we need to make handover to a GSM cell. PS IRAT SUCCESS RATE = pmNoOutIratCcSuccess/pmNoOutIratCcAtt

  3. Flowchart for IRATCC from UTRAN to GPRS

  4. STEPS FOR PS IRAT OPTIMIZATION • To start with , Neighbour List Tuning has to be done. Prominent 2G neighbours should be added and Far-off neighbours should be deleted. • 3G cells with very low number of 2G relations have to be identified . It is preferred to have atleast 7 gsmrelations per utrancell. • Proper Selection Priority for gsmrelations has to be given based on 2G-2G Handover Matrix ,Tier and distance.The colocated 2G cell, 2G cells of the same site and TIER 1 neighbours should be given selection priority as 1, selection priority as 2 to TIER 2 neighbours and so on. • The 2G definitions like LAC , CI, BCCH, BSIC have to be checked if they are defined correctly in the RNC/MSS or not. • To check 2G definitions in the RNC, we can use following command line in the RNC- getexternalgsmcell = GSM Cell Name This has been illustrated with an example in the next slide

  5. BSIC=nccbcc = 21

  6. Identifying worst gsmrelations • After all neighbour tuning, checking cell definitions has been done , it has to be checked if the IRAT failure is occuring for some particular gsmrelations. Observing trends of pmNoOutIratCcSuccess and pmNoOutIratCcAtt per utrancell per gsmrelation can help in finding such worst gsmrelations • After the worst gsmrelations identification has been done , we should check the packet channel allocation attempts and packet channel allocation failures .The 2G counters for finding the same are: PCHALLATT for Number of packet channel allocation attempts and PCHALLFAIL for Number of packet channel allocation failed • Hard Blocking and Soft Blocking in the worst gsmrelations have also to be checked .High packet channel failure implies 2G congestion.

  7. CONGESTION IN 2G CELLS • The counter pmNoOutIratCcReturnOldChhas also to be verified. This counter provides the total number of the PS Inter-RATCC attempts for UE on DCH where the UE returns to old channel. It is stepped for Inter-RATCC from UTRAN to GPRS, UE on DCH. The counter is increased when the “Cell change order from UTRAN failure” RRC message is received from the UE.ONE REASON FOR RETURN TO OLD CHANNEL (i.e 3G) IS HIGH PDCH ALLOCATION FAILURE. • To improve PS IRAT in such cases, following actions might be taken: 1.2G congestion has to be resolved which can be done by allocating more PDCH channels . In cases of extreme congestion, additional TRXs may be installed. 2.3G parameters can be retuned to trigger IRAT from 3G to 2G only when 3G coverage becomes very poor and 2G radio conditions are very good. The parameters to be tuned have been explained in the upcoming slide.

  8. Optimizing 3G parameters • By lowering the value of the parameters like serviceOffest2dEcNo and serviceoffset2dRscp we can delay the compress mode and can avoid unnecessary compress mode .The counters pmcmattdlhls and pmcmsuccdlhls can be used to find the number of HLS attempts and success respectively. The value of the parameter ‘gsmthresh3a’ can also be increased to trigger IRAT only when 2G radio conditions are very good. This will reduce PS IRAT attempts and will also improve PS IRAT success rate. An example of the parameter settings is: gsmthresh3a can be increased to -90 serviceOffest2dEcNo to -3 serviceoffset2dRscp to -5 (The setting of these parameters may vary from network to network) • However ,it is advisable to change service offsets only for following UeRC states: 64/64,128/128,64/128 and 128/64 • If the PS IRAT remains poor even after tuning the above parameters and adding additional PDCH , then NEGATIVE INDIVIDUAL OFFSET can be set for some particular worst gsm relations. However, this will affect CS IRAT as well so care should be taken of. • The ICM bands in 2G have also to be checked.

  9. ICM band ICM BAND-INTRODUCTION If ICM is active, GPRS/EGPRS Channel Administration can use the ranking of channels into interference bands as helpful information when selecting channels from the circuit switched domain to be configured as dedicated or on-demand PDCHs. When a PDCH is reconfigured to a TCH, the channel is placed in the interference band it was in before it was allocated as PDCH. Idle Channel Measurements are not performed on PDCHs . For idle channel measurement there are four object types for FR/HR and OL/UL i.e Overlaid and Underlaid. In these object types there are counters for the accumulated number of idle channels in each interference band viz. ITFUSIBi ,ITHUSIBi,ITFOSIBi ,ITHOSIBi i as 1,2,...,5. RELATED KPIs ITFOSIB1 + ITHOSIB1 = OLICM 1, ITFOSIB2 + ITHOSIB2 = OL ICM 2, ITFOSIB3 + ITHOSIB3 = OLICM 3,ITFOSIB4 + ITHOSIB4 = OL ICM 4, ITFOSIB5 + ITHOSIB5 = OL ICM 5, ITFUSIB1 + ITHUSIB1 = UL ICM 1 , ITFUSIB2 + ITHUSIB2 = UL ICM 2 , ITFUSIB3 + ITHUSIB3 = UL ICM 3 , ITFUSIB4 + ITHUSIB4 = UL ICM 4 , ITFUSIB5 + ITHUSIB5 = UL ICM 5

  10. Correlating icm band with PS IRAT SUCCESS RATE If ICM Band is showing high value in ICM Band 4 (which is above -98 dBm) and ICM Band 5(which is above -88dBm) , then there is definitely some source of external interference in the 2G cell and this may also cause PS IRAT FAILURE in the cells. A spectral scan using Spectrum Analyser should be done in high interference cells. We can also use Band Pass filter or CDMA filter to resolve the issue. The screenshots below show two cells of Aircel J&K where ICM Band 4 and ICM Band 5 are showing high values and corresponding PS IRAT Success rate are also very low. Its probable that because of external interference in the 2G cell, the PS IRAT attempts are not becoming successful.

  11. 2G PARAMETER-ICMSTATE • The parameter ICM STATE also needs to be checked. ICM STATE is a parameter defined in the BSC that sets the idle channel measurements to ACTIVE, PASSIVE or NOALLOC. NOALLOC means that the idle channel measurements are used for statistics only, and not for channel allocation. RECOMMENDED VALUE Some additional 3G parameters and counters that can be checked for PS IRAT optimization have been explained in the next few slides.

  12. Parameter- gsmAmountPropRepeat • This parameter decides how many times RNC will command UE to re-attempt cell change to the GSM cell repeatedly based on the same measurement report excluding the first attempt. A few UEs under such circumstances contribute highly in the of count of pmnooutiratccatt and may cause low PS IRAT Success Rate. • So the parameter gsmAmountPropRepeatwhich is generally set to 4 can be reduced to 2 or 1.This will reduce IRAT attempts and will also improve PS IRAT success rate. • The functionality of this parameter can be well understood from the flowchart given in the next slide

  13. EVENT 3a

  14. Parameter - fachMeasOccaCycLenCoeff • Fach Measurement Occasion Cycle Length coefficient - A factor used when the UE performs inter-frequency and inter-system measurements. The UE uses this parameter to calculate the interval length in order to determine the repeating cycle of the measurement. • Value mapping: 0 : not broadcasted in SIB 11. 1 : not used. 2 : not used. 3 : used when inter frequency and GSM neighbors. 4 : used when inter frequency or GSM neighbors. 5 - 12 not used. If fachMeasOccaCycLenCoeff is set to 0, the parameter is not sent in system information and the UE is not allowed to leave the SCCPCH in order to perform measurements on other frequencies and RATs and if fachMeasOccaCycLenCoeff is set to a value 4,the UE performs inter-RAT measurements during FACH occasions . It is recommended to change this parameter to 4 if is set to 0.

  15. Pdf Counter-PMPROPAGATIONDELAY • The pdf counter –pmPropagationDelay can be used to observe samples of a cell . If a cell is serving at a very long distance, then phsical optimization may also help to reduce the number of PS IRAT attempts. • Example: After downtilting the cell UBB071Z(BHURNC1-Aircel),the irat attempts reduced from as high as >100 to <10, and all samples were then observed from distance less than 1.5 km PRE POST Samples coming from more than 10 km No samples from far range

  16. Issue of Rau rejection/failure • The “RAU Rejection” during IRAT HO may also cause low PS IRAT handover success rate. • The occurances of RAU rejection can be known from SGSN trace or from the Drive test log files .The TEMS DT files shows RautingArea Update Failure/Reject RAU REQUEST INSTANCE OF RAU REJECTION WHILE UE IS IN 2G • IN 2G: L3 MSG : DETAILS SHOW :The mobile station does not support the PS Handover. If such issues are observed, there is a high probability that the issue is mainly from the core sideand it needs to be checked.

  17. UETR, UEH TRACING FAILED IRAT CELL CHANGE • Timestamp     lh  UE  RBS   RNC  CN  Prot    Message  • ------------------------------------------------------------------------------------------------------------------------- • [02:20:18.653]01,2385 <<--------<< (RRC) cellChangeOrderFromUTRAN(rrcTID=0) (targetIRAT:BSIC/BCCH=10/48) • [02:20:18.787]01,2385 (MEAS) TRANSPORT_CHANNEL_BER (0:2) • [02:20:18.849]01,2385 (MEAS) TRANSPORT_CHANNEL_BER (0:2) • [02:20:19.008]01,2385 (MEAS) UL_DCH_BLER (nrOfTransportBlocks=5) (nrOfFaultyTransportBlocks=0) • [02:20:19.025]01,2385 >>--->> (NBAP) DedicatedMeasurementReport (tID=16859L) (RNC.CCID=23) (measID=1) (RL-SetID=0) (sIR-ErrVal=-18.5dB) • [02:20:19.037]01,2385 >>--->> (NBAP) DedicatedMeasurementReport (tID=16860L) (RNC.CCID=23) (measID=300) (rL-ID=0) (txCodePwrVal=18.5dBm) • [02:20:19.827]01,2385 (MEAS) TRANSPORT_CHANNEL_BER • [02:20:19.849]01,2385 (MEAS) TRANSPORT_CHANNEL_BER • [02:20:19.925]01,2385 >>--->> (NBAP) RadioLinkFailureIndication (tID=16861L) (RNC.CCID=23) (RL-SetID=0) (cause:radioNetwork/synchronisation-failure) • [2011-11-03 02:20:38.656] 000800/RncLmUePT(UEH_EXCEPTION) ../src/UehIratCcUtranGsmC.cpp:1481 TRACE1:ExceptionCode = 512; TIMER cellChangeTimerId has expired; InterfaceTimout (Internal); CN; RRCConRel; Dropped Call Release Pending; callProc = UehProcIndIRATCellChange; UeRef = 2385; IMSI = 404371140260784; cellId = 50001; cellFroId = 0; S-RNTI = 35153; RLs in DRNC = 0; Best RL in DRNC: No; conntype = uehPacket64Hs targetConnType = uehNotValid RNC is sending CC order to Ue but not receiving RAU update from Ue, due to missing Access & sync to target 2G cell . UETR snap shows IRAT CC [cellChangeOrderFromUTRAN] and the unsuccessful UEH_EXCEPTION  :ExceptionCode = 512; TIMERcellChangeTimerId has expired.

  18. THANK YOU

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