Huawei - Access failures troubleshooting work shop

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Huawei - Access failures troubleshooting work shop

  1. 1. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Security Level: www.huawei.com Huawei Workshop Troubleshooting Access Failures May 17th, 2011
  2. 2. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Contents • Call Setup Procedure (step by step & all protocols) • General Causes of failures • How to chase and to solve specific access failures:  RRC Access Failure Troubleshooting.  Paging Access Failure Troubleshooting  RACH Access Failure Troubleshooting Page 2
  3. 3. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Mobile Terminated Call Setup Procedure (I) Page 3 UE Node B RNC MSC / VLR MGW RRC 3. PCH: PCCH: PAGING TYPE 1 <TM> RRC 2. PAGING RANAP RANAP RRC 4. RACH: CCCH: RRC CONNECTION REQUEST <TM> RRC 1. IAM ISUP 5. RADIO LINK SETUP REQUEST 6. RADIO LINK SETUP RESPONSE 9. DOWNLINK SYNCHRONISATION 12. SYNCH IND 7. ESTABLISHMENT REQUEST (AAL2) 8. ESTABLISHMENT CONFIRM (AAL2) Start RX NBAPNBAP NBAPNBAP ALCAP ALCAP ALCAP ALCAP DCH-FPDCH-FP L1 L1 Start TX 11. FACH: CCCH: RRC CONNECTION SETUP <UM> RRCRRC 14. DCCH: RRC CONNECTION SETUP COMPLETE <AM> RRCRRC 10. UPLINK SYNCHRONISATION DCH-FP DCH-FP 13. RADIO LINK RESTORE INDICATION NBAPNBAP Can be either RRC Connection setup (to this cell and or inter freq to another one when DRD) or Reject. Here the Node-B will start RL with DL transmission Here the UE will start to send the PRACH and wait for AICH and then send RACH message Here the UE will do DL synchronization (using N312=1, T312=1, N313=20 andT313=3) . Then the UE will start UL TX transmission and the Node-B will detect UL SYNCH (based on N_INSYNCIND=8, N_OUTOFSYNCIND=8,TRLFAILURE=20) Here the RNC will perform a DRD decision and CAC decision for RRC
  4. 4. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Mobile Terminated Call Setup Procedure (II) Page 4 UE Node B RNC MSC / VLR MGW 28. RAB ASSIGNMENT REQUEST RANAP RANAP 26. DT [ CALL CONFIRMED ] RANAP RANAP 25. DCCH: ULDT [ CALL CONFIRMED ] <AM> RRCRRC 24. DCCH: DLDT [ SETUP ] <AM> RRCRRC RANAP RANAP 15. DCCH: INITIAL DT [ PAGING RESPONSE ] <AM> RRCRRC RANAP RANAP RRCRRC RRCRRC 19. SECURITY MODE COMMAND RANAP RANAP 20. SECURITY MODE COMMAND 21. SECURITY MODE COMPLETE 22. SECURITY MODE COMPLETE 16. SCCP CONNECTION RQ [ INITIAL UE MESSAGE [ PAGING RESPONSE ] ] 27. BINDING ID, SPEECH CODE TYPE, B PARTY ROUTE RANAP RANAP 18. COMMON ID 23. DT [ SETUP ] 17. SCCP CONNECTION CONFIRM SCCP SCCP SCCP SCCP Here the RNC will perform a DRD decision and CAC decision for RAB
  5. 5. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Mobile Terminated Call Setup Procedure (III) Page 5 UE Node B RNC MSC / VLR MGW 46. DT [ CONNECT ACK ] 46. DCCH: DLDT [ CONNECT ACK ] <AM> RANAPRANAP RRCRRC 39. DCCH: ULDT [ ALERTING ] <AM> 40. DT [ ALERTING ] RANAP RANAP RRCRRC 42. DCCH: ULDT [ CONNECT ] <AM> 43. DT [ CONNECT ] RANAP RANAP RRCRRC 37. RAB ASSIGNMENT RESPONSE RANAP RANAP 41. ACM ISUP 47. ANS (CONNECT) ISUP 36. DCCH: RADIO BEARER SETUP <AM> 38. DCCH: RADIO BEARER SETUP COMPLETE <AM> RRC RRCRRC RRC 29. ESTABLISHMENT REQUEST ( AAL2 ) 30. ESTABLISHMENT CONFIRM ( AAL2 ) ALCAP ALCAP ALCAP ALCAP 33. ESTABLISHMENT REQUEST (AAL2) 34. ESTABLISHMENT CONFIRM (AAL2) ALCAP ALCAP ALCAP ALCAP 31. RADIO LINK RECONFIG PREPARE 32. RADIO LINK RECONFIG READY NBAPNBAP NBAPNBAP 44. OPEN CONNECTION 35. RADIO LINK RECONFIG COMMIT NBAPNBAP Terminating UEs are considered to be in a call after CC Connect ACK Originating UEs are considered to be in a call after CC Connect message
  6. 6. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential General Causes of failures (I) • RF Reasons • Radio Parameter Problems • Miscellaneous causes Page 6
  7. 7. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential General Causes of failures - RF reasons (II)  Poor DL coverage. The “fake coverage” phenomenon (the user sees the 3G icon on the screen in idle but cannot connect to any service). The cause could be overshooting cells but also excessive values of Qqualmin like -22 dB. Solution: Adjust the antenna azimuth and down tilt, add repeaters and RRUs, add micro cells. Any user should get a better signal than EcIo = -18 dB.  Lack of Dominance (no clear Best server): Continuous change of best server leads to RRC failures and RAB failures.Solution: Establish a best server everywhere. Clear dominance.  Poor UL coverage: The UE has not enough TX power to communicate with Node-B (even when there is low UL traffic on the cell). Solution: Adjust the antenna azimuth and down tilt, add repeaters, reduce CPICH power.  Strong UL interference: Due to external interference or high UL traffic (the cell shrinking phenomenon). The UE will not be able to increase to more than 21 dBm for the preamble power and the RACH will fail - or synch will fail later. Solution: Up to operator‟s decision (implement more tilt ,CPICH power reduction, chase external source of interference or increase the number of Node-Bs to cope with traffic)  Strong DL interference: Usually due to overshooting cell, external interference, high DL traffic on this cell and surrounding cells. The UE will miss the AI message for RACH and will fail to establish a call - or will fail to get synch in DL. Solution: Improve best server area (strong dominance)  RF radiating system problems:  Antenna‟s footprint not touching the ground properly: sites with over 120 m height and tilts around 3 degrees. More than 3/4 of the antenna pattern will not be touching the ground with a decent level of signal. Most calls are handled on side lobes.  RF jumpers (feeding the antennas with RRU signal) are too long (should be no more than 3 meters, we‟ve seen cases in --- with 10 meters of ½” jumpers). This definitely leads to high noise factors and call setup failures. Also UL and DL coverage is very much limited.  Missing neighbours: Leads to call setup failures due to poor signal. Page 7
  8. 8. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Poor DL coverage.  The “Fake coverage” phenomenon (user gets the 3G icon on his screen in idle but either cannot pass an RRC or a RAB). Cause is overshooting cells but also excessive values of Qqualmin like -22 dB. Solution: Adjust the antenna azimuth and down tilt, add repeaters and RRUs, add micro cells, improve best server, change Qqualmin. Any user should get a better signal than EcIo=-18 dB. If this level cannot be achieved it is better to display ” no service” on. user screen. Page 8 When -16>EcIo>-2 then RRC_SR>95%When -18>EcIo>-16 ; 95%>RRC_SR>80%When -22>EcIo>-18 ; 80%>RRC_SR>20% User experience: 3G icon,3G signal bars, great service accessibility. User „s perception: Very Positive. User experience: 3G icon,3G signal bar, good service accessibility. User „s perception: Positive. User experience: 3G icon, no 3G bar, no service accessibility. User „s perception: Very negative. Qqualmin PRO CONS Comments -22 dB • User always see the 3G icon on his phone‟s screen (although it‟s a “fake” coverage the user does not always attempt to use the service) •Maximum traffic possible • Bad customer experience but less NW signalling. •Not all call attempts are counted (not a clear perception of accessibility). Will grab all extreme traffic leading quickly into DL Power congestion and accessibility issues. -18 dB • The user will not always have the 3G Icon on his phone‟s screen (but when icon is present service is 100% accessible) • Potential traffic decrease • Great and real customer experience but increased signalling (coverage lost); • All “Call attempts” are counted (better performance perception of accessibility) due to this RRC_SR KPI may (or may not) be improved. No more “fake coverage”. Decrease in DL Power Congestion. -20 dB Qqualmin=-20dB is suggested as a trade-off solution by Huawei.
  9. 9. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential General Causes of failures – Radio Parameter Problems(II) Page 9 • Excessive values in object UCELLSELRESEL: Examples: Qqualmin<-18, IDLESINTRASEARCH ≠ 127, IDLEQHYST2S>1, IDLEQHYST1S>3. • Improper settings of access parameters: No discrepancies found in UCELLACCESSRESTRICT • Inappropriate settings of preamble power ramp step and retransmission times: Current set of parameters is NOK (PREAMBLERETRANSMAX=20, CONSTANTVALUE-20, PowerRampStep=2, Mmax=8). • Inappropriate setting of adjacent cells for UINTRAFREQNCELL: Qoffset1sn, Qoofset2sn out of the range (-4dB;+4dB). Wrong settings for Sintra (like 0 dB), Sinter( also like 0 dB). • Inappropriate settings of synchronization parameters: Synch and Out-Of-Synch parameters for UL (N_INSYNC_IND=8, N_OUTSYNC_IND=8,and T_RLFAILURE=20), DL (T312=1, N312=1, N313=D20 ,T313=3 and N315=D20). Please remember that call re-establishment is activated for both UL and DL (great KPIs but acceptable user perception) • Unsuitable power allocation rate for DL common channel: No discrepancies found (PSCHPower, SSCHPower, BCHPower , MaxFachPower, PCHPower, AICHPowerOffset, PICHPowerOffset) • Unsuitable initial power of uplink and downlink dedicated channel: No discrepancies found for UL (DPCCH_Initial_Power = PCPICHPower - CPICH_RSCP + Uplink interference + DefaultConstantValue) and DL initial SIR target • Unsuitable setting of uplink Initial SIR target value of dedicated channel: No discrepancies found for DL initial SIR Target • Inappropriate setting of adjacent cells for UINTERFREQNCELL: • When 1900 and 850 MHz have significant azimuth difference why there is DRD just towards one 1900 cell and not for the other 1900 cell as well? • Why Qoffset1sn, Qoofset2sn are out of the range (-4;+4) on top of the IdleQhyst1s >2?
  10. 10. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential General Causes of failures –Miscellaneous causes(II) Page 10 •Transmission issues (fluctuating PATH, high BER, reduced capacity, routers down in the IP cloud). •Alarms on cells, on Node-Bs, on RNC, on transmission •Planning issues: traffic not properly shared between layers and NodeB, lack of a clear best server( no dominance), paging congestion due to LAC splitting issue. •Radio Congestion: • CE • DL Power • UL Power • R99 Codes • Iub bandwidth • SPU bottleneck • WMPT board bottleneck
  11. 11. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential How to identify and solve different issues? Page 11
  12. 12. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 12 RRC Access Failure Troubleshooting (I) Is cell/NodeB/RNC configuration the correct one? YES NO Should be done daily (automatically and network wide) based on a defined template. Where there any alarms on investigated cells (or any of it's neighbouring cells, intra or inter) ? YES NO Every morning there should be an email with cells unavailable on previous day and duration of unavailability. Is it a repetitive failure or a "one time" event? YES NO If one time event, please wait one more day before to conclude. Could be a social event If a repetitive failure (according to KPI values in the past) is it a slowly degradation (with traffic increase) or an event one (degraded seriously from a specific moment)? YES NO If event one, go back to that day and see what was changed at that time and reconsider that change Is the SHO factor less than 50%? YES NO If not, please review its best server area, tilt, azimuth and CPICH power Is this cell having full overlapping with other neighbouring cells? ( i.e. there's no direction user can move without having good coverage). Is any user, in any indoor environment within the footprint of this cell, able to get a decent RSCP and EcIo? YES NO If no review your targeted coverage and accept current limitations and constraints due to location and/or number of Node-Bs. Is the height of the antenna less than 100m? YES NO If No, please do not expect a good RRC Success rate. Is the total tilt of the cell more than 3 degree downtilt? YES NO If no (and footprint is on a plain terrain) please take immediate actions to increase downtilt. Antenna RF pattern is hardly touching the ground, users are handled on side lobes. DL Power issues will occur. is the cell Idle sintrasearch=127? YES NO If no, please do not expect a good RRC Success rate. is the cell idleQoffset1sn<4? YES NO If no, please do not expect a good RRC Success rate with idleQoffset1sn>4dB is the cell Idle idleQoffset2sn<2? YES NO If no, please do not expect a good RRC Success rate with idleQoffset2sn>4dB is the cell idleQhyst1<4? YES NO If no, please do not expect a good RRC Success rate with idleQhyst1>4dB is the cell idleQhyst2<2? YES NO If no, please do not expect a good RRC Success rate with idleQhyst2>4dB
  13. 13. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 13 Date---- RNC1 RNC2 RNC3 RNC4 Sum of VS.RRC.AttConnEstab.Sum 6154003 7115377 5397822 1920647 Sum of Cell.RRC.Att.Fail 46702 73768 87275 12471 Sum of VS.RRC.Rej.Redir.Service 0 0 0 0 Sum of VS.RRC.Rej.ULIUBBand.Cong 0 0 0 0 Sum of VS.RRC.Rej.ULPower.Cong 14 10 0 0 Sum of VS.RRC.Rej.DLPower.Cong 135 118 1965 290 Sum of VS.RRC.Rej.DLIUBBand.Cong 0 0 0 0 Sum of VS.RRC.Rej.ULCE.Cong 1144 1352 721 507 Sum of VS.RRC.Rej.DLCE.Cong 822 11 0 0 Sum of VS.RRC.Rej.Code.Cong 12 41 372 0 Sum of VS.RRC.Rej.RL.Fail 30 50 419 0 Sum of VS.RRC.Rej.TNL.Fail 0 0 0 0 Sum of VS.RRC.FailConnEstab.Cong 2343 1552 3070 802 Sum of VS.RRC.Rej.Sum 2373 1602 3489 802 Sum of VS.RRC.SetupConnEstab 6151630 7113775 5394333 1919845 Sum of VS.RRC.FailConnEstab.NoReply 44006 71818 83566 11667 Sum of RRC.SuccConnEstab.sum 6107301 7041609 5310547 1908176 Conclusion: Most RRC failures (over 90%) are due to RRC no reply. For RRC issues, focus on overshooting cells first (to solve No reply), second on congested cells. Here are most of the RRC failures occurring indicating poor UL coverage (overshooting) RRC Access Failure Troubleshooting (II)
  14. 14. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 14 RRC Access Failure Troubleshooting (III) Identify if RRC failures for a cell are due to SPU : (check ADD NODEB command to find the SPU for a cell/Node-B) . Identify top N cells (more than 2000 RRC attempts per day and success rate is less than 98%) SPU board is the issue when (VS.RRC.SuccConnEstabCPU / VS.RRC.AttConnEstabCPU) <97% (daily stats) Solution: Open a ticket to TAC (should not happen after SPH226) Identify if more than 10% of the failures for a cell are due to congestion : YES NO YES Solution: On the RNC LMT, run the PING IP command to the IP of the NodeB during failing hours. If packet loss rate is greater than 0.1% please contact transmission engineers (to troubleshoot or upgrade) VS.RRC.Rej.ULIUBBand.Cong VS.RRC.Rej.DLIUBBand.Cong VS.RRC.Rej.ULPower.Cong Check configuration(ULTOTALEQUSERNUM=160; NBMULCACALGOSELSWITCH=ALGORITHM_SECOND). Solution: Increase ULTOTALEQUSERNUM to 180. If still failing: add carrier or reduce/balance traffic to other layers/cells. VS.RRC.Rej.DLPower.Cong Check configuration :UPCPICH and MAXTXPOWER should be at least 10 dB between the 2 values. DLOLCTRIGTHD=95.DL_UU_OLC=0. Solution1:add carrier or reduce/balance traffic to other layers/cells Solution2: change NBMDLCACALGOSELSWITCH=ALGORITHM_THIRD VS.RRC.Rej.ULCE.Cong Solution per cell: change ULTTICREDITSFRESTHD from SF8 to 4SF4. CE resources for admission is in congestion status the new admitted 2ms HSUPA terminals will be mapped onto the 10ms TTI radio bearer. 2ms TTI HSUPA users whose bit rate is below the threshold of TTI reconfiguration(800Kbps) will be reconfigured to 10ms TTI Solution per RNC: decrease ULGBR from 32 to 16 for specific services VS.RRC.Rej.DLCE.Cong Solution per cell: ??? Solution per RNC: decrease DLGBR from 64 to 32 for specific services VS.RRC.Rej.Code.Cong Solution per cell is to activate Code reshuffling algo: in object UCELLALGOSWITCH change CELL_CODE_LDR to 1 Identify if more than 10% of failures for a cell are due to RL.Failure : VS.RRC.Rej.Rl.Fail Solution 1: If failures correlated with VS.IUB.FailRLSetup.NoReply then it is WMPT board congestion( add UTRP Board) Solution 2: run the PING IP command on the IP of the NodeB to detect congestion on the IuB. Solution 3: If failures correlated with RLM.FailRLSetupIub.Cong then it is WBBP board congestion GO TO NEXT SLIDE NO
  15. 15. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 15 RRC Access Failure Troubleshooting (IV) Identify if more than 10% of failures for a cell are due to TNL (Transport Network Layer) : VS.RRC.Rej.TNL.Cong Solution 1: Recheck configuration( IPPATHs of Nodeb has same capacity of transmission one;same for pair one) Solution 2: Run the PING IP command on the IP of the NodeB to detect congestion on the IuB. Identify if more than 10% of failures for a cell are due to FACH congestion : YES NO YES Solution 1: (After SPH226) MOD UCELLALGOSWITCH: CellId=xxxxx, RsvdPara1=RSVDBIT5-1; (will improve CS success rate, will degrade PS success rate) Solution 2: Offload traffic VS.RRC.AttConnEstab.Msg >> VS.RRC.AttConnEstab.Sum VS.CellFACHUEs>25 Solution: Offload traffic VS.CRNCIubBytesFACH.Tx or VS.CRNCIubBytesPSR99.CCH.Tx are flat in time( limited) Solution1: Offload traffic VS.MaxRTWP - VS.MeanRTWP > 10 dB Solution 1: reduce HSUPA traffic Solution 2: Offload traffic Solution 3: Check external interference Check missing neighbours Solution 1: Add important Neighbours Solution 2: Increase tilt to avoid risky overlaping footprints If RRC Estab SR for whole RNC<99% and UU no reply is major cause Solution 1 per RNC : modify RRC estab type to be on DCH SET URRCESTCAUSE:RRCCAUSE=TERMCAUSEUNKNOWN, SIGCHTYPE=DCH_3.4K_SIGNALLING, EFACHSWITCH=OFF; Take care as this will improve the RRC SR but will increase DL Power Solution 2 per RNC : stop SRB over HSDPA when DRD could be present SET UFRCCHLTYPEPARA, SRBCHLTYPE=HSUPA, SRBCHLTYPERRCEFFECTFLAG=TRUE Identify if more than 10% of failures for a cell are due to VS.RRC.FailConnEstab.NoReply : NO FROM PREVIOUS SLIDE YES Please ask for HUAWEI support if after all those steps a cause for poor RRC failure could not be found NO FACH Channel utilisation>80% Solution1: Offload traffic
  16. 16. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 16 •. Here are most of the RRC failures occurring indicating poor UL coverage (overshooting) Top offending cell in xxx area with more than 10.000 RRC attempts per day: cell yyyyy Data cellID=yyyyy Sum of VS.RRC.AttConnEstab.Sum 73083 Sum of Cell.RRC.Att.Fail 17110 Sum of VS.RRC.Rej.Redir.Service 0 Sum of VS.RRC.Rej.ULIUBBand.Cong 0 Sum of VS.RRC.Rej.ULPower.Cong 0 Sum of VS.RRC.Rej.DLPower.Cong 163 Sum of VS.RRC.Rej.DLIUBBand.Cong 0 Sum of VS.RRC.Rej.ULCE.Cong 0 Sum of VS.RRC.Rej.DLCE.Cong 0 Sum of VS.RRC.Rej.Code.Cong 0 Sum of VS.RRC.Rej.RL.Fail 0 Sum of VS.RRC.Rej.TNL.Fail 0 Sum of VS.RRC.FailConnEstab.Cong 163 Sum of VS.RRC.Rej.Sum 163 Sum of VS.RRC.FailConnEstab.NoReply 16944 Sum of VS.RRC.SetupConnEstab 72920 Sum of RRC.SuccConnEstab.sum 55973 RRC_SR 76.59%
  17. 17. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 17 •. Here are most of the RRC failures occurring indicating poor UL coverage (overshooting) Data cellID=yyyyy Sum of VS.RRC.AttConnEstab.Sum 75048 Sum of Cell.RRC.Att.Fail 5324 Sum of VS.RRC.Rej.Redir.Service 0 Sum of VS.RRC.Rej.ULIUBBand.Cong 0 Sum of VS.RRC.Rej.ULPower.Cong 0 Sum of VS.RRC.Rej.DLPower.Cong 115 Sum of VS.RRC.Rej.DLIUBBand.Cong 0 Sum of VS.RRC.Rej.ULCE.Cong 0 Sum of VS.RRC.Rej.DLCE.Cong 0 Sum of VS.RRC.Rej.Code.Cong 0 Sum of VS.RRC.Rej.RL.Fail 0 Sum of VS.RRC.Rej.TNL.Fail 0 Sum of VS.RRC.FailConnEstab.Cong 115 Sum of VS.RRC.Rej.Sum 115 Sum of VS.RRC.FailConnEstab.NoReply 5208 Sum of VS.RRC.SetupConnEstab 74933 Sum of RRC.SuccConnEstab.sum 69724 RRC_SR 92.91% 2nd offending cell in xxx area with more than 10.000 RRC attempts per day: cell yyyyy
  18. 18. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 18 •. Here are most of the RRC failures occurring indicating poor UL coverage (overshooting) Data cellID=yyyyy Sum of VS.RRC.AttConnEstab.Sum 39512 Sum of Cell.RRC.Att.Fail 2602 Sum of VS.RRC.Rej.Redir.Service 0 Sum of VS.RRC.Rej.ULIUBBand.Cong 0 Sum of VS.RRC.Rej.ULPower.Cong 0 Sum of VS.RRC.Rej.DLPower.Cong 0 Sum of VS.RRC.Rej.DLIUBBand.Cong 0 Sum of VS.RRC.Rej.ULCE.Cong 0 Sum of VS.RRC.Rej.DLCE.Cong 0 Sum of VS.RRC.Rej.Code.Cong 0 Sum of VS.RRC.Rej.RL.Fail 0 Sum of VS.RRC.Rej.TNL.Fail 0 Sum of VS.RRC.FailConnEstab.Cong 0 Sum of VS.RRC.Rej.Sum 0 Sum of VS.RRC.FailConnEstab.NoReply 2602 Sum of VS.RRC.SetupConnEstab 39512 Sum of RRC.SuccConnEstab.sum 36910 RRC_SR 93.41% 3rd offending cell in xxx area with more than 10.000 RRC attempts per day: cell yyyyy
  19. 19. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 19 •. Here are most of the RRC failures occurring indicating poor UL coverage (overshooting) 4th offending cell in xxxx area with more than 10.000 RRC attempts per day: cell yyyyy Data cellID=yyyyy Sum of VS.RRC.AttConnEstab.Sum 75162 Sum of Cell.RRC.Att.Fail 3583 Sum of VS.RRC.Rej.Redir.Service 0 Sum of VS.RRC.Rej.ULIUBBand.Cong 0 Sum of VS.RRC.Rej.ULPower.Cong 0 Sum of VS.RRC.Rej.DLPower.Cong 439 Sum of VS.RRC.Rej.DLIUBBand.Cong 0 Sum of VS.RRC.Rej.ULCE.Cong 0 Sum of VS.RRC.Rej.DLCE.Cong 0 Sum of VS.RRC.Rej.Code.Cong 4 Sum of VS.RRC.Rej.RL.Fail 0 Sum of VS.RRC.Rej.TNL.Fail 0 Sum of VS.RRC.FailConnEstab.Cong 443 Sum of VS.RRC.Rej.Sum 443 Sum of VS.RRC.FailConnEstab.NoReply 3137 Sum of VS.RRC.SetupConnEstab 74719 Sum of RRC.SuccConnEstab.sum 71579 RRC_SR 95.23%
  20. 20. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 20 Paging Access Failure Troubleshooting-(I)- case of one SCCPCH  2 Physical channels: – PICH (Paging Indicating Channel): This is just to inform the UE that it needs to initiate an RRC Connection request. Those are the details for this channel. – SCCPCH (Secondary Common Control Physical Channel). It carries paging messages themselves as well as packet messages for mobiles in cell FACH.
  21. 21. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 21 Paging Access Failure Troubleshooting-(II) -case of two SCCPCH  2 Physical channels: – PICH (Paging Indicating Channel): This is just to inform the UE that it needs to initiate an RRC Connection request. Those are the details for this channel. – 2nd SCCPCH (Second Secondary Common Control Physical Channel). It carries only paging messages themselves. 2nd SCCPCH
  22. 22. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Paging Access Failure Troubleshooting-(III) PICH timing in relation to P-CCPCH and S-CCPCH (extras from 3GPP 25.211-700) : Paging indicator Paging message (3 IMSI or 5 TMSI) Paging ocassion
  23. 23. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Paging Access Failure Troubleshooting-(IV) PICH channel parameters: • SF 256 used all the time.Each UE looks for a particular PICH timeslot according to several parameters broadcasted on SIBs : • PI number of paging indicators per radio frame. 3GPP allows values 18,38,72,144. It is broadcasted in Sysinfo5: PI-countperframe • SFN of the P-CCPCH where the PICH frame started. The SFN is known by UE immediately after synchronization with P-CCPCH. SFN range is from 0 to 4096. • K number of S-CCPCH and can be found in Sysinfo5 . Usually 1 or 2 ( same like in GSM combined or non-combined BCCH). • DRX cycle. UE will use the DRX=min (DRXPS,DRXCS). DRX cycle is broadcasted in Sysinfo1: cn-DRX-CycleLengthCoefficient (2 values broadcasted, one for each CN domain) • IMSI known from U-SIM. • Frame offset =Ts-ccpch,k –Tpich (see previous slide). Ts-ccpch,k = Tk  256 chip, Tk  {0, 1, …, 149} and can be found in Sysinfo5: and it is called timming offset. For particular UTRAN timming offset=0(S-CCPCH and P-CCPCH are time aligned). Tpich = 7680 chips as a fix value forced by 3GPP. • A paging indicator set to “1” indicates that the UE should read the S-CCPCH of the corresponding frame. • Total number of chips in one 10msec radio frame is 38400. PICH channel can transmit (38400/256) 150 indicator modulation symbols or (150X2) 300 bits. Only the first 288 of these are used, leaving the last 12 bits undefined • More details in 3GPP specs: 25.211-700 and in 25.331-710 RRC protocol specification • PO= {(IMSI div K) mod (DRX cycle length div PBP)} * PBP + n * DRX cycle length + Frame Offset Where n = 0,1,2… as long as SFN is below its maximum value ,for FDD PBP=1 PI = DRX Index mod Np Where DRX Index = IMSI div 8192 If we consider particular settings: DRXcycle=7=>128 frames Frame offset =-7860 chips PBP=1 K=1 (there„s only one S-CCPCH that carries PCH) PI=Np=36 PO= (IMSI)mod128+ n* 128 -7860 chips PI=(IMSI/8192) mod36
  24. 24. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Paging Access Failure Troubleshooting-(V) •• PICH frame structure : • A group of bi=1 means there‟s a paging and UE should read it‟s very first paging occasion. • A group of bi=0 means there‟s no paging and UE could go back to idle till next paging indicators. • More bits inside a PI means a greater probability to decode the paging indicator but less capacity of the paging channel and power consumption for UE. Less bits means a lower probability for the UE to decode the paging indicator but longer battery life of the UE. Best solution is a mid-way one: PI=36.
  25. 25. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Paging Access Failure Troubleshooting-(VII) • From all this information what do you need to know?: • there can be several places where paging could get congested: Iu interface, IuB interface, RNC boards, or PCH interface . PICH channel is the only channel that is never congested! • Check with CN how many paging repetitions have, how do they page: by IMSI or by TMSI. If first paging fails how many repetitions? Last paging is network wide or LAC wide only? • --- is currently facing PCH channel load: all smart phones are in cell PCH state. In this state can only receive paging but can not transmit any data. Any paging for a UE it is sent specifically to that cell. How RNC knows where is such an UE? By cell update!. Every time UE changes the cell in cell PCH there is a cell update+cellupdate confirm, utran mobility information confirm. That means that the RNC is aware about new location of the UE. • How much is the paging success now in --- network? • What solutions we have to offload the PCH channel?: • LAC split. • Page by TMSI • Reduce ping-pongs (and reselections) • Improve best server area and reduce overlapping
  26. 26. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 26 •Why are RACH parameter VERY important? Because it impacts strongly user experience (also called E2E=end-to-end user experience) RACH Access Failure Troubleshooting (I) Enough performance counters No performance indicators. Only estimation by RTWP, load of the RACH channel etc..
  27. 27. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 27 RACH Access Failure Troubleshooting (II) Uplink/UE/PRACH Preamble 1 Message part…. …. Max_TX_power_on_PRACH Preamble n Preamble_Retrans_Max : MMax The answer on AICH must be a specific positive response for the specific RACH sent Parameters for RACH/PRACH: •NBO1( 0 NBO1min  NBO1  NBO1max ) is the time between 2 ramping power of the preamble within the same preamble cycle. •Preamble_Retrans_Max is the maximum number of preamble that can be sent in a cycle. •Mmax is the maximum number of preamble cycles. •Preamble_Initial_Power = Primary CPICH TX power – CPICH_RSCP + UL interference + Constant Value •Constant value is an initial value to start the first preamble power usually is -24. •UL interference is the latest value broadcasted by the NodeB in SIB7. Ue needs to decode this value before being able to transmit RACH. •Power_Ramp_Step is the how much the preamble power should be increased after each No ack received on AICH. •Power offset P p-m = Pmessage-control – Ppreamble, measured in dB, between the power of the last transmitted preamble and the control part of the random-access message. •AICH_Transmission_Timing is the time when the RACH message must be transmitted after positive AICH was received( there are other parameters too) RACH is a common type transport channel in the uplink. RACHs are always mapped one-to-one onto physical channels (PRACHs), i.e. there is no physical layer multiplexing of RACHs, and there can only be one RACH TrCH and no other TrCH in a RACH CCTrCH. Service multiplexing is handled by the MAC layer. In one cell several RACHs/PRACHs may be configured. If more than one PRACH is configured in a cell, the UE performs PRACH selection NB01 Preamble_Initial_Power : Power_Ramp_Step : Pp-m : AICH_Transmission_Timing RACH message mandatory parameters: -UE identity( IMSI,IMSI+LAI, TMSI, IMEI-when no USIM is inserted) -RRC establishment cause (31 causes) -radio bearer ID( AS or NAS, UM or TM or AM) -release5 indicator -measurements results on RACH(like EcNo of the serving cell).
  28. 28. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential RACH Access Failure Troubleshooting-(III) • From all this information what do you need to know?: • Current RACH parameters are not optimal: allows the UE to increase the power 20 dBm more than the RTWP(CONSTANTVALUE=-20, PREAMBLERETRANSMAX=20, POWERRAMPSTEP=2). Due to this RTWP increase, due to this RACH increases and so on(it creates an avalanche effect). Better have longer call setup time for one UE (RACH failures due to missing NB relations of overshooting cells) instead of having entire cell shrinked due to one UE not being able to transmit RACH message. • Missing neighbours, lack of best server area and poor UL coverage influence a lot the RACH success rate. • Cell radius is now at 29.000 km. Make sure there are no UE from a larger distance(path distance) else will fail on RACH. • Spreaders inside the Node-B are limited. Multipath ( long distance) is not good for resource consumptions and so RACH messages might be missed.
  29. 29. HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Preliminary conclusions • Most attempt failures are related to planning • Plenty of attempts failures not recorded within the performance file (When EcIo is worse than -18 very few RACH “reach” the Node-Bs) Page 29
  30. 30. Thank you www.huawei.com

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