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  1. 1. W-Handover and Call Drop Problem Optimization Guide For internal use only2009-10-10 All rights reserved Page 1 of 201Product name Confidentiality levelWCDMA RNP For internal use onlyProduct versionTotal 201 pages3.3W-Handover and Call Drop Problem OptimizationGuide(For internal use only)Prepared by Jiao Anqiang Date 2006-03-16Reviewed by Xie Zhibin, Dong Yan, HuWensu, Wan Liang, YanLin, Ai Hua, Xu Zili, andHua YunlongDateReviewed by Wang Chungui DateApproved by DateHuawei Technologies Co., Ltd.All Rights Reserved
  2. 2. W-Handover and Call Drop Problem Optimization Guide For internal use only2009-10-10 All rights reserved Page 2 of 201Revision RecordsDate Version Description Author2005-02-01 2.0Completing V2.0 W-Handover and Call DropProblems.Cai Jianyong,Zang Liang, andJiao Anqiang2006-03-16 3.0According to V3.0 guide requirements,reorganizing and updating V2.0 guide, focusingmore on operability of on-site engineers. All trafficstatistics is from RNC V1.5. The update includes:Updating flow chart for handover problemoptimizationMoving part of call drop due to handover problemto handover optimization partSpecifying operation-related part to be moreapplicable to on-site engineersUpdating RNC traffic statistics indexes to V1.5Integrating traffic statistics analysis to NASTAR ofthe network performance analysisOptimizing some cases, adding new cases, andremoving outdated cases and termsMoving content about handover and call drop to theappendix, and keeping operations related to them inthe bodyAdding explanations to SRB&TRB and RLFAILURE.Jiao Anqiang2006-04-303.1Adding HSDPA-related description HSDPAhandover DT/CQT flow, definitions of trafficstatistics in HSDPA handover, HSDPA handoverproblems. Adding algorithms and flows of HSDPAhandover.Zhang Hao andLi Zhen
  3. 3. W-Handover and Call Drop Problem Optimization Guide For internal use only2009-10-10 All rights reserved Page 3 of 201Date Version Description Author2006-10-303.11Adding V17-related handover description as below:Changes in signaling flow for H2D HHOChanges in triggering events of H2D and D2HD2H handover in HSDPA based on traffic andtimersUpdating description of HSDPA serving cell andtraffic statistics of HSDPA-DCH handoverAdding call drop indexes in HSDPA DT/statisticsWang Dekai2007-08-09 3.2 Adding HSUPA-related description. Zhang Hao2008-12-153.3Adding MBMS-related description.Yearly reviewWangDekai /Hu Wensu
  4. 4. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page4 , Total201Contents1 Introduction .............................................................................................................................142 Handover and Call Drop Performance Indexes......................................................................162.1 Handover Performance Indexes ......................................................................................162.2 Call Drop Performance Indexes.......................................................................................193 Handover Index Optimization .................................................................................................203.1 DT/CQT Index Optimization Flow.....................................................................................203.1.1 SHO DT Index Optimization Flow...........................................................................203.1.2 HHO CQT Flow .....................................................................................................243.1.3 Inter-RAT Handover CQT Flow..............................................................................273.1.4 DT/CQT Flow for HSDPA Handover ......................................................................293.1.5 DT/CQT Flow for HSUPA Handover ......................................................................323.1.6 SHO Ratio Optimization.........................................................................................323.1.7 MBMS Mobility Optimization ..................................................................................323.2 Traffic Statistics Analysis Flow.........................................................................................343.2.1 Analysis Flow for SHO Traffic Statistics .................................................................353.2.2 Analysis Flow of HHO Traffic statistics...................................................................363.2.3 Traffic Statistics Analysis Flow for Inter-RAT Handover..........................................373.2.4 Traffic Statistics Analysis for HSDPA Handover .....................................................403.2.5 Traffic Statistics Analysis for HSUPA Handover .....................................................413.3 SHO Cost Optimization....................................................................................................434 CDR Index Optimization..........................................................................................................444.1 Definition of Call Drop and Traffic Statistics Indexes ........................................................444.1.1 Definition of DT Call Drop ......................................................................................444.1.2 Descriptions of Traffic Statistics Indexes................................................................444.2 DT/CQT Optimization Flow..............................................................................................454.2.1 Call Drop Cause Analysis ......................................................................................464.2.2 Frequently-adjusted Non-handover Algorithm Parameters......................................484.2.3 Judgment Tree for Call Drop Causes .....................................................................494.3 Traffic Statistics Analysis Flow.........................................................................................504.3.1 Analyzing RNC CDR..............................................................................................514.3.2 Analyzing Causes to Call Drop...............................................................................514.3.3 Check Cells...........................................................................................................524.3.4 Further DT for Relocating Problems.......................................................................524.4 Optimization Flow for Tracing Data..................................................................................524.4.1 Obtaining Single Subscriber Tracing Message .......................................................534.4.2 Obtaining Information about Call Drop Point ..........................................................534.4.3 Analyzing Call Drop due to SRB Reset ..................................................................544.4.4 Analyzing Call Drop due to TRB Reset...................................................................544.4.5 Analyzing Abnormal Call Drop ...............................................................................544.4.6 Performing CQT to Recheck Problems ..................................................................55
  5. 5. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page5 , Total2014.5 Optimization Process for MBMS Call Drop.......................................................................555 FAQs Analysis.........................................................................................................................565.1 SHO Problems ................................................................................................................565.1.1 Over High SHO Rate due to Improper SHO Relative Threshold .............................565.1.2 Delayed Handover due to Over Great Intra-frequency Filter Coefficient..................575.1.3 Missing Neighbor Cell............................................................................................585.1.4 Redundant Neighbor Cells.....................................................................................625.1.5 Pilot Pollution.........................................................................................................655.1.6 Turning Corner Effect ............................................................................................715.1.7 Needlepoint Effect .................................................................................................745.1.8 Quick Change of Best server Signal.......................................................................755.2 HHO Problems................................................................................................................775.2.1 Intra-frequency Ping-pong HHO due to Improperly Configured 1D Event Hysteresis775.2.2 Delayed Origination of Inter-frequency Measurement due to Improper Inter-frequencyMeasurement Quantity ..................................................................................................785.3 Inter-RAT Handover Problems.........................................................................................805.3.1 Ping-pong Reselection...........................................................................................805.3.2 PS Inter-RAT Ping-pong Handoff ...........................................................................815.3.3 Failure in handoff from 3G to the 2G network.........................................................825.3.4 Inter-RAT Handover Call Drop ...............................................................................845.4 Call Drop Problems .........................................................................................................915.4.1 Over Weak Coverage ............................................................................................915.4.2 Uplink Interference ................................................................................................925.4.3 Abnormal Equipment .............................................................................................955.5 HSDPA-related Problems................................................................................................975.5.1 HSDPA Handover Problems..................................................................................975.5.2 HSDPA Call Drop ..................................................................................................985.6 HSUPA Problems..........................................................................................................1006 Summary................................................................................................................................1017 Appendix................................................................................................................................1027.1 SRB&TRB Reset ...........................................................................................................1027.1.1 RAB ....................................................................................................................1027.1.2 SRB ....................................................................................................................1037.2 RL FAILURE .................................................................................................................1047.3 SHO Flow......................................................................................................................1097.3.1 Analyzing Signaling Flow for Adding Radio Link...................................................1097.3.2 Analyzing Signaling Flow for Deleting Radio Link.................................................1127.3.3 Analyzing Signaling Flow for Adding and Deleting Radio Link ..............................1137.3.4 SHO Algorithm ....................................................................................................1167.4 Ordinary HHO Flow .......................................................................................................1237.4.1 Ordinary HHO (lur Interface and CELL_DCH State) .............................................1237.4.2 Inter-CN HHO Flow..............................................................................................1257.5 HHO Algorithm ..............................................................................................................1287.5.1 Intra-frequency HHO Algorithm............................................................................1287.5.2 Inter-frequency HHO Algorithm............................................................................1287.6 Concept and Classification of HSDPA Handover............................................................1307.6.1 Concept of HSDPA Handover..............................................................................1307.6.2 Classification of HSDPA Handover ......................................................................1307.6.3 Signaling Flow and Message Analysis of HSDPA Handover.................................1317.6.4 HS-PDSCH Serving Cell Update due to DPCH SHO............................................1327.6.5 HS-PDSCH Serving Cell Update due to DPCH HHO............................................1397.6.6 DPCH Intra-frequency HHO with HS-DSCH Serving Cell Update.........................1407.6.7 DPCH Inter-frequency HHO with HS-DSCH Serving Cell Update.........................141
  6. 6. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page6 , Total2017.6.8 Handover Between HSDPA and R99...................................................................1437.6.9 Handover between HSDPA and GPRS................................................................1527.6.10 Direct Retry of HSDPA.......................................................................................1527.6.11 Switch of Channel Type .....................................................................................1547.7 Concept and Classification of HSUPA Handover............................................................1577.7.1 Basic Concepts....................................................................................................1577.7.2 Classification of HSUPA Handover ......................................................................1577.7.3 Signaling Flow and Message Analysis of HSUPA Handover.................................1587.7.4 SHO from a HSUPA Cell to a Non-HSUPA Cell ...................................................1647.7.5 SHO from a Non-HSUPA Cell to a HSUPA Cell ...................................................1697.7.6 Handover Between a HSUPA Cell and a GSM/GPRS Cell ...................................1727.7.7 Direct Retry of HSUPA.........................................................................................1727.7.8 Switch between Channel Types...........................................................................1747.8 Handover from WCDMA to GSM ...................................................................................1757.9 Handover from GSM to WCDMA ...................................................................................1797.10 Handover from WCDMA to GPRS................................................................................1827.11 Handover from GRPS to WCDMA................................................................................1867.12 Parameters of Handover from 3G to 2G Network .........................................................1897.13 Data Configuration for Supporting Bi-directional Roaming and Handover Between WCDMA andGSM/GPRS........................................................................................................................192
  7. 7. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page7 , Total201FiguresFigure 3-1 SHO DT data analysis flow................................................................................................ 21Figure 3-2 Optimization flow for HHO CQT......................................................................................... 26Figure 3-3 Inter-RAT handover CQT flow............................................................................................ 28Figure 3-4 DT/CQT flow for HSDPA handover .................................................................................... 31Figure 3-5 Movement of the MBMS UE between PTM cells................................................................ 32Figure 3-6 Analysis flow for handover traffic statistics data.................................................................. 35Figure 3-7 Voce inter-RAT outgoing handover flow ............................................................................. 38Figure 4-1 Flow chart for analyzing call drop ...................................................................................... 46Figure 4-2 Judgment tree for call drop causes.................................................................................... 49Figure 4-3 Flow for analyzing call tracing............................................................................................ 53Figure 5-1 SHO relative threshold ...................................................................................................... 57Figure 5-2 Signaling flow recorded by UE before call drop.................................................................. 58Figure 5-3 Scrambles recorded by UE active set and scanner before call drop ................................... 59Figure 5-4 Scrambles in UE active set before call drop....................................................................... 60Figure 5-5 UE intra-frequency measurement control point before call drop ......................................... 61Figure 5-6 Analyzing signaling of UE intra-frequency measurement control before call drop................ 61Figure 5-7 Confirming missing neighbor cell without information from scanner.................................... 62Figure 5-8 Location relationship of 2G redundant neighbor cells......................................................... 64Figure 5-9 Pilot pollution near Yuxing Rd............................................................................................ 65Figure 5-10 Best ServiceCell near Yuxing Rd. .................................................................................... 65Figure 5-11 The 2nd best ServiceCell near Yuxing Rd. ....................................................................... 66Figure 5-12 The 3rd best ServiceCell near Yuxing Rd......................................................................... 66Figure 5-13 The 4th best ServiceCell near Yuxing Rd......................................................................... 67Figure 5-14 Composition of pilot pollution near Yuxing Rd. ................................................................. 67Figure 5-15 RSSI near Yuxing Rd....................................................................................................... 68Figure 5-16 RSCP of Best ServiceCell near Yuxing Rd....................................................................... 68Figure 5-17 RSCP of SC270 cell near Yuxing Rd................................................................................ 69
  8. 8. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page8 , Total201Figure 5-18 Pilot pollution near Yuxing Rd. after optimization.............................................................. 70Figure 5-19 Best ServiceCell near Yuxing Rd. after optimization......................................................... 70Figure 5-20 RSCP of best ServiceCell near Yuxing Rd. after optimization........................................... 71Figure 5-21 RSCP of SC270 cell near Yuxing Rd. after optimization ................................................... 71Figure 5-22 Turning corner effect-signals attenuation ......................................................................... 72Figure 5-23 Turning corner effect-signal attenuation recorded by the UE ............................................ 72Figure 5-24 Turning corner effect-traced signaling recorded by the RNC............................................. 73Figure 5-25 Needle point-signal variance............................................................................................ 74Figure 5-26 Call drop distribution of PS384K intra-frequency hard handover....................................... 75Figure 5-27 Signal distribution of cell152 vs. cell88 (signal fluctuation in handover areas)................... 76Figure 5-28 Reporting 1D event ......................................................................................................... 77Figure 5-29 Increasing hysteresis to reduce frequently reporting of 1D event...................................... 78Figure 5-30 Attenuation relationship of RSCP and Ec/No.................................................................... 79Figure 5-31 Indoor 3G RSCP distribution............................................................................................ 83Figure 5-32 Analyzing weak signals.................................................................................................... 91Figure 5-33 Uplink interference according to RNC signaling ............................................................... 93Figure 5-34 Uplink interference according to UE signaling.................................................................. 93Figure 5-35 Uplink interference information recorded by UE ............................................................... 94Figure 5-36 RTWP variation of the cell 89767..................................................................................... 94Figure 5-37 RTWP variation of the cell 89768..................................................................................... 95Figure 5-38 Pilot information recorded by scanner.............................................................................. 97Figure 7-1 UMTS QoS structure....................................................................................................... 102Figure 7-2 SRB and TRB at user panel............................................................................................. 103Figure 7-3 Signaling flow for adding radio link....................................................................................110Figure 7-4 Signaling flow for deleting radio link..................................................................................112Figure 7-5 SHO signaling flow for adding and deleting radio link........................................................114Figure 7-6 Measurement model.........................................................................................................116Figure 7-7 Example 1A event and trigger delay .................................................................................118Figure 7-8 Periodic report triggered by 1A event................................................................................119Figure 7-9 Example of 1C event....................................................................................................... 120Figure 7-10 Example 1D event......................................................................................................... 121Figure 7-11 Restriction from hysteresis to measurement report......................................................... 121Figure 7-12 Example of 1E event ..................................................................................................... 122Figure 7-13 Example of 1F event ..................................................................................................... 122
  9. 9. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page9 , Total201Figure 7-14 Ordinary HHO flow (lur interface and CELL_DCH state) ................................................ 124Figure 7-15 Ordinary inter-CN HHO flow .......................................................................................... 126Figure 7-16 Intra-NodeB synchronization serving cell update............................................................ 133Figure 7-17 Inter-NodeB synchronization serving cell update............................................................ 135Figure 7-18 Inter-NodeB HS-DSCH cell update after radio link is added ........................................... 137Figure 7-19 Inter-NodeB HS-DSCH cell update during HHO (single step method) ............................ 139Figure 7-20 DPCH intra-frequency HHO with HS-DSCH serving cell update..................................... 141Figure 7-21 DPCH inter-frequency HHO with HS-DSCH serving cell update..................................... 142Figure 7-22 handover from HSDPA to R99 ....................................................................................... 143Figure 7-23 Intra-frequency handover from R99 to R5...................................................................... 143Figure 7-24 DPCH SHO with handover from HSDPA to R99 (inter-NodeB)....................................... 145Figure 7-25 DPCH SHO with handover from R99 to HSDPA............................................................. 146Figure 7-26 Inter-NodeB SHO with handover from HSDPA to R99 (V17) .......................................... 147Figure 7-27 Intra-frequency HHO with handover from R5 to R99 ...................................................... 148Figure 7-28 Intra-frequency HHO with handover form R99 to R5 ...................................................... 148Figure 7-29 Intra-frequency HHO with handover from R5 to R99 (V17)............................................. 149Figure 7-30 Inter-frequency HHO from HS-PDSCH to DCH.............................................................. 150Figure 7-31 Inter-frequency HHO from DCH to HS-PDSCH.............................................................. 151Figure 7-32 Handover between HSDPA and GPRS.......................................................................... 152Figure 7-33 Flow for direct retry during setup of a service................................................................. 153Figure 7-34 Direct retry triggered by traffic........................................................................................ 153Figure 7-35 Switch of channel type................................................................................................... 155Figure 7-36 Intra-frequency SHO between two HSUPA cells............................................................. 159Figure 7-37 Signaling for HSUPA cell update triggered by a 1D event............................................... 159Figure 7-38 Signaling for HSUPA cell update triggered by a 1D event (reported by the monitor set).. 160Figure 7-39 Intra-frequency HHO between two HSUPA cells ............................................................ 160Figure 7-40 Signaling for intra-frequency HHO between two HSUPA cells ........................................ 161Figure 7-41 Inter-frequency HHO between two HSUPA cells ............................................................ 161Figure 7-42 Signaling for inter-frequency HHO between two HSUPA cells ........................................ 162Figure 7-43 Inter-RNC HSUPA handover.......................................................................................... 163Figure 7-44 SHO from a HSUPA cell to a non-HSUPA cell................................................................ 165Figure 7-45 Addition of an R99 cell when the service is on the E-DCH.............................................. 166Figure 7-46 Intra-frequency HHO from a HSUPA cell to a non-HSUPA cell ....................................... 167Figure 7-47 Signaling for intra-frequency HHO from a HSUPA cell to a non-HSUPA cell ................... 167
  10. 10. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page10 , Total201Figure 7-48 Inter-frequency HHO from a HSUPA cell to a non-HSUPA cell ....................................... 168Figure 7-49 Signaling for inter-frequency HHO from a HSUPA cell to a non-HSUPA cell ................... 169Figure 7-50 SHO from a non-HSUPA cell to a HSUPA cell................................................................ 170Figure 7-51 SHO from a non-HSUPA cell to a HSUPA cell (triggered by a 1B event)......................... 170Figure 7-52 Intra-frequency HHO from a non-HSUPA cell to a HSUPA cell ....................................... 171Figure 7-53 Signaling for intra-frequency HHO from a non-HSUPA cell to a HSUPA cell ................... 171Figure 7-54 Inter-frequency HHO from a non-HSUPA cell to a HSUPA cell ....................................... 172Figure 7-55 Direct retry from an R99 cell to a HSUPA cell................................................................. 173Figure 7-56 Direct retry from a HSUPA cell to an R99 cell................................................................. 173Figure 7-57 Direct retry from a HSUPA cell to another HSUPA cell.................................................... 174Figure 7-58 Switch between HSUPA channel types.......................................................................... 174Figure 7-59 Signaling flow for handover from WCDMA to GSM......................................................... 176Figure 7-60 Tracing signaling of handover from WCDMA to GSM..................................................... 176Figure 7-61 Signaling flow for handover from GSM to WCDMA ........................................................ 179Figure 7-62 Tracing signaling of handover from GSM to WCDMA..................................................... 180Figure 7-63 Flow of handover from WCDMA to GPRS (1)................................................................. 183Figure 7-64 Flow of handover from WCDMA to GPRS (2)................................................................. 183Figure 7-65 Tracing signaling of handover from WCDMA to GPRS................................................... 184Figure 7-66 Signaling flow for handover from GPRS to WCDMA (1) ................................................. 186Figure 7-67 Signaling flow for handover from GPRS to WCDMA (2) ................................................. 187Figure 7-68 Data configuration in the location area cell table ............................................................ 193Figure 7-69 Data configuration of neighbor cell configuration table ................................................... 194Figure 7-70 Configuration table for external 3G cells ........................................................................ 196Figure 7-71 Configuration table for GSM inter-RAT neighbor cells .................................................... 197Figure 7-72 Configuration table for 2G reselection parameters ......................................................... 198Figure 7-73 Parameter configuration table for inter-RAT handover.................................................... 199
  11. 11. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page11 , Total201TablesTable 2-1 Handover performance indexes and reference values ......................................................... 16Table 2-2 HSDPA handover performance indexes and reference value............................................... 17Table 2-3 HSUPA handover performance indexes and reference value............................................... 17Table 2-4 CDR index and reference value........................................................................................... 19Table 3-1 SHO failure indexes............................................................................................................ 36Table 3-2 HHO failure indexes............................................................................................................ 36Table 3-3 Traffic statistics indexes of CS inter-RAT handover preparation failure................................. 38Table 3-4 Traffic statistics indexes of PS inter-RAT outgoing handover failure ..................................... 39Table 4-1 Types of CDR indexes......................................................................................................... 45Table 4-2 Thresholds of EcIo and Ec .................................................................................................. 46Table 4-3 Traffic statistics indexes for analyzing causes to call drop.................................................... 51Table 5-1 Relationship between the filter coefficient and the corresponding tracing time...................... 58Table 5-2 2G handover times.............................................................................................................. 63Table 5-3 Best servers and other cells ................................................................................................ 67Table 7-1 Timers and counters related to the synchronization and asynchronization.......................... 104Table 7-2 Timers and counters related to call drop at lub interface .................................................... 107Table 7-3 Flow of serving cell update triggered by different events in SHO........................................ 132Table 7-4 Scenarios of handover between HSDPA and R99 (V17) .................................................... 144Table 7-5 Handover between two HSUPA cells................................................................................. 158Table 7-6 Handover between a HSUPA cell and a non-HSUPA cell ................................................... 163Table 7-7 Parameters of handover from 3G to 2G............................................................................. 190
  12. 12. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page12 , Total201W-Handover and Call Drop Problem Optimization GuideKey words:Handover, call drop, and optimizationAbstract:This document, aiming at network optimization of handover success rate and call drop rate, detailsthe specific network operation flow. In addition, it analyzes common problems during networkoptimization.Acronyms and abbreviations:Acronyms and Abbreviations Full SpellingAMR Adaptive MultiRateCHR Call History RecordCDR Call Drop RateDCCC Dynamic Channel Configuration ControlRAN Radio Access NetworkRNP Radio Network PlanningSRB Signaling Radio BearerTRB Traffic Radio BearerSHO Soft HandoverHHO Hard HandoverPCH Physical ChannelCN Core NetworkO&M Operation and maintenanceMNC Mobile Network CodeMCC Mobile Country CodeLAC Location Area CodeCIO Cell Independent OffsetHSUPA High Speed Uplink Packet AccessE-DCH Enhanced uplink Dedicated ChannelE-AGCH E-DCH Absolute Grant Channel
  13. 13. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page13 , Total201E-RGCH E-DCH Relative Grant Channel
  14. 14. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page14 , Total2011 IntroductionThis document aims to meet the requirements by on-site engineers on solving handover andcall drop problems and making them qualified during network optimization. It describes themethods for evaluating network handover and call drop performance, testing methods,troubleshooting methods, and frequently asked questions (FAQs).The appendix provides fundamental knowledge, principles, related parameters, and dataprocessing tools about handover and call drop. This document serves to network KPIoptimization and operation and maintenance (O&M) and helps engineers to locate and solvehandover and call drop problems.The RRM algorithms and problem implementation in this document are based on V16 RNC. Ifsome RRM algorithms are based on V17 RNC, they will be highlighted. HSUPA is introduced inV18 RNC, so the algorithms related to HSUPA are based on RNC V18. The following sectionsare updated:l Traffic Statistics Analysis for HSDPA Handoverl Handover Between HSDPA and R99l Direct Retry of HSDPAl Switch of Channel TypeActually handover is closely relevant to call drop. Handover failure probably leads to call drop.Therefore handover-caused call drop is arranged in handover success rate optimization part.The CDR optimization includes all related to call drop except handover-caused call drop.This document does not include usage of related tools.This document includes the following 12 chapters:l 1 Introductionl 2 Handover and Call Drop Performance Indexesl 3 Handover Index Optimizationl 4 CDR Index Optimizationl 5 FAQs Analysisl 6 Summaryl 7 Appendix
  15. 15. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page15 , Total201The traffic statistics analysis is based on RNC V1.5 counter. It will be updated upon the updateof RNC counters.
  16. 16. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page16 , Total2012 Handover and Call Drop Performance Indexes2.1 Handover Performance IndexesAccording to RNA KPI baseline document, Table 2-1 lists the handover performance indexesand reference values.Table 2-1 Handover performance indexes and reference valuesIndex Service Statistics methodReferencevalueSHO success rate CS&PS DT&Stat. 99%Intra-frequency HHOsuccess rateVoice DT&Stat. 90%VP DT&Stat. 85%PS UL64K/DL 64K DT&Stat. 85%PS UL64K/DL 144K DT&Stat. 80%PS UL64K/DL 384K DT&Stat. 75%Inter-frequency HHOsuccess rateVoice DT&Stat. 92%VP DT&Stat. 90%PS UL64K/DL 64K DT&Stat. 90%PS UL64K/DL 144K DT&Stat. 87%PS UL64K/DL 384K DT&Stat. 85%Inter-RAT handoversuccess rateVoice handover out DT&Stat. 95%PS handover out DT&Stat. 92%SHO ratio N/A DT 35%SHO cost N/A Stat. 40%
  17. 17. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page17 , Total201Table 2-2 lists the HSDPA handover performance indexes and reference value.Table 2-2 HSDPA handover performance indexes and reference valueIndex Service Reference valueHSDPA-HSDPA intra-frequencyserving cell updatePS (HSDPA) 99%HSDPA-HSDPA inter-frequencyserving cell updatePS (HSDPA) 92%HSDPA-R99 intra-frequency handover PS (HSDPA) 99%HSDPA-R99 inter-frequency handover PS (HSDPA) 90%Success rate of R99-to-HSDPA cellhandoverPS (HSDPA) 85%HSDPA-to-GPRS inter-RAT handover PS (HSDPA) 92%Note: The HSDPA handover KPIs are to be updated after formal issue by WCDMA&GSM PerformanceResearch Department.Table 2-3 HSUPA handover performance indexes and reference valueIndex Service Reference valueSuccess rate of inter-cellSHO in HSUPA (includingadding, replacing, anddeleting)PS (HSUPA) –Success rate of inter-cellSHO serving cell update inHSUPAPS (HSUPA)–Success rate ofDCH-to-E-DCHreconfiguration in SHOmode (including replacingand deleting)PS (HSUPA)–Success rate ofE-DCH-to-DCHreconfiguration in SHOmode (including replacingand deleting)PS(HSUPA)–Success rate of inter-cellintra-frequency HHO inHSUPAPS (HSUPA)–
  18. 18. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page18 , Total201Index Service Reference valueSuccess rate ofintra-frequency HHO from aHSUPA cell to anon-HSUPA cellPS (HSUPA)–Success rate ofDCH-to-E-DCHreconfiguration in single-linkmode (the second step ofinter- or intra-frequencyHHO from a non-HSUPAcell to a HSUPA cell)PS (HSUPA)–Success rate of inter-cellinter-frequency HHO inHSUPAPS (HSUPA)–Success rate ofinter-frequency HHO from aHSUPA cell to anon-HSUPA cellPS (HSUPA)–Success rate ofHSUPA-to-GPRS inter-RAThandoverPS (HSUPA) 92%Note:The HSUPA handover KPIs are unavailable and to be updated after formal issue by WCDMA&GSMPerformance Department.Decide the specific value according to project requirements or contract requirements of commercial network
  19. 19. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page19 , Total2012.2 Call Drop Performance IndexesTable 2-4 lists the CDR index and reference value.Table 2-4 CDR index and reference valueIndex ServiceStatisticsmethodReferencevalueCDRVoice DT&Stat.&CQT 2%VP DT&Stat.&CQT 2.5%PS planned fullcoverage rateDT&CQT 3%PS (UL DCH fullcoverage rate/DLHSDPA)DT 3%PS Stat. 10%PS (UL HSUPA/DLHSDPA)DT 3%The values listed in Table 2-4 are only for reference. Decide the specific value according toproject requirements or contract requirements of commercial network.The call drop rate of HSDPA is not defined yet, so engineers use call drop rate of PStemporarily.
  20. 20. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page20 , Total2013 Handover Index Optimization3.1 DT/CQT Index Optimization FlowDT and CQT are important to network evaluation and optimization. DT/CQT KPIs act asstandards for verifying networks. Overall DT helps to know entire coverage, to locate missingneighbor cells, and to locate cross-cell coverage. HHO and inter-RAT handover are used incoverage solutions for special scenarios, in while CQT is proper.The following sections describe the DT/CQT index optimization flow in terms of SHO, HHO, andinter-RAT handover.3.1.1 SHO DT Index Optimization FlowFigure 3-1 shows the SHO DT data analysis flow.
  21. 21. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page21 , Total201Figure 3-1 SHO DT data analysis flowInputting Analysis DataPerform DT. Collect DT data, related signaling tracing, RNC CHR, and RNC MML scripts.Obtaining When and Where the Problem OccursDuring the test, SHO-caused call drop might occur or SHO might fail, so record the location andtime for the problem occurrence. This prepares for further location and analysis.
  22. 22. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page22 , Total201Missing Neighbor CellDuring the early optimization, call drop is usually due to missing neighbor cell. Forintra-frequency neighbor cells, use the following methods to confirm intra-frequency missingneighbor cell.l Check the active set Ec/Io recorded by UE before call drop and Best Server Ec/Iorecorded by Scanner. Check whether the Best Server scramble recorded byScanner is in the neighbor cell list of intra-frequency measurement control before calldrop. The cause might be intra-frequency missing neighbor cell if all the followingconditions are met:− The Ec/Io recorded by UE is bad.− The Best Server Ec/Io is good.− No Best Server scramble is in the neighbor cell list of measurement control.l If the UE reconnects to the network immediately after call drop and the scramble ofthe cell that UE camps on is different from that upon call drop, missing neighbor cellis probable. Confirm it by measurement control (search the messages back from calldrop for the latest intra-frequency measurement control message. Check theneighbor cell list of this measurement control message)l UEs might report detected set information. If corresponding scramble information isin the monitor set before call drop, the cause must be missing neighbor cell.Missing neighbor cell causes call drop. Redundant neighbor cells impacts network performanceand increases the consumption of UE intra-frequency measurement. If this problem becomesmore serious, the necessary cells cannot be listed. Therefore pay attention to redundantneighbor cells when analyzing handover problems. For redundant neighbor cells, see 5 .Pilot PollutionPilot pollution is defined as below:l Excessive strong pilots exist at a point, but no one is strong enough to be primarypilot.According to the definition, when setting rules for judging pilot pollution, confirm the followingcontent:l Definition of strong pilotWhether a pilot is strong depends on the absolute strength of the pilot, which ismeasured by RSCP. If the pilot RSCP is greater than a threshold, the pilot is astrong pilot. Namely, AbsoluteRSCPThRSCPCPICH __ >.l Definition of "excessive"When judging whether excessive pilots exist at a point, the pilot number is thejudgment criteria. If the pilot number is more than a threshold, the pilots at a pointare excessive. Namely, NThNumberCPICH >_l Definition of "no best server strong enough"When judging whether a best server strong enough exist, the judgment criteria is therelative strength of multiple pilots. If the strength different of the strongest pilot andthe No.)1( +NThstrong pilot is smaller than a threshold, no best server strongenough exists in the point. Namely,
  23. 23. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page23 , Total201llativeRSCPthThst ThRSCPCPICHRSCPCPICH N Re_)1(1 )__( <− +Based on previous descriptions, pilot pollution exists if all the following conditions are met:l The number of pilots satisfying AbsoluteRSCPThRSCPCPICH __ >is morethan NTh.llativeRSCPthThst ThRSCPCPICHRSCPCPICH N Re_)1(1 )__( <− +Set dBmTh AbsoluteRSCP 95_ −= , 3=NTh , and dBTh lativeRSCP 5Re_ = , the judgment standardsfor pilot pollution are:l The number of pilots satisfying dBmRSCPCPICH 95_ −> is larger than 3.ldBRSCPCPICHRSCPCPICH thst 5)__( 41 <−Improper Configuration of SHO Algorithm ParametersSolve the following two problems by adjusting handover algorithm parameters.l Delayed handoverAccording to the signaling flow for CS services, the UE fails to receive active set updatecommand (physical channel reconfiguration command for intra-frequency HHO) due tothe following cause. After UE reports measurement message, the Ec/Io of original cellsignals decreases sharply. When the RNC sends active set update message, the UEpowers off the transmitter due to asynchronization. The UE cannot receive active setupdate message. For PS services, the UE might also fail to receive active set updatemessage or perform TRB reset before handover.Delayed handover might be one of the following:− Turning corner effect: the Ec/Io of original cell decreases sharply and that of thetarget cell increases greatly (an over high value appears)− Needlepoint effect: The Ec/Io of original cell decreases sharply before it increasesand the Ec/Io of target cell increase sharply for a short time.According to the signaling flow, the UE reports the 1a or 1c measurement report ofneighbor cells before call drop. After this the RNC receives the event and sends theactive set update message, which the UE fails to receive.l Ping-pong HandoverPing-pong handover includes the following two forms− The best server changes frequently. Two or more cells alternate to be the best server.The RSCP of the best server is strong. The period for each cell to be the best server isshort.− No primary pilot cell exists. Multiple cells exist with little difference of abnormalRSCP. The Ec/Io for each cell is bad.According to the signaling flow, when a cell is deleted, the 1A event is immediatelyreported. Consequently the UE fails because it cannot receive the active set updatecommand.
  24. 24. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page24 , Total201Abnormal EquipmentCheck the alarm console for abnormal alarms. Meanwhile analyze traced message, locate theSHO problem by checking the failure message. For help, contact local customer serviceengineers for confirm abnormal equipment.Reperforming Drive Test and Locating ProblemsIf the problem is not due to previous causes, perform DT again and collect DT data. Supplementdata from problem analysis.Adjustment and ImplementationAfter confirming the cause to the problem, adjust the network by using the following pertinentmethods:l For handover problems caused by pilot pollution, adjust engineering parameters ofan antenna so that a best server forms around the antenna. For handover problemscaused by pilot pollution, adjust engineering parameters of other antennas so thatsignals from other antennas becomes weaker and the number of pilots drops.Construct a new site to cover this area if conditions permit. If the interference is fromtwo sectors of the same NodeB, combine the two cells as one.l For abnormal equipment, consult customer service engineer for abnormal equipmentand transport layer on alarm console. If alarms are present on alarm console,cooperate with customer service engineers.l For call drop caused by delayed handover, adjust antennas to expand the handoverarea, set the handover parameters of 1a event, or increase CIO to enable handoverto occur in advance. The sum of CIO and measured value is used in eventevaluation process. The sum of initially measured value and CIP, as measurementresult, is used to judge intra-frequency handover of UE and acts as cell border inhandover algorithm. The larger the parameter is, the easier the SHO is and UEs inSHO state increases, which consumes resources. If the parameter is small, the SHOis more difficult, which might affects receiving quality.l For needle effect or turning corner effect, setting CIO to 5 dB is proper, but thisincreases handover ratio. For detailed adjustment, see SHO-caused call drop ofFAQs Analysis.l For call drop caused by Ping-pong handover, adjust the antenna to form a bestserver or reduce Ping-pong handover by setting the handover parameter of 1B event,which enables deleting a cell in active set to be more difficult. For details, increasethe 1B event threshold, 1B hysteresis, and 1B delay trigger time.3.1.2 HHO CQT FlowHHO TypesHHO includes the following types:l Intra-frequency HHOThe frequency of the active set cell before HHO is the same as that of the cell after HHO.If the cell does not support SHO, HHO might occur. HHO caters for cross-RNC
  25. 25. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page25 , Total201intra-frequency handover without lur interface, limited resources at lur interface, andhandover controlled by PS service rate threshold of handover cell. The 1D event ofintra-frequency measurement events determines intra-frequency HHO.l Inter-frequency HHOThe frequency of the active set cell before HHO is different from that of the cell afterHHO. HHO helps to carry out balanced load between carriers and seamless proceeding.Start compression mode to perform inter-frequency measurement according to UEcapability before inter-frequency HHO. HHO judgment for selecting cell depends onperiod measurement report.l Balanced load HHOIt aims to realize balanced load of different frequencies. Its judgment depends onbalanced load HHO.Inter-frequency coverage usually exists in special scenarios, such as indoor coverage, so CQTare used. The following section details the optimization flow for inter-frequency CQT.Optimization Flow of HHO CQTFigure 3-2 shows the optimization flow for HHO CQT.
  26. 26. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page26 , Total201Figure 3-2 Optimization flow for HHO CQTAdjustmentThe optimization flow for HHO is similar with that of SHO and the difference lies in parameteroptimization.Confirming inter-frequency missing neighbor cell is similar to that of intra-frequency. When calldrop occurs, the UE does not measure or report inter-frequency neighbor cells. After call drop,the UE re-camps on the inter-frequency neighbor cell.HHO problems usually refer to delayed handover and Ping-pong handover.Delayed HHO usually occurs outdoor, so call drop occurs when the UE is moving. There arethree solutions:l Increase the threshold for starting compression mode.The compression mode starts before inter-frequency or inter-RAT handover. Measure thequality of inter-frequency or inter-RAT cell by compression mode. Compression modestarts if the CPICH RSCP or Ec/Io meets the conditions. RSCP is usually the triggeringcondition.The parameter "inter-frequency measurement quantity" decides to use CPICH Ec/No orEc/Io as the measurement target for inter-frequency handover. When setting"inter-frequency measurement quantity", check that the cell is at the carrier coverageedge or in the carrier coverage center. If intra-frequency neighbor cells lie in all directionof the cell, the cell is defined as in the carrier coverage center. If no intra-frequency celllies in a direction of the cell, the cell is defined as at the carrier coverage edge.
  27. 27. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page27 , Total201In the cell at the carrier coverage edge, when UE moves along the direction where nointra-frequency neighbor cell lies, the CPICH Ec/No changes slowly due to the identicalattenuation rate of CPICH RSCP and interference. According to simulation, whenCPICH RSCP is smaller than the demodulation threshold (–100 dBm or so), the CPICHEc/No can still reach –12 dB or so. Now the inter-frequency handover algorithm basedon CPICH Ec/No is invalid. Therefore, for the cell at the carrier coverage edge, usingCPICH RSCP as inter-frequency measurement quantity to guarantee coverage is moreproper.In the cell in the carrier coverage center, use CPICH RSCP as inter-frequencymeasurement quantity, but CPICH Ec/No can better reflect the actual communicationquality of links and cell load. Therefore use CPICH Ec/No as inter-frequencymeasurement quantity in the carrier coverage center (not the cell at the carrier coverageedge), and RSCP as inter-frequency measurement quantity in the cell at the carriercoverage edge.In compression mode, the quality of target cell (inter-frequency or inter-RAT) is usuallymeasured and obtained. The mobility of MS leads to quality deterioration of the currentcell. Therefore the requirements on starting threshold are: before call drop due to thequality deterioration of the current cell, the signals of the target cell must be measuredand reporting is complete. The stopping threshold must help to prevent compressionmode from starting and stopping frequently.The RNC can distinguish CS services from PS services for inter-frequency measurement.If the RSCP is smaller than –95 dBm, compression mode starts. If the RSCP is greaterthan –90 dBm, compression mode stops. Adjust RSCP accordingly for special scenarios.l Increase the CIO of two inter-frequency cells.l Decrease the target frequency handover trigger threshold of inter-frequencycoverage.For Ping-pong HHO problems, solve them by increasing HHO hysteresis and delay trigger time.The intra-frequency HHO optimization is similar to that of inter-frequency. Decrease thehysteresis and delay trigger time of 1D event according to local radio environment to guaranteetimely handover.3.1.3 Inter-RAT Handover CQT FlowFlow ChatFigure 3-3 shows the inter-RAT handover CQT flow.
  28. 28. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page28 , Total201Figure 3-3 Inter-RAT handover CQT flowData ConfigurationInter-RAT handover fails due to incomplete configuration data, so pay attention to the followingdata configuration.l GSM neighbor configuration is complete on RNC. The configuration includes:− Mobile country code (MCC)− Mobile network code (MNC)− Location area code (LAC)− GSM cell identity (CELL ID)− Network color code (NCC)− Base station color code (BCC)− Frequency band indicator (FREQ_BAND)− Frequency number− Cell independent offset (CIO)Guarantee the correctness of the previous data and GSM network.
  29. 29. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page29 , Total201l Add location area cell information near 2G MSC to location area cell list of 3G MSC.The format of location area identity (LAI) is MCC + MNC + LAC. Select LAI as LAItype. Select Near VLR area as LAI class and add the corresponding 2G MSC/VLRnumber. The cell GCI format is: MCC + MNC + LAC + CI. Select GCI as LAI type.Select Near VLR area as LAI class and add the corresponding 2G MSC/VLRnumber.l Add data of WCDMA neighbor cells on GSM BSS. The data includes:− Downlink frequency− Primary scramble− Main indicator− MCC− MISSING NEIGHBOR CELL− LAC− RNC ID− CELL IDAccording to the strategies of unilateral handover of inter-RAT handover, if the dataconfiguration is complete, the inter-RAT handover problems are due to delayed handover. Afrequently-used solution is increasing CIO, increasing the threshold for starting and stoppingcompression mode, increasing the threshold to hand over to GSM.CausesThe causes to call drop due to 3G-2G inter-RAT handover are as below:l After the 2G network modifies its configuration data, it does not inform the 3Gnetwork of modification, so the data configured in two networks are inconsistent.l Missing neighbor cell causes call drop.l The signals fluctuate frequently so call drop occurs.l Handset problems causes call drop. For example, the UE fails to hand over back orto report inter-RAT measurement report.l The best cell changes upon Physical channel reconfiguration.l Excessive inter-RAT cell are configured (solve it by optimizing number of neighborcells).l Improperly configured LAC causes call drop (solve it by checking data configuration).3.1.4 DT/CQT Flow for HSDPA HandoverTypeAccording to the difference of handover on DPCH in HSDPA network, the HSDPA handoverincludes:l SHO or softer handover of DPCH, with HS-PDSCH serving cell update
  30. 30. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page30 , Total201l Intra-frequency and inter-frequency HHO of DPCH, with HS-PDSCH serving cellupdateAccording to different technologies used in the serving cell before and after handover, HSDPAhandover includes:l Handover in HSDPA systeml Handover between HSDPA and R99 cellsl Handover between HSDPA and GPRS cellsMethodsFor HSDPA service coverage test and mobility-related test (such as HHO on DPCH withHS-PDSCH serving cell update, handover between HSDPA and R99, and inter-RAT handover),perform DT to know the network conditions.For location of HSDPA problems and non-mobility problems, perform CQT (in specified point orsmall area).FlowWhen a problem occurs, check R99 network. If there is similar problem with R99 network, solveit (or, check whether the R99 network causes HSDPA service problems, such as weak coverage,missing neighbor cell. Simplify the flow).Figure 3-4 shows the DT/CQT flow for HSDPA handover.
  31. 31. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page31 , Total201Figure 3-4 DT/CQT flow for HSDPA handoverThe problems with handover of HSDPA subscribers are usually caused by the faulty handoverof R99 network, such as missing neighbor cell and improper configuration of handoverparameters. When the R99 network is normal, if the handover of HSDPA subscribers is stillfaulty, the cause might be improper configuration of HSDPA parameters. Engineers can checkthe following aspects:l Whether the HSDPA function of target cell is enabled and the parameters arecorrectly configured. Engineers mainly check the words of cell and whether thepower is adequate, whether the HS-SCCH power is low. These parameters mightnot directly cause call drop in handover, but lead to abnormal handover and loweredthe user experience.l Whether the protection time length of HSDPA handover is proper. Now the baselinevalue is 0s. Set it by running SET HOCOMM.l Whether the threshold for R99 handover is proper. The handover flow for HSDPA isgreatly different from that of R99, so the handover of R99 service may succeed whilethe HSDPA handover may fail. For example, in H2D handover, when the UE reports1b event, it triggers RB reconfiguration in the original cell, reconfigures servicebearer to DCH, and updates the cell in active set. If the signals of the original celldeteriorate quickly now, the reconfiguration fails.l Whether the protection time length of D2H handover is proper. Now the baselinevalue is 2s. Set it by running SET HOCOMM.
  32. 32. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page32 , Total2013.1.5 DT/CQT Flow for HSUPA HandoverThe DT/CQT flow for HSUPA handover is similar to that for HSDPA. For details, refer to DT/CQTFlow for HSDPA Handover.For the test of HSUPA service coverage and mobility-related tests (such as the test of successrate of HSUPA serving cell update), perform DT to know the network conditions. For locatingHSUPA problems and the problems unrelated to mobility, perform CQT (in specified spot orarea).3.1.6 SHO Ratio OptimizationThis part is to be supplemented.3.1.7 MBMS Mobility OptimizationCurrently, the radio network controller (RNC) V18 supports only the broadcast mode of themultimedia broadcast multicast service (MBMS); the MBMS user equipment (UE) moves onlybetween point-to-multipoint (PTM) cells.Figure 3-5 Movement of the MBMS UE between PTM cellsThe movement of the MBMS UE between PTM cells is similar to the movement of UEperforming PS services in the CELL-FACH state. The UE performs the handover between cells
  33. 33. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page33 , Total201through cell reselection and obtains a gain through soft combining or selective combiningbetween two cells to guarantee the receive quality of the service. The UE first moves to thetarget cell and then sends a CELL UPDATE message to notify the serving radio networkcontroller (SRNC) that the cell where the UE stays is changed. The SRNC returns a CELLUPDATE CONFIRM message. The UE receives an MBMS control message from the MCCH inthe target cell and determines whether the MBMS radio bearer to be established is consistentwith that of the neighboring cell. If they are consistent, the original radio bearer is retained. TheMBMS mobility optimization, which guarantees that the UE obtains better quality of service atthe edge of cells, covers the following aspects:l Optimize cell reselection parameters to guarantee that the UE can be reselected tothe best cell in time.l Guarantee that the power of the FACH in each cell is large enough to meet thecoverage requirement of the MBMS UE at the edge of the cells.l Guarantee that the transmission time difference of the UE between different linksmeets the requirement of soft combing or selective combining*.l Guarantee that the power, codes, transmission, and CE resources of the target cellare not restricted or faulty, and that the MBMS service is successfully established.The UE can simultaneously receive the same MBMS service from two PTM cells and combinethe received MBMS service. The UE supports two combining modes:Soft combining: The transmission time difference between the current cell and the neighboringcell is within (one TTI + 1) timeslots and the TFCI in each transmission time interval (TTI) is thesame.Selective combining: The transmission time difference between the current cell and theneighboring cell is within the reception time window stipulated by the radio link controller (RLC).The SCCPCH is decoded and the transmission blocks are combined in the RLC PDU phase
  34. 34. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page34 , Total2013.2 Traffic Statistics Analysis FlowThe traffic statistics data is important to network in terms of information source. In addition, it isthe major index to evaluate network performance.The handover traffic statistics data is includes RNC-oriented data and cell-oriented data. RNC–oriented data reflects the handover performance of entire network, while cell-oriented datahelps to locate problematic cells.The analysis flow for SHO, HHO, inter-RAT handover, and HSDPA handover is similar, but thetraffic statistics indexes are different from them.Figure 3-6 shows the analysis flow for handover traffic statistics data.
  35. 35. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page35 , Total201Figure 3-6 Analysis flow for handover traffic statistics data3.2.1 Analysis Flow for SHO Traffic StatisticsThe SHO success rate is defined as below:SHO success rate = SHO successful times/SHO timesAccording to the flow, SHO includes SHO preparation process and SHO air interface process.The SHO preparation process is from handover judgment to RL setup completion. The SHO airinterface process is active set update process.l Check the SHO success rate of entire network and cell in busy hour. If they are notqualified, analyze the problematic cells in details.l Sort the SHO (or softer handover) failure times of the cell by TOP N and locate thecells with TOP N failure times. List the specific indexes of failure causes. If locatingspecific causes from traffic statistics is impossible, analyze the corresponding CHR.Table 3-1 lists the detailed traffic statistics indexes to SHO (or softer handover) failureand analysis.
  36. 36. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page36 , Total201Table 3-1 SHO failure indexesFailure causes AnalysisConfiguration nonsupportThe UE thinks the content of active set update for RNC to add/delete linksdoes not support SHO. This scenario seldom exists in commercial networks.SynchronizationreconfigurationnonsupportThe UE feeds back that the SHO (or softer handover) for RNC to add/deletelinks is incompatible with other subsequent processes. The RNCguarantees serial processing upon flow processing. This cause is due to theproblematic UE.Invalid configurationThe UE thinks the content of active set update for RNC to add/delete links isinvalid. This scenario seldom exists in commercial networks.No response from UEThe RNC fails to receive response to active set update command foradding/deleting links. This is a major cause to SHO (or softer handover)failure. It occurs in areas with weak coverage and small handover area. RFoptimization must be performed in the areas.l Perform DT to re-analyze problems. The traffic statistics data provides the trend andpossible problems. Further location and analysis of problems involves DT and CHRto the cell. DT is usually performed on problematic cells and signaling flow at the UEside and of RNC is traced. For details, see 3.1.3 .3.2.2 Analysis Flow of HHO Traffic statisticsThe HHO traffic statistics includes outgoing HHO success rate and incoming HHO success rate:l Outgoing HHO Success Rate = Outgoing HHO Success Times/Outgoing HHOTimesl Incoming HHO Success Rate = Incoming HHO Success Times/Incoming HHOTimesUpon HHO failure, pay attention to indexes related to internal NodeB, between NodeBs, andbetween RNCs.Table 3-2 lists the HHO failure indexes.Table 3-2 HHO failure indexesFailure cause AnalysisHHO preparation failureRadio link setup failure Analyze RL setup failure.Other causes Analyze the problem further based on CHR logs.Internal NodeB/Between NodeBs/Between RNCs HHO failureConfigurationnonsupportThe UE thinks it cannot support the command for outgoing HHO,because it is incompatible with HHO.PCH failure The cause is probably weak coverage and strong interference.SynchronizationreconfigurationnonsupportThe UE feeds back HHO is incompatible with other consequent processesdue to compatibility problems of UE.
  37. 37. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page37 , Total201Cell updateCell update occurs upon outgoing HHO. These two processes lead tooutgoing HHO failure.Invalid configurationThe UE thinks the command for outgoing HHO as invalid. This is acompatibility problem of UE.Other causes Analyze the problem further based on CHR logs.3.2.3 Traffic Statistics Analysis Flow for Inter-RAT HandoverThe inter-RAT handover success rate includes voice inter-RAT handover success rate and PSinter-RAT handover success rate.Voice Inter-RAT Outgoing Handover Success Rate = Voice Inter-RAT Outgoing HandoverSuccess Times/Voice Inter-RAT Outgoing Handover Attempt TimesVoice Inter-RAT Outgoing Handover Success Times: when the RNC sends a RELOCATIONREQUIRED message.Voice Inter-RAT Outgoing Handover Attempt Times: during CS inter-RAT outgoing, when theRNC receives an IU RELEASE COMMAND message, with the reason value SuccessfulRelocation, or Normal Release.PS Inter-RAT Outgoing Handover Success Rate = PS Inter-RAT Outgoing Handover SuccessTimes/PS Inter-RAT Outgoing Handover Implementation TimesPS Inter-RAT Outgoing Handover Success Times: the RNC sends a CELL CHANGE ORDERFROM UTRAN message to UE.PS Inter-RAT Outgoing Handover Implementation Times: when the RNC receives an IURELEASE COMMAND message, with the reason value Successful Relocation, or NormalRelease.Voice Inter-RAT Outgoing Handover Success RateThe voice inter-RAT outgoing handover includes handover preparation process andimplementation process.Figure 3-7 shows the voice inter-RAT outgoing handover flow.
  38. 38. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page38 , Total201Figure 3-7 Voce inter-RAT outgoing handover flowDuring CS inter-RAT outgoing handover process, when the RNC sends a RELOCATIONREQUIRED message to CN, if the current CS service is AMR voice service, count it as aninter-RAT handover preparation. When the RNC receives the IU RELEASE COMMANDmessage replied by CN, count it as inter-RAT outgoing handover success according to theSRNC cell being used by UE.If CS inter-RAT handover fails, check the failure statistics indexes listed in Table 3-3.Table 3-3 Traffic statistics indexes of CS inter-RAT handover preparation failureFailure cause AnalysisRNC-level inter-RAT outgoing handover preparation failureExpiration ofwaiting for SRNSrelocationcommandThe CN does not respond the corresponding command for handoverpreparation request, because the CN parameter configuration or thecorresponding link connection is problematic. To solve this problem,analyze the causes according to CN and BSS signaling tracing.SRNS relocationcancellationAfter the RNC requests handover preparation, it receives the releasecommand from CN. This includes the following two cases:l The inter-RAT handover request occurs during signaling process likelocation update, so the flow is not complete before location update iscomplete. Finally the CN sends a release message.l The subscribers that are calling hang UE before handover preparation,so the CN sends a release message.The previous two cases, despite incomplete handover, are normal nestingflows.SRNS relocationexpirationIt corresponds to incorrect configuration of CN, so you must analyze thecauses according to CN and BSS signaling tracing.SRNS relocationfailure in targetCN/RNC/systemIt corresponds to incorrect configuration of CN or BSS nonsupport, so youmust analyze the causes according to CN and BSS signaling tracing.
  39. 39. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page39 , Total201Unknown targetRNCIt corresponds to incorrect configuration of MSC parameters withoutinformation like LAC of target cell, so you must check the parameterconfiguration. It occurs easily after adjustment of 2G networks.UnavailableresourceIt corresponds to incorrect configuration of MSC parameters or unavailableBSC resources, so you must analyze the causes according to CN and BSSsignaling tracing.Other causes Analyze the causes according to CN and BSS signaling tracing.Cell-level inter-RAT outgoing handover preparation failureSRNS relocationexpirationThe CN parameter configuration or the corresponding link connection isproblematic, so you must analyze the causes according to CN and BSSsignaling tracing.SRNS relocationfailure in targetCN/RNC/systemIt corresponds to incorrect configuration of CN or BSS nonsupport, so youmust analyze the causes according to CN and BSS signaling tracing.SRNS relocationnonsupport intargetCN/RNC/systemThe BSC fails to support some parameters of inter-RAT handover request,so you must analyze the causes according to CN and BSS signalingtracing.Other causes Analyze the causes according to CN and BSS signaling tracing.RNC-level/CELL-level inter-RAT outgoing handover failureConfigurationnonsupportThe UE fails to support the handover command in the network, so the UEis incompatible with the handover command.PCH failureThe 2G signals are weak or the interference is strong so the UE fails toconnect to the network.Other causesAnalyze the problem further according to CHR logs and CN/BSS signalingtracing.PS Inter-RAT Handover Success RateAfter the RNC sends the CELL CHANGE ORDER FROM UTRAN message, the PS inter-RAToutgoing handover fails if it receives the CELL CHANGE ORDER FROM UTRAN FAILUREmessage. You must check the indexes listed in Table 3-4.Table 3-4 Traffic statistics indexes of PS inter-RAT outgoing handover failureFailure cause AnalysisRNC-level/CELL-level PS inter-RAT outgoing handover preparation failureConfigurationnonsupportThe UE fails to support the handover command of the network, becausethe UE is incompatible with the command.PCH failureThe 2G signals are weak or the interference is strong, so the UE fails toaccess the network.Radio networklayer causeThe UE is probably incompatible. The UE detects that the sequencenumber of SNQ in the AUTN message is correct, so the handover fails.The value is synchronization failure.Transport layercauseThe corresponding transport link is abnormal.
  40. 40. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page40 , Total201Other causes You must analyze the causes according to CN and BSS signaling tracing.3.2.4 Traffic Statistics Analysis for HSDPA HandoverHSDPA switch includesl H-H (HS-DSCH to HS-DSCH) intra-frequency serving cell updatel H-H inter-frequency serving cell updatel HSDPA-R99 intra-frequency switchl HSDPA-R99 inter-frequency switchl HSDPA-GPRS switchThe traffic statistics indexes are defined as below:l Success rate of H-H intra-frequency serving cell update = (Times of successfulupdate of serving cell)/(attempt times update of serving cell)When the RNC sends UE the PHYSICAL CHANNEL RECONFIGURATION message,if the serving cell is updated, engineers count the attempt times of serving cell in theoriginal serving cell. When the RNC receives the PHYSICAL CHANNEL RECFGCOMPLETE message, if the serving cell changes, the RNC counts the times ofsuccessful update of serving cells in the original serving cell when the UE is in the SHOmode not in the HHO mode.l Success rate of H-H inter-frequency serving cell update = Times of successfuloutgoing inter-frequency HHO from HS-DSCH to HS-DSCH/Times of requestedoutgoing inter-frequency HHO from HS-DSCH to HS-DSCHWhen the RNC sends UE the PHYSICAL CHANNEL RECONFIGURATION message,and the inter-frequency HHO is from HS-DSCH to HS-DSCH, the RNC counts the timesof requested outgoing inter-frequency HHO from HS-DSCH to HS-DSCH. When theRNC receives the PHYSICAL CHANNEL RECFG COMPLETE message from UE, andthe inter-frequency HHO is from HS-DSCH to HS-DSCH, engineers count the times ofsuccessful outgoing inter-frequency HHO from HS-DSCH to HS-DSCH.l Success rate of H-H inter-frequency serving cell update = successful times ofoutgoing inter-frequency HHO from HS-DSCH to HS-DSCH/attempt times HHO fromDCH to HS-DSCH in the cellWhen the RNC sends the UE the PHYSICAL CHANNEL RECONFIGURATIONmessage, if the switch is the inter-frequency HHO from HS-DSCH to HS-DSCH, theRNC counts the successful times of inter-frequency HHO from HS-DSCH to HS-DSCHin the cell.l Success rate of H-to-R99 intra-frequency SHO = successful times of switch fromHS-DSCH to DCH in multi-link mode in the cell/attempt times switch from HS-DSCHto DCH in multi-link mode in the cell.Success rate of R99-to-H intra-frequency SHO = successful times of switch fromDCH to HS-DSCH in multi-link mode in the cell/attempt times switch from DCH toHS-DSCH in multi-link mode in the cell.In the DCCC or RAB MODIFY process, if the RNC decides to switch the channel in thecell, it sends the UE the RF RECONFIGURATION message. According to the channelstate of the UE before and after reconfiguration, the RNC counts the previous indexes inthe HSDPA serving cell.
  41. 41. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page41 , Total201l Success rate of H-to-R99 intra-frequency HHO = successful times of outgoingintra-frequency HHO from HS-DSCH to DCH in the cell/attempt times outgoingintra-frequency HHO from HS-DSCH to DCH in the cell.When the RNC sends the UE the PHYSICAL CHANNEL RECONFIGURATIONmessage, if the switch is the intra-frequency switch from HS-DSCH to DCH, the RNCcounts the attempt times of inter-frequency HHO from HS-DSCH to DCH in the cell.When the RNC receives the PHYSICAL CHANNEL RECFG COMPLETE messagefrom the UE, if the switch is the intra-frequency HHO from HS-DSCH to DCH, theRNC counts the successful times of outgoing intra-frequency HHO from HS-DSCH toDCH in the cell.Success rate of H-to-R99 inter-frequency switch updateThe RNC algorithm is unavailable now, so this index is unavailable.l Success rate of H-to-R99 inter-frequency switch update = successful times ofoutgoing HHO from HS-DSCH to DCH in the cell/attempt times outgoinginter-frequency HHO from HS-DSCH to DCH in the cellWhen the RNC sends the UE the PHYSICAL CHANNEL RECONFIGURATIONmessage, if the switch is the inter-frequency switch from HS-DSCH to DCH, the RNCcounts the attempt times inter-frequency HHO from HS-DSCH to DCH in the cell. Whenthe RNC receives the PHYSICAL CHANNEL RECFG COMPLETE message from theUE, if the switch is the inter-frequency HHO from HS-DSCH to DCH, the RNC countsthe successful times of outgoing inter-frequency HHO from HS-DSCH to DCH in thecell.Success rate of R99-to-HThe RNC algorithm is unavailable now, so this index is unavailable.l Success rate of R99-to-H switch = successful times of switch from DCH toHS-DSCH in the cell/attempt times of switch from DCH to HS-DSCH in the cellIn the DCCC or RAB MODIFY process, if the RNC decides to switch the channel in thecell, it sends the UE the RF RECONFIGURATION message. According to the channelstate of the UE before and after reconfiguration, the RNC counts the attempt times ofswitch from DCH to HS-DSCH in the HSDPA serving cell. In the DCCC or RABMODIFY process, if the RNC receives the RB RECONFIGURATION COMEPLTEmessage from UE, and the reconfiguration enables UE to switch from the DCH toHS-DSCH in the same cell, the RNC counts the successful times of switch from DCH toHS-DSCH in the HSDPA serving cell.l Success rate of H-to-GPRS handover updateThe traffic statistics does not include the index, and the index will be supplemented later.The causes to failure and analysis methods will be summarized later.3.2.5 Traffic Statistics Analysis for HSUPA HandoverThe traffic statistics indexes for HSUPA are defined as below:l Success rate of SHO between HSUPA cells (including adding, replacing, anddeleting) = attempt times of active set update/complete times of active set update.l Success rate of SHO serving cell update between HSUPA cells = successful timesof SHO serving cell update/attempt times of SHO serving cell update.
  42. 42. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page42 , Total201l Success rate of reconfiguration from DCH to E-DCH in the cell (SHO,intra-frequency HHO, and inter-frequency HHO) = successful times of handover fromDCH to E-DCH/attempt times of handover from DCH to E-DCH.l Success rate of reconfiguration from E-DCH to DCH in the cell (including adding andreplacing) = successful times of handover from E-DCH to DCH in SHOmode/attempt times of handover from E-DCH to DCH in SHO mode.l Success rate of intra-frequency HHO serving cell between HSUPA cells = successfultimes of intra-frequency HHO serving cell between HSUPA cells/attempt times ofintra-frequency HHO serving cell between HSUPA cells.l Success rate of intra-frequency HHO from E-DCH to DCH from a HSUPA cell to anon-HSUPA cell = successful times of intra-frequency HHO from E-DCH toDCH/attempt times of intra-frequency HHO from E-DCH to DCH.l Success rate of inter-frequency HHO serving cell update between HSUPA cells =successful times of inter-frequency HHO serving cell update between HSUPAcells/attempt times of inter-frequency HHO serving cell update between HSUPAcells.l Successful times of inter-frequency HHO from a HSUPA cell to a non-HSUPA cell =successful times of inter-frequency HHO from E-DCH to DCH/request times ofinter-frequency HHO from E-DCH to DCH.
  43. 43. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page43 , Total2013.3 SHO Cost OptimizationTo be supplemented.
  44. 44. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page44 , Total2014 CDR Index Optimization4.1 Definition of Call Drop and Traffic Statistics Indexes4.1.1 Definition of DT Call DropAccording to the air interface signaling recorded at the UE side, during connection, DT call dropoccurs when the UE receives:l Any BCH message (system information)l The RRC Release message with the release cause Not Normal.l Any of the CC Disconnect, CC Release Complete, CC Release message with therelease cause Not Normal Clearing, Not Normal, or Unspecified.4.1.2 Descriptions of Traffic Statistics IndexesA generalized CDR consists of CN CDR and UTRAN CDR. RNO engineers focus on UTRANCDR, so the following sections focus on KPI index analysis at UTRAN side.The related index at UTRAN side is the number of RAB for each service triggered by RNC. Itconsists of the following two aspects:l After the service is set up, the RNC sends CN the RAB RELEASE REQUESTmessage.l After the service is set up, the RNC sends CN the IU RELEASE REQUESTmessage. Afterwards, it receives the IU RELEASE COMMAND sent by CN.Upon statistics, sort them by specific services. Meanwhile, traffic statistics includes the cause torelease of RAB of each service by RNC.CS CDR is calculated as below:%*SuccessCSRABSetupiggedByRNCCSRabrelTrCDRCS 100_∑∑=PS CDR is calculated as below:
  45. 45. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page45 , Total201%*SuccessPSRABSetupiggedByRNCPSRabrelTrCDRPS 100_∑∑=The failure cause indexes are sorted in Table 4-1.Table 4-1 Types of CDR indexesCDR type Cause Corresponding signaling processDue to airinterfaceRF RLC reset and RL FailureExpirationof processtimerRB RECFGExpiration of PHY/TRCH/SHO/ASUHHO failureNot due toairinterfaceHardwarefailureThe transport failure between RNC and NodeB. NCPreports failure.FP synchronization failure.Transportlayer failureALCAP report failureSubscribersarereleased byforce byMMLO&M interventionThe definition of RAN traffic statistics call drop is according to statistics of lu interface signaling,including the times of RNCs originating RAB release request and lu release request. The DTcall drop is defined according to the combination of messages at air interface and fromnon-access lay and cause value. They are inconsistent.4.2 DT/CQT Optimization FlowFigure 4-1 shows flow chart for analyzing call drop.
  46. 46. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page46 , Total201Figure 4-1 Flow chart for analyzing call drop4.2.1 Call Drop Cause AnalysisCall drop occurs usually due to handover, which is described in chapter 3 . The followingsections describe the call drop not due to handover.Weak CoverageFor voice services, when CPICH Ec/Io is greater than –14 dB and RSCP is greater than –100dBm (a value measured by scanner outside cars), the call drop is usually not due to weakcoverage. Weak coverage usually refers to weak RSCP.Table 4-2 lists the thresholds of Ec/Io and Ec (from an RNP result of an operator, just forreference).Table 4-2 Thresholds of EcIo and EcServiceBit rate ofserviceDL EbNoEcIothresholdsEc thresholdsCS 12.2 12.2 8.7 –13.3 –103.1
  47. 47. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page47 , Total201CS 64 64 5.9 –11.9 –97.8PS 64 64 5.1 –12.7 –98.1PS 128 128 4.5 –13.3 –95.3PS 384 384 4.6 –10.4 –90.6Uplink or downlink DCH power helps to confirm the weak coverage is in uplink or downlink bythe following methods.l If the uplink transmission power reaches the maximum before call drop, the uplinkBLER is weak or NodeB report RL failure according to single subscriber tracingrecorded by RNC, the call drop is probably due to weak uplink coverage.l If the downlink transmission power reaches the maximum before call drop and thedownlink BLER is weak, the call drop is probably due to weak downlink coverage.In a balanced uplink and downlink without uplink or downlink interference, both the uplink anddownlink transmit power will be restricted. You need not to judge whether uplink or downlink isrestricted first. If the uplink and downlink is badly unbalanced, interference probably exists in therestricted direction.A simple and direct method for confirming coverage is to observe the data collected by scanner.If the RSCP and Ec/Io of the best cell is low, the call drop is due to weak coverage.Weak coverage might be due to the following causes:l Lack of NodeBsl Incorrectly configured sectorsl NodeB failure due to power amplifier failureThe over great indoor penetration loss causes weak coverage. Incorrectly configured sectors ordisabling of NodeB will occur, so at the call drop point, the coverage is weak. You mustdistinguish them.InterferenceBoth uplink and downlink interference causes call drop.In downlink, when the active set CPICH RSCP is greater than –85 dBm and the active set Ec/Iois smaller than –13 dB, the call drop is probably due to downlink interference (when thehandover is delayed, the RSCP might be good and Ec/Io might be weak, but the RSCP of Ec/Ioof cells in monitor set are good). If the downlink RTWP is 10 dB greater than the normal value(–107 to –105 dB) and the interference lasts for 2s–3s, call drop might occur. You must payattention to this.Downlink interference usually refers to pilot pollution. When over three cells meets the handoverrequirements in the coverage area, the active set replaces the best cell or the best cell changesdue to fluctuation of signals. When the comprehensive quality of active set is bad (CPICH Ec/Iochanges around –10 dB), handover failure usually causes SRB reset or TRB reset.Uplink interference increases the UE downlink transmit power in connection mode, so the overhigh BLER causes SRB reset, TRB reset, or call drop due to asynchronization. Uplinkinterference might be internal or external. Most of scenario uplink interference is external.Without interference, the uplink and downlink are balanced. Namely, the uplink and downlinktransmit power before call drop will approach the maximum. When downlink interference exists,
  48. 48. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page48 , Total201the uplink transmit power is low or BLER is convergent. When the downlink transmit powerreaches the maximum, the downlink BLER is not convergent. It is the same with uplinkinterference. You can use this method to distinguish them.Abnormality AnalysisIf the previous causes are excluded, the call drop might due to problematic equipment. Youneed to check the logs and alarms of equipment for further analysis. The causes might be asbelow:l An abnormal NodeB causes failure of synchronization, so links keeps being addedand deleted.l The UE does not report 1a measurement report so call drop occurs.You need to focus on the call drop due to abnormal testing UE, which occurs easily during CQT.Namely, the data recorded in DT does not contain the information reported by UE for a period.HSPA Call Drop AnalysisFor HSPA call drop analysis, refer to previous causes to R99 call drop.4.2.2 Frequently-adjusted Non-handover Algorithm ParametersThe frequently-adjusted non-handover algorithm parameters in call drop are as below:Maximum Downlink Transmit Power of Radio LinkConfiguring the transmit power of dedicated link to a great value helps to eliminate call droppoints due to weak coverage, but it brings interference. The power of a single subscriber isallowed to be great, so the subscriber might impact other subscribers or lower downlink capacityof system when the subscriber consumes great power at the edge of a cell.The configuration of downlink transmit power is usually provided by link budget. An increase ordecrease of 1–2 dB has little impact on call drop in signal DT, but it can be seen from trafficstatistics indexes. The CDR of some cells is high due to weak coverage, you can increase themaximum transmit power of DCH. The access failure probability of some cells is high due toover high load, you can lower the maximum downlink transmit power of radio link.Maximum Retransmission Times of Signaling and ServicesWhen the BLER of the channel is high, the signaling is reset because the retransmissionreaches the maximum times. A reset of signaling causes call drop. The services using AM modefor service transmission will also retransmit signaling. If the retransmission reaches themaximum times, the signaling is reset. The system configures the maximum reset times. Whenthe reset times reaches the maximum, the system starts to release the service, which causescall drop.The default configuration of system guarantees that burst blocks will not cause abnormal calldrop, and call drop occurs when UE moves to an area with weak coverage and when the resetis time, so the system releases resources. In some scenarios, burst interference or needleeffect exists, so 100% block error occurs during burst interference. If you want have less calldrop, increase the retransmission times improper to resist burst interference.This parameter is configured for RNC.
  49. 49. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page49 , Total2014.2.3 Judgment Tree for Call Drop CausesBased on various causes to call drop, the judgment tree for analyzing call drop is as shown inFigure 4-2.Figure 4-2 Judgment tree for call drop causesPreparing DataThe data to be prepared include:l Data files collected by DTl Single subscriber tracing recorded by RNCl CHR recorded by RNCObtaining Call Drop LocationYou need to use special software to process DT data. For example, the software Assistant helpsto obtain call drop time and location, PICH data collected by scanner, information about activeset and monitor set collected by UE, and the signaling flow.
  50. 50. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page50 , Total201Analyzing Signal Variation of Best server From ScannerAnalyze the signal variation of best server from scanner.l If the signals of best server are stable, analyze RSCP and Ec/Io.l If the signals of best server fluctuate sharply, you must analyze the quick variation ofbest server signals and the situation without best server. Consequently you cananalyze call drop due to ping-pong handover.Analyzing RSCP and Ec/Io of Best cellObserve the RSCP and Ec/Io of best cell according to scanner.l If both RSCP and Ec/Io are bad, call drop must be due to weak coverage.l If RSCP is normal but Ec/Io is bad (delayed handover is excluded, intra-frequencyneighbor cell interference), call drop must be due to downlink interference.l If both RSCP and Ec/Io are normal,When the cell in UE active set is inconsistent with the best cell according to scanner, calldrop must be due to missing neighbor cell and delayed handover.When the cell in UE active set is consistent with the best cell according to scanner, calldrop must be due to uplink interference or must be abnormal.Re-perform DT to Solve ProblemsA DT might not help to collect all information needed to locate call drop problems, so further DTsare needed. In addition, you can confirm whether the call drop point is random or fixed byfurther DT. You must eliminate fixed call drop points, but you can choose to eliminate randomcall drop points.4.3 Traffic Statistics Analysis FlowWhen analyzing traffic statistics indexes, you need to check RNC call drop indexes and masterthe overall situation of network operation. Meanwhile, you must analyze the cell concern fordetailed call drop indexes. You can obtain call drop of different services and approximatecauses to call drop by using traffic statistics analyzers.To analyze traffic statistics indexes, you must analyze the cells with obviously abnormal indexes.If the KPIs of the cell are good, there must be problems with version, hardware, transport,antenna-feeder, or data. Based on alarms, you can check these aspects.If there are no abnormalities, you can form a list of cells with bad KPIs by classifying sectorcarriers. Analyze traffic statistics indexes of these cells (such as more indexes related, analyzingthe interval between two periods, indexes leading to call drop, and handover indexes), andcheck the causes to call drop based on CHR. When solving problems, you need to focus on oneindex and combine other indexes.When the traffic volume reaches a certain level, the traffic statistics indexes work. For example,a CDR of 50% does not indicate a bad network. Only when the absolute value of call times, callsuccess times, and total times of call drop is meaningful in terms of statistics, the traffic statisticsindexes work.The flow for analyzing traffic statistics is as below.
  51. 51. W-Handover and Call Drop Problem Optimization Guide For internal use only2008-12-22 All rights reserved Page51 , Total2014.3.1 Analyzing RNC CDRThe RNC CDR involves the number of RAB of each service triggered by RNC, including twoaspects:l After a service is established successfully, the RNC sends CN the RAB RELEASEREQUEST message.l After a service is established successfully, the RNC sends CN the IU RELEASEREQUEST message, and then receives the IU RELEASE COMMAND message sentby CN.AMR CDR = VS.RAB.Loss.CS.RF.AMR / VS.RAB.SuccEstab.AMR.VP CDR = VS.RAB.Loss.CS.Conv64K / VS.RAB.SuccEstCS.Conv.64.To analyze PS call drop of various rates, you can analyze the following indexes:l VS.RAB.Loss.PS.64K / VS.RAB.SuccEstPS.64l VS.RAB.Loss.PS.128K / VS.RAB.SuccEstPS.128l VS.RAB.Loss.PS.384K / VS.RAB.SuccEstPS.384Based on analysis of previous indexes, you can obtain the performance of various services andrates in the network, as well as SHO/HHO call drop. More important, you can obtain the cellswith bad indexes and periods.4.3.2 Analyzing Causes to Call DropIn traffic statistics analysis, you must analyze the major causes to call drop.Table 4-3 lists the major indexes for analyzing traffic statistics.Table 4-3 Traffic statistics indexes for analyzing causes to call dropFailure cause AnalysisOM interference The O&M tasks cause call drop.Causes due to RABpreemptionHigh-priority preemption causes release of CS links. This kind of call dropoccurs when the load and resources are limited. Performing expansiondepends on the times of occurrence.Causes due to UTRANThe causes due to UTRAN in the cell lead to abnormal release of link. Thiscorresponds to abnormal process, so you must further analyze it based onCHR.Uplink RLC resetUplink RLC reset causes release of links, because the coverage quality(including missing neighbor cell and over mall handover area) is bad.Downlink RLC resetDownlink SRB reset causes release of links, because the coverage quality(including missing neighbor cell and over mall handover area) is bad.Uplink synchronizationfailureUplink synchronization failure causes abnormal release of links. Thecoverage quality (including missing neighbor cell and over mall handoverarea) is bad, so the UE powers off the transmitter abnormally or uplinkdemodulation is asynchronous.

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