PowerPoint

GSM Handover Problems & Solutions:: : 32-36pt:

:: : 24pt: To master different types of handover and their signaling flows;To master handover statistical signaling point and MR tasks;To know common handover problem and the handling procedures.Objectives> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Overview of handoverFlow of handover signalingHandover problem analysisContents> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Why there are handovers?1.To keep calls going on during movement;2.To improve network service quality;3.To decrease call drop rate;4.To decrease congestion rate.Aims of handover> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.1.Intra-CELL2.Intra-BSC3.Inter-BSC4.Inter-MSCHandover classification> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Overview of handoverFlow of handover signalingHandover problem analysis

Contents> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Signaling flow of intra-cell handover

> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Signaling flow of inter-cell handover within one BSC

> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Signaling flow of inter-BSC handover

> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Basic signaling flow of Inter-MSC handover

> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.1.Inter-cell handover within BSC: There is no HO-Request message for intra-BSC handover; all information is analyzed within BSC; Once a target cell in the BSC fulfilling handover conditions is found, BSC send Channel activation message directly.2.Inter-BSC handover within MSC: BSC reports CGI and handover causes of original cell and target cell to MSC through HO-Request; After MSC finds target cell LAC, it sends HO-Request to the BSC which the target cell belong to; Target BSC activates channel in target cell, and executes the following flow.Basic flow of handover signaling> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.3.Inter-MSC handover: MSC inquires REMOTLAC sheet (including LAC and route address of adjacent MSC); MSC sends Perform-HO message to the target MSC-B according to the route address; According to the Perform-HO message, target MSC-B sends HO-Request message to BSC-B; After the target MSC-B receives HO-Request ACK, it sends Radio Chan ACK message to the original MSC, and executes the following flow.Basic flow of handover signaling> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Main differences between intra-BSC handover and inter-BSC handoverMSC participates or notCGI is carried or notMSC transmits HO-REQ message, and CGI of original cell and target cell is carried in the message.As for inter-BSC handover, MSC participates in it since HO-Request.AS for intra-BSC handover, HO-Performed message is sent to MSC only after the handover is completed; MSC doesnt participate before that.For intra-BSC handover, CGI isnt carried in any message, Its handled within BSC.Inter-BSC handoverIntra-BSC handover> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Flow of handover algorithmMSBTSBSCMSCTarget BSCTarget MSCBCCH frequency point, BSIC and level values of the six adjacent cells(with strongest level) and serving cell.UL MRProcess of MRConfirmation of adjacent cell CGIExecution of handover decisionSelection of target cellExternal cell?Channel activationNOYESHO RequestIntra-MSC handoverHO RequestHO RequestList of cells under one LAC> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.T3107: Suitable for: intra-cell handoverStart-up: BSC sends assignment commandStop counting: when assignment completed or assignment failure is received; Common timers at BSCMSBTSBSCChannel activateChannel activate ackAssignment commandSet T3107T3107 Timeout> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.T3103Suitable for: inter cell handoverStart-up: BSC sends handover commandStop counting: when handover completed or handover failure is received.Common timers at BSCMSOld BTSNew BTSBSCChannel activationChannel activation ACKHandover commandHandover commandSet T3103T3103 Timeout> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.MR is sent to BTS in SACCH UL direction:When MS is in SDCCH, MR cycle is 470ms/time;When MS is in TCH, MR cycle is 480ms/time.MR cycle> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Overview of handoverFlow of handover signalingHandover problem analysisContents> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.1.Analysis of handover problems2.Location method of handover problemsAnalysis handover problems> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Common handover problemsCommon handover problemsPossible influencesHandover nonoccurrenceHandover failureFrequent HandoverHandover HysteresisResult in call dropAffect call quality and result in calldropAffect call quality and increase system loadAffect call quality and result in call drop> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Flow of handover problem checkingToo high TCH handover failure rate of a cellIs radio parameter setting reasonable?Interference exists?Coverage problem exists?Any equipment faults?Any antenna problems?CompleteAdjust parametersCheck & eliminate interferenceImprove coverageEliminate equipment faultsSolve antenna problemsYESYESYESYESYES> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Analyze traffic statistics Check handover statistics measurement, identify problem range: If just some cells fail to make handover to the cell, check handover data, check if there is same frequency and same BSIC exist; If the cell fails to make handover from all other cells, check its data.Check warnings: board malfunction, transmission and clock malfunctions, etc.;Check whether radio parameters are set reasonably: whether same frequency and same BSIC exist among adjacent cells; whether handover parameters are set reasonably; whether data configuration of external cells is correct.Location methods of handover problems> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Interference checkingDT analysisSignaling analysis: Um interface, Abis interface, A interfaceHardware checking: like CDU, TRX, RF connection lines between boardsAntenna system checkingLocation methods of handover problems> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Coverage & interferenceAntenna systemBTS hardwareTransmissionBSC hardwareA interface malfunctionBusy target cellAnalysis of handover problems> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Coverage: 1.Poor coverage: due to influence from forest, complex landforms, houses, indoor coverage etc; 2.Isolated site: no adjacent cells around 3.Skip-zone coverage: no adjacent cells available due to isolated-island effect.Interference: It makes MS unable to access in UL, or DL signal , receiving problem will be resulted.Coverage & interference> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Too large VSWRReversed installation of antennaNon-standard antenna installationUnreasonable azimuth, down-tiltBelow-standard antenna insulationTwisted cables, loosened connectors and wrong connections;

Antenna system problems> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Problem about:Single boardClock generator malfunctionInternal communication cable malfunctionBTS hardware> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.Transmission fault: unstable transmission, too high transmission error rateBSC hardware malfunctions:1.Clock generator malfunction: unconformity among clocks in different BTSs due to clock generator malfunction;2.Problem about single board3.Wrong data configuration4.Unreasonable setting of handover threshold5.CGI, BCCH and BSIC values in external cell data sheet do not match up to those in the corresponding BSC;6.Wrong BSC signaling point in list of cell under a LAC in MSC.Transmission and BSC problems> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved.A interface malfunction: abnormal handover due to lack of link resource, abnormal callsHandover between equipment from different suppliers: Difference in signaling at interface A and interface E between ZTE and other suppliers equipment, causing non-recognition or non-support problem, including speech version, handover code and addressing mode(CGI or LAI) etc., which will result in handover failure.A interface malfunction> G91, B170G137, B207G174, B239G171, B189:: : 30-32pt:

(1-5):: : 28-12pt: ZTE Corporation. All rights reserved. ZTE Corporation. All rights reserved.Thanks!MSMSCBSCBTSBTS2BSC2BSC2