移动手机为啥读取WCDMA信号-LTE案例

移动手机为啥读取WCDMA信号--LTE案例1.背景介绍4月26日中国移动VOLTE例行测试中终端在LTE网络先后发起业务和TAU请求；而在TAU拒绝回送BYE请求后，读取WCDMA网络消息显示联通3G图标；最后终端选择驻留GSM网络，继续语音测试任务；中国移动4G终端为什么会在业务测试中读联通3G网络信息呢？让我们对整个事件和信令消息，对照3GPP规范做一下回顾和分析；

图表1.终端由LTE到GSM流程消息2.业务请求和TAU拒绝终端在(TAC:13643CELLID:9951513)小区于16:10:58.824和16:10:58.825发起业务请求(ServiceRequest）和TAU请求(图2）；Log回放显示:终端发起业务请求后，MAC层的RACH接入失败（图3）；而终端发起TAU请求时MAC层的RACH成功（图4）；网络TAU拒绝EMMCause=111Protocolerror,unspecified（图5）；

图表2.终端发起业务和TAU请求

图表3.业务请求后RACH失败

图表4.TAU请求和RACH成功

图表5.终端TAU被拒绝3.TAU请求和拒绝定义（3GPP24.301）5.5.3Trackingareaupdatingprocedure(S1modeonly)ThetrackingareaupdatingprocedureisalwaysinitiatedbytheUEandisusedforthefollowingpurposes:-

normaltrackingareaupdatingtoupdatetheregistrationoftheactualtrackingareaofaUEinthenetwork;.7

Abnormalcasesonthenetworkside

IftheTRACKINGAREAUPDATEREQUESTmessagehasbeenreceivedwithaprotocolerror,thenetworkshallreturnaTRACKINGAREAUPDATEREJECTmessagewithoneofthefollowingEMMcausevalues:

#96:invalidmandatoryinformationelementerror;

#99:informationelementnon-existentornotimplemented;

#100:

conditionalIEerror;or

#111:

protocolerror,unspecified.4.终端脱网后PLMN搜索16:11:08.083终端接收到服务小区（TAC13643eNodeB9951513SectorID3PCI498）信号良好（RSRP-97.68SINR10.30，下图左）；而16:11:08.084服务小区无信号(下图右)，判断：底层链路中断，终端脱网。

图表6.网络底层链路中断前后16:11:08.084终端进入(EMMREGISTEREDNOCELLAVAILABLE)

状态;NAS层启动(GMM_PLMN_SEARCH)网络搜索流程;

图表7.NAS层GMM触发PLMN搜索TS24.301clause.5Ifthetrackingareaupdatingcannotbeacceptedbythenetwork,theMMEsendsaTRACKINGAREAUPDATEREJECTmessagetotheUEincludinganappropriateEMMcausevalue.UponreceivingtheTRACKINGAREAUPDATEREJECTmessage,theUEshallstoptimerT3430,stopanytransmissionofuserdata,andtakethefollowingactionsdependingontheEMMcausevaluereceived.

5.PLMN搜索协议规定TS23.122

3.5

Nosuitablecell(limitedservicestate)ThereareanumberofsituationsinwhichtheMSisunabletoobtainnormalservicefromaPLMN.Theseinclude:a)

FailuretofindasuitablecelloftheselectedPLMN;b)

NoSIMintheMS;c)

A"PLMNnotallowed"responsewhenanLRisreceived;d)

An"illegalMS"or"illegalME"responsewhenanLRisreceived(AnySIMintheMEisthenconsidered"invalid");e)

An"IMSIunknowninHLR"responsewhenanLRisreceived(AnySIMintheMEisthenconsidered"invalid"fornon-GPRSservices);f)

A"GPRSservicesnotallowed"responsewhenanLRofaGPRSMSattachedtoGPRSservicesonlyisreceived(ThecellselectionstateofGPRSMSsattachedtoGPRSandnon-GPRSdependsontheoutcomeofthelocationupdating),oran"EPSservicesnotallowed"responseisreceivedwhenanEPSattach,trackingareaupdateorservicerequestisperformed;org)

Powersavingmode(PSM)isactivated(see3GPP

TS

23.682

[27A]).(InautomaticPLMNselectionmode,itemsa,candfwouldnormallycauseanewPLMNselection,buteveninthiscase,thesituationmayarisewhennoPLMNsareavailableandallowableforuse).

3GPP36.304小区选择和重选5.2

CellselectionandreselectionTheNAScancontroltheRAT(s)inwhichthecellselectionshouldbeperformed,forinstancebyindicatingRAT(s)associatedwiththeselectedPLMN,andbymaintainingalistofforbiddenregistrationarea(s)andalistofequivalentPLMNs.TheUEshallselectasuitablecellbasedonidlemodemeasurementsandcellselectioncriteria.Inordertospeedupthecellselectionprocess,storedinformationforseveralRATsmaybeavailableintheUE.Whencampedonacell,theUEshallregularlysearchforabettercellaccordingtothecellreselectioncriteria.Ifabettercellisfound,thatcellisselected.ThechangeofcellmayimplyachangeofRAT.Detailsonperformancerequirementsforcellreselectioncanbefoundin[10].图表8

LTE终端网络搜索流程图6.UMTS网络搜索根据3GPP36.304（5.2）16:11:16.069和16:11:23.683终端分别搜到TDSCDMA和WCDMA网络：

图表9终端对TD+WCDMA网络搜索7.GSM重选驻留16:11:39.139搜索到GSM网络，根据3GPP36.133重选到GSM网络；

图表10

终端搜索GSM网络7.1小区重选（3GPP36.133）4.2

CellRe-selection4.2.1

IntroductionThecellreselectionprocedureallowstheUEtoselectamoresuitablecellandcamponit.WhentheUEisineitherCampedNormallystateorCampedonAnyCellstateonacell,theUEshallattempttodetect,synchronise,andmonitorintra-frequency,inter-frequencyandinter-RATcellsindicatedbytheservingcell.Forintra-frequencyandinter-frequencycellstheservingcellmaynotprovideexplicitneighbourlistbutcarrierfrequencyinformationandbandwidthinformationonly.UEmeasurementactivityisalsocontrolledbymeasurementrulesdefinedinTS36.304,allowingtheUEtolimititsmeasurementactivity.4.2.2

RequirementsTheUEshallsearcheverylayerofhigherpriorityatleasteveryThigher_priority_search=(60*Nlayers)secondswhentheUEisnotconfiguredwitheDRX_IDLEcycle,andatleasteveryThigher_priority_search=MAX(60*Nlayers,oneeDRX_IDLEcycle)whenUEisconfiguredwitheDRX_IDLEcycle,whereNlayersisthetotalnumberofconfiguredhigherpriorityE-UTRA,UTRAFDD,UTRATDD,CDMA20001xandHRPDcarrierfrequenciesandisadditionallyincreasedbyoneifoneormoregroupsofGSMfrequenciesisconfiguredasahigherpriority.16:12:20.849在GSM网络LUA完成和驻留（LAC13888CELLID17131）小区。

图表11

终端驻留GSM网络8.GSM语音呼叫根据业务请求（测试计划）在呼叫失败后，终端于16:13.02