Lte Inter Frequency Handover Trouble Shooting Case c6q27

LTE INTER-FREQUENCY HANDOVER Trouble shooting case study-Missing measurement gaps LTE L12A Shawn zhang Mar 1, 2012

Issue Measurement Based Inter-frequency handover in sprint LTE network is failing due to no A5 event received from UE. (Blind inter-frequency handover works)

Inter-Freq Handover OVERVIEW › Handover between two cells with different center frequency (earfcn). › Two events are triggered: – A2 Event: Serving becomes worse than threshold – A5 Event: serving becomes worse than threshold1 and neighbor becomes better than threshold2

› Two Inter-Frequency Handover preparation methods: – blind inter-frequency handover: . eNodeB configures event A2 based on UE report. after A2 measurement report from UE, RBS identifies coverage of selected cell, and start a Blind IFHO handover process, if prerequisites are followed. – measurement based inter-frequency handover: If no cell available for blind handover, A5 measurement will be assigned on the UE, UE starts measurements on reported cells and triggers A5 event. Once UE triggers the event, RBS will start IFHO if prerequisites are followed.

Inter-Freq Handover OVERVIEW

Source Source eNB eNB RRC CONNECTED

Target Target eNB eNB

S-GW

S-GW

MME

MME

Source

Target

Source

Target

1. RRC CONNECTION RECONFIGURATION

(Bearer Setup,Measurement conf)) 2. RRC Measurement Report

S1 Handover

(Event A5)

3. HO Decision 4. S1 HANDOVER REQIRED (Source to Target Transparent Container )

5. S10 FORWARD RELOCATION REQUEST

TS1RELOrep

6. S11 CREATE BEARER REQ/RES 7. S1 HANDOVER REQUEST

8. ission Control

9. S1 HANDOVER REQUEST ACKNOWLEDGE 10. S10 FORWARD RELOCATION RESPONSE 11. S11 CREATE BEARER REQ/RES

12. S1 HANDOVER COMMAND

T304

UP Forwarding

12. RRC CONNECTION RECONFIGURATION

(Handover Command,Measurement conf) 13 MAC: CFRA Random Access Preamble

Regenerate Security Keys

14. MAC Random Access Response (UL allocation + TA) 15. RRC CONNECTION RECONFIGURATION COMPLETE

(Handover Confirm)

16. S1 HANDOVER NOTIFY

17.Data Transfer in Target

RRC CONNECTED

19. S1 UE CONTEXT RELEASE COMMAND (Cause: Successful Handover)

18.S10 FORWARD RELOCATION COMPLETE/ ACK

REQUIREMENTS 1.

General requirement: ›

licenseStateInterFrequencyLTEHandover is Enabled.

›

featureStateInterFrequencyLTEHandover is Active.

›

EUtranFreqRelation and EUtranCellRelation should be created

›

the UE capability s inter-frequency handover. This is indicated in bit 13 of the featureGroupIndicators which is part of the Information Element UE-EUTRA-Capability as described in TS 36.331

2.

3.

For Blind Handover: ›

covTriggerdBlindHoAllowed set to true on Serving cell

›

mobilityAction on EUtranFreqRelation MO must be “HANDOVER”

›

coverageIndicator on EUtranCellRelation MO should be set to 1 ( Cover)

›

isHoAllowed on EUtranCellRelation MO should be set to 1

For Measurement Based Handover: ›

ueMeasurementActive set to true.

›

mobilityAction on EUtranFreqRelation MO must be “HANDOVER”

›

isHoAllowed on EUtranCellRelation MO should be set to 1

OTHER PARAMETERS The following parameters allows to fine tune the behavior of the UE to trigger the HO events. › triggerQuantityA2Prim/ triggerQuantityA2Sec attributes on ReportConfigEUtraBadCovPrim MO: The quantity that triggers the eventA2 for the primary/secondary eventA2 measurement. Primary and secondary measurement parameters refer to the option to use different settings for two simultaneous measurements for eventA2. set to 0 for RSRP and 1 for RSRQ › triggerQuantityA5 on ReportConfigA5 MO: The quantity that triggers the eventA5 for the eventA5 measurement. set to 0 for RSRP and 1 for RSRQ › a2ThresholdRsrpPrim › a5ThresholdXRsrp: where X can be 1 or 2 › a2ThresholdRsrqSec › a2ThresholdRsrqPrim › a5ThresholdXRsrq: where X can be 1 or 2

Trouble shooting-ENB TRACE SIGNAL FLOW UE eNB TeNB MME |====>| | | (RRC) rrcConnectionRequest eCause:mo-Signalling :|:::: :|: ::::|: ::: ::| :::::: |<====| | | UE:388 (RRC) ueCapabilityEnquiry |====>| | | UE:388 (RRC) ueCapabilityInformation |========== ====>| UE:388 (NAS) AttachComplete | |=========>| UE:388 (S1AP) UECapabilityInfoIndication |<====| | | UE:388 (RRC) rrcConnectionReconfiguration |<==============| UE:388 (NAS) AttachAccept:ParsingFailure (ciphered) |====>| | UE:388 (RRC) rrcConnectionReconfigurationComplete :|:::: :|: ::::|::: :::| :::::: |==============>| UE:388 (NAS) AttachComplete :|:::: :|: ::::|::: :::| :::::: |====>| |<====| |====>| |====>| |====>| |====>| |====>| |====>| :|:: :::|:::: |====>|

| | | | | | | | | | | | | | | | :| ::::| | |

UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) :::::: UE:388 (RRC)

measurementReport measId:2 rsrp:-113 rrcConnectionReconfiguration rrcConnectionReconfigurationComplete measurementReport measId:2 rsrp:-113 measurementReport measId:2 rsrp:-113 measurementReport measId:2 rsrp:-113 measurementReport measId:2 rsrp:-114 measurementReport measId:2 rsrp:-114 measurementReport measId:2 rsrp:-121

measObjectToAddModList { measObjectId 1, measObject measObjectEUTRA : { carrierFreq 8665, ........... reportConfigToAddModList { reportConfigId 2, reportConfig reportConfigEUTRA : { triggerType event : { eventId eventA2 : {a2-Threshold threshold-RSRP:30}, hysteresis 2, timeToTrigger ms640}, triggerQuantity rsrp, reportQuantity both,

maxReportCells 4, eNB sends A2 config. info correctly to UE, UE triggers A2 event at condition meet-> No problem at this point reportInterval ms480,

Trouble shooting-ENB TRACE SIGNAL FLOW UE eNB TeNB MME |====>| | | (RRC) rrcConnectionRequest eCause:mo-Signalling :|:::: :|: ::::|: ::: ::| :::::: |<====| | | UE:388 (RRC) ueCapabilityEnquiry |====>| | | UE:388 (RRC) ueCapabilityInformation |========== ====>| UE:388 (NAS) AttachComplete | |=========>| UE:388 (S1AP) UECapabilityInfoIndication |<====| | | UE:388 (RRC) rrcConnectionReconfiguration |<==============| UE:388 (NAS) AttachAccept:ParsingFailure (ciphered) |====>| | UE:388 (RRC) rrcConnectionReconfigurationComplete :|:::: :|: ::::|::: :::| :::::: |==============>| UE:388 (NAS) AttachComplete :|:::: :|: ::::|::: :::| :::::: |====>| |<====| |====>| |====>| |====>| |====>| |====>| |====>| :|:: :::|:::: |====>|

| | | | | | | | | | | | | | | | :| ::::| | |

UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) :::::: UE:388 (RRC)

measurementReport measId:2 rsrp:-113 rrcConnectionReconfiguration rrcConnectionReconfigurationComplete measurementReport measId:2 rsrp:-113 measurementReport measId:2 rsrp:-113 measurementReport measId:2 rsrp:-113 measurementReport measId:2 rsrp:-114 measurementReport measId:2 rsrp:-114 measurementReport measId:2 rsrp:-121

measObjectToAddModList { { measObjectId 2, measObject measObjectEUTRA : { carrierFreq 8040, { measObjectId 3, measObject measObjectEUTRA : { carrierFreq 8340, { reportConfigId 7, reportConfig reportConfigEUTRA : { triggerType event : { eventId eventA5 : { a5-Threshold1 threshold-RSRP : 20, a5-Threshold2 threshold-RSRP : 4 }, hysteresis 2, timeToTrigger ms640 }, triggerQuantity rsrp, }

Inter_freq

A5 condition: Serv RSRP<-120 Nerb RSRP >-136

measIdToAddModList { { measId 7, measObjectId 3,

7 eNB seems correctly send A5 config info to UE after eventreportConfigId A2, UE doesn’t trigger A5 at condition meet -> UE’s problem ???

Comparing with other good enb trace Failed HO

Good HO measIdToAddModList { { measId 5, measObjectId 1, reportConfigId 5 }, { measId 6, measObjectId 1, reportConfigId 6 }, { measId 7, measObjectId 2, reportConfigId 7 }, { measId 8, measObjectId 3, reportConfigId 8 } }, measGapConfig setup : { gapOffset gp0 : 26

measIdToAddModList {

Comapring rrcConnectionReconfiguration after event A2, NO measGapConfig on customer’s site eNB tracing

{ measId 5, measObjectId 1, reportConfigId 5 }, { measId 6, measObjectId 2, reportConfigId 6 }, { measId 7, measObjectId 3, reportConfigId 7 }, { measId 8, measObjectId 4, reportConfigId 8 }, {

What is measurement GaPS and how to let enb send it? 3GPP 36.331 Measurement gaps: Periods that the UE may use to perform measurements, i.e. no (UL, DL) transmissions are scheduled. Value gapOffset of gp0 corresponds to gap offset of Gap Pattern Id “0” with MGRP = 40ms, gapOffset of gp1 corresponds to gap offset of Gap Pattern Id “1” with MGRP = 80ms. Also used to specify the measurement gap pattern to be applied, as defined in TS 36.133 [16]. 3GPP 36.300 -Intra-frequency neighbour (cell) measurements: The UE shall be able to carry out such measurements without measurement gaps. -Inter-frequency neighbour (cell) measurements: compared to the current cell. The UE should not be assumed to be able to carry out such measurements without measurement gaps. Whether a measurement is non gap assisted or gap assisted depends on the UE's capability and current operating frequency. The UE determines whether a particular cell measurement needs to be performed in a transmission/reception gap and the scheduler needs to know whether gaps are needed: Conclusion: There is no parameter in eNB to set if measurement gap sends or not, eNB makes decision based on UE’s capability information ( eNB can change UE measurement gaps either 40ms or 80 ms by systemconstant).

Measurement GaP

Does UE’ capability require measurement Gaps? UE eNB TeNB MME |====>| | | (RRC) rrcConnectionRequest eCause:mo-Signalling :|:::: :|: ::::|: ::: ::| :::::: |<====| | | UE:388 (RRC) ueCapabilityEnquiry |====>| | | UE:388 (RRC) ueCapabilityInformation |========== ====>| UE:388 (NAS) AttachComplete | |=========>| UE:388 (S1AP) UECapabilityInfoIndication |<====| | | UE:388 (RRC) rrcConnectionReconfiguration |<==============| UE:388 (NAS) AttachAccept:ParsingFailure (ciphered) |====>| | UE:388 (RRC) rrcConnectionReconfigurationComplete :|:::: :|: ::::|::: :::| :::::: |==============>| UE:388 (NAS) AttachComplete :|:::: :|: ::::|::: :::| :::::: |====>| |<====| |====>| |====>| |====>| |====>| |====>| |====>| :|:: :::|:::: |====>|

| | | | | | | | | | | | | | | | :| ::::| | |

UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) UE:388 (RRC) :::::: UE:388 (RRC)

measurementReport measId:2 rsrp:-113 rrcConnectionReconfiguration rrcConnectionReconfigurationComplete measurementReport measId:2 rsrp:-113 measurementReport measId:2 rsrp:-113 measurementReport measId:2 rsrp:-113 measurementReport measId:2 rsrp:-114 measurementReport measId:2 rsrp:-114 measurementReport measId:2 rsrp:-121

measParameters { bandListEUTRA { { interFreqBandList { { interFreqNeedForGaps TRUE } }, interRAT-BandList { { interRAT-NeedForGaps FALSE }, { ,

Bit13&25:UE featureGroupIndicators '01100110 00001101 11011000 10011000'B Interfrequency handover

UE does require measurement Gaps, so it seems eNB who should be blamed!

Further analysis and fix Further more, we found below error from te log read 000100/LmCellPT6 UehMeasDataCapabilityHandlerD.p:273 ERROR:!<0xa92>! No valid sourceBand or targetBand found in the edBandListEUTRA IE The mobile phone we were testing was working in Band 25. Band 25 is only used in sprint network. We suspect eNB doesn’t interpret band 25 information correctly at handling assembling measurement gap IE. TR HP26018 was raised at this point. Designer quickly confirmed our analysis and fix was delivered in L12A 1 in TR answer: CAUSE OF FAULT ------------------------------UehMeasDataCapabilityHandlerD contains a list to be able to map frequencies against frequency-bands. This list was not updated when CR1134 was implemented. Therefore only parts of the system handled the new frequency-bands defined in later 3GPP specifications. The result of the fault is that the eNodeB can not determine the capability of the UE on this frequency-band. So the result is that meas-gap is not activated, because we do not know if the UE s meas-gap. SYSTEM IMPACT -----------------------Inter-frequency measurements is not started. So measurement based handovers is not triggered. SOLUTION ----------------The list in UehMeasDataCapabilityHandlerD to map frequency against frequency-bands is updated.