opt topics handovers
DESCRIPTION
HandoversTRANSCRIPT
For internal use only1 © Nokia Siemens Networks Presentation / Author / Date
LTE OptHO Optimization topics
For internal use only2 © Nokia Siemens Networks Presentation / Author / Date
Source material• See LTEPAR for RL10 idle and connected mode mobility parameter information
• https://sharenet-ims.inside.nokiasiemensnetworks.com/Overview/D421448082
• See NetEng Enabling for information on RL20 CSFB to UTRAN and GERAN via redirect
• https://sharenet-ims.inside.nokiasiemensnetworks.com/livelink/livelink/overview/D427222800
• See NetEng Enabling for information on RL20 intra-LTE inter-frequency handover
• https://sharenet-ims.inside.nokiasiemensnetworks.com/Overview/D427222796
• See NetEng Enabling for information on RL20 S1 handover• https://sharenet-ims.inside.nokiasiemensnetworks.com/Overview/D427222798
• See NetEng Enabling for information on RL20 ANR• https://sharenet-ims.inside.nokiasiemensnetworks.com/Overview/D427222802
Presentation / Author / Date
For internal use only3 © Nokia Siemens Networks Presentation / Author / Date
Optimization topics
• Recap on measurement events• Reducing HO drops • HO problem due to missing neighbours• Reducing HO user plane interruption time• A2 triggered redirect to 2G/3G
Presentation / Author / Date
For internal use only4 © Nokia Siemens Networks Presentation / Author / Date
time
RSRPRSRP Neighbour Cell
Serving Cell RSRP
a3TimeToTrigger
MeasurementReport
a3offset
eNB
a3Report Interval
MeasurementReport
Handovers Event A3 used for Better Cell HO
RSRP at serving cell + a3Offset < RSRP at neighbor cell
A3 condition met
reporting condition metafter Time To Trigger
For internal use only5 © Nokia Siemens Networks Presentation / Author / Date
time
threshold3a
RSRP
Neighbour Cell RSRP
Serving Cell RSRP
a5TimeToTriggerMeasurement
Report
eNB
a5Report Interval
MeasurementReport
Handovers Event A5
RSRP at serving cell < threshold3AND (&&)
RSRP at target > threshold3a
threshold3
-140 dBm
thre
shol
d3a
thre
shol
d3
For internal use only6 © Nokia Siemens Networks Presentation / Author / Date
RRC connection release with redirect
LNCEL: threshold4 defines the absolute RSRP level of serving cell for eNB to trigger RRC connection release with redirection.
RSRP
time
threshold4
-140 dBm
thre
shol
d4
A2 condition metreporting condition metafter Time To Trigger
MeasurementReport
a2TimeToTriggerRedirect
Serving Cell RSRP
For internal use only7 © Nokia Siemens Networks Presentation / Author / Date
HO optimization, reducing HO drops
• HO optimization, how to reduce HO drops?• Typical low-level symptoms:
• UE drops during or immediately after HO• UE drops just before handover (HO triggers too late)
Presentation / Author / Date
For internal use only8 © Nokia Siemens Networks Presentation / Author / Date
HO optimization, reducing HO drops when UE drops during or immediately after HO• UE cannot successfully access the PRACH in the target cell or UE drops soon after sending RRC Connection Reconfig Complete in target cell• Symptom: T304 expires. In this case timer T304 expires and UE makes RRC Connection Re-establishment with cause “handoverFailure”
• T304 is started after receiving HO command in source cell and stopped in target cell after successful PRACH procedure
• Symptom: UE log from dt tool indicates RRC Conn Reconf Complete (“PRACH msg3”) is transmitted but no further DL messages from target cell are seen and call drops• Possible fix: increase T304 timer to 1000ms or longer, parameter t304IntraLte• Possible fix: increase the max number of UL HARQ retransmissions, parameter harqMaxTrUl. NOTE: Parameter harqMaxMsg3 is for contention-based RA with non-dedicated preamble.• Possible fix: increase initial preamble target receive power, parameter ulpcIniPrePwr
• NOTE: this has been found very effective in RL20 where default pddb and Golden config value is -104dBm. Value of -90dBm decreased HO drops considerably in a test network.
Presentation / Author / Date
。
For internal use only9 © Nokia Siemens Networks Presentation / Author / Date
HO optimization, reducing HO drops when UE drops just before handover (HO triggers too late)• Symptom: HO is triggered too late, UE drops before HO command • Possible fix: If using A3 handover reduce a3offset and time to trigger. In some cases also filterCoefficientRSRP may need to be reduced.• Problem: ping-pong HOs increase if A3 used for bad RF reduced tput in cell edge areas, increased probability of drop call per time unit• One should consider using A5 triggered coverage-based HO to quickly trigger HO in bad RF. This way, there is no need to reduce A3 trigger time, and less ping-pong results.
• In this HO strategy, A3 is the HO for “normal usage” and A5 is the “bad-RF quick reaction HO”.
Presentation / Author / Date
For internal use only10 © Nokia Siemens Networks Presentation / Author / Date
HO optimization, missing neighbours• Typical drive test log example of missing neighbours
Presentation / Author / Date
Time Subchannel Direction Message09:32:19.745 DCCH Downlink RRCConnectionReconfiguration09:32:19.745 DCCH Uplink RRCConnectionReconfigurationComplete09:32:19.874 DCCH Downlink RRCConnectionReconfiguration09:32:19.874 DCCH Uplink RRCConnectionReconfigurationComplete09:32:19.874 BCCH-BCH Downlink MasterInformationBlock09:32:19.874 BCCH-SCH Downlink SystemInformationBlockType109:37:44.920 DCCH Uplink MeasurementReport09:37:45.915 DCCH Uplink MeasurementReport09:37:46.949 DCCH Uplink MeasurementReport09:37:47.911 DCCH Uplink MeasurementReport09:37:49.026 DCCH Uplink MeasurementReport09:37:49.935 DCCH Uplink MeasurementReport09:37:50.960 DCCH Uplink MeasurementReport09:37:51.994 DCCH Uplink MeasurementReport09:38:11.383 DCCH Uplink MeasurementReport09:38:13.006 BCCH-BCH Downlink MasterInformationBlock09:38:13.024 BCCH-SCH Downlink SystemInformationBlockType109:38:13.126 BCCH-SCH Downlink SystemInformation09:38:13.165 CCCH Uplink RRCConnectionReestablishmentRequest09:38:13.244 CCCH Downlink RRCConnectionReestablishmentReject09:38:13.969 BCCH-BCH Downlink MasterInformationBlock09:38:14.014 BCCH-SCH Downlink SystemInformationBlockType109:38:14.014 Uplink TRACKING_AREA_UPDATE_REQUEST09:38:14.014 CCCH Uplink RRCConnectionRequest09:38:14.143 CCCH Downlink RRCConnectionSetup
For internal use only11 © Nokia Siemens Networks Presentation / Author / Date
HO optimization, missing neighbours due to IP and X2 connectivity problems• In RL10, neighbour IP@ had to be added to both eNBs, otherwise X2 setup failed HO is not triggered regardless of UE sending multiple measurement reports• In RL20 it is enough to add neighbour IP@ at one X2 endpoint, the other end is automatically added to eNB database• Neighbour problems have also been noticed when there is a IP routing problem in access network X2 setup fails even if IP@ have been correctly defined.
• Symptom: SCTP/X2 alarm in BTS.
• Other missing neighbour problems due to IP connectivity• SCTP X2 port mismatch problem. SCTP X2 port must match at both
ends.• Especially during sw upgrade from RL10 to RL20. In RL20 X2 SCTP
port hard-coded to 36422
Presentation / Author / Date
For internal use only12 © Nokia Siemens Networks Presentation / Author / Date
HO optimization, missing neighbours due to IP and X2 connectivity
For internal use only13 © Nokia Siemens Networks Presentation / Author / Date
Reducing HO UP interruption time• UP interruption time has been noticed to be too high in trials, especially with FTP • According to tests, with properly tuned parameters < 50-60ms FTP layer interruption time can be achieved in good RF conditions (lab) • Tricks:
• Check that eNB PDCP status reporting is on, parameter statusRepReq=3, this should be PDDB default in RL20. Helps reduce UL UP interruption time.
• PDCCH CQI shift for Samsung UEs, parameter pdcchCqiShift = -5• Negatively biasing OLQC in access to target cell, reduce heavily
dlOlqcDeltaCqiMin and dlOlqcDeltaCqiIni from default, these are vendor parameters. UE does not jump to 64QAM too fast retransmissions reduced
• Minimize PRACH access latency, maximize preamble initial power. See PKDB for further info on PRACH tuning
Presentation / Author / Date
For internal use only14 © Nokia Siemens Networks Presentation / Author / Date
A2 triggered redirection to WCDMA• Event A2 triggers RRC release with redirection information
• For 3G the redirect info is UARFCN only• March’11: In initial lab tests >10sec between redirect in LTE and RRC CONN REQ in 3G
Presentation / Author / Date
RRC SIGNALING MESSAGE
Time: 13:58:17.065
RRCConnectionRelease (3GPP TS 36.331 ver 8.7.0 Rel 8)
DL-DCCH-Messagemessage
c1rrcConnectionRelease
rrc-TransactionIdentifier : 3criticalExtensions
c1rrcConnectionRelease-r8
releaseCause : otherredirectedCarrierInfo
utra-FDD : 10662
RRC SIGNALING MESSAGE
Time: 13:52:23.467
MeasurementReport (3GPP TS 36.331 ver 8.7.0 Rel 8)
UL-DCCH-Messagemessage
c1measurementReport
criticalExtensionsc1
measurementReport-r8measResults
measId : 4measResultServCell
rsrpResult : 46rsrqResult : 28
A2 triggered measurement report RRC release with redirect