06_a OPT Topics Handovers

For internal use only1 © Nokia Siemens Networks Presentation / Author / Date

LTE OptHO Optimization topics


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

https://sharenet-ims.inside.nokiasiemensnetworks.com/Overview/D421448082

https://sharenet-ims.inside.nokiasiemensnetworks.com/livelink/livelink/overview/D427222800





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



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


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


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


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)



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.


。


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”.



HO optimization, missing neighbours• Typical drive test log example of missing neighbours


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


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



HO optimization, missing neighbours due to IP and X2 connectivity


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



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


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

06_a OPT Topics Handovers

Documents

Transcript of 06_a OPT Topics Handovers