MRO: Handover failures signalling

Continuing on the Self-organising Network (SON) feature of Mobility Robust Optimisation, Handover failures.

Click on image to enlarge

One of the discussions I had with a colleague is how would the signalling happen in case of Handover failures I mentioned earlier.

After the handover failure, when the connection is successfully established again either as a normal Setup or Re-Establishment or RRC Reconfiguration then a new optional field is available:

rlf-InfoAvailable-r10 ENUMERATED {true} OPTIONAL,

This is used to indicate to the network that the UE has some information relating to the RL Failure that occurred.

The network will then use the UE Information Request I blogged about earlier to ask for this information. The UE will send the information back in the response.

It should be noted that this UEInformationRequest and Response messages were introduced part of Release-9 but there has been since some updates in Release-10. The Response message now looks as follows:

RLF-Report-r9 ::= SEQUENCE {

measResultLastServCell-r9 SEQUENCE {

rsrpResult-r9 RSRP-Range,

rsrqResult-r9 RSRQ-Range OPTIONAL

},

measResultNeighCells-r9 SEQUENCE {

measResultListEUTRA-r9 MeasResultList2EUTRA-r9 OPTIONAL,

measResultListUTRA-r9 MeasResultList2UTRA-r9 OPTIONAL,

measResultListGERAN-r9 MeasResultListGERAN OPTIONAL,

measResultsCDMA2000-r9 MeasResultList2CDMA2000-r9 OPTIONAL

} OPTIONAL,

...,

[[ locationInfo-r10 LocationInfo-r10 OPTIONAL,

failedPCellId-r10 CHOICE {

cellGlobalId-r10 CellGlobalIdEUTRA,

pci-arfcn-r10 SEQUENCE {

physCellId-r10 PhysCellId,

carrierFreq-r10 ARFCN-ValueEUTRA

}

} OPTIONAL,

reestablishmentCellId-r10 CellGlobalIdEUTRA OPTIONAL,

timeConnFailure-r10 INTEGER (0..1023) OPTIONAL,

connectionFailureType-r10 ENUMERATED {rlf, hof} OPTIONAL,

previousPCellId-r10 CellGlobalIdEUTRA OPTIONAL

]]

}

Everything after the extension marker ellipses (...) is added in release 10. More information in Release-10 RRC specs (36.331)