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Wednesday, 30 November 2011

Reducing CSFB Timing with RRC R9 Optimisations

While in the initial testing CSFB timing used to be between 6-8 seconds, most Rel-8 phones can complete the CSFB procedure between 4-4.5 seconds. Unfortunately this is still a lot in terms of signalling. To reduce this in Rel-9 there is a simple optimisation that has been done.
In the RRC Connection Release message, there is a possibility to add UTRAN/GERAN System Information messages. In the picture above, I have only shown UTRA System Information but a similar picture can be drawn for GERAN.

Once all the Mandatory SIB's are sent to the UE then it can immediately camp on without the need to read any other additional system info. This will reduce the CSFB time between 1-2 seconds.

The lesser the CSFB time, the better the Quality of end user experience

3 comments:

kalmness said...

Hi Zahid,

I've been trying to find out more the details for this in the 3GPP specifications without any success. Do you know where I can find this in the specs? The closest I found was in TS 36.306 section 4.3.7 .22 and 4.3.7.23

4.3.7.22 e-RedirectionUTRA
This parameter defines whether the UE supports use of UTRA system information provided by RRCConnectionRelease upon redirection.
4.3.7.23 e-RedirectionGERAN
This parameter defines whether the UE supports use of GERAN system information provided by RRCConnectionRelease upon redirection.
A UE that supports CS fallback to GERAN shall support e-Redirection to GERAN.

gabriel said...

Kalmness,
You need to look at 36.331 Rel 9, RRCConnectionRelease message. These fields have been added:

CellInfoListGERAN-r9 ::= SEQUENCE (SIZE (1..maxCellInfoGERAN-r9)) OF CellInfoGERAN-r9

CellInfoGERAN-r9 ::= SEQUENCE {
physCellId-r9 PhysCellIdGERAN,
carrierFreq-r9 CarrierFreqGERAN,
systemInformation-r9 SystemInfoListGERAN
}

CellInfoListUTRA-FDD-r9 ::= SEQUENCE (SIZE (1..maxCellInfoUTRA-r9)) OF CellInfoUTRA-FDD-r9

CellInfoUTRA-FDD-r9 ::= SEQUENCE {
physCellId-r9 PhysCellIdUTRA-FDD,
utra-BCCH-Container-r9 OCTET STRING
}

Hardik Kakadia said...

I had several questions on this :


what is the expected UE behavior when the UE received several SI in the RRC connection release under following condition

When UE found PSC that match with one of the SI in RRC connection release
When UE didn’t find PSC that match with any of the SI in the RRC connection release, what is the order of search
When UE found PSC that match with one of the SI in the RRC connection release but another PSC much stronger
When UE found the PSC that match with one of the SI in the RRC connection release but the LAC in the SI is different than the one over the air in SIB (wrong information in SI)
When UE receive 16 SI in the RRC connection release, and found several of them in the air (some stronger than others), which one to chose