11 Repeated SACCH

3GPP44.006Data Link (DL) layer specificationMobile Station - Base Station System (MS - BSS) interfaceRelease 17TS

11.1 General

The Repeated SACCH functionality is applicable when a layer 3 message unit is to be sent or received in a SAPI=0 frame (i.e. in unacknowledged mode) on the SACCH channel. The MS shall support the Repeated SACCH functionality. The BSS may use the Repeated SACCH functionality when it considers it to be appropriate.

11.2 Procedure for Repeated SACCH on the downlink

If a downlink SACCH block is incorrectly decoded (prior to combining with any previously received SACCH block), and the next uplink SACCH block is not a repetition as per the Repeated SACCH procedure (see sub-clause 11.3), then the MS shall set the SACCH Repetition Request in the next uplink SACCH block to "Repeated SACCH required" (see 3GPP TS 44.004). If a downlink SACCH block is correctly decoded (prior to combining with any previously received SACCH block), and the next uplink SACCH block is not a repetition as per the Repeated SACCH procedure (see sub-clause 11.3), the MS shall set the SACCH Repetition Request in the next uplink SACCH block to "Repeated SACCHnot required".

At the BSS side, if a transmitted downlink SACCH block contains a SAPI 0 frame and is not already a repetition, then it is a repetition candidate. If a SACCH block is a repetition candidate then the BSS may, based on the value of the last correctly received SACCH Repetition Request from the MS, or based on implementation-dependent criteria, repeat this SACCH block at the next SACCH period. If a SAPI 3 frame was also scheduled to be sent at this next SACCH period, the BSS may delay the sending of the SAPI 3 frame by one SACCH period in order to make room for the repetition.

When receiving a downlink SACCH block, the MS shall first attempt to decode it without combining with any previously received SACCH block. If this decoding fails, then a new decoding using the information from this SACCH block and from the SACCH block received at the previous SACCH block period shall be performed.

11.3 Procedure for Repeated SACCH on the uplink

The BSS may set the value of the SACCH Repetition Order (see 3GPP TS 44.004) of any downlink SACCH block based on implementation-dependent criteria.

At the MS side, if a transmitted uplink SACCH block contains a SAPI 0 frame and is not already a repetition, then it is a repetition candidate. If a SACCH block is a repetition candidate and if the last correctly received SACCH Repetition Order was set to "Repeated SACCH required", then the MS shall repeat this SACCH block at the next SACCH block period. If a SAPI 3 frame was also scheduled to be sent at this next SACCH period, the MS shall delay the sending of the SAPI 3 frame by one SACCH period in order to make room for the repetition.

When receiving an uplink SACCH block, the BSS may first attempt to decode it without combining with any previously received SACCH block. If this decoding fails, then a new decoding using the information from this SACCH block and from the SACCH block received at the previous SACCH block period may be performed.

Annex A (normative):
Random access procedures