Kent Pedersen

ARQ considerations for the new GSM/EDGE flexible layer one

A major enhancement of the GSM/EDGE Radio Access Network (GERAN) is the Flexible Layer One (FLO) concept, due to he introduced in Release 6 nf the 3GPP standards. FLO greatly simplifies the introduction of new services to the GERAN system, allowing for “tailor-made” provision of any given Quality of Service (QnS), significantly enhancing GERAN’s flexibility, and ensuring it will evolve on par with other 3G systems. In the GERAN Iu mode, FLO supports data transfer in transparent, unacknowledged and acknowledged RLC (Radio Link Control) modes. In the latter mode, the RLC applies backward error correction (BEC) through an ARQ (Automatic Repeat reQuest) mechanism Considering ARQ mechanisms, Hybrid Type I1 ARQ (aka. incremental redundancy) is a very efficient technique that requires a close interaction between the retransmission protocol at the RLC layer and the channel encoderldecoder at the physical layer. This paper first introduces the concept of FLO, and then describes how hybrid type I1 ARQ can he implemented in the FLO physical layer. Finally, we present the performance gains possible by introducing incremental redundancy to FLO, especially when compared to the performance of Chase combining.