Rateless Coding Based Incremental Redundancy HARQ Scheme for SCMA Systems

Abstract

In this paper, we present a rateless coding based incremental redundancy (IR) HARQ scheme for sparse code multiple access (SCMA) systems over fading channels, where each user is assumed to use rateless codes. Two different IR-HARQ strategies are proposed for the SCMA system to investigate the performance from different angles. One scheme mainly focuses on how to combine the incremental decoding and the multi-user detection (termed as the original rateless coding based IR-HARQ strategy). The other scheme employs the iteration between the incremental decoding and the multi-user detection to improve the performance (termed as the joint detection-decoding rateless coding based IR-HARQ strategy). We investigate the performance of these two strategies over the AWGN and fast-fading channels. Simulation results show that, with the proposed IR-HARQ scheme, the SCMA system performance improves with the increase of the retransmission. Furthermore, with the help of the iteration between the detector and the decoding, the SCMA system with the joint detection-decoding rateless coding based IR-HARQ strategy outperforms the original one.