Complexity Reduction Strategy for RAID in Multi-User Relay Systems

In this paper, distributed Interleave-Division- Multiplexing Space Time Codes (dIDM-STC) in Multi- User Decode-and-Forward Relay Systems are considered. Due to decoding errors at the relays, which are unavoidable in practical systems, error propagation to the destination occurs. In order to cope with this error propagation, recently a Reliability-Aware Iterative Detection Scheme (RAID) at the destination was proposed by the authors, which takes the decoding success at the relays, as well as the decoding reliability of the relays into account. This scheme requires a CRC check and also the estimation of the error probability at each relay. In this paper, a modification of RAID is presented, which only requires a CRC check at the relays, completely avoiding the estimation of the error probabilities at the relays and the signaling to the destination. Instead, the determination of the error probabilities is shifted to the destination reducing the complexity at the relays and the overall signaling overhead. As will be shown, the proposed complexity reduced RAID scheme (CR-RAID) allows for the same end-to-end performance in terms of frame-error-rates as the original RAID.