Selective Random Cyclic Delay Diversity for HARQ in Cooperative Relay

In the next generation cellular system, relay has been considered to increase coverage extension and cell-edge throughput. Cooperative relay can provide transmission diversity gain to improve outage probability, overall throughput and energy efficiency. Cooperative beamforming has been considered as one of the cooperative relay if the relay nodes can get the feedback information from the destination. In this paper, a new cooperative relay scheme is proposed for hop-by-hop HARQ in cooperative relay. The scheme is to adopt selective random cyclic delay diversity (CDD) to the retransmission in HARQ, which can get rid of the relative bad relay nodes and form a better frequency selective channel to exploit diversity gain when channel coding is used. Performance evaluation and analysis have shown that the selective random CDD can achieve higher throughput and lower transmission delay than the conventional cooperative beamforming.