Hybrid ARQ Based Cooperative Relaying in Wireless Dual-Hop Networks

In wireless decode-and-forward (DF) relaying networks, the hybrid ARQ (HARQ) process suffers severe latency, especially when centralized scheduling is employed. We propose a new distributed HARQ based cooperative relaying (DHCR) protocol to reduce the latency. Based on the reception quality of the 1st hop, each relay station (RS) independently processes and forwards the data stream in such a manner that, from the perspective of the destination, three cooperative relaying modes can be effectively formed and one of them is adaptively selected: spatial multiplexing (SM), space-time transmit diversity (STTD) and unicast (UC). The proposed DHCR protocol places priority on SM and it is throughput-oriented. In addition, we develop a new analytical model based on the Markov chain to facilitate the performance analysis of the proposed protocol. Based on the new model, we have derived the exact expressions for spectral efficiency, latency and the distribution of latency. It is revealed that the new DHCR protocol can decrease the latency by around 40% at high signal-to-noise ratio (SNR) without loss of spectral efficiency compared with the centralized approach.