Efficient Relay Selection Scheme for Delay-Limited Non-Orthogonal Hybrid-ARQ Relay Channels

We consider a half-duplex wireless relay network with hybrid-automatic retransmission request (HARQ) and Rayleigh fading channels. In this paper, we analyze the outage probability of the multirelay delay-limited HARQ system with opportunistic relaying scheme in decode-and-forward mode, in which the best relay is selected to transmit the source’s regenerated signal. A simple and distributed relay selection strategy is proposed for multi-relay HARQ channels. Then, we utilize the non-orthogonal cooperative transmission between the source and selected relay for retransmitting of the source data toward the destination if needed, using space-time codes or beamforming techniques. We analyze the performance of the system. We first derive the cumulative density function (CDF) and probability density function (PDF) of the selected relay HARQ channels. Then, the CDF and PDF are used to determine the outage probability in the l-th round of HARQ. The outage probability is required to compute the throughput-delay performance of this half-duplex opportunistic relaying protocol. The packet delay constraint is represented by L, the maximum number of HARQ rounds. An outage is declared if the packet is unsuccessful after L HARQ rounds. Furthermore, closed-form upper-bounds on outage probability are derived and subsequently are used to investigate the diversity order of the system. Based on the derived upper-bound expressions, it is shown that the proposed schemes achieve the full spatial diversity order of N + 1, where N is the number of potential relays. Our analytical results are confirmed by simulation results. Behrouz Maham and Aydin Behnad are with School of ECE, College of Engineering, University of Tehran, North Karegar, Tehran 14395-515, Iran. Mérouane Debbah is with Alcatel-Lucent Chair on Flexible Radio, SUPÉLEC, Gif-sur-Yvette, France. Preliminary version of a portion of this work was appeared in Proc. IEEE Vehicular Technology Conference (VTC 2010-Fall). Emails: [email protected],[email protected],[email protected]. Submitted 11.2011 to IEEE Transactions on Vehicular Technology 2