Probabilistic relay selection for fast selection cooperation in half-duplex wireless networks

Opportunistic relaying has been recently proposed to eliminate the need of symbol synchronization and challenging code design in distributed space-time coded (DSTC) cooperation yet achieving the same diversity multiplexing tradeoff. In opportunistic relaying, the relay terminal that possesses the best relay-destination channel quality is selected by the destination for cooperative forwarding. Combining opportunistic relaying with the automatic-retransmission request (ARQ) protocol that has already been used to recover the transmission error can further improve the communication reliability in error-prone wireless channels. However, the relay selection process taking place in the scale of the channel coherence time gives rise to additional delay. Furthermore, each relay terminal needs to perform error detection on a per frame basis to determine its eligibility for cooperative relaying. The caused overhead may be fast accumulated as the data rate increases. In this paper, we propose a fast relay selection protocol that selects the assisting relay without using any extra signaling than existing ARQ protocols. Only channel state information (CSI) available at the receiver side is required to perform the selection. We theoretically analyze the proposed scheme, and verify the accuracy of the theoretical analysis through simulations. Numerical results show that, the proposed scheme outperforms the classical ARQ protocols in terms of outage probabilities, using the same amount of signaling.