A Threshold-Based Hybrid Relay Selection Scheme

Unlike the previous work, which relies on cyclic redundancy check (CRC) to decide the decoding accuracy at the relay nodes, in this paper, we propose a simple threshold-based hybrid relay selection (THS) scheme for cooperative communications over block fading channels. A specific signal-to-noise ratio~(SNR) threshold is designed in comparison with the instantaneous SNR to determine if the frame can be decoded correctly or not. The relays that decode correctly will choose decode-and-forward~(DF) protocol and be included in the DF relay group. The rest will employ amplify- and-forward~(AF) protocol and be included in the AF relay group. Then, among all the relays in the AF and DF relay groups, the one that realizes the maximum destination SNR will be finally selected as the optimal relay. The performance of the proposed THS scheme is analyzed, and a simple asymptotic SER and FER expressions are derived. The analytical results are verified through simulations. Both theoretical analysis and simulated results also show that the THS scheme achieves almost the same performance as that attaching CRC codes.