A new low-complexity relay selection scheme based on switch-and-examine diversity combining for dual-hop relay networks

In this paper, we present a new low-complexity relay selection scheme for channel-state information (CSI)-assisted dual-hop amplify-and-forward (AF) cooperative networks. The scheme is mainly based on the switch-and-examine (SEC) diversity combining technique where a relay out of multiple relays is only used to forward the source signal to destination. The selection process is performed based on a predetermined switching threshold. In analyzing the scheme performance, a lower bound on end-to-end (e2e) SNR is first used. Then, the probability density function (PDF) and the cumulative distribution function (CDF) are derived in a Rayleigh fading environment. After that, accurate approximations for both the outage probability and the bit error rate (BER) are evaluated. The maximal-ratio combining (MRC) is used at the destination to combine the signal on the relay path with that on the direct link. The Monte Carlo simulations show the validity of the analytical results and the tightness of the used bound, specially, at the high SNR values. Finally, we provide some numerical results to illustrate the effectiveness of the proposed scheme in reducing the system complexity and to verify the effect of other system parameters as the switching threshold and the number of relays on system behavior.