Relay selection for asynchronous AF relay networks with frequency selective channels

In this paper, relay selection schemes in asynchronous multi-relay network for frequency selective channels have been investigated. In particular, distributed Alamouti space time coding and amplify-and-forward (AF) relaying are exploited, and orthogonal frequency division multiplexing (OFDM) is implemented with adaptive cyclic prefix (CP) to deal with the frequency selectivity of the channels and timing errors. Several optimal and suboptimal relay selection and joint relay-subcarrier selection schemes have been proposed based on two selection criteria. The first selection criterion uses the end-to-end signal-to-noise ratio (SNR) and the second one uses the effective capacity which is a function of both the end-to-end SNR and the CP length. Simulation results reveal that the optimal relay selection based on effective capacity performs better in terms of network outage probability compared to the selection based on the SNR alone. Also, it is shown that the more severe the frequency selectivity of the channels the larger the gain.