Relay Selection for Low-Complexity Coded Cooperation

This paper explores relay selection and selection diversity for coded cooperation in wireless sensor networks, with complexity constraints for the sensor nodes. In previous work, a relaying scheme based on repeat-accumulate (RA) codes was introduced, where it was assumed that the relay does not perform decoding and simply uses demodulated bits to form codewords. However, in a network setting with multiple potential relays where relays do not decode the source transmission, it is not obvious how to select the best relay. The optimal choice involves finding the best relay possibly using density evolution, but is quite complex and time-consuming. It is shown here that the mutual information of the equivalent relay channel, which is much simpler than using DE, is a good selection heuristic. With surprisingly poor performance when a naive selection scheme is used, the importance of a good relay selection scheme is emphasized.