Distributed switch-and-examine combining with threshold-based relaying

We study the distributed switch-and-examine combining with threshold-based relaying (DSEC-T). In this scheme, relay selection is performed in a similar fashion to switch-and-examine combining (SEC) considering the source-relay channel signal-to-noise ratio (SNR) in conjunction with threshold-based relaying. In particular, the same relay remain selected as long as its SNR is above a predefined threshold; should this condition be violated, the remaining relays are tested against the threshold in a predefined order. This testing process is repeated until either an acceptable relay is found or no relay is left to be examined. In the latter case none of the relay is chosen for communication. On the other hand, if an acceptable relay is identified, the switch-and-examine process is interrupted and the identified relay assists the source-destination communication working as an amplify-and-forward (AF) relay. Lower bounds for the outage probability and symbol error rate (SER) are derived assuming Rayleigh multi-path fading channels. Numerical results demonstrate that the proposed DSEC-T scheme achieves the same diversity order as the partial relay selection (PRS) where the best relay is selected based on source-relay SNR for earch transmission.