Analysis of amplify-and-forward DSTBCs over the random set relay channel

We study the performance of amplify-and-forward (AF) distributed space-time block coded (DSTBC) cooperative systems over the random set relay channel (RSRC) that results when each of N available relays is allowed to decide independently whether to relay the source's information or not, based on its own instantaneous receive signal-to-noise ratio (SNR). In particular, we derive analytical bit error rate (BER) expressions for linearly dispersed full-rate DSTBCs characterized by a diversity order eta over the random set relay channel with arbitrary fading statistics per brach and assuming constant average transmit power per relay. The system concept is interesting in which no coordination amongst relays is required, and only backward channel state information (CSI) is assumed. Employing the formulae with eta = 1 so as to capture the performance of ideal (full-rate-full-diversity) codes, we then study the BER performance of AF-DSTBCs over the RSRC with Rayleigh fading per link. The analysis reveals that a substantial gain in spectrum efficient, and surprisingly even some improvement in raw BER, are achieved by the autonomic relaying mechanism, compared to the alternative of full-time all-relay cooperation, despite the fact that the total receive power at destination increases with the number K of active relays. Finally, we complement the analytical findings with simulation results employing the GABBA codes that corroborates the analysis.