Sensitivity of achievable rates for half-duplex relay channel

This paper investigates the sensitivity of achievable rates for the half-duplex AWGN relay channel to the choice of modulation, receiving time fraction, and source-relay correlation. Our study is motivated by practical considerations that limit the choice of parameters in a real relay network. We show that BPSK modulation suffices to achieve much of the relaying throughput in the SNR range where relaying is most advantageous. We also show that smartly choosing either completely correlated or uncorrelated signals incurs negligible loss in rate compared to optimally correlated signals. Furthermore, the achievable rate is not diminished significantly if we use equal time slots for relay transmission and reception, instead of using the optimum time ratio. Finally, we demonstrate that even when time and correlation are both restricted, relaying with appropriate power control still carries substantial gains over direct and two-hop channels.