On the achievable rate of AWGN relay channel with finite input constellations

Achievable rate for a single-relay channel with finite input practical constellations like QAM and PSK, which operates under the decode and forward protocol, is studied. An achievable rate is computed for full duplex relay (FDR) channel and half duplex relay (HDR) channel. We consider the cases: (i) the source node's and relay node's signals can be correlated for the FDR channel, (ii) repetition coding scheme and (iii) independent symbol coding scheme for the HDR channels, and propose for both the FDR and the HDR channels a superposition coding scheme with finite alphabets. Through simulation results it is shown that for the FDR channels, the proposed superposition coding achieves higher rate than the correlated signaling scheme for the BPSK input alphabet and for the HDR channels, the superposition coding outperforms the independent symbol coding as well as the repetition codes.