On the optimal subcarrier mapping scheme in OFDM decode-and-forward relay systems

BER performance of the DPSK (Differentially Phase Shift Keying) modulated dual-hop OFDM based DF (Decode and Forward) relay system, implementing subcarrier mapping (SCM) at the relay (R) station, is examined. Closed form BER expressions are derived for the two SCM schemes, denoted as BTB SCM (Best-to-Best Subcarrier Mapping) and BTW SCM (Best-to-Worst Subcarrier Mapping) in the scenario with Rayleigh fading on both hops. The accuracy of the obtained analytical results is verified through comparison with the simulation results. It is shown that BTB SCM scheme achieves the lowest BER results for all SNRs (Signal-to-Noise Ratios) of interest, which approves it to be the optimal SCM scheme in dual-hop OFDM DF relay systems, as it has already been known that the same SCM scheme maximizes the capacity.