On constellation permutations in decode-and-forward relay communications

The paper considers the use of constellation permutation at both the source and the relay nodes to enhance the performance of a decode-and-forward (DF) relay system in a Rayleigh fading environment. Optimum constellation permutations for QPSK, 8-PSK and 8-QAM are found and an upper-bound on the bit error probability is derived in order to estimate the system performance. Obtained simulation results for different propagation scenarios are in a good agreement with the analytical prediction. For good source-relay links, constellation permutation provides noticeable performance improvement as compared to Gray mapping.