Performance of circular QAM constellations using partial channel coding with parallel double gray mapping

This paper proposes a parallel double Gray mapping scheme that is suited to circular quadrature amplitude modulation (QAM) constellations using partial channel coding associated with collaborative decoding. Using the proposed scheme, We compare the bit error rate (BER) performance of circular 1024QAM and 2048QAM schemes to that of rectangular 1024QAM and cross 2048QAM schemes, respectively. Computer simulation results show that the required received signal-to-noise power ratio at the BER of 10
^-5
for collaborative decoding is decreased by approximately 6.5 dB compared to that for independent decoding for partial turbo coding employing the parallel double Gray mapping. We also show that circular 1024QAM exhibits greater robustness against time-varying phase noise than rectangular 1024QAM when using partial turbo coding with the parallel double Gray mapping. We show however that rectangular 1024QAM provides slightly better BER performance compared to circular 1024QAM with parallel double Gray mapping using collaborative decoding in an additive white Gaussian noise channel with time-varying phase noise.