Improving the performance of QPSK BICM-ID by mapping on the hypercube

This paper introduces a new mapping of QPSK signals viewed as a vertices of a multi-dimensional hypercube, to improve the performance of bit-interleaved coded modulation with iterative decoding (BICM-ID) over a Rayleigh fading channel. The distance criterion to find the best mapping in terms of asymptotic performance is analytically derived. A general algorithm to construct the best mapping of a hypercube is then proposed. Numerical and simulation results show that the proposed mapping offers a significant coding gain over the conventional mappings of QPSK in a BICM-ID system. Such a coding gain is obtained without any bandwidth or power expansion and with a small increase in the receiver complexity.