EXIT Chart Analysis of Iterative Demodulation and Decoding of MPSK Constellations with Signal Space Diversity

Abstract

Bit interleaved coded modulation (BICM) schemes have been shown to increase the diversity order. This paper studies the extension of such schemes with iterative demodulation and decoding (ID) using error correcting codes coupled with rotated MPSK signal constellations with different symbol mappings and signal space diversity (SSD). Using extrinsic information transfer (EXIT) charts, an analysis of the impact of the rotation angle on the performance of the system is presented. It is shown that for a given signal constellation, labeling, error correcting code and Eb=N0-value, where conventional BICM-ID system’s decoding trajectory gets stuck in a Rayleigh fading channel, SSD with a well considered choice of the rotation angle allows for the convergence of iterative demodulation and decoding. Furthermore, it is shown that the proposed system can lead to a significant performance gain over BICM-ID. The optimal choice of the rotation angle for the coded system is shown to be dependent upon the signal labeling and the error correcting code being employed. Factors (degrees of freedom) that can effect the convergence behavior of the iterative demodulation and decoding of the proposed system are identified and their effect is analyzed.