High-rate BICM-ID with superposition modulation over amplify-and-forward relay channels

This paper studies the error performance of a high-rate bit-interleaved coded modulation with iterative decoding (BICM-ID) system using superposition modulation over a nonorthogonal amplify-and-forward (NAF) half-duplex single relay channel. Based on extrinsic information transfer (EXIT) chart analysis, we investigate both asymptotic coding gain and the convergence property of the systems under consideration. Analytical and simulation results indicate that the superposition modulation method provides significant performance gains over a wide range of code rates as compared to the optimal precoding scheme developed earlier for uncoded NAF systems. As an illustrative example, it is demonstrated that a high-rate BICM-ID scheme can achieve a coding gain of 1.7 dB, 2.2 dB, and 2.7 dB with coding rate of 1/2, 3/4, and 5/6, respectively, at BER of 10^-4 by varying the number of decoding iterations.