Performance optimization of bit-interleaved coded modulation with iterative decoding

The bandwidth efficient bit-interleaved coded modulation with iterative decoding (BICM-ID) has been demonstrated to achieve better performance than that of symbol-interleaved trellis coded modulation in both additive white Gaussian noise (AWGN) and Rayleigh fading channels. The purposes of this paper are to analyze the performance of a BICM-ID system, to identify those key factors affecting performance, and to optimize system performance by modification of system structure without incurring too much additional complexity. To reach our goals, we first examine the upper bounds on the bit error rate of a BICM-ID system over AWGN and fading channels. From the upper bounds, we learn the performance of a BICM-ID system depends on the distance spectrum of forward error correction code and the effective bit Euclidean distances of signal constellations. Instead of conducting joint design of encoder structure and modulation format which is too complex and time consuming, we consider to select encoder output mapping rules and asymmetric modulations to achieve better performance. Numerical results show the proposed scheme can improve performance of a BICM-ID system by 1 to 2 dBs.