On the design of bit-interleaved turbo-coded modulation

Bit-interleaved turbo-coded modulations (BITCM) have been shown to achieve bit error rate performance very close to the capacity limit over both additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. So far, most studies have been done on BITCM systems designed using rectangular QAM signal sets. In this paper, we address the problem of finding some constellations that would be more suitable than rectangular QAM for designing power efficient BITCM. When the parameter M is in the form M=2^2p where p is an integer, we show that rectangular QAM constellations are surprisingly the most attractive signal sets for the design of power-efficient BITCM schemes over AWGN channels. This is not necessarily true with Rayleigh fading channels