Bandwidth-Efficient communication through AWGN and Rayleigh fading channels using Serially-Concatenated LDGM codes

Serially-concatenated low-density generator matrix (SCLDGM) codes constitute a practical means to approach channel capacity on several channel models. Recently, the authors have proposed SCLDGM codes for binary-input channels constructed using an optimization procedure based on tracking the decoding behaviour of the sum-product algorithm (SPA) by means of extrinsic information transfer (EXIT) functions. In this paper we extend these previous results to more bandwidth-efficient modulation formats transmitting over both AWGN and Rayleigh fading channels. In addition, we investigate the use of the A-min* version of the SPA to considerably reduce decoding complexity at the expense of very little performance degradation. In both channel models, the optimized SCLDGM codes exhibit better performance than other recently proposed bandwidth-efficient schemes with similar coding/decoding computational costs, such as irregular repeat-accumulate (IRA) codes