LDPC code design for Gaussian multiple-access channels using dynamic EXIT chart analysis

We consider the degree distribution design of the low-density parity-check (LDPC) code ensembles for symmetric Gaussian multiple-access channels (GMAC). To characterize the probability density function (PDF) of the message passing in the process of joint decoding, we propose a new scheme to construct the associated Gaussian mixture (GM) distribution, where each GM component is assigned according to the corresponding signal group transmitted by the users. By tracking the variation of the GM components in the iterative decoding process, more accurate mutual information can be obtained for the extrinsic information transfer (EXIT) chart analysis. Simulation results show that the performance of our proposed LDPC codes is better than that of the existing methods.