Design of distributed multi-edge type LDPC codes for multiple access relay channels

This paper studies the problem of determining the optimum degree distribution for distributed LDPC codes in multiple-access relay channels. Based on the framework of multi-edge type LDPC codes, we propose a methodology to asymptotically optimize the code´s ensemble when different segments within the distributed codeword are transmitted through different channels and experience different SNRs. An average noise threshold is formulated in order to compute the convergence threshold of the distributed LDPC codes under density evolution and also to act as the performance gap between the optimized distributed codes and the theoretical limit. We demonstrate that our distributed LDPC code performs asymptotically to within a fraction of a dB from the theoretical limit.