Design of Distributed Multi-Edge Type LDPC Codes for Two-Way Relay Channels

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