Abstract:

The bilayer density evolution algorithm is always used to design bilayer lengthened LDPC codes for the decode-and-forward relay system. The general approach is to fix the lower variable degree distribution and then find an upper variable degree distribution, which has higher complexity. To solve this problem, the Gaussian approximation algorithm is proposed to implement the overall optimization for the lower and upper variable degree distributions. The proposed algorithm aims at maximizing the rates of the source-to-relay and the source-to-destination link simultaneously, which has lower complexity. Simulation results show that the gap between the convergence threshold and the theoretical limit of the proposed LDPC codes is smaller and that BER performance is almost the same as that of the ensembles obtained by bilayer density evolution.

Key words: relay channel, LDPC codes, Gaussian approximation, global optimization