Design of Nested LDGM-LDPC Codes for Compress-and-Forward in Relay Channel

TL;DR

This paper proposes a nested LDGM-LDPC coding scheme for a relay channel with binary erasure channels, achieving near Slepian-Wolf limits by optimizing degree distributions and employing belief propagation decoding.

Contribution

It introduces a practical coding scheme using nested LDGM-LDPC codes for compress-and-forward relay systems, optimizing code parameters for capacity achievement.

Findings

Achieves the cut-set bound on capacity.

Performance is close to Slepian-Wolf theoretical limit.

Optimized degree distributions ensure BP decoding convergence.

Abstract

A three terminal relay system with binary erasure channel (BEC) was considered, in which a source forwarded information to a destination with a relay's "assistance". The nested LDGM (Low-density generator-matrix) -LDPC (low-density parity-check) was designed to realize Compress-and-forward (CF) at the relay. LDGM coding compressed the received signals losslessly and LDPC realized the binning for Slepian-Wolf coding. Firstly a practical coding scheme was proposed to achieve the cut-set bound on the capacity of the system, employing LDPC and Nested LDGM-LDPC codes at the source and relay respectively. Then, the degree distribution of LDGM and LDPC codes was optimized with a given rate bound, which ensured that the iterative belief propagation (BP) decoding algorithm at the destination was convergent. Finally, simulations results show that the performance achieved based on nested codes is very close to Slepian-Wolf theoretical limit.