Quantize-map-and-forward relaying: Coding and system design

Quantize-map-and-forward (QMF) is a relaying scheme that has been shown to achieve the capacity of Gaussian relay networks to within a constant gap. Under QMF the compression indices forwarded by relays are not decoded explicitly. Instead, the message is decoded jointly with the compression indices. In this work we present a practical coding and signaling framework that captures this aspect of QMF. We outline the framework for a simple Gaussian network with a single half-duplex relay. We propose a scheme where binary LDPC codes are used for encoding at the source and at the relay. For suitable choice of codes and quantizer we show that the joint decoding operation for QMF can be reduced to belief propagation over a Tanner graph. Simulation results are given to justify the proposed coding scheme. The proposed framework can be extended for use with high order signal constellations.