High-Performance Cooperative Demodulation With Decode-and-Forward Relays

Cooperative communication systems using various relay strategies can achieve spatial diversity gains, enhance coverage, and potentially increase capacity. For the practically attractive decode-and-forward (DF) relay strategy, we derive a high-performance, low-complexity coherent demodulator at the destination in the form of a weighted combiner. The weights are selected adaptively to account for the quality of both source-relay-destination and source-destination links. Analysis proves that the novel coherent demodulator can achieve the maximum possible diversity, regardless of the underlying constellations. Its error performance tightly bounds that of maximum-likelihood (ML) demodulation which probably quantifies the diversity gain of ML detection with DF relaying. Simulations corroborate the analysis and compare performance of the novel decoder with existing diversity-achieving strategies, including analog amplify-and-forward and selective relaying.