Efficient demodulation in cooperative schemes using 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 an efficient demodulator at the destination in the form of at 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 demodulator can achieve the maximum possible diversity, regardless of the underlying constellation. Its error performance tightly bounds that of maximum-likelihood (ML) demodulation which provably quantifies the diversity gain of ML detection with DF relaying. Simulations corroborate our theoretical analyses and compare performance of the novel decoder with existing diversity-achieving strategies including analog amplify-and-forward and selective-relaying.