Double Differential Modulation for Decode-and-Forward Cooperative Communications

In this paper, we consider a scenario, where all the links in the cooperative system are perturbed by the different random carrier offsets. We have implemented double differential modulation in cooperative communications to overcome the problem of carrier offsets. The performance analysis of decode-and-forward relaying with double differential modulation is performed. We derive an upper bound over symbol error rate and also propose optimal power allocation to improve the performance of the system. The proposed scheme outperforms the same rate direct transmission scheme for moderate to high SNR values and the previously proposed differential scheme based on amplify-and-forward protocol.