Distributed modulation for cooperative wireless communications

The modulation techniques in cooperative wireless systems are distributed in nature since the signal is modulated at the source and at the relays for transmission to the destination. The four distributed modulation schemes are coherent amplify-and-forward (CAF), coherent decode-and-forward (CDF), differential amplify-and-forward (DAF) and differential decode-and-forward (DDF). The distributed modulation and combining techniques resemble conventional single-hop noncooperative, multichannel communication techniques. The performance of all cooperative schemes depend on the relative locations of the cooperating nodes.