Differential modulation for two-user cooperative diversity systems

Cooperative transmission is an alternative approach to achieve diversity in wireless systems. So far the research has focused on the situation where perfect channel state information is available and coherent detection is employed at at the destination receiver. This paper proposes a differential modulation scheme for a two-user cooperative diversity system which does not require channel state information at either users or destination. The relaying protocols such as fixed decode-and-forward, selection relaying, and incremental relaying protocols are compared. The proposed scheme achieves spatial diversity gains when the signal-to-noise ratios between cooperative users are sufficiently high.