Cooperative diversity for wireless fading channels without channel state information

Relaying and cooperative diversity allow multiple wireless radios to effectively share their antennas and create a virtual antenna array, thereby leveraging the spatial diversity benefits of multiple-input, multiple-output (MIMO) antenna systems. This paper examines the benefits of cooperative diversity for scenarios in which the receivers cannot exploit accurate channel state information (CSI). In particular, noncoherent demodulation is explored for two classes of relay processing, namely, detect-and-forward and amplify-and-forward. A complete maximum likelihood (ML) framework for noncoherent demodulation is developed for detect-and-forward, and is shown to naturally extend the corresponding framework for coherent demodulation. By contrast, the intractability of ML demodulation for noncoherent amplify-and-forward is demonstrated, suggesting a disconnect from the well-developed framework for coherent demodulation. Simulation results exhibit the diversity benefits of the detect-and-forward algorithms.