Cooperative space-time code for amplify-and-forward relay networks

In this paper, we propose a distributed space-time coded cooperative protocol with amplify-and-forward relaying. Motivated by protocol (III) presented in [1], we propose a distributed space-time coding for an arbitrary number of relay nodes. The pairwise error probability (PEP) is derived and the theory analysis demonstrates that our protocol achieves a diversity of order N +1 where N is the number of relay nodes. Quasi-orthogonal space-time codes are used as they give much better performance than random linear-dispersion codes. As the transmission power of the source node is a critical parameter in this protocol because it transmits in both phases, the optimal power allocation is derived using numerical and theoretical analysis. Simulation results demonstrate an improvement over the existing orthogonal protocols for different source-destination channel conditions.