Cooperative diversity with multiple-antenna nodes in fading relay channels

In this paper, we investigate the performance of a single-relay cooperative scenario where the source, relay and destination terminals are equipped with multiple transmit/receive antennas. We assume that conventional space-time block codes are employed in the underlying source-to-destination (S → D), source-to-relay (S → R) and relay-to-destination (R → D) links, and consider both decode-and-forward (DaF) and amplify-and-forward (AaF) relaying techniques. For the latter one, we consider two variants based on the availability of channel state information (CSI); namely, blind AaF and CSI-assisted AaF. Through the derivation of pairwise error probability, we quantify analytically the impact of multiple antenna deployment for each relaying technique under various scenarios which involve relay location and power control assumptions imposed on cooperating nodes. Our transmission model assumes that the source and destination terminals are equipped with M _S transmit and N receive antennas, respectively, and the relay terminal is equipped with M_R receive and M_T transmit antennas. For a scenario where R → D and S → D links are balanced and S → R link experiences sufficiently large SNR, our performance analysis demonstrates that the maximum achievable diversity order is M_T min(M_S, N)+M_SN for blind AaF scheme and N(M _T+M_S) for both CSI-assisted AaF and DaF schemes. For another scenario where R → D link has a sufficiently large SNR and S → R and S → D links are balanced, CSI-assisted AaF, blind AaF and DaF schemes achieve diversity orders of M_S(N + M_R), M _S(N + M_T), and M_SN, respectively. Other scenarios involving the availability of non-fading R → D link and poor inter-user channel quality are further investigated. An extensive Monte Carlo simulation study is also presented to corroborate the analytical results and to provide detailed performance comparisons among the three relaying techniques under consideration.