Effects of outdated channel state information in partial relay selection systems with multiple antennas at the destination

Cooperative relays have been proposed as effective solutions for radio range extension in mobile and wireless broadband networks. As such, a cooperative system is studied in this paper that consists of one single-antenna source node, L single-antenna relay nodes, and one M-antenna destination node. The impact of feedback delay to partial relay selection scheme is investigated, where a best relay is selected according to the instantaneous source-relay channel state information (CSI). The outage probability and symbol error rate (SER) are derived in closed-form expressions, and further simplified in exponential expressions to explicitly characterize the diversity order and array gain. Monte Carlo simulations verify our analytical results, which indicate that when CSI is outdated, the diversity order is reduced to 1 regardless of the accuracy degree. Results also show that better performance can be achieved when relays are placed closer to the source relative to the destination.