Diversity-multiplexing tradeoff of opportunistic relay system with multiple-antenna destination

In this study, the authors investigate the diversity-multiplexing tradeoff (DMT) of a wireless system in which user equipments (UEs) are equipped with only one antenna while the destination has multiple antennas. Each UE is assisted by M half-duplex cooperative users serving as relay nodes. They combine the opportunistic relaying scheme and the cooperative spatial multiplexing (C-SM) scheme to produce an opportunistic C-SM (OC-SM) scheme. The fraction of time allocated to the source-relay link and the relay-destination link is treated as a design parameter to minimise the outage probability of the system. At high signal-to-noise ratio regime, the optimal time allocated factor is obtained in a closed-form expression through DMT analysis. Based on the DMT result of the proposed OC-SM scheme, an adaptive OC-SM (AOC-SM) approach in which the system can switch between different C-SM models adaptively based on the rate transmitted is proposed. To reduce the complexity of the relay nodes, an AOC-SM scheme with relay selection (SAOC-SM) in which a constant number of relay nodes is selected from the set of relay nodes that have successfully decoded the source message is investigated. The DMT results of the SAOC-SM scheme and the AOC-SM scheme are obtained and compared.