Joint Relay-and-Antenna Selection in Multi-Antenna Relay Networks

For the decode-and-forward protocol in relay networks, opportunistic relaying (OR) and selection cooperation (SC) are two major relay selection schemes, which have been studied only for single antenna terminals. We study OR and SC in a multi-antenna relay network where each terminal has multiple antennas. To fully exploit multiple antennas without incurring high feedback overhead, we adopt transmit antenna selection (TAS). Specifically, we first propose two joint relay-and-antenna selection schemes which combine OR and SC, respectively, with TAS: joint OR-TAS and joint SC-TAS. For each joint selection scheme, a single best transmit antenna at the source, a single best relay, and a single best transmit antenna at this selected relay are jointly determined in an optimum sense. In this network, at the first time slot, the selected antenna at the source transmits a symbol to the selected relay; at the second time slot, the selected antenna at the selected relay retransmits the detected symbol to the destination. We derive the outage probability of joint OR-TAS. Also, we obtain the outage probability of joint SC-TAS by proving that the outage probability of joint SC-TAS is identical to that of joint OR-TAS.