Outage Performance of Optimal Relay and Antenna Selection Schemes with TAS/MRC and TAS/SC for Spectrum-Sharing Network under Imperfect CSI

Cooperative relaying and multiple-input multiple-output transmission technologies exploit spatial diversity to improve the performance of the secondary users in an underlay spectrum sharing network. For this, we present an optimal relay and transmit antenna selection (ORTAS) scheme and an optimal relay and antenna pair selection (ORAPS) scheme by employing transmit antenna selection/maximal ratio combining and transmit antenna selection/selection combining strategies, respectively. Assuming imperfect channel knowledge of the interference links to the primary receiver, the secondary source and relays sufficiently back-off their transmit powers to satisfy an interference outage constraint. We derive closed-form expressions for the outage probability of the secondary network under non-identically distributed Rayleigh fading channels for both the schemes. We also derive insightful asymptotic outage probability expressions for the ORTAS scheme considering two distinct scenarios in order to guarantee different quality of service requirements for the primary network. Both the proposed schemes substantially outperform several other relay and antenna selection schemes, and can be served as a better performance/complexity tradeoff.