Outage probability of single-carrier cooperative spectrum sharing systems with decode-and-forward relaying and selection combining

For cyclic prefixed single-carrier (CP-SC) spectrum sharing relaying systems, a two-hop decode-and-forward (DF) relaying protocol with a direct link and selection combining are employed in the secondary user relay network. For this cooperative CP-SC spectrum sharing system, the end-to-end signal-to-noise ratio (e2e-SNR) is first derived, and then the outage probability performance of the secondary user relaying system is investigated. Having derived an asymptotic expression for the cumulative distribution function of the e2e-SNR, the asymptotic outage diversity is obtained under a limited maximum transmit power at the secondary source and relay while satisfying the maximum allowable interference at the primary user. Notably, when the maximum allowable interference is independent of a limited transmission power, an outage probability floor is observed. Moreover, under the assumption of an unlimited transmit power at the secondary nodes, the asymptotic outage diversity is derived as a function of the interference. It can be seen that the same outage diversity gain can be achieved as in the non-spectrum-sharing CP-SC relaying system. Analytically derived asymptotic outage diversity gains for limited and unlimited transmission power cases are verified by Monte Carlo simulations.