Performance analysis of cyclic prefixed single-carrier spectrum sharing relay systems in primary user interference

For cyclic prefixed single-carrier (CP-SC) spectrum sharing relay systems, the joint impact of the primary transmitter and primary receiver on the performance of secondary networks is investigated. A two-hop amplify-and-forward (AF) relay protocol is employed, and then its end-to-end signal-to- interference-ratio (e2e-SIR) is defined. An upper bound on the cumulative distribution function (CDF) of this e2e-SIR is derived for the CP-SC system. Having investigated an asymptotic expression for the CDF, the asymptotic outage diversity and coding gain can be obtained. Also, under a total transmission constraint, a suboptimal power allocation (sub-OPA) is derived for approximately minimizing the asymptotic outage probability. Monte Carlo simulations verify the derived outage probability and its asymptotic diversity gain with and without power allocation. It is shown that the primary transmitter has a major impact on the secondary network performance. Importantly, it is observed that when the interference from the primary transmitter proportionally increases with the interference power constraint at the primary receiver, the spectrum-sharing system results in no diversity gain for the full range of the SIR.