Cooperative Spectrum Sharing Protocol with Selective Relaying System

In this paper, we propose a two-phase protocol based on cooperative relaying for a secondary system to achieve spectrum access along with a selective relaying primary system. The primary system comprises of a transmitter-receiver pair PT-PR and M relays R_i, i G {1,2,⋯ , M}. The secondary system is a multi-user system with N transmitters R_i, i ϵ {M +1, M + 2, ⋯ , M + N } which intend to communicate with a common receiver SR. In the proposed protocol, terminals R_i, i ϵ M₁ = {1, 2, ⋯ , M + Q} are designated as possible candidates for assisting the primary system while the remaining secondary transmitters R_i´, i´ ϵ M₂ = {M + Q + 1, M + Q + 2, ⋯ ,M + N} are chosen as possible candidates for secondary spectrum access, where 0 ≤ Q ≤ N. The relaying terminal R_p, p ϵ M₁ which achieves the request target rate for the primary system and has the best channel to PR, is first selected from M₁ to serve as a decode-and-forward (DF) relay for the primary system. With the cooperation of R_p, the primary system is able to tolerate some interference lower than a certain threshold in the relaying phase, without degrading its outage performance. The secondary transmitter R_s, s ϵ M₂ which satisfies this interference constraint and optimizes the outage performance for the secondary system, is then selected from M₂ to access the spectrum band simultaneously when R_p is relaying the primary signal. Analytical and simulation results confirm the efficiency of the proposed spectrum sharing protocol. We show that there exists an optimal value for Q and both primary and secondary systems are able to achieve better outage performance with increasing N.