Cooperative spectrum sharing with relay selection

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. The secondary system is a multi-user system with N transmitters which intend to communicate with a common receiver SR. In the proposed protocol, Q out of N secondary transmitters are designated as possible candidates for assisting the primary system while the remaining secondary transmitters are chosen as possible candidates for secondary spectrum access, where 0 ≤ Q <; N. One relaying terminal R_p which achieves the request target rate for the primary system and has the best channel to PR, is first selected 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 which satisfies this interference constraint and optimizes the outage performance for the secondary system, is then selected to access the spectrum band simultaneously when R_p is relaying the primary signal. We show that both primary and secondary systems are able to achieve better outage performance with increasing N.