Cooperative spectrum sharing protocol with secondary user 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 primary system. The primary system comprises of a transmitter-receiver pair PT-PR, and the secondary system comprises of M transmitters ST_i, i ε {1,2,M} and a common receiver SR. The secondary transmitter ST_p which achieves the request target rate for the primary system is selected to serve as a decode-and-forward (DF) relay for the primary system. With the cooperation of ST_p, the primary system is able to tolerate interference lower than a certain threshold in the relaying phase, without degrading its outage performance. The secondary transmitter ST_s, which satisfies this interference constraint and provides the optimal outage performance for the secondary system, is then selected to access the spectrum band simultaneously when ST_p is relaying the primary signal. Theoretical and simulation results confirm the efficiency of the proposed spectrum sharing protocol, and we show that both primary and secondary systems are able to achieve better outage performance with increasing M.