Cooperative spectrum sharing in two‐way multi‐user multi‐relay networks

In this study, the authors consider a cooperative spectrum sharing network with multiple primary users (PUs) and multiple secondary users (SUs). Hereby, one end‐PU communicates bidirectionally with one of the best selected other end‐PUs with the cooperation of the best selected SU using time division broadcast protocol. Based on an overlay approach, the selected SU allocates its partial power to relay the PUs’ signals and utilises the remaining power to transmit its own signal. The authors devise a low‐complexity distributed PU–SU selection strategy to minimise the overall outage probability of the primary system. For Nakagami‐ m fading, the authors derive tight expressions of outage probability for both primary and secondary systems of the considered scheme. Further, by deriving their asymptotic behaviour at high signal‐to‐noise ratio, the authors highlight the performance gain accrued by cooperative and multiuser diversity along with that offered by the channels under Nakagami‐ m fading. Besides, the authors demonstrate the effective locations for the SUs to access the spectrum. Above all, the authors illustrate that the increase of the number of SUs is more desirable than the number of PUs to explore the spectrum sharing opportunities. Numerical and simulation results substantiate the effectiveness of the proposed scheme and the theoretical analysis.