Opportunistic cognitive relaying with network and superposition coding for multiple secondary receivers in primary MAC

In this paper, we propose a cognitive relaying protocol using network and superposition coding in primary multiple access channels (MAC), where two licensed primary transmitters PT₁ and PT₂ transmit to a common receiver PR with the assistance of an unlicensed secondary transmitter ST that acts as a relay. Furthermore, we analyze the opportunistic transmission among the multiple secondary receivers (SRs) in order to improve the performance of secondary system. The secondary transmitter ST attains the opportunity of spectrum sharing by relaying the primary users´ messages. Network coding and superposition coding are utilized at ST that superimposes its own message on network-coded primary signals. ST transmits its own signal to a best secondary receiver b*, SR_b*, which is selected with opportunistic strategy. In this paper, the probabilities of outage region are computed for MAC as well as the achievable region. Based on the probabilities of these regions, we analytically derive the outage probabilities for both the primary and secondary systems under the cognitive relaying protocol with opportunistic secondary transmission in primary MAC.