Opportunistic and cooperative hybrid spectrum access protocol for cognitive radio network

This paper presents a hybrid opportunistic spectrum access (OSA) and cooperative spectrum sharing (CSS) protocol for cognitive radio networks. In the proposed protocol, secondary (i.e. cognitive) network (SN) switches its mode between OSA and CSS based on the state of primary network (PN). The activity status of PN is modeled as a two state discrete time Markov chain model in which steady state probabilities of PN are used to derive the outage probability of the hybrid system. Due to hybrid nature of the protocol, SN is always benefited since it can communicate either via OSA or CSS mode. In CSS mode, we analyze a two-phase hierarchical spectrum sharing protocol based on cooperative decode and forward relay transmission wherein it is assumed that the secondary system is equipped with multiple antennas. Closed form expressions for outage probability have been derived for both SN and PN. Through the theoretical and simulation results, the effect of network parameters, such as steady state probability of primary transmitter (PT), the distance between primary and secondary nodes, the transmit power at secondary transmitter (ST), has been shown on the performance of SN. The performance of the proposed scheme has also been validated by comparing it with conventional OSA. The numerical results show that the hybrid approach outperforms the conventional OSA.