Performance of Cooperative Diversity in Cognitive Relay Networks

In a network with dynamic spectrum access, secondary users equipped with frequency-agile cognitive radios communicate with one another via spectrum that is not being used by the primary users or licensed users of the spectrum . We consider a scenario in which a secondary transmitter can communicate with a secondary receiver via a direct communication link or a relay channel. Cooperative relay communications or cooperative diversity has received a lot of attention in recent years. Two well known cooperative strategies are known as Amplify And Forward (AAF) and Decode And Forward (DAF). In this paper, the AAF strategy will be considered, which achieves diversity by using Maximal Ratio Combining (MRC) and Fixed Ratio Combining (FRC) which is not clarified until now. From simulation results, we can conclude that using both of the direct and relay channels, the transmissions performance of the secondary system can be improved significantly , Moreover, exploiting cooperative spectrum sensing technique for applications in a relay based cognitive radio network , it is seen that detection probability increases by using relay channel . The best performance was achieved when the relay is at equal distance from the sender and the destination or slightly closer to the sender.