Cooperative Diversity in Cognitive Relay Networks using Different Coding Techniques

Cognitive radios (CR) represent new technique that can effectively improve the spectrum efficiency of future wireless networks. In this paper, the problem of cooperative relay in CR networks will be investigated for further improve network performance. A scenario in which a secondary transmitter can communicate with a secondary receiver via a direct communication link or a relay channel will be considered. Cooperative relay communications or cooperative diversity has emerged as a promising technique to combat fading in wireless communications. Two well-known cooperative diversity are known as Decode –And-Forward (DAF) and Amplify-AndForward (AAF). In this paper, the DAF strategy will be considered, which achieves diversity by using Maximal Ratio Combining (MRC) and Fixed Ratio Combining (FRC). Convolutional Code (CC) and Low Density Parity Check (LDPC) will be investigated which is not clarified until now. The analysis of the system will be made. From simulation results; we can conclude that by using both of the direct and relay channels, the transmission performance of the secondary system can be improved significantly. Moreover, by exploiting the cooperative spectrum sensing technique for applications in relay based cognitive radio network, it is seen that detection probability increases by using relay channel. Comparisons between convolutional code for different rates will be made under using AWGN. Also, the effect of the positions of the relay will be studied. The best performance was achieved when the relay is at equal distance from the sender and the destination or slightly closer to the sender in the case of MRC and FRC.