Outage performance of cognitive DF relay networks with nonidentical Rayleigh fading channels and maximal ratio combining

In the expression of end-to-end signal-to-noise ratio (SNR) of cognitive relay networks, the channel gaina of the interference links (from secondary nodes to primary nodes in the networks) are usually shared by multiple items in the expression. These shared variables lead to the so called correlation issue, which results in the higher complexity of outage performance analysis for such networks. Till now, for cognitive relay networks with decode-and-forward (DF) relay scheme, we have not found works obtaining explicit closed-form expression of exact outage probability (OP) meanwhile treating the correlation issue completely. In this paper, for cognitive DF relay networks with maximal ratio combing (MRC) and independent non-identical Rayleigh fading channels, we obtain a closed-form expression of exact OP taking consideration of the correlation issue completely. Additionally, by shrinking or expanding the triangular integral region to suitable rectangular regions, we obtain simpler closed-form expressions of the lower and upper bounds of both OP and symbol error probability (SER). Furthermore, the asymptotic expressions of OP and SER are also obtained. The correctness of our analysis results are verified through numerical simulations. Both analysis results and simulation results show that how the correlation issue is treated can affect the coding gain whereas has no effect on the diversity gain of the network. Simulation results also indicate that, exact OP and SER are bounded from both sides by the lower bound and the upper one tightly, whereas the upper bounds of OP and SER are more tighter than the lower bounds.