Outage Analysis of Orthogonal Space–Time Block Code Transmission in Cognitive Relay Networks With Multiple Antennas

The outage performance of cognitive relay networks (CRNs) for a decode-and-forward (DF) protocol in a spectrum sharing scenario with orthogonal space-time block code (OSTBC) transmission is presented in this paper. Both the exact formulas of the outage probability and its approximation in a high-SNR region are derived over Rayleigh fading channels. The theoretical results are validated by simulations. It shows that there is an outage saturation phenomenon due to both the maximum transmit power limit and the interference power constraint, which is similar to CRNs with a single antenna. Meanwhile, our results also show that increasing the number of antennas may not improve the outage performance when the interference power constraint or the transmit power constraint is very small; however, it will significantly improve the outage performance when the number of antennas is large enough. Through the asymptotic analysis, it shows that the CRN where the source and the relay are both equipped with N antennas can achieve full degree of diversity, i.e., 2N-order diversity.