In this study, the authors evaluate secrecy performance of cooperative protocols with relay selection methods under impact of co-channel interference. In particular, the authors propose an optimal selection scheme to maximise the secrecy capacity obtained at the cooperative phase. In addition, the authors also consider suboptimal and random selection schemes which reduce the complexity of implementation, when compared with the optimal one. For performance evaluation, the authors derive exact and asymptotic closed-form expressions of secrecy outage probability and probability of non-zero secrecy capacity for the considered schemes over Rayleigh fading channels. Monte Carlo simulations are performed to validate the derivations.

In cognitive spectrum sharing systems, interference probability (IP) is one of the most important performance metrics illustrating the interference level at the primary network. In this paper, the interference probability of the primary network due to secondary underlay partial relay selection networks is investigated under the assumption of imperfect channel state information (CSI) of interference links. Numerical results show that it depends not only on the correlation efficient of interference links but also on the transmit power of secondary transmitters. It is also shown that the back-off technique is an efficient approach to guarantee the given quality of service (QoS) of the primary network. For secondary networks, we derive the outage probability over Rayleigh fading channels. Monte-Carlo simulations are performed to verify the correctness of the analysis.Index Terms-Cognitive radio, imperfect CSI, outage Probability, interference probability.

In this paper, the secure communication of a cognitive radio network (CRN) over Nakagami-m fading channel is investigated. An underlay protocol is used in the considered network, where the unlicensed users or secondary users (SUs) can operate simultaneously with the primary users (PUs) in the same spectrum bands providing that the transmit power of the SUs is constrained by not only the maximum tolerance interference at the PU's receiver but also the maximum transmit power at the SU's transmitter. The exact closed-form expressions of important secure performance metrics, i.e., secrecy outage probability (SOP) and secrecy capacity (SC), are derived. In addition, to give a deep insight into the secure performance trends, the asymptotic expression of the SOP is also obtained when the average signal-to-noise ratio (SNR) of the legitimate channel is high. It is proven that the considered system achieves full diversity gain regardless of the number of antennas at the eavesdropper. Finally, the correctness of our mathematical framework is verified by Monte Carlo simulations. Index TermsPhysical layer security, cognitive radio networks, secrecy outage probability, wiretap channel, multiple antennas.

Abstract-In this paper, we introduce a mathematical approach for system-level analysis and optimization of densely deployed multiple-antenna cellular networks, where low-energy devices are capable of decoding information data and harvesting power simultaneously. The base stations are assumed to be deployed according to a Poisson point process and tools from stochastic geometry are exploited to quantify the trade-off in terms of information rate and harvested power. It is shown that multiple-antenna transmission is capable of increasing information rate and harvested power at the same time.