Secrecy outage analysis of multi-user cellular networks in the face of cochannel interference

In this paper, we explore the physical-layer security of a multi-user cellular network in the presence of an eavesdropper, which is made up of multiple users communicating with a base station while the eavesdropper may intercept the communications from users to the base station (BS). Considering that multiple users are available in cellular network, we present three multi-user scheduling schemes, namely the round-robin scheduling scheme, the suboptimal and optimal user scheduling schemes to improve the security of communication (from users to BS) against the eavesdropping attack. In the suboptimal scheduling, we only need to assume that the channel state information (CSI) of the main link spanning from users to BS are known. In contrast to the suboptimal scheduling, the optimal scheduling is designed by assuming the CSI of the main link and wiretap link (spanning from users to the eavesdropper) that are available. We obtain the calculus form of the secrecy outage probability to analyze the secrecy diversity performance. Secrecy diversity analysis is carried out, which shows that the round-robin always achieves only one diversity order, whereas the suboptimal and optimal user scheduling schemes achieve the full diversity order. In addition, the results of the secrecy outage show that the optimal scheduling has the best performance and the round-robin performs the worst in terms of defending against the eavesdropping attack. Lastly, as the number of users increases, both the secrecy outage probabilities of the suboptimal and optimal scheduling schemes have a significant secrecy performance improvement.