Research On Secrecy Outage Probability In Antenna Selection Systems

Security is considered to be one of the key issues in 5G systems, and physical layer security based on information theory is a new focus of researches. Multiple antennas can enhance the confidentiality of wireless communications by using the characteristics of channels. Considering secrecy problems in antenna selection (AS) systems, this dissertation investigates the secrecy outage probability and its related properties. Secrecy effects of weighting errors, switch combining and non-identical channel conditions are analyzed. Also, novel schemes are explored with the aim of security enhancement. The main contributions are listed as follows:1. Secrecy outage effects of channel estimation errorsSince the secrecy performance is affected by estimation errors, statistical properties and secrecy outage probabilities are analyzed through the measure of power correlation coefficients. The saddle point method is introduced to obtain the new cumulative distribution function (CDF) and the asymptotic outage probability. It shows that secrecy outage can be decreased by 30% as long as the antenna number is allocated appropriately.2. Secrecy analysis of switch-and-examine combining (SEC) at the receiverIn the scenario with limited requirement at the legitimate receiver, secrecy performance of transmit antenna selection along with receive SEC is studied. Closed-form expressions of secrecy outage probability are derived. The outage diversity order is shown to be NA, which is equal to the number of transmit antennas. Moreover, an optimal switching threshold is calculated to improve the secrecy performance. The full diversity order is obtained, which is equal to the product of antenna numbers at the transmitter and the legitimate receiver.3. AS schemes with the consideration of securityIn the distributed antenna systems, the selection that exploits the feedbacks from both the legitimate receiver and the eavesdropper is proposed. Secrecy outage expressions are then calculated. Meanwhile, a new information-guided selection scheme is proposed. Through hiding information in the channel symbol space and the radiated symbol space, the outage probabilities based on the qualities of the two channels are derived accordingly.4. Joint antenna and user selection in multiuser scenariosIn the virtual antenna selection system, suppose that there are several eavesdropping users, the joint probability density function (PDF) and the corresponding secrecy outage are derived. Then, an eavesdropper is supposed to be outside, secrecy outage results are calculated for the different average channel qualities of users. Moreover, an efficient closed-form derivation is presented to evaluate the ε-outage secrecy capacity. It realizes a theoretic approximation rather than the numerical root-finding, in which the difference can be smaller than 5%.Based on the above four aspects, secrecy performance of AS systems in physical layer is analyzed in the view of secrecy outage probability. New AS schemes are also studied to guarantee the secure transmissions for certain scenarios. Currently, as one of the key technologies in physical layer security area, AS has been adopted in the researches of 5G National 863 Plan Projects.