Research On Physical Layer Security In Wireless Networks With Possion Spatially Distributed Eavesdroppers

The broadcast nature of wireless medium makes the wireless communications vulnerable to eavesdroppers. By contrast, using the randomness of wireless channels to improve the security performance,physical layer security (PLS) demands less computation and can secure the transmission in a low complexity. Thus, there has been a growing interest in PLS.However, in most works of PLS, the authors didn’t consider the relative physical locations of the legitimate uses and the eavesdroppers,and large-scale path loss was ignored. It is difficult for us to obtain the location information of the eavesdroppers since they work in a passive way.Recently, with the help of stochastic geometry theory, PLS in large-scale wireless networks has been receiving more and more attention. And Possion point process (PPP) is widely used for modeling the locations of spatially random nodes especially the locations of unknown eavesdroppers.How to secure the transmission in wireless networks with spatially random eavesdroppers is an issue worth considering. In two kinds of wireless network where the eavesdroppers are randomly distributed according to a PPP, the dissertation uses cooperative jamming to improve the security performance of the systems. In the process of analysis and research with the help of PPP theory and optimization method, the major contributions of the dissertation are summarized as follows:First, the dissertation studies the PLS in point-to-point wireless networks with Possion spatially distributed eavesdroppers. The source uses the wiretap code to encode the confidential message, and it is allowed to use part of its power to transmit cooperative jamming signals which can be completely removed from the signal received at the destination. Based on point process theory, the dissertation derive the closed-form expressions for the connection outage probability and the secrecy outage probability to characterize the reliability and the security performance, respectively. And the expressions for outage probability are validated through Monte Carlo simulations. Both theoretical derivation and simulation results show, for the system, a higher transmit signal to noise ratio (TSNR) and a lower codeword transmission rate lead to a lower connection outage probability,a higher TSNR and a lower redundancy rate of the wiretap code lead to a higher secrecy outage probability. Considering both the reliability and the security performance, the dissertation use the secrecy throughput to evaluate the overall performance. And the dissertation determine the optimal power allocation factor and wiretap code rates which maximize the secrecy throughput of the wiretap channel under secrecy outage probability constraint.Then the dissertation considers the PLS in cognitive radio networks with Possion spatially distributed eavesdroppers. The use of underlay spectrum sharing is considered in the system. Under an interference constraint set by the primary user, the secondary source uses cooperative jamming to improve the security performance of the secondary system.The dissertation derive the closed-form expression for the connection outage probability and an easy-to-compute expression for the secrecy outage probability to characterize the reliability and the security performance, respectively. Both theoretical derivation and simulation results show, for the secondary system, a bigger distance between the secondary source and the primary, and a lower codeword transmission rate lead to better reliability performance, a bigger distance between the secondary source and the primary, and a lower redundancy rate of the wiretap code lead to worse security performance. Considering both the reliability and the security performance, the dissertation use the secrecy throughput to evaluate the overall performance of the secondary system.Then the dissertation determine the optimal power allocation factor and wiretap code rates which maximize the secrecy throughput of the secondary system under interference constraint and secrecy outage probability constraint.