Research On Proactive Eavesdropping Strategies Based On Physical Layer Security

Wireless communication technology has broken the time and space constraints,and brought great convenience to people's work and life,making high-speed wireless connections can be accessed anytime and anywhere,such as online payment,online office,and palm banking.However,due to the broadcast nature of the wireless channel and the openness of the air interface,wireless communication is vulnerable to malicious attacks.And it is also extremely easy to be abused by suspicious users to conduct illegitimate information interaction with advanced wireless transceiver equipment.In response to this problem,from the perspective of national security,government departments need to utilize effective monitoring methods to monitor and interfere with potentially suspicious communications in wireless networks.Motivated by this,this dissertation starts from the legitimate monitoring strategies based on physical layer security,focusing on the proactive eavesdropping strategies for friendly relay assisting legitimate monitor and suspicious relay assisting potential suspicious users.The specific research contents and main contributions of this dissertation are summarized as follows:(1)The basic theory and mathematical model of the Rayleigh fading channel are first reviewed,and the relaying protocols in the wireless cooperative communication system are studied.The modes and signal sending receiving methods of two protocols are further emphasized,and the characteristics are also compared.Meanwhile,the theoretical basis of proactive eavesdropping and full-duplex(FD)technology are introduced.(2)Aiming at the problem that the monitor is far away from the suspicious users in order to avoid being detected,which affects the eavesdropping performance,a proactive eavesdropping scheme based on FD relay is proposed.Considering that the relay adopts the decode-and-forward protocol,which decodes and forwards the eavesdropped suspicious information to the central monitor and causes co-channel interference to the suspicious receiver simultaneously,thereby the suspicious communication rate is reduced to improve the monitoring performance.First,the closed-form expressions are derived,including the connecting outage probability for the suspicious link and the eavesdropping outage probability for the eavesdropping link.And the analytic expression of the average eavesdropping rate is also obtained.Secondly,in order to maximize the average eavesdropping rate and promote legitimate surveillance performance,the jamming power and location deployment at the relay are optimized.For power optimization,the closedform value of approximate optimal relay jamming power with fixed relay position is deduced and an algorithm for maximizing the average eavesdropping rate based on the bisection is further proposed to verify the correctness of the approximate result.For location optimization,the optimal relay location deployment with optimal relay jamming power is numerically evaluated.Finally,the simulation results validate that the proposed scheme achieves better eavesdropping performance than that without optimization,which can be used to guide the parameter design of eavesdropping relay nodes in proactive eavesdropping scenarios.(3)Aiming at the scenario where suspicious users utilize suspicious relay nodes to extend their communication range to enhance signal transmission quality,a proactive monitoring mechanism is designed to adaptively choose the optimal eavesdropping mode,according to the surveillance performance.Considering a dual-hop suspicious communication network,the suspicious relay adopts the amplify-and-forward protocol to assist suspicious communication.In accordance with the channel conditions,the legitimate monitor adaptively selects among the following three eavesdropping modes:first eavesdropping and then jamming,always eavesdropping in both time slots,and first jamming and then eavesdropping.First,the closed-form expressions are derived,including accurate and approximate values,namely suspicious connecting outage probability and eavesdropping outage probability,under three different eavesdropping modes.And the corresponding eavesdropping non-outage probability is also obtained.Secondly,aiming at the problem of limited application scenarios of a single eavesdropping scheme,based on the three eavesdropping modes,an optimal eavesdropping mode selection method for maximizing the eavesdropping non-outage probability is further presented.Finally,the simulation results show that compared with the existing first eavesdropping and then jamming scheme,the first jamming and then eavesdropping scheme has better eavesdropping performance.The optimal eavesdropping mode selection method significantly ameliorates the surveillance performance,and increases the eavesdropping non-outage probability.Moreover,the monitor can adaptively choose a suitable eavesdropping mode in different signal-to-noise ratio regimes to achieve the optimal performance,which solves the problem of incompatibility in a single eavesdropping scenario.