Research On Proactive Legitimate Eavesdropping Over Wireless Communication System

Wireless communication technology has brought huge conventince to our life,while it also take new challege to communication security.With the application of online payment and online bank,wireless network is an indispensable part of people's daily lives.However,since the wireless air interface is open and accessible to all people and the broadcast nature of wireless network,wireless communication networks are likely to be used by criminals and terrorists to facilitate crime activities.Then there should be a government-authorized legitimate monitor to eavesdrop and intervene the suspicious communications over wireless network to prevent crime activities from worsening.Motivated by the above observations,we investigate the wireless information surveillance in this dissertation.First,considering the large-scale distributed communication nodes,an proactive eavesdropping scheme over multiple suspicious links is proposed.The legitimate monitor intervenes the suspicious links through either interfering or assisting.Meanwhile,considering the power constraint at eavesdropper and the different risk degree of suspicious information,our objective is to maximize risk degree based eavesdropping rate of multiple suspicious links via jointly optimizing their intervention strategies(jamming or spoofing relaying)and the corresponding transmit powers at eavesdropper.The formulated problem is shown to be a MINLP problem,which is complex in general.According to the two different strategies of monitor,we decouple the energy of monitor into jamming energy and relay energy.Then,we decouple the complex MINLP(Mixed Integer Nonlinear Programming)problem into two subproblems: a jamming subproblem and a relaying subproblem.These two subproblems are then solved by the character of successful eavesdropping.Numerical simulations show that our proposed approach can achieve higher eavesdropping rate than conventional eavesdropping approaches.Next,considering the legitimate monitor is an energy limited device,energy consumption of monitor is also an important performance indicator in addition to the eavesdropping rate.Moreover,suspicious transmitter can also take correspinding measures to improve its communication performance,such as adaptive power transmission.Motivated by these,we propose a objective of maximizing eavesdropping energy efficiency under the consideration of successfully eavesdropping ratio and eavesdropping rate,and solve out the optimal eavesdropping scheme between the trade-off of them.What's more,we compare the eavesdropping performance under two different transmission strategies,which are fixed power transmission and adaptive power transmission.Numerical results show that our proposed eavesdropping schemes outperform the proactive jamming scheme and average-power eavesdropping scheme.In addition,our proposed eavesdropping scheme can solve the game problem caused by the adaptive power transmission of suspicious transmitter.Finally,when the legitimate monitor need eavesdrop multiple suspicious links within the area of surveillance,the legitimate monitor can be overload when there are too much suspicious links required to be eavesdropped at the same time,and the monitor cannot guarantee the eavesdropping performance of some suspicious links far away.We propose a cooperative eavesdropping scheme,where a primary legitimate monitor and an assistant legitimate monitor cooperatively jam the suspicious links.The price of the cooperation is the jamming energy transfer from primary monitor to assistant monitor.The objective is to maximize the eavesdropping energy efficiency of our proposed cooperative eavesdropping scheme.Furthermore,the formulated problem is still a MINLP problem.To solve the problem efficiently,a threshold-based policy of optimal jamming power allocation is proposed.Therefore,the original optimization problem is decoupled into two sub-problems: the selection of optimal eavesdropper and the selection of optimal jammer.Numerical results show that our proposed cooperative eavesdropping achieves higher eavesdropping energy efficiency and eavesdropping rate than other eavesdropping schemes.