Research On Covert Surveillance And Secure Transmission In Wireless Communication Network

Covert Surveillance is studied for a wireless eavesdropping system,where a full-duplex legitimate monitor eavesdrops a suspicious link with artificial noise(AN)assistance.Different from the existing work,the suspicious receiver is assumed to be capable of detecting the presence of AN.Once such receiver detects the AN,the suspicious user will stop transmission,which degrades the surveillance performance.Hence,to improve the surveillance performance,AN should be transmitted covertly with a low detection probability.Under these assumptions,an optimization problem is formulated to maximize the eavesdropping non-outage probability under a covert constraint.Then,based on the detection ability at the suspicious receiver,a novel scheme is proposed to solve the optimization problem using an iterative search.Moreover,we investigate the impact of both the suspicious and the jamming links uncertainties on the covert surveillance performance.Simulations are performed to verify the analyses.We show that the suspicious link uncertainty enhances the surveillance performance,while the jamming link uncertainty can degrade the surveillance performance.Moreover,secrecy transmission is investigated,where active and passive eavesdroppers coexist in a wireless network.Active eavesdroppers who not only overhear the legitimate information but also jam the legitimate signal,and passive eavesdroppers who only overhear the legitimate information.We proposed a two-fold zero-forcing jamming and beamforming scheme.By taking the instantaneous channel state information between the jammer and the active eavesdropper into account,the total transmission power allocation between the legitimate receiver and eavesdroppers is optimized to maximize the achievable secrecy rate.Numerical results show that the proposed scheme can achieve better secrecy performance than the conventional AN scheme with beamforming.The main contributions of this paper are summarized as follows:1.This paper consider a wireless surveillance system,where a full-duplex legitimate monitor eavesdrops the suspicious communication with AN assistance.Different from the previous works,the suspicious receiver is capable of detecting the AN signal.Specifically,if the suspicious receiver detects the AN from the legitimate monitor,it will inform the suspicious transmitter to stop transmitting.Hence,the AN from the legitimate monitor should be injected covertly.For this case,the performance of the surveillance system under a covert constraint is investigated for the first time.2.Considering that channel uncertainty is inevitable in practice,we analyze the suspi-cious receiver's AN detection ability under channel uncertainties in the suspicious link and the jamming link.Interestingly,we find that the AN detection ability at the suspicious receiver decreases with the suspicious link uncertainty,while it has a non-monotonic relationship with the jamming link uncertainty.For the extreme case of perfect suspicious link channel knowledge,the legitimate monitor cannot inject AN to assist its eavesdropping.By contrast,when there exists uncertainty for the suspicious link,even if the suspicious receiver has perfect knowledge of the jamming link,the legitimate monitor can still inject AN without being detected.3.We investigate the impact of channel uncertainty on the eavesdropping non-outage probability for the proactive surveillance scheme.Numerical results reveal that the suspicious link uncertainty enhances covert surveillance performance.By contrast,the jamming link uncertainty affects the surveillance system performance only when the AN power introduces a higher level of interference power at the suspicious receiver than the self-interference power at the legitimate full-duplex monitor.4.Considering the active and passive eavesdroppers coexist in a wireless network,we propose a cooperative zero-forcing jamming scheme.In the proposed scheme,a multi-antenna jammer treats the active and passive eavesdroppers differently.Since both the instantaneous channel state information of the active eavesdropper link and partial channel state information of the passive eavesdropper links are exploited,the total transmission power is allocated among the legitimate information signal,AN for the active eavesdropper,and AN for the passive eavesdroppers to maximize the secrecy rate.Numerical results show that the proposed jamming scheme can significantly improve the secrecy rate.