Research On Physical Layer Security Transmission Design In Wireless Networks

Owing to the inherent broadcast nature of wireless medium,confiden-tial messages in wireless systems are highly vulnerable to eavesdropping at-tacks,which poses a major challenge to the transmission of confidential in-formation in wireless networks.Since conventional encryption-based secure approaches have inherent difficulties and vulnerabilities in secret key manage-ment and complexity.It is necessary to use physical layer security technique to ensure the secure transmission of data in different wireless communication scenarios.This paper mainly studies the application of physical layer security transmission technology in two-way relay(TWR)communication scenarios,downlink non-orthogonal multiple access(NOMA)communication scenarios,and energy-limited Internet of Things(IoT)communication scenarios.The con-tribution of this article is described in detail as follows:Firstly,in this paper,the artificial noise(AN)-aided robust secure beam-forming design of multiple-input multiple-output TWR system with physical layer network coding(PNC)is studied in the TWR communication scenario.Two system models are given based on the number of eavesdroppers.For a TWR system with an eavesdropper,two robust beamforming designs are proposed from the perspective of the users' received signal-to-interference-and-noise ratio(SINR).Our aim is to optimize the worst-case secrecy sum rate(SSR)of the systems,where the channel state information(CSI)of the eavesdroppers is imperfect.In low SINR regime,a robust joint beamforming optimization design scheme is given.Since the optimization problem is non-convex,a zero-forcing constraint on AN beamforming is employed,and after approximating the objective function,the non-convex problem is formulated into a semidefinite programming.On the other hand,in high SINR regime,a quality-of-service(QoS)-based robust beamforming design is provided,in which the non-convex problem can be converted to the convex one by employ-ing an approximate technique based on Taylor expansion and semidefinite re-laxation techniques.For the TWR system with multiple colluding eavesdrop-pers,we also designed the robust secure transmission beamforming by combin-ing PNC with AN together,and two secure beamforming optimization architec-tures are established.One secure beamforming design formulation is to min-imize the total transmit power under the users' QoS requirements constraints in the TWR networks,and the other one is to optimize the SSR of the systems under the total transmit power constraint in the worst-case.Numerical results show the efficiency of the proposed schemes.Secondly,in this paper,the confidential transmission problems in the down-link cooperative NOMA communication scenarios are studied,in which base station emits secret messages to two legitimate users in the presence of multiple eavesdroppers.In light of this,a cooperative simultaneous wireless information and power transfer NOMA secure transmission protocol is proposed,where the legitimate user with a stronger channel condition acts as an energy harvesting relay to help that with a weaker channel condition.Following this,a SSR max-imization problem is formulated,under the constraints of transmit power and successive interference cancellation as well as users' QoS requirements.The non-convex problems in the two secure transmission schemes can be converted to convex problems by convex optimization techniques finally.Then the off-the-shelf optimization solvers is employed to solve the convex problem.The simulation results show that the proposed scheme in this paper can improve the security of the downlink NOMA system.Finally,this paper studies the security of data transmission in downlink energy-limited IoT communication scenarios.In the IoT system,the transmis-sion is exposed to multiple eavesdroppers,and all the eavesdroppers collude to form joint receive beamforming,in an attempt to enhance their interceptions.Two different optimization schemes are given to maximize the SSR of the IoT system under the constraints of the transmit power,the users'QoS requirements and the energy harvesting(EH)based on the CSI of the eavesdroppers.For the case that the eavesdropper CSI is unavailable(i.e.,passive eavesdropper sce-nario),the artificial noise-aided secure beamforming scheme is proposed.Since the optimization problem is non-convex,we transform it into convex one by Epigraph Reformulation,instead of two-dimensional search which needs high computation complexity.For the case that the eavesdropper CSI is available(i.e.,active eavesdropper scenario),an orthogonal-proj ection-based beamform-ing scheme is given,and by employing the successive convex approximation method,the suboptimal solution of the optimization problem is found.