Research On Physical Layer Security In IRS-Aided Multiple-Input Single-Output Wireless Powered Communication Networks

In the process of wireless communication network development,two major problems are worthy of further studying.First problem is the energy limitation in traditional wireless networks.Studies have shown that,because of radio frequency signals can carry energy,WPCN is able to power the terminals during signal transmission,which is a very promising and attractive methods to solve the problems of energy limitation in wireless networks.The second problem is information security transmission in wireless channels.PLS technology is an endogenous security mechanism by using the physical characteristics of wireless channels.It effectively overcomes the shortcomings of traditional encryption technology,which makes it widely used in the field of information security.IRS is a technology that has emerged in the field of wireless communication in recent years.By using the reflection characteristics of its surface array elements,IRS can enhance or weaken the targeted signals,which can effectively improve the performance of wireless communication networks.Applying IRS in PLS is supposed to further improve the security of wireless networks to a new level.The main works of this paper is summarized as follows:1.Firstly,aiming at the problem of physical layer security in the MISO WPCN communication system with one terminal node and one eavesdropper,an IRS-assisted physical layer security communication resource allocation scheme is proposed.With the goal of maximizing the security capacity,the scheme jointly optimizes the base station energy beamforming vector,IRS energy reflection coefficient and IRS information reflection coefficient.There is a coupling of multiple optimization variables in this problem,which is nonconvex and difficult to solve.In this paper,we adopt the AO technique to transform the multivariate coupling problem into several sub-problems with one single variable.And then we use fractional programming and SDR technique to convert the non-convex problems to convex ones to solve.The simulation results have shown that the proposed IRS-assisted communication scheme can significantly improve security capacity of the system,which verifies the feasibility of IRS-assisted PLS transmission.2.Secondly,for the problem of physical layer security in MISO WPCN system with multiterminals,a TDMA resource allocation scheme for IRS-assisted physical layer security communication is proposed.The scheme aims at maximizing the security capacity of the system by jointly optimizing base station energy beamforming vector,IRS energy reflection coefficient,IRS information reflection coefficient and time allocation factor.There is a coupling problem of multiple variables in the object function,and it is difficult to solve.We use AO technology to decouple the optimization variables at first.And then we use first-order Taylor expansion and SDP methods to transform the original non-convex problems into solvable convex optimization ones.Finally,we design a SCA algorithm to iteratively search the sub-optimal solution,and we find that this sub-optimal solution is consistent with the optimal solution of the original problem.The simulation results have shown that the proposed optimization scheme can significantly improve the security performance of the WPCN system,which also has very good security performance when the quality of the legitimate channel is relatively poor.