Research On Physical Layer Security In Wireless Cooperative Communication Networks

With the rapid development of information techniques,the number of wireless communication devices is exploding and the communication frequency bands keep getting higher.In order to relieve the pressure of power consumption and expand the coverage of wireless networks,two low-power cooperative relaying techniques,including the simultaneous wireless information and power transfer(SWIPT)enabled relay and intelligent reflecting surface(IRS),can be adopted.However,due to the open nature of wireless environment and the increasing calculating performance of computers,traditional encryption methods may not be sufficient to ensure the information security for wireless cooperative networks in the future,and private messages may be under huge risk of eavesdropping.Fortunately,physical layer security technique points to a new direction for solving above challenges.Aiming at solving security problems in both SWIPT-enabled relay and IRS cooperative communication networks,the cooperative jamming scheme is focused and optimization algorithms are proposed in the thesis,to maximize the secrecy capacity(SC)of the system.The main research work is as follows:(1)The basic concept of physical layer security and the definition of the SC are first studied.Several typical architectures of SWIPT receivers and their signal models are described,and then the hardware structure of IRS and corresponding channel models are analyzed.Finally,the basic theory and algorithm flow of related optimization methods are summarized.(2)For security problems in SWIPT-enabled relay network,the full-duplex destination-aided jamming scheme is proposed to guarantee the safe communication between legitimate users.A joint optimization problem on the power splitting(PS)ratio of the relay and power allocation(PA)coefficient of the system are established to maximize the SC,considering that the relay needs to perform information decoding and energy harvesting concurrently,and the system needs to allocate the power of information and jamming signals from source and destination,respectively.And then an alternating optimization(AO)algorithm is proposed to decompose the problem into two sub-problems on the PS and PA ratios,respectively,and their closed-form expressions are obtained.Simulation results show that the two closed-form solutions matches well with the optimal results obtained by exhaustive search,and the proposed AO can achieve fast convergence and obtain the same security performance with much lower computational complexity than that of the exhaustive search.(3)For the security in the IRS cooperative communication network,a jamming strategy based on full-duplex receiver transmitting the AN is proposed.To maximize the SC,an optimization problem is formulated for jointly designing parameters,including the transmit beamforming of base station,phase shifts of the IRS and PA coefficient of the system.Considering that the problem is nonconvex,an efficient AO algorithm is developed to decompose the problem into three sub-problems,and the closed-form optimal solutions of transmit beamforming and PA coefficient are obtained,and the optimal phase shifts of the IRS are also derived with the help of two optimization algorithms,that is,semidefinite relaxation programming(SDR)and Riemannian manifold optimization(RMO).Simulation results show that the SC performance curves overlap based on RMO and SDR,while the computational complexity of the former is lower.Compared with benchmark schemes of using random phase shifts and fixed PA coefficient or beamforming vectors,theoretical optimal solutions can achieve higher SC and obtain better security performance for the network.