Research On Wireless Physical Layer Security Technology Based On Direction Modulation

Directional modulation(DM),as an emerging physical layer security technology,can be utilized to enhance the wireless network transmission due to its directivity.With the increasing number of users in wireless network and the worser environment,it is still important to ensure the confidentiality of information and the security of communication.Simultaneously,in practical applications,due to the great demand of data,densely distributed small and medium cells and large-scale antenna arrays will bring higher hardware costs and energy consumption.Therefore,how to reasonably utilize other physical layer security technologies in DM system so that the system can obtain a good trade-off between energy consumption,cost and performance is particularly significant for DM-based wireless secure transmission.This thesis focuses on the physical layer security technology in the context of DM system.Our main contributions and innovations are as follows:1)In order to study the influence of the phase error caused by finite-quantized digitalcontrolled phase shifter on DM system,a model is established based on the DM transmitter with an analog beamforming structure.The closed-form expression of the secure performance with respect to the number of quantization bits is derived though the law of large numbers,including the signal-to-interference-plus-noise ratio(SINR)of target receiver and secrecy rate(SR)of system.The expressions and simulation results both show that the loss of secure performance gradually decreases as the number of quantization bits increases.When the number of quantization bits is greater than or equal to 3,the loss of SINR is less than 0.3 d B.Compared with the case of finite quantization bit,the performance gain of SR is less than 0.1bits/s/Hz when the number of quantization bits is infinite.The derived expression provides an effective guidance for how to choose the minimum number of quantization bits for phase shifters,so that a good balance between system performance and hardware cost can be achieved.2)In response to the problem of only one confidential bit stream(CBS)transmission limitation of DM system in point-to-point multiple-input multiple-output(MIMO)free space,a passive intelligent reflecting surface(IRS)with no self-interference is introduced so that two confidential messages can be simultaneously transmitted to legitimate users.Firstly,two alternating iterative algorithms are proposed to jointly design transmit beamforming vectors and IRS phase-shift matrix.To maximize the SR,a high-performance general alternating iterative(GAI)algorithm is proposed,and the gradient ascent algorithm is used to ingeniously solve the constant modulus constraint of the phase-shift matrix.Additionally,in order to force the two channels of CBS to be spatially independent in space,another low-complexity nullspace projection(NSP)algorithm is proposed.Here,each CBS is transmitted separately in the null-space of other channels and cannot be leaked to eavesdropper.Simulation results show that the proposed GAI and NSP can both achieve a high SR performance with IRS helped.Moreover,the convergence of the proposed algorithm can be ensured within several iterations,which verified the feasibility of proposed methods.Due to the IRS,the friendly multipath links can improve SR and overcome the limitation of DM system in white gaussian channels.In this case,the proposed algorithms can nearly double the secrecy rate in the case of dual CBS transmission than single CBS.Furthermore,the optimal position of IRS is analyzed through simulation.