Research On Key Technologies Of Secure Transmission And Precise Jamming In Wireless Communication

With the explosive increasing of demand for data services and wireless applications,wireless communication technology has developed rapidly.However,due to the broadcast and open nature of wireless transmission,wireless signal is vulnerable to be eavesdropped and tampered by illegal users.Information security is playing a more and more important role in wireless networks.Physical layer security technology can reduce the ability of illegal eavesdroppers to intercept confidential message by utilizing beamforming and artificial noise(AN),so as to effectively improve the security of information transmission.This thesis focuses on the research on secure wireless information transmission and precise jamming.Our main contributions and innovations are as follows:1)In order to significantly weaken the ability of sensitive eavesdroppers,a secure integrated framework of precise jamming and communication is constructed by utilizing random subcarrier selection,directional modulation,and beamforming under phase alignment constraint(PAC).Two good-performance beamforming algorithms: minimum transmit power(Min-TP)and minimum regularized transmit power(Min-RTP)are proposed.The latter is proposed by introducing regularized penalty to address the singular problem of the former.Simulation results show that in the medium and high signal-to-noise ratio(SNR)regions,the proposed Min-TP and Min-RTP algorithms perform much better than existing equal amplitude and null-space projection algorithms in terms of secrecy rate.The performance of Min-RTP is slightly better than that of Min-TP.The secrecy performance difference between the proposed two beamforming algorithms becomes trivial as the number of transmit antennas approaches large.Specifically,the proposed two beamforming algorithms form two main energy peaks at Eve and Bob,respectively,which effectively interferes with eavesdroppers and increases the secrecy rate of the desired receiver.2)In order to achieve a good balance between secrecy performance and circuit cost,a secure hybrid digital and analog beamforming algorithm based on mixed digital-to-analog converter(DAC)is proposed in the millimeter wave communication system.Namely,the mixed-DAC architecture consists of cheap low-resolution DAC and expensive full-resolution DAC.On the basis of the above,a closed-form approximation expression of the average secrecy rate(ASR)with partial eavesdropping channel knowledge available is derived.Then,by means of maximizing ASR criterion,a secure alternating iteration hybrid beamforming framework is proposed.The basic idea is to combine Dinkelbach plus Majorization-Minimization methods to optimize analog beamforming subject to constant module constraint,and design confidential message beamforming and AN beamforming vectors by low-complexity gradient descent algorithm.Simulation results show that the proposed alternating iteration algorithm can achieve a higher ASR performance than existing algorithms in the medium and high SNR regions.Moreover,the proposed algorithm performs much better in the mixed-DAC architecture.