Research On Secure Precise Wireless Transmission Based On Directional Modulation

With the rapid development of mobile communication in recent years,the demand for wireless communication technology in various scenarios is increasing.Due to the broadcast characteristics of wireless channel,a large number of private information in the communication process is vulnerable to be eavesdropped and attacked.This is also a great challenge for wireless communication in recent years.The traditional communication method based on encryption technology is not suitable for the wireless internet with high privacy requirements because its secret key exchange needs an additional secure channel,which may also be eavesdropped in the communication process.As a physical layer security technology,directional modulation(DM)can achieve secure transmission without using security key.In recent years,it has gradually come into people's view,and has been widely concerned by the academic community.Based on DM,this paper focuses on the secure precise wireless transmission(SPWT)technology,which is divided into two parts.Firstly,the practicability and robustness of SPWT are studied,including sub-carrier selection method,SPWT system with hybrid analog-to-digital structure and SPWT beamforming algorithm with measurement error.Then,the implementation of SPWT in different scenarios is studied.The main research work and innovation are as follows.(1)Traditional SPWT schemes can only guarantee the average security performance,but in practical applications,SPWT based on random subcarriers selection method can not guarantee the security performance for each single symbol.In order to achieve SPWT for every transmitted private symbol,we propose two subcarriers selection methods,i.e.the randomization method of quadratic subcarrier sequence and prime subcarrier sequence.Specifically,the impact of subcarriers on the security performance of SPWT system is studied first,and a randomization scale is defined.It is analyzed that the larger the randomization scale of subcarriers,the better the security performance of the system.Then,based on this conclusion,all generated subcarriers are grouped and modulated,and the remaining subcarriers sequences are zeroing block interleaved.After repeated sufficient times,a secure random subcarriers sequence is obtained in the end.The simulation results show that the two schemes can significantly reduce side-lobe height and improve the security performance in practical application.(2)In order to reduce the complexity of traditional full digital SPWT system,a hybrid digital and analog(HDA)SPWT scheme is proposed.Based on the HDA model,a method based on maximizing signal to leakage and noise ratio(SLNR)is proposed to obtain the digital beamforming vector and analog beamforming vector,and next the optimal artificial noise vector is obtained based on the artificial noise to leakage and noise ratio(ANLNR)method.Finally,the complexity of the scheme is analyzed and compared with the traditional full digital beamforming(FDB)method.The simulation results show that the security performance of the proposed scheme is very close to the traditional FDB scheme,and the complexity is significantly reduced.(3)To address the problem of error existing in measurement of expected direction angle and distance in SPWT,we propose a robust SPWT algorithm for transmitting the privacy information to the desired receiver measurement error region.At the same time,to address the problem that the expected measurement error is a probability function and the single measurement error is uncertain,a regional robust SPWT algorithm is proposed.Specifically,the error region of the measured expected users and eavesdropper are set as the secure region and wiretap region,respectively,then,let the energy of the privacy information in the security region to be the largest,while the privacy information in the eavesdropping region is the smallest,thus SPWT can be achieved.Based on this background,we first propose a method based on maximizing the regional SLNR of secure region to obtain the optimal beamforming vector,so that the energy of privacy information is concentrated in the security region,while only a few privacy information energy is leaked into the wiretap region.Then,a method to maximize the ANLNR of the wiretap region is proposed,which makes the artificial noise concentrate on the wiretap region to interfere the eavesdropper,and makes the energy of the artificial noise leaking to the secure region smaller.Finally,we propose a low complexity algorithm based on energy maximization of main lobe points.Simulation results show that the proposed two region robust SPWT algorithms can achieve SPWT with considering the measurement error,and their SR is significantly higher than that of the non-robust SPWT algorithm.(4)Considering the different application scenarios of SPWT,a more practical 3D(3dimension,3D)SPWT algorithm with both azimuth angle and pitch angle is proposed.At the same time,intelligent reflecting surface(IRS)is introduced to achieve SPWT by using reflection path to solve the problem that the expected user's direct path may be blocked by obstacles.Specifically,considering the single user scenario with unknown eavesdroppers' location,the optimal transmitter beamforming vector and the optimal IRS reflection phase are obtained by maximizing the signal to interference and noise ratio(SINR).Then,considering the multi-user scenario,the unexpected users are regarded as eavesdroppers,and the optimal solution is obtained by maximizing the security rate(SR)method combined with convex optimization.Finally,a low complexity alternating iterative algorithm based on maximizing SLNR and SNLNR is proposed,which can significantly reduce the complexity of the maximizing SR method.The simulation results show that the multiple IRS-aided SPWT algorithm can form a single confidential signal energy peak in the desired user's location for the single user scenario,while out of the desired user's location,the SINR is very small and far lower than that of the desired user.In the multi-user scenario,the security rate of the two multi-IRS-aided algorithms are significantly better than that of the traditional methods without IRS.(5)Considering that in the 3D UAV-based scenarios,the position of UAV can be changed as transmitter.Compared with the traditional SPWT model,transmitter,expected receiver and eavesdropper are located on fixed positions,which limited security performance.Therefore,we propose an optimal transmitter position scheme based on UAV SPWT system.Firstly,we determine the beamforming vector and AN vector of the transmitter by maximizing the SINR of desired user.Then the SINR expression of the eavesdropping receiver is derived,and the steering vector solution which makes the SINR of the eavesdropper to be zero can be obtained.Finally,two different minimum receiver power solutions are obtained through azimuth angle and pitch angles,respectively.The simulation results show that the transmitter position obtained by the scheme can significantly improve the SR compared with the traditional method of non transmitter position designing scheme.Moreover,as the eavesdropper is at the zero point of SINR,the transmitter can concentrate all the power on transmitting confidential messages,and the AN can be eliminated in the system,which not only enhances the energy efficiency,but also reduces the artificial noise memory consumption of the transmitter.