Research On The Receiving Beamforming Method Of Directional Modulation Networ

With the rapid development of wireless communication technology,due to the broadcast characteristics of wireless transmission,confidential message can be easily stolen during the communication process.Therefore,the physical layer security of wireless communication has become the research focus of scholars at home and abroad.Directional modulation as a key technology for the secure transmission of the wireless communication physical layer,can realize the directionality of signal transmission,thereby effectively improving the security of wireless network transmission.In actual scenarios,due to the increasing number of users,the addition of a large number of base stations will cause mutual interference of transmitted signals between neighboring base stations.In order to solve this problem,low-cost passive intelligent reflecting surface(IRS)technology is introduced,which not only can effectively isolate the transmission channel,but also provides the possibility of controllable multipath transmission for wireless communication.The thesis is based on the research of DM-based physical layer security transmission technology.The main research contents and innovations are as follows:1)Aiming at the problem of passive eavesdropping of private information in the traditional eavesdropping channel model,a DM system model with full-duplex malicious attackers is first proposed.Discuss the design of receive beamforming(RBF)and artificial noise in this model to improve the security rate(SR)performance of the system,and propose four design schemes:Whitening-filter-based maximum ratio combining(WFMRC)algorithm,Maximizing the secrecy rate(Max-SR)algorithm,low-complexity minimum mean square error(MMSE)algorithm,and Maximizing WF receive power(Max-WFRP)based on the null-space projection(NSP)criterion algorithm.It is worth mentioning that the above-mentioned algorithms all derive closed solutions.The simulation results show that the proposed Max-SR,WFMRC and low-complexity MMSE algorithms have the best SR performance.At the same time,compared with the traditional MRC algorithm,the proposed NSP-based Max-WFRP algorithm has strong robustness to the change of malicious attacker’s transmit power.2)In order to create friendly multipath transmission in the traditional line-of-sight transmission channel environment,IRS technology is introduced into the DM system model.In order to reduce the detection complexity of the receiving end and improve the safety performance of the system,taking the maximum receive power sum(Max-RPS)as the criterion,two designs of RBF and IRS phase shift matrix(PSM)scheme: General alternating optimization(GAO)algorithm and low-complexity NSP algorithm based on null-space projection.The simulation results show that the GAO algorithm and NSP algorithm proposed based on IRS assistance can both improve the SR performance of the DM system compared with the no-IRSassisted scheme and the no-PSM optimization scheme.At the same time,compared with the GAO algorithm,the proposed NSP algorithm has a faster convergence speed.In particular,when Eve is located in the path channel between the base station and the IRS,the proposed NSP algorithm is robust,that is,the SR performance does not deteriorate.