Research On Physical Layer Security Of UAV Assisted Wireless Network Based On Millimeter Wave Communications

In the UAV assisted wireless network based on millimeter wave communications,On the one hand,UAV as an aerial base station can provide air to ground millimeter wave communications links for ground users to supplement the existing ground cellular networks,which can enhance the wireless communications capacity and expand the wireless coverage.On the other hand,due to the serious attenuation of millimeter wave and the obstruction of non-line-of-sight transmission,UAV as an aerial relay provides stable communication links.However,in the millimeter wave communications UAV assisted wireless network,the wireless broadcast characteristics of the millimeter wave signals lead to the wireless transmission signal is open to legitimate users and eavesdroppers,and there is a risk of malicious attack and eavesdropping in the absence of protection.Compared with the traditional high-level encryption technology,which mainly on cracking to generate the key and requires high computational complexity to ensure the effectiveness of the encryption algorithm,the physical layer security based on information theory method does not need complex mathematical key to encryption the confidential information,but it can still effectively provide security for wireless communications.Therefore,this paper uses the emerging technology of reconfigurable intelligent surface and directional modulation technology in advanced physical layer security means.The physical layer security mechanism of UAV assisted wireless network based on millimeter wave communications are studied and the multi-users average security rate enhancement method based on reconfigurable intelligent surface and the optimization method of combining direction modulation and reconfigurable intelligent surface security transmission are established respectively.The main work of this paper includes the following aspects.(1)The application of reconfigurable intelligent reflect surface in the physical layer of UAV assisted wireless networks in millimeter wave communications is studied,and the base station,reconfigurable intelligent reflector and multi-users system are constructed.The Lagrangian dual function method and the lower bound function approximation method of the objective function are used to optimize the parameters of the transmission covariance and the reflection coefficient,and the alternating iterative optimization algorithm is proposed.The simulation results show that the security transmission rate of the system using the reconfigurable intelligent reflect surface technology is higher than that without one,and the security transmission rate of the alternating iterative optimization algorithm is higher than that of the semi-definite relaxation method.(2)The optimization method of secrecy transmission rate based on the fusion of directional modulation and reconfigurable intelligent reflect surface technology in the UAV assisted wireless network of millimeter wave communication.In this paper,the intelligent reflect surface technology is added to the traditional directional modulation technology,which further improves the security of the system.For the non-convexity of the optimization problem,the eigenvalue eigenvector method and the gradient rising method are used to solve the problem alternatively.The simulation results show that secure transmission rate using reconfigurable intelligent reflect surface in directional modulation is higher than using only directional modulation,and the secure transmission rate increase with the increase of transmit power,the number of transmit antennas and the number of reflection units.