| In recent years,with the development of Unmanned Aerial Vehicles(UAVs)and wireless communication technology,UAVs have been widely used in the present and future wireless communication systems.As a flexible and mobilizable device,UAV have the advantages of on-demand deployment and Line of Sight(LOS),which can exploit the greater potential of wireless communication system.However,the transmission medium of wireless communication,the electromagnetic wave,has the characteristics of broadcast transmission and is easy to be eavesdropped by illegal users How to ensure the secure transmission of information is a key problem in the wireless communication system.Physical Layer Security(PLS),as a supplement to the upper-layer encryption algorithms of traditional communication networks,using the characteristics of wireless channels to securely transmit confidential information has received more attention and research interests from both industry and academia in recent yearsAiming at the problem of secure transmission in wireless communication system,combining the security technology of UAV and physical layer,this thesis mainly.studies the problem of UAV trajectory design and resource allocation scheme of the UAV cooperated secure communication system.The main works include:(1)A Wireless Secure Communication System based on cooperative jamming UAV is studied which includes a passive eavesdropping user with incomplete Channel State Information(CSI),and the UAV serves as a mobile cooperative jammer to send interference signals to the eavesdropper to deteriorate its Signal to Interference plus Noise Ratio(SINR).Cooperative jamming UAV utilizes its mobility advantage to approach eavesdropper and stay away from legal user to improve the secure transmission rate of ground wireless secure communication system.In addition,this thesis also consider the influence of No-fly Zones(NFZs)on trajectory design of UAV.(2)An UAV-enabled Cognitive Wireless Secure Communication System is studied.which includes a Primary Network(PN)and a Cognitive Radio Network(CRN).The cognitive network communicate with secondary user by opportunistically accessing the authorized band of primary network and there is an eavesdropper which attempts to eavesdropping the confidential information of the cognitive network.UAV serves as the cognitive transmitter transmits confidential information to multiple cognitive users on the ground.UAV needs to control its flight trajectory and optimize its transmit power and subcarrier allocation strategy to maximize the secure transmission rate of cognitive network whiles ensuring that the interference to primary network caused by UAV is less than a certain threshold.(3)For the above two research scenarios,this thesis proposes two non-convex optimization problems which maximize the secure transmission rate of the communication system by jointly optimizing the UAV trajectory design and resource allocation schemes respectively.In order to solve the proposed optimization problems,the Block Coordinate Descent method(BCD)and Successive Convex Approximation(SCA)method are applied.The original problems are decomposed and transformed,and an iterative algorithm based on the idea of alternative optimization(AO)is proposed respectively.Based on convex optimization theory,the approximate solution of the original optimization problem is obtained by solving the iterative algorithms.Finally,we use Matlab to solve the trajectory design and resource allocation problems Simulation results show that the proposed optimization schemes can significantly improve the security performance of wireless communication system. |
