Trajectory Optimization For UAV-aided Secure Communication System

Unmanned aerial vehicle(UAV)relay secure communication system is a system based on the existing physical layer security technology and equipped with a relay UAV.Compared with the traditional UAV assisted relay communication system,the system has the advantages of high transmission security and low probability of successful eavesdropping.However,the security performance of UAV relay networks is significantly reduced because of the rapid mobility and limited endurance of UAVs.Therefore,this thesis presents optimization schemes of UAV path planning for security performance enhancement.The main contributions of this thesis are as follows:(1)To improve the physical layer security and energy efficiency of UAVs in single-hop wireless networks,one approach is to optimize the UAV trajectory to maximize the secrecy energy efficiency.Firstly,the expression of the secrecy energy efficiency is analytically derived based on the secrecy throughput and the UAV's total energy consumption.Then,the trajectory optimization scheme is proposed to maximize the secrecy energy efficiency based on fractional programming.Finally,numerical simulations verify the accuracy of the proposed scheme.(2)With respect to the security performance improvement of Single-Input Single-Output(SISO)UAV relay communication systems,we develop an optimal design for UAV path planning and power allocation based on convex optimization theory.Firstly,the SISO-UAV relay network in the presence of eavesdroppers(EVE)is studied.Next,the analytical expression of the secrecy capacity is written based on the signal-to-noise ratio(SNR).Then,the power allocation and relay path are jointly optimized for secrecy capacity maximization.Further then,the secrecy performance of SISO-UAV relay networks is theoretically analyzed in terms of closed-form formulas based on Taylor series.Finally,simulation tools are used to analyze the secrecy performance of the proposed optimization method.(3)To achieve significant security improvement of Multiple-Input Multiple-Output(MIMO)UAV relay communication systems,the optimization scheme of UAV path planning and receive beamforming is proposed based on secrecy capacity maximization.Firstly,the MIMO-UAV relay network in the presence of eavesdroppers is studied.Then,we obtain the secrecy capacity of the relay network,which is a function of the UAV heading angle and the beamforming weight vector.Next,an optimal design for receive beamforming and UAV trajectory is given to maximize the secrecy capacity via convex optimization.Further then,the closed-form expression for the secrecy outage probability is derived to analyze the security performance.Finally,Monte Carlo results are used to verify the correctness of the proposed method.