Security Transmission Strategy Of UAV Relay System Based On Joint Trajectory Optimization And Power Control

In recent years,UAV has been widely used in the field of wireless communication because of its low cost,small size,flexible deployment and mobile controllability.In particular,UAV with high mobility play an important role as mobile relay in remote communication and complex communication scenarios.Compared with the traditional ground-based relay,UAV as a relay has obvious advantages:(1)UAV can make full use of its mobility characteristics to dynamically adjust its position to best adapt to the communication environment,and can serve multiple ground nodes at the same time.(2)The miniaturized UAV has incomparable advantages in the communication environment with poor communication environment or complex terrain.However,UAV brings some disadvantages that can not be ignored while providing greater convenience.The uncertainty of relay system communication network structure caused by its mobility and the broadcast characteristics of wireless channel itself,especially the LoS link between UAV and ground users,make the information transmitted by UAV easier to be eavesdropped,and the security communication also faces greater challenges.Based on the current technology and future development trend,in order to ensure the security of UAV relay communication system,we can use the inherent randomness and reciprocity of wireless channel to encrypt information through physical layer security technology to achieve safe and reliable communication.Based on the above background,for the UAV assisted mobile relay system,this paper mainly studies the UAV security transmission strategy in two scenarios:fully known exact location of multiple eavesdroppers and incompletely known exact location of multiple eavesdroppers,making full use of the UAV's mobility,achieving information security by jointly optimizing the UAV trajectory and power control in different communication scenarios The main research work of transmission is as follows:1.UAV relay system with the exact location of multiple eavesdroppers is fully known.In this part,we study the UAV assisted dual hop relay system on the premise of fully knowing the location information of multiple eavesdroppers.First,we establish the mathematical model of the UAV relay system based on the decoding and forwarding(DF)protocol.By jointly optimizing the trajectory and transmission power of the UAV,we analyze and deduce the problem of maximizing the worst security rate achieved by the system.Secondly,for the optimization objective,we propose an alternative optimization(AO)algorithm,which decomposes the problem of maximizing the security rate into two subproblems,and solves the trajectory and transmission power of UAV alternately.Numerical results show that the proposed joint optimization algorithm can significantly improve the security performance of the system compared with other benchmark schemes.2.UAV relay system with the exact location of multiple eavesdroppers is not completely known.The research of this part further considers the scene where the distribution of the ground eavesdropper is known in the general area and the exact position is unknown,and establishes the UAV Communication system mathematical model with the exact position of the eavesdropper node not fully known.Under the condition that the UAV mobility and peak power constraints are satisfied,a robust algorithm for joint optimization of UAV trajectory and power control is proposed to maximize the system The worst average secrecy rate available.Since the problem of maximizing the security rate is continuous and nonconvex,it is difficult to solve it optimally.Based on the block coordinate descent method,the problem of maximizing the security rate is divided into two subproblems,which are solved iteratively by combining S-Procedure and SCA algorithm in an alternating way.Numerical simulation results show that the algorithm can significantly improve the worst average security rate of the system compared with the non robust algorithm.