Optimal Beamforming And Trajectory Design For Uav-assisted Communication System With SWIPT

In recent years,with the rapid development of mobile Internet and intelligent technologies,various of innovative services and products constantly emerge.People’s demand for mobile data is increasing day by day,and the communication scene is becoming more and more complex and changeable.The existing traditional mobile communication system is facing great challenges.With the advantages of high mobility and good environmental adaptability,unmanned aerial vehicles (UAVs) assisted communication system can make up for the deficiency of traditional communication system,solve the cost and geographical location limitations of base station deployment and conduct base station deployment anytime and anywhere according to the communication requirements.In various natural disaster scenarios,UAVs provide the timely restoration of communication services and reliable communication coverage for end users to ensure the emergency rescue.In addition,simultaneous wireless information and power transfer (SWIPT) essentially resolves the energy supply concern of communication nodes through collecting the energy stored in signals and realizing the parallel transmission of power and information.In this paper,two UAV-assisted wireless communication networks with SWIPT are investigated,including a basic system and a multiuser system.This paper aims to improve the energy harvesting performance of the communication systems by optimizing beamformers and UAV trajectory.The principal contributions are summarized as following:1.An UAV-assisted SWIPT downlink system model and a multiuser UAV-assisted S WIPT system model are proposed,in which UAV employed as a mobile base station is in charge of transmitting information to the ground users.2.Based on worst-case model,a joint optimization problem of beamformers and UAV trajectory restrained by the UAV’s transmit power constriction,UAV motion constraints and signal to interference plus noise ratio (SINR) restrictions of ground users are formulated to maximize the minimum harvested energy at all receivers.The established problem is non-convex and involves numerous variates which is difficult to solve.3.To tackle the complex non-convex problem,this paper derives an alternative optimization (AO) algorithm based on semidefinite relaxation(SDR) and successive approximation (SCA) which is efficient to converge.The original optimization problem is divided into two subproblems.For beamforming optimization subproblem,SDR method is utilized to transform the non-convex issue into a convex semidefinite programming by introducing positive semidefinite beamforming matrices and relaxing the rank-one constraints.The eigenvector approximation method is used to achieve an approximately optimal result since the obtained solutions are not necessarily rank-one generally.For trajectory optimization subproblem,SCA technique is applied to reform a convex problem based on the property of the first-order Taylor approximation.The Simulation results show that our proposed design outperforms other benchmarking schemes in terms of the minimum harvested energy for this system.