Research On Resource Optimization Methods For Unmanned Aerial Vehicle Platform Based Relay System

With the continuous development of technology and reduction of cost,umanned aerial vehicles(UAVs)have been widely used in various scenarios,such as cargo transportation,aerial photography,unmanned inspection,search and rescue,etc.UAV can be used as an airborne wireless communication platform to enhance the coverage of the network and ensure the communication quality of ground users.With the explosive growth of the number of UAVs,how to establish a communication link with the ground according to the mission requirements of UAV becomes a key task.Unlike traditional terrestrial wireless communications,UAVs typically have line-of-sight(Lo S)links with terrestrial nodes,thus providing better channel conditions than terrestrial fading channels.Second,UAVs are characterized by rapid deployment and flexible maneuvers.A better communication channel can be obtained by flexibly adjusting the position of UAV;in addition,due to the limitations of the size,payload and energy of UAV itself,the optimization problem of the UAV communication system is brought new challenges.This paper studies the resource optimization technology of relay system based on UAV platform,including resource optimization such as time,power and UAV trajectory,to improve system resource efficiency and system communication performance.In UAV relay system with fixed trajectory,the joint time and power optimization algorithms are proposed for the outage problem caused by air-ground channel path loss,time-varying fading and noise in relay communication link.The outage probability is minimized by resource optimization.When there is no line-of-sight(NLo S)signal between UAV and the ground node,the air-ground channel can be described by the Rayleigh fading channel,and the convex optimization algorithm is used in each time slot to realize the optimal allocation of resources.An iterative algorithm is proposed in each UAV flight cycle to obtain a suboptimal solution of the minimum average outage probability.When there is a line-of-sight(Lo S)signal between the UAV and the ground node,the air-ground channel is described by the Rician fading channel.And the first-order Maclaurin series approximation method is proposed.The first-order asymptotic solution for time and power optimization problems is obtained by the convex optimization algorithm under high SNR.The simulation results show that the proposed algorithms can significantly improve the outage probability with different UAV flight radii.In UAV relay system that needs to transmit a large amount of data,a joint power and UAV trajectory optimization algorithm is proposed for the problem of variant equivalent channel state caused by different UAV positions.The throughput can be maximized by allocating more resources in locations with better equivalent channel state.The channel state between UAV and the ground node changes due to the change of the UAV position,so the variant air-ground channel can be utilized to optimize the throughput by jointly optimizing power and UAV trajectory.Iterative algorithms are proposed to solve the subproblem of power allocation with fixed UAV trajectory and the suboptimal solution of UAV trajectory optimization with fixed power allocation.Then an iterative algorithm for alternately optimizing these two sub-problems is proposed to obtain a suboptimal solution.The simulation results show that the proposed joint power and UAV trajectory optimization algorithm can significantly improve the throughput.In UAV relay system that needs to achieve stable communication rate,joint power and UAV trajectory optimization algorithms are proposed for the problem of rate change caused by the change of the equivalent channel state.Improve the efficiency of system resource utilization under fair conditions.The resource utilization efficiency can be improved subject to the constraint of sfairness.Two scenarios are investigated.The first iterative optimization algorithm for jointly optimizing power and UAV trajectory is proposed,which solves the problem of maximizing the minimum rate of each time slot when given total power budget.The second joint power and UAV trajectory optimization algorithm is proposed to solve the problem of minimizing the power consumption with given minimum rate.The simulation results show that the proposed joint optimization algorithm can improve the resource utilization efficiency subject to the constraint of sfairness.In a time division multiple access(TDMA)multi-user communication system using a single UAV relay,an iterative algorithm for joint optimization of time,power and UAV trajectory is proposed for the problem of unfairness rate among different users and low resource utilization efficiency.The the average communication rate of each pair of users can be improved by resource optimization.Due to the different channel conditions between users and the UAV,the average allocation of resources leads to a large communication rate difference between different users,and may waste communication resources in ti me slots with poor channel conditions.Therefore,a joint optimization algorithm of time,power and UAV track resources is proposed in this paper.An iterative algorithm for solving the resource allocation problem is proposed by block coordinate descent me thod.The simulation results show that the proposed algorithm significantly improves the average rate of each pair of users.