Research On Optimal Transmission Strategy For UAV-enabled Multi-mode Communication Systems

With flexible maneuverability and low cost,unmanned aerial vehicles(UAVs)-enabled data transceiver and relay technology has been widely used in wireless sensor network,cellular network and mobile Ad hoc network,while which is still facing many challenges,one of the most serious challenges is the endurance.For the above issues,on the one hand,it can be focused on the dimension of UAV flight time.The limited battery capacity determines that UAV must return home regularly during the communication mission to replace the battery or supplement the power,which will lead to the large system delay and further waste of energy.Therefore,via the joint optimization design of UAV trajectory and resource allocation,the communication requirement should be achieved in the shortest time under the condition of limited energy.On the other hand,by analyzing and establishing the models of UAV promotion and communication-related energy consumption,the performance of UAVenabled communication systems can be optimized directly with the goal of total energy consumption to satisfy the communication requirements with the least energy.In view of the above two aspects,this thesis mainly studies the communication scenarios of UAV-enabled data collection or distribution,and the data relay between multiple pairs of ground users,as described below.1.The thesis studies the optimal transmission strategy of UAV-enabled data collection or distribution system.First,an air-ground integrated wireless sensor network is established where the UAV is equipped with a communication module and adopts a frequency division multiple access(FDMA)among all the ground nodes.Based on the above discussion,the problem with respect to the minimum completion time is formulated.In order to meet the minimum requirement of system delay,the minimum rate requirement(MRR)constraint of the ground nodes at any time is fully considered in this problem.In this communication system,the time discrete method is first used to approximate the linear state-space conversion of the original continuous domain problem,and then the convex optimization theory and the global dichotomy algorithm are adopted,the optimal resource allocation and trajectory optimization scheme of the system under the multivariable joint design is obtained and with the initial trajectory based on the Travelling salesman problem(TSP)solution.2.This thesis investigates the optimal transmission strategy of UAV-enabled data relay system between multiple pairs of users.In the established wireless mobile relaying network,the UAV acts as a mobile relay for multiple pairs of ground users with the time division multiple access(TDMA)communication protocol and the decode-and-forward(DF)data transmission protocol,and the problem of minimizing the total energy consumption is formulated.For this problem,it is divided into three sub-problems with respect to the time slot length and allocation,power allocation and UAV trajectory.And then,these subproblems can be efficiently solved by the formulated iterative optimization algorithm by utilizing the successive convex approximation(SCA),block coordinate descent(BCD)and path discrete methods with the guarantee of convergence.For the information-causality constraints and different throughput requirements of relay communication,a novel trajectory initialization scheme based on pickup-and-delivery problem(PDP)and fly-hover-communicate(FHC)protocol is proposed for the first time,where the solution of PDP is derived to obtain the optimal visiting order for all the ground users,and the FHC protocol is applied to find the optimal hovering(or communication)position of the UAV in the initial trajectory.Moreover,in the original of relay communication,avoiding the no-fly zones is further studied.For the design scheme and optimization algorithm involved in the above research content,the corresponding simulation results are derived,which verify that the proposed scheme can contribute to the high gains in algorithm convergence,UAV trajectory optimization,resource allocation and optimization results comparison under different communication requirements.