Joint Design Of Resource Allocation And Trajectory Planning For UAV-assisted Backscatter Communication Systems

Backscatter communication emerges as a low-power,low-complexity and low-cost wireless communication paradigm,and is recognized as a core technology for Internet of Things networks.Unmanned aerial vehicle(UAV)-based flying communication platforms have great potential in future communication systems due to its superiority in high mobility.This thesis considers a UAV-assisted backscatter communication network,in which a rotary-wing UAV is applied to collect data of passive backscatter devices(BDs)located on the ground.In this network,passive BDs are wireless-powered by incident carrier waves sent from carrier emitters(CEs),and transmit information by reflecting incident signals to the UAV.The UAV's limit on-board energy is a critical issue on the design of this network.Taking into account the time division multiple access(TDMA)and virtual multiple-input multiple-output(MIMO)transmission in the uplink respectively,this thesis studies the energy efficiency(EE)optimization problem for the UAV-assisted backscatter communication system,and propose the optimal joint design of the system's resource allocation and the UAV's trajectory planning that maximize the EE.First,for the TDMA-based UAV-assisted backscatter communication system,a dynamic TDMA transmission strategy and a static TDMA transmission strategy are investigated for the EE maximization of the system,respectively.Optimization problems of the two strategies are formulated to jointly optimize the BDs' uplink schedule,each BD's communicate time,CEs' transmit power and the UAV's flying trajectory.Two algorithms are also proposed respectively based on the block coordinated descent(BCD)method,integrating with the cutting-plane method,the Dinkelbach methodand the successive convex approximation(SCA)technique,to obtain suboptimal solutions of the two optimization problems.Then,for the virtual-MIMO based UAV-assisted backscatter communication system,a virtual MIMO channel is obtained by utilizing the mobility of the UAV,and the second-order moment match technique is applied to obtain the lower bound of the uplink transmission rate.Similarly,an EE optimization problem is formulated to jointly optimize the UAV's stationary hovering positions and each BD's power reflection coefficient.Moreover,a time-based line search algorithm,integrating with the BCD method,the Dinkelbach method and the SCA technique,is proposed toobtain a suboptimal solution of the problem.In addition,the convergence of the proposed three algorithms is proved and the complexity is analyzed.Finally,simulation results show that the EE of the dynamic TDMA-based strategy is significantly higher than that of the other two strategies.Furthermore,the EE of the virtual MIMO transmission strategy is higher than that of the static TDMA transmission strategy when the total operation time is short,but the situation becomes converse when the total operation time is relatively long.For different uplink transmission strategies,more time resources are always allocated to BDs which are located much closer to their associated CEs,and the UAV's trajectory shows different flying patterns for the three uplink transmission strategies.