| In today’s 5G era,UAV has attracted extensive attention because of its high mobility,low cost,maneuverability and the ability to build a good line of sight(LOS)channel.It can provide more reliable communication services and realize many functions that are difficult to be realized by ground communication systems.The combination of UAV and wireless information and power transfer(SWIPT)technology gives UAV the ability to transmit energy,which can solve the problem of difficult node battery replacement in wireless sensor networks and effectively prolong the service life of the whole network.In the related research of UAV SWIPT system,the existing resource allocation schemes are based on the linear energy harvesting model,while the actual energy harvesting model is nonlinear and has a saturation value.At present,the research related to the nonlinear energy harvesting model is still very insufficient.Based on this background,this paper carried out the following research:(1)This paper studies the resource allocation scheme of UAV SWIPT system with nonlinear energy harvesting model when using power splitting(PS)protocol.Considering the saturation characteristics of the energy receiver of actual terminal node,this scheme takes the maximization of the energy harvested by the terminal node as the goal to jointly optimize the flight trajectory of the UAV and the PS coefficient of the node receiver.Through simulation,compared with the optimal PS scheme proposed under the linear energy harvesting model,the results show that the linear model has a wrong estimation of the energy harvesting capacity of the system,and the PS scheme has a waste of resources under the nonlinear model.The simulation results also show that the optimal flight trajectory of UAV is flight hover flight.UAV only transmits information during flight,SWIPT when hovering over each node,and transmits information and energy;Moreover,PS protocol is not suitable for resource allocation scheme design under nonlinear energy harvesting model.(2)This paper studies the resource allocation of UAV SWIPT with nonlinear energy harvesting model when using time switching(TS)protocol.Aiming at maximizing the average information transmission rate of the system in the hovering phase,the scheme jointly optimizes the hovering time allocation of the UAV and the working state of the terminal node receiver in each time slot.Due to the coupling relationship between two optimization variables and the duality of the working state of the terminal node receiver in each time slot,the optimization problem is nonconvex.In this paper,a special step-by-step optimization algorithm is proposed to optimize two coupled variables respectively,and the splitting idea,time-division strong duality theorem and Lagrange duality method are used to help solve the optimization problem.The simulation results show that the UAV tends to hover over the node closer to the total distance of each node for a longer time.When the distribution of nodes expands to a certain range,the effect of optimizing hover time allocation on system performance will become very weak.In addition,in each time slot during the hover phase of SWIPT,the terminal node receiver switches to the information receiver when the channel power gain is large or small,and to the energy receiver when the channel power gain is moderate. |
