UAV-Aided Wireless Information And Power Transmission For High-Speed Railway Communications

High-speed railway is developing rapidly around the world,which has been one of the typical scenarios considered by the fifth generation mobile communication system.The safety of high-speed railway is very important,and the communication system is the cornerstone to guarantee the safety of high-speed railway.Traditional high-speed railway vehicle-ground communication system is unable to meet the needs of emergency communication such as natural disasters.In order to remedy this deficiency,the high-speed railway emergency communication system based on unmanned aerial vehicle(UAV)has attracted extensive attention in the industry as a feasible solution.With high mobility and flexibility in positioning,UAVs are suitable for rapidly establishing wireless connections for high-speed railway.Therefore,UAVs can provide communication service for high-speed train(HST)when the communication infrastructure is destroyed.And base on it,the main contents of this paper are summarized as follows:Firstly,in view of the limited energy of UAV relay communication,we propose a UAV relay high-speed railway communication system based on simultaneous wireless information and power transfer(SWIPT).More specifically,we build a mobility model complying with the UAV and a channel model according to the line of sight(LoS)characteristics of high-speed railway communication.By designing the information and energy transmission process,we deduce the closed-form outage probability expression of the system,and analyze the influence of the forwarding protocol,energy harvesting protocol,channel parameters,mobile topology and the range of communication on the system performance.It is found that the outage probability of the system can be reduced by about 5 times whe the time switching coefficient ? of the energy harvesting protocol decreasing from 0.8 to 0.5.Secondly,for the flexibility of UAV flight altitude,we design to optimize the performance of the high-speed railway emergency communication system.To be specific,we model the air-to-ground path loss as a function of UAV's altitude and derive the closed-form outage probability and bit error rate expressions of the system.Then,we obtain the UAV's flight altitude with optimal system performance under different relay forwarding protocols,energy harvesting protocols and modulation formats through simulation analysis.It is shown that the bit error rate of DBPSK modulation system is only about 1/4 of that of BPSK modulation system when the UAV is flying at the optimal altitude.Finally,for the dynamic change of UAV flight trajectory,we further improve the system throughput when UAV provides emergency communication services for HST.Concretely speaking,we optimize the trajectory of UAV with the goal of maximizing throughput.We use a successive convex optimization to approximately solve a non-convex problem of UAV trajectory optimization.On this basis,the optimization theory is used to solve the problem and we obtain the optimal trajectory of the UAV when HST is traveling in two typical high-speed railway tracks,namely straight line and curve.It is shown that the system throughput after UAV trajectory planning is about double that of the system throughput of the stationary UAV relay.In conclusion,this paper studies the SWIPT based UAV relay HST communication system.We derive the key system performance indexs such as outage probability and bit error rate,and optimize the flight altitude and trajectory of the UAV.The research results provide a theoretical basis for UAV based high-speed railway emergency communication,as well as provide a great-leap-forward development for China's high-speed railway.