Research On Wireless Access And Services Multiplexing Technology For Vacuum Tube High-speed Flying Train

In the past decade,China's high-speed railway(HSR)has made great achievements in industrialization,technological innovation and road network construction.With energy and environmental protection gradually becoming the national development core,the next trend of HSR is to further save energy and reduce environmental noise while continuously improving security,speed and transportation efficiency.It is found that dense atmosphere is the fundamental factor limiting the maximum speed of the ground rail transportation.Vacuum tube high-speed flying train(vactrain)is a new type of maglev rail technology,in which the restrictions of the dense atmosphere are eliminated by extracting the air in the tube to reach a low-vacuum environment.Thus,the maglev train can run in the mode of no mechanical friction,low air resistance and noise at a speed of more than 1000 km/h in the vacuum tube.The safe operation of vactrain is inseparable from the support of train-ground wireless communication system.Due to the ultra-high speed(up to 1000 ? 4000 km/h)and the special operation scenario of vactrains,the requirements for stability and reliability of wireless communication are higher than that of current HSR.However,the current wireless communication system(including 4G and 5G)only supports a maximum speed of 500 km/h.These wireless communication systems cannot effectively deal with the serious Doppler effect and frequent handover issues in the wireless communication for vactrain.Therefore,it is necessary to conduct the prospective research on the key technologies of train-ground wireless communication for vactrain.Firstly,the characteristics of wireless communication in vactrain scenario are analyzed in terms of operation environment,handover process and channel propagation conditions.In addition,the bandwidth and Quality of Service(Qo S)requirements of vactrain's train-to-ground communication services are analyzed quantitatively,including the service type,transmission rate,bit error rate,delay,priority and other indicators.Secondly,aiming at the problem of frequent handover,we propose a centralized cloud wireless access network architecture based on the vactrain scenario and the current high-speed railway wireless access schemes.In terms of the handover management,the moving cell scheme is adopted,which greatly reduces the time required for cell handover and the handover loss.Thirdly,we proposed a leaky waveguide with simple architecture but high performance to deal with the problem of wireless coverage and serious Doppler effect inside the tube.The leaky waveguide can radiate leaky electromagnetic wave in the form of cylindrical wave inside the tube.The simulation of the leaky waveguide is conducted,and the results show the uniform phase distribution along the horizontal direction of the tube,but also the smooth field distribution at the point far away from the leaky waveguide,which can greatly suppress Doppler effect,indicating that the time-varying frequency-selective fading channel could be approximated as a stationary channel.Therefore,an on-train electromagnetic lens system is proposed to achieve direct wireless coverage for passengers.The shape of the electromagnetic lens is designed,thus then the phase of leaky electromagnetic wave could be adjusted during the transmission in the lens to achieve a more uniform coverage for passengers.Finally,this paper studies the optimization of burst operational services(BOS)and users internet services(UIS)multiplexing transmission.We tackle the download resource scheduling of BOS and UIS based on the puncturing approach.The optimization problem aims to maximize the UIS data rate while satisfying the BOS critical constraints.In this paper,the optimization problem is divided into two subproblems: one is the resource blocks(RBs)allocation problem;the other is the resource scheduling problem of BOS and UIS.First,the RBs allocation problem is modeled as a 2-dimensions hopfield neural networks(2D-HNN)and the energy function of 2D-HNN is investigated to solve the RBs allocation problem.Then,the resource scheduling problem of BOS and UIS is formulated as an optimization problem with chance constraint.The cumulative distribution function(CDF)of the stochastic BOS traffic is investigated to relax the chance constraint into a linear constraint.The simulation results show efficiency of the proposed dynamic scheduling approach.