Study Of Data Transmission Mechanism In Two-Hop Access System Of High Speed Railway

High-speed railway has become a new and strategic emerging industry in the world.With the gradual increase of train speed and the widespread popularity of small handheld mobile terminals,the high-speed railway network puts forward higher requirements and challenges for high-speed railway communication in order to ensure a good communication experience for passengers.In this dissertation,a two-hop high-speed railway communication system is considered.By erecting an antenna on the top of the train,the first-hop communication is between vehicle antenna and the Radio Antenna Unit(RAU)on the rail side(‘rail-side antenna-vehicle antenna’ link).After processing the received signal,the second hop communication between the vehicle antenna and the user terminals is accomplished through the Access Apoint(AP)distributed inside the carriage(‘vehicle antenna-user terminals’ link).In the two-hop high-speed railway communication system,most of the existing research consider the network layer performance,but the research on the link layer performance is very few.However,l-ink layer is responsible for the reliable transmission of data to the target,so t-he data transmission of link layer is crucial for the system performance.This dissertation focuses on data transmission in the system link layer.In the "rail-side antenna-vehicle antenna" link,the effects of three factors(frequent train handover,multi-antenna technology,high-speed movement of the train and complex and changeable communication environment)on the performance of data transmission mechanism under high-speed railway environment are discussed.In the "vehicle antenna-user terminals" link,considering the lack of routing equipment,the characteristics of data broadcasting performance in tree and mesh broadcasting networks are considered respectively.The main research results are summarized as follows:Firstly,consider the frequent handover of trains,an improved data transmission mechanism is designed to improve the system handover performance without increasing the cost and equipment.In the "rail-side antenna-vehicle antenna" l-ink,the shortcomings of the existing data transmission strategy in the case of frequent train handover are analyzed,that is to say,the link layer begins to communicate normally after a period of communication preparation time,which is called the communication delay problem of the link layer.To ensure the continuity ofcommunication,a improved data transmission mechanism based on over-frequent handover of high speed train is proposed,that is,the serving RAU transfers data packets to the target RAU at the beginning of handover.The aim is to ensure that the target RAU starts communication immediately after it enters the system and eliminate the delay problem of link layer communication.After parameterizing the traffic arrival,data transmission and other factors,the performance of the improved mechanism is quantitatively analyzed by establishing a loss-based Geom/G/1 queuing model to verify the effectiveness of the proposed mechanism.Secondly,the influence of multi-antenna technology on data transmission performance is quantitative studied.In the ‘rail-side antenna-vehicle antenna’ link,By reconstructing the Geom/Geom/c/c loss model,the performance of multi-channel data transmission mechanism is quantitatively analyzed,and the analytical expressions of system loss rate,average queue length,delay,throughput are obtained.At the same time,the influence of multi antenna technology on the performance of high-speed rail communication is discussed,which provides theoretical support for improving the quality of high-speed rail communication,and provides reference for the design,planning and optimization of higher wireless access technologyThirdly,in view of the high-speed movement of trains and the complex and changeable communication environment,the technology of Selective Repeat Automatic Repeat reQuest Adaptive Modulation and Coding,(SR-ARQ-AMC)is introduced to improve channel utilization.In the "rail-side antenna-vehicle antenna" link,firstly,according to the high-speed movement of trains and the complex and changeable characteristics of communication environment,the non-stationary characteristics of high-speed rail channel are obtained,that is,the high-s-peed rail communication conditions change rapidly with time.In order to improve the channel utilization and guarantee the system reliability,SR-ARQ-AMC technology is introduced into the high-speed railway communication system to dynamically adjust the frame rate according to the signal-to-noise ratio(SNR).At the same time,the data transmission performance of SR-ARQ-AMC system is quantitatively analyzed by establishing Geom/G/1/M queuing model with timer,and the analytical formula of system packet loss rate is obtained.Finally,some modification suggestions for system design are put forward through numerical analysis.Fourthly,considering the lack of routing equipment in the carriage,ARQ technology is introduced into the tree broadcasting link,and five reliable data broadcasting protocols are proposed.In the "vehicle antenna-user Terminals" link,five data broadcasting protocols(ARN,SW-E2E-ARQ,SW-HBH-ARQ,SW-HBH-oiARQ,SW-HBH-ieARQ)are designed based on the statistical reliability,consider the lack of routing equipment(all information is transmitted through broadcasting links)and the energy limitation of handheld terminals.At the same time,the quantitative analysis of the maximum number of retransmissions,the minimum system energy consumption and the system delayare theoretically solved in the broadcasting network.Then the protocol selection schemes for the actual system design are proposed through comparing the five protocols numerically.Fifthly,collaborative communication technology is introduced to realize Mesh network structure,and four data cooperative broadcasting protocols are proposed.In the "vehicle antenna-user terminals" link,considering the broadcasting characteristics of radio waves of the receiving end and the energy consumption of Mesh network.,four data broadcasting protocols(SW-HBH-CARQ,SW-HBH-oiCARQ,SW-HBHieCARQ,SW-HBH-oieCARQ)are designed to extend tree network to Mesh network through introducing cooperative communication technology.At the same time,the analytical formulas of the maximum number of retransmissions,the minimum energy consumption and the system delay of the four protocols are given.Then,the advantages of the cooperative broadcasting protocols are verified by numerical simulation.