Research On Coverage Technologies Of New Generation Wideband Railway Mobile Communications And Their Applications In Trial Systems

As an artery of national economy,an important national infrastructure,and a popular transportation tool,railway plays an irreplaceable role in economic development and national defense construction.Recently,countries all over the world have competed to carry out the research and development of high-speed railway technology.As a significant guarantee of railway operation and a crucial part of railway construction,the railway wireless mobile communication system needs to be constructed and developed simultaneously.However,the railway wireless mobile communication has the characteristics,such as the high mobility,large Doppler frequency shift,fast channel variation,overfreqnent handoff,and strict coverage requirement.The existing wireless access technologies for railway communication cannot well meet the needs of future intelligent railway construction.In view of this,this thesis will investigate the architecture and coverage performance of the new generation railway communication wireless access network(RCWAN),and discuss the applications of the proposed coverage techniques in the trial system.The main contributions include the following five parts.Considering that the existing network architectures cannot meet the needs of the new generation RCWAN,this thesis improves traditional network architectures and presents three novel network architectures for RCWAN based on chain cell(CC),carrier aggregation(CA)and cell free massive multiple input multiple output(CF-m MIMO),respectively.All of the proposed network architectures rely on the on-broad access point(OBAP)for relaying communication,and the whole communication link is divided into the base station(BS)-OBAP link and the OBAP-user link,so as to avoid the problem of large penetration loss caused by the direct communication between the BS and the user.In addition,the CC-based architecture adopts narrow-strip-shaped cells and introduces hard handover hysteresis factor to avoid ping-pong effect,which improves the wireless coverage performance of RCWAN.The CC-based architecture aggregates the scattered spectrum to improve the spectrum utilization.The CF-m MIMO-based architecture discards the traditional cellular structure and introduces massive MIMO technology,which reduces the handover frequency and further improves the system performance.For the CC-based RCWAN architecture,this thesis investigates the coverage performance and optimization of the system.Under the conditions of narrow-striped CCs and the hard handoff,the theoretical expressions of cell edge coverage probability(ECP)and the percentage of cell coverage area(CCA)are derived,which can be used to quickly evaluate the system coverage performance.Moreover,to further improve the coverage performance,the optimization problem of minimizing the number of BSs is formulated under the coverage constraint and the total coverage distance constraint,and then an optimal BS deployment scheme is proposed to solve the problem.Numerical simualtion results verify the accuracy of the derived theoretical expressions and the effectiveness of the proposed BS deployment scheme.For the CA-based RCWAN architecture,the coverage performance and optimization of the system are studied.First,the system model based on CA is constructed.Then,the statistical characteristics of the received signal-to-noise ratio(SNR)are analyzed.For the systems with and without CA,the theoretical expressions of the ECP and the percentage of CCA are derived,respectively.After that,a chance-constained coverage optimization problem is formulated to improve the system coverage performance,and a heuristic algorithm is proposed to solve the problem.Numerical simualtion results verify the accuracy of the derived theoretical expressions and the effectiveness of the proposed coverage optimization scheme.Moreover,the impacts of key system parameters such as CA,transmission power,cell radius,received SNR threshold,and railway scenarios on coverage performance are further discussed.For the CF-m MIMO-based RCWAN architecture,this thesis derives and analyzes the coverage performance bound of the system.First,we provide the CF-m MIMO-based system and channel model assumptions.Based on this,the signal transmission processes of uplink training,uplink data transmission and downlink data transmission are analyzed,respectively.By using the principle of deterministic equivalent analysis,a theoretical expression of deterministic signal-to-interferencenoise ratio(SINR)in downlink data transmission and a tight upper bound of coverage probability are derived.Moreover,the asymptotic coverage performance in the high power regime is also analyzed.Numerical simualtion results verify the correctness of the derived theoretical expressions.Moreover,the effects of downlink transmission power,access point(AP)’s antenna number,AP’s density,user number,and channel fading parameter on system coverage performance are also discussed.This thesis introduces the established new generation RCWAN trial system,and discusses the application of the proposed coverage technologies in the trial system.First,the 5G-R system architecture given by the national railway corporation and the trial system built by the project team are introduced,respectively.Then,aiming at the problems existing in the existing trial system(such as insufficient coverage cabilities of hot spots,frequent handoff caused by the use of traditional cellular architecture,difficult equipment expansion and so on),the applications of the proposed coverage technologies(such as CA,CF-m MIMO,and quick disassembly interface design)in the trial system are discussed,which provide ideas and preliminary solutions for the further optimization design of 5G-R trial system.