Architecture And Performance Analysis Of Broadband Wireless Networks For High-speed Railway

ABSTRACT:The evolution of wireless communications has a goal, which is that people can communicate with any one at any place and for any time. As one of the most impor-tant modern transportation vehicles, high-speed trains are closely connected with human. In the journey of several hours, the passengers would like using their mobile terminals to enjoy many kinds of wireless communication service, for example call, emails, internet and live video games. It has been a new and hot topic that providing information service to the passengers onboard high-speed trains. There are many challenges in this area, such as fast varying fading channels, doppler shift, fast handover, limited spectrum, complex interference and high reliability. However, existing wireless systems can not handle these problems. Therefore, under the condition of high mobility, it is significant to investigate the new architecture and performance of public broadband wireless access network for high-speed railways.The architecture and performance analysis of public broadband wireless access net-work for high-speed railways have been studied by using tools of special functions, prob-ability theory and random matrix. For the scenarios of high-speed railway, we analysis the characters of channel model, propose a new network architecture, study the key per-formance of high-speed railway network. Based on generalized fading models, we derive the expressions of channel capacity, outage probability, bit error rate (BER), error expo-nent, cutoff rate, expurgated exponent and effective rate. From these significant formulas, we can evaluate the performance of high-speed railway wireless systems, find the law of limited performance, get the effect of system and channel parameters on network. Our results can provide a theory foundation for the design, optimization of high-speed railway network. Moreover, the main contributions of this thesis include:1. For the channel model and system architecture, based on the measured data, we analysis the statistic characteristics of large-and small-scale fading channels of high-speed railway scenarios. Because of the complexity and diversity of scenar-ios, the η-μ and K-μ distributions have been used in this thesis as generalized small-scale fading models. The probability density functions (PDFs) of the envelope and power of η-μ and k-μ random variables are provided as mathematical tools for the performance analysis. The η-μ and K-μ distributions can include several common distributions as special cases. For example, the η-μ distribution cover-s Hoyt, Rayleigh and Nakagami-m distributions and the k-μ distribution includes Ricean, One-Side Gaussian, Rayleigh and Nakagami-m distributions. Then, we analysis pros and cons of the existing wireless systems for high-speed railways, such as satellite communications, leaky cable, UMTS and WiMAX. Furthermore, the network scheme based on vehicle-mounted base station (BS) and radio over fiber (RoF) has been proposed in this paper. With the antennas mounted on the top of trains, the BS communicates with the track-side radio antenna unit (RAU) directly, decodes the received signal and transmits it to the users’terminals by the antennas distributed in the carriage. The proposed scheme has low cost, handover time, and low interference. It can support many communication systems. More importantly, the complex algorithms for estimation time-varying channels and anti-doppler effect are moved to the vehicle-mounted BS, which is more powerful than the common terminals. In addition, the handover of this scheme is simple and can be successful with a high probability.2. For the performance analysis of high-speed railway wireless systems, we analysis the classic Shannon metrics of the link between the RAU and the vehicle-mounted BS. A generalized η-μ/Gamma composite fading model has been proposed by con-sidering path loss, shadowing and small-scale fading. Based on the PDF and CDF expressions of the power, the exact outage probability and BER formulas have been provided. Moreover, we exploit the performance metrics of high-speed railway net-work in terms of error exponent and effective rate. The relationship between the number of antennas, coherence time, length of codeword, shadowing, parameters of small-scale fading and random coding error exponent (RCEE) has been investigat-ed for multiple-input multiple-output (MIMO) Space Time Block Coding (STBC) systems. Furthermore, we provide the exact and approximated analytical expres-sions for the channel capacity, cutoff rate and expurgated exponent. The exact and approximated analytical expressions for the effective rate of multiple-input single-output (MISO) systems over η-μ and k-μ fading channels are derived to combine the Quality of Service (QoS) of data link layer and transmit rate of physical lay-er. These universal results include and validate previous works on Nakagami-m, Rician and Raileigh fading channels.3. For the viaduct scenario of high-speed railway, we prove a spacing of antennas based scheme which maximizes the channel capacity of MIMO systems. The con- ventional MIMO system can not achieve full capacity because of the singular cor-relation matrix in the line of sight (LoS) environment. In order to get a full rank correlation matrix, an antennas spacing law has been proposed for2x2MEMO systems. The product of the spacing of transmitted antennas s1and the spacing of received antennas52is correlated with carrier frequency, the distance between transmitter and receiver, and the angle of antennas, while is independent of the height of antennas. Then, we extend this scheme to the case of any number of antennas and find that the product s1s2increases with the reduction of transmitter antennas. The maximize capacity MIMO scheme has huge advantage when applied in the scenario of high-speed railway. The top area of high-speed trains is large to mount many antennas, which is different from common user terminals. Moreover, we discuss the application of this scheme in the LoS channel and the curve of rail-way. The simulation results demonstrate the advantage of our proposed generalized scheme, which can derive high rate and is suitable for viaduct scenario.