【作者】 李柯漫；

【导师】 郝莉；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2010， 硕士

【摘要】 为了满足铁路运输向高速化、信息化、智能化方向发展的需求,铁路通信技术也需要向数字化、无线移动化、综合业务化及宽带化方向发展。目前我国铁路系统正在使用基于2G(2rd Generation)技术的GSM-R(GSM for Railway)通信平台,但GSM-R通信系统仅能支持速率为9.6kb／s的话音传输,无法满足未来对高速数据传输的需求。此外,铁路环境中的无线信道有其特殊性,具有多径环境简单、直射波占主导位置、多普勒频移较大等特点。LTE(Long Term Evolution)是常被人们称作“3.9G”的五个无线传输标准中的一个,其性能优势主要包括：更低的比特开销、提供更好的服务、更加灵活的带宽分配策略、更简单的网络结构和频谱利用率的提升。MIMO(Multiple Input Multiple Output)做为LTE的关键技术之一,可以有效地利用信道的随机衰落和多径传播,在不额外增加功率和带宽条件下成倍增加传输速率和大幅度改善链路质量。因此研究MIMO技术在铁路通信中的应用对寻找下一代铁路无线通信技术有重要意义。本文首先研究了MIMO信道建模,从模型分类、天线间空间相关矩阵计算方法、参数设置等方面,对基于Kronekcer积的空时相关统计特性建模(KBSM, Kronekcer-based Spatial Model)方法进行详细的阐述,并进行了仿真。给出了信道时间色散特性、频率相关性、空间相关性以及多普勒功率谱等信道特性,论证了KBSM建模的合理性。其次,本文参照LTE标准内容,介绍了LTE下行信道的帧结构和下行物理信道处理过程,并对下行物理信道处理过程进行仿真。然后还讨论了三种MIMO检测技术：迫零算法,最小均方误差算法和串行干扰消除算法,对它们的理论进行了推导,并进行了仿真比较,仿真结果表明将串行干扰消除算法与ZF(Zero Forcing)和MMSE(Minimum Mean Square Error)算法相结合,可以有效的提高系统的误码率性能,且算法复杂度较低、耗时较少、易于实现。本文主要贡献是基于列车车身较长的特点,讨论了一种适用于列车的分布式MIMO系统。与一般讨论较多的发射端天线为分布式的系统不同,列车的分布式MIMO系统采用发射端单MIMO组,而在列车上分布多个MIMO天线组。根据此分布式MIMO的特点研究了两种基于范数的方法进行MIMO天线组选择并对其进行了仿真。仿真结果表明,采用分布式MIMO系统可以大幅度提升误码率性能,对信道容量也有一定的提升,且算法简单易于实现。更多还原

【Abstract】 In order to meet the high-speed, informationization and intelligent demands of railway transport, railway communication technologies also need to move towards the direction to provide digital, wireless mobile and broadband integrated services. Currently, while the GSM-R (GSM for Railway) communications platform has been utilized in our country, it can only support voice services of data rate 9.6kb/s and can not meet the future demands of railway transport for high-rate data transmissions. In addition, the wireless channel in railway environment possesses its particularity including simple multipath environment, direct wave in dominant position, larger Doppler frequency shift and so on.LTE (Long Term Evolution)is one of five major wireless standards referred to as "3.9G" the performance advantages of which involves lower bit-cost, better service quality, more flexible bandwidth allocations, simpler network architecture and higher spectral efficiency. As one of the key technologies of LTE, MIMO (Multiple Input Multiple Output) can effectively utilize the random channel fading and multipath propagation to increase the transmission rate and improve the link performance without additional power and bandwidth consumption. Therefore, researches on the application of MIMO technology in railway communications is important for searching next generation railway wireless communication system.This thesis discusses the channel modeling of MIMO system firstly. On the basis of discussions on the classification of channel models, computational methods of spatial correlation matrix as well as the parameter configuration, the thesis elaborates the method of Kronekcer-based Spatial Model (KBSM) in detail and provides a corresponding simulation. Moreover, certain characteristics such as the time dispersion, frequency correlation, spatial correlation as well as the Doppler power spectrum are also presented in this paper to demonstrate the feasibility of KBSM channel modeling. Secondly, taking the LTE standards as the reference, the thesis introduces the frame structure and the processing of downlink physical channels, based on which, the simulation of the downlink physical channel are provided. Further, three types of MIMO detection techniques, zero forcing(ZF), minimum mean square error (MMSE) and successive interference canceling(SIC), are discussed and compared through the simulation results, which show that combining SIC with ZF and MMSE can effectively improve the bit error rate performance with feasible the algorithm complexity and time-consuming.This main contribution of this thesis is that, on the basis of the characteristic that the train body is relatively long, a distributed MIMO system is proposed. Different from the conventional distributed transmit antenna system, the proposed scheme employs single MIMO antenna group at the transmitter and multiple distributed MIMO groups at the receiver which are installed on the train. According to the characteristics of the proposed distributed MIMO system, two kinds of norm-based approaches are discussed to implement MIMO group selection at the receiver side. Simulation results show that distributed MIMO system can be used to enhance the BER performance and channel capacity significantly with a acceptable complexity and feasibility.更多还原