Research On Distributed MIMO Wireless Communication System Based On LTE Under Environment Of Railway

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.