Research On Mimo Technology For High Speed Train-Ground Wireless Communication

In order to satisfy the requirements of high speed railway, the railway communication technologies will have to move towards the direction to provide digital, wireless mobile and broadband integrated services. Therefore, it is very promising to deliver broadband wireless network (BWN) to high speed railway. On the one hand, the control systems of high speed railway need BWN to enable a safer transmission of railway operational information. On the other hand, there is a strong demand to provide various multimedia services for users on high speed railway. However, the currently utilized GSM-R (GSM for Railway) system can only support voice service and low data rate service, which are apparently insufficient for the future demand of railway communication system with high data rate. In addition, the existing public mobile communication system, neither railway coverage nor coverage quality, can meet the needs of users on high speed railway.As one of the key technologies of LTE, MIMO (Multiple Input Multiple Output) adopts the advanced wireless transmission and signal processing techniques and takes the advantage of multipath propagation of wireless channel to increase the quality and data rate of wireless communication without increment of bandwidth and transmission power. Therefore, the MIMO technology is regard as an important technological breakthrough in current communication and will be widely used in high speed railway communication in the future.In order to increase the channel capacity, a train-ground joint distributed MIMO system for high speed railway is proposed in this thesis, which is based on geographical features of high speed railway, the long length of train coaches and the location and speed information provided by the train control system. In addition, considering the hardware cost, signal processing complexity, vehicle antennas installation constrains and other relevant factors, the implementation solution of the vehicle-mounted antennas for a typical around200m long train with eight coaches is presented. The simulation results show that our proposal can get double macrodiversity gain to diminish the influence of shadow fading on channel capacity.In order to improve the quality of communication, an adaptive switching scheme between multiplexing and diversity in MIMO system based on the hidden Markov model is proposed in this thesis. Firstly, a time-varying MIMO channel model based on the hidden Markov model is constructed and the simulation results show that the model can illustrate the time-varying MIMO channel for high speed railway and the data obtained from the simulation are in good accord with the measurement. Then an adaptive switching scheme between multiplexing and diversity in MIMO system for high speed railway is presented on the basis, and the detailed implementation steps are given. The simulation results show that the proposed scheme can effectively reduce the bit error rate of the communication system with low complexity and high efficiency.