Researches On Distributed Comp Based On LTE-A For High Speed Railways

In high-speed railway scenario, high mobility of the train leads to problems such as frequent handovers, severe Doppler spread and so on. The rapid change in the channel also affects the accuracy of channel modeling and channel estimation, which degrades the performance of the communication system. Therefore, this paper designs an LTE-A based train-to-ground communication system, and its performance is evaluated by system level simulation. In order to simulate the high-speed railway scenario more properly, two kinds of network topology structures are designed for the simulation platform, namely the linear network and the cellular network. The former is mainly suitable for the rural areas, where the population density is lower. While the latter can be applied in the high population density areas, such as urban and suburban areas. The channel model used in this paper is the WINNER II D2channel model, i.e. the Rural Moving Network model, which is designed for high mobility scenario.One of the key technologies of LTE-A system is MIMO, in which signals can be transmitted independently through multiple antennas in the transmitter, and then are received and recovered in the receiver with multiple antennas. The core idea of MIMO is to improve channel capacity with the use of spatial degrees of freedom, provided by multiple transmit and receive antennas, so as to enhance transmission rate and to improve the system performance. The spatial degrees of freedom is related to the spatial correlation of the channel matrix, and this correlation will directly influence the rank of the channel matrix. The stronger the correlation is, the smaller the rank and the spatial degrees of freedom will be, leading to a lower channel capacity.The high speed trains generally run in the open areas with few scatters, so the signals between the base station and the train mostly go through line of sight propagation. In this situation, the channel matrix is rank deficient, and high correlation of the channel matrix will limit the channel capacity. In order to solve this problem and reduce the adverse effects caused by frequent handovers, distributed antenna technology is introduced to the high-speed railway scenario. Through cooperation among distributed antennas, the channel quality can be improved, and the rank of the channel matrix can be enhanced, so as to improve the channel capacity and the system performance.In addition, in order to solve the problem of low spectral efficiency in the cell edge, this paper combines CoMP technology and distributed antenna technology. The quality of the received signals can be enhanced by using this distributed CoMP technology. And the system performance of the distributed CoMP technology is analyzed on the system level simulation platform designed. The simulation results show that, the use of distributed CoMP technology can significantly increase channel capacity, and improve spectral efficiency not only in the whole area but also in the cell edge.