Research On Channel Modeling And Simulation Method Based On Propagation Graph Theory In Tunnel Environment

The subway is one of the popular transportation tools. Studying the wireless channel characteristics of the subway environment and establishing a reliable communication system can ensure the efficient operation of the subway. This dissertation introduces a propagation graph theory, which is used for modeling and simulation of the wireless environment of tunnel scenario.Firstly, this dissertation introduces that the propagation graph theory is suitable for modeling of the wireless environment with known geometrical dimensions. The tunnel environment’s structure is simple and the geometry size can be easily confirmed, which is suitable for using the propagation graph theory to model. Propagation graph theory describes the signal transmission process with the relationship between the points and the edges. The points of the traditional graph theory are classified into three categories: transmitting antennas, receiving antennas and scattering objects. Before introduced to the subway wireless environment, it needs appropriately modification.Secondly, in response to the characteristics of tunnel environment, the part of the scattering points of propagation graph theory is improved:First, a method of curved tunnel segmentation is introduced. The curve is divided into some parts according to the bending radius and angle of the tunnel. Next, a method of tunnel walls’ geometric segmentation is introduced. According to the different cross-sections, the tunnel is divided into different parts. Then, a method of using points to describe the tunnel wall is introduced, which is according to the geometry of the tunnel walls. Besides that, a visibility matrix of the tunnel wall is introduced, according to the geometry of the tunnel, judging if the scattering points on the tunnel walls are visible to each other. After that, compared the original graph theory and the new graph theory, it can find that the new method can express the multipath information better.Thirdly, in this dissertation, the field measurement of the Nantong tunnel center is conducted. The tunnel is composed of a rectangular tunnel and an arch tunnel. Channel impulse response is obtained after measurement. Then, by measuring the geometrical dimensions of the tunnel, another channel impulse response is obtained by using the propagation graph theory to simulate. The comparison is done between these two channel impulse responses, it can find that the RMS error is less than lOdB. After that, using the SAGE algorithm to calculate these data’s angle of departure and angle of arrival. The contrast of the results shows that these two results are similar.Fourthly, in this dissertation, a subway tunnel model is built according to the subway construction standard, and the model simulation is carried out by using the propagation graph theory. The transmission antennas are placed at the top of the train’s head. The research and analysis are carried out by selecting three typical locations of the train passing through the tunnel. First, the visibility matrix of the three are compared. It can be found that the transmitting antennas can erase the visibility matrix. Then compare the correlation matrix of the three positions, calculate the AOA and AOD of the three positions, and then further calculate the angular expansion, combined with the correlation matrix to analyze the characteristics of the three positions. After that, calculate to obtain the channel capacity, and compare with the straight distance of this scenario, and get the conclusion that the corners of the channel capacity is higher than straight channel capacity under the condition of the same distance between senders and receivers. The channel matrix is decomposed by SVD, found that the reduced rank of channel matrix.Finally, the dissertation summarizes the previous research results and puts forward to new directions of the propagation graph theory under the tunnel wireless scenario.