The Propagation Characteristics Of Millimeter Wave In Subway Tunnels

To learn the characteristics of wave propagation in tunnels could give some practical and theoretical guidance for designing a radio system. The main purposes of this dissertation are to model the wave propagation in tunnels,as well as studying the characteristics of millimeter wave propagation in subway tunnels by simulations and experimentations.Two improved ray-tracing models, which named vertical plain rotation and section projection model respectively, are presented in this paper. These two models could directly calculate the path vector or the coordinates of all reflection points on a path. They avoid the computationally complex ray-tracing step. The knowledge about 38GHz band wave propagation characteristics is scarce. A radio transceiver and a signal strength measure system operating at 38GHz are developed in this paper. Later, wave propagation measurements are conducted using these devices which are calibrated by standard instruments. Substantive wave propagation simulations based on classical GO method are carried out. The measure and simulation results are carefully analyzed based on experiential models for wave propagation. The main labor and creative work are as follows:1. In order to overcome the drawback of ray-tracing method, the vertical plain rotation and section projection models based on geometric-optical theory are presented, which deduced from the ray propagation in rectangular tunnel. These two models avoid the ray-tracing step, and greatly reduce the computational complexity of traditional model. Theoretical reasoning and simulation results show that it can accurately and effectively predict the characteristics of wave propagation in rectangular tunnels. These methods could also apply to other tunnel with non-rectangular section by transforming the non-rectangular section to a rectangular one with the same area as that of the former.2. Wave propagation in tunnels is a complicated non-linear system, which determined by many factors. Multi-layer forward feed neural network (FNN) could accurately depict the non-linear relationship between any input and output. In this paper, A BP (back propagation) neural network is firstly introduced to predict the characteristics of wave propagation in tunnels, these BP network could accurately predict the path-loss and time delay of wave propagation in tunnels. At present, the real-time channel parameters are obtained by experiential models in simulation of communication system. Because of the neglectable time and high accuracy of prediction, the BP could be used as the model to predict the characteristics of wave propagation in tunnels for real-time simulation of communication system.3. A 38GHz radio transmission and a train-carried signal-strength measure system are designed. Utilizing these devices, some wave propagation experiments are performed in several different tunnels. The effect of antenna on propagation and the path-loss characteristics are analyzed based experimental results.4. Based on theoretical analysis, the parameters of predicting model in Wireless-Insite software are selected. Some simulations are performed in Wireless-Insite to research the effect of simulation parameters on the prediction results. The accuracy of Wireless-Insite is tested and the simulation parameters are carefully attuned based on experimental results. In order to research the effect of propagation condition on propagation characteristics of 38GHz radio wave in subway tunnels, a lot of simulations are implemented using the calibrated simulation model in Wireless-Insite. The simulation results give some valuable guidance for designing a 38GHz radio system in subway tunnels.Combined with some interrelated national 863 projects, the characteristic of 38GHz radio wave propagation in tunnels is studied in detail. The predicting models presented in this paper are original and practical; they could give accurate predicting results with relatively little time. Some new results of millimeter wave propagation in subway tunnels are attained by experiments and simulations; these have higher reference value for designing a radio system in tunnels. The 38GHz transceiver and train-carried signal strength measure system already have played important role in engineering application.