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摘要：电波传播特性预测是无线电系统设计的基础，其中路径损耗特性关系到系统覆盖范围，决定系统布局，时延特性决定数字通信系统的最大数据传输速率。提出一种预测隧道中电波传播特性的方法，该方法可以通过几何光学原理精确地计算出由发射天线到达接收天线的电波主要路径，使用新模型避免了复杂度很高的射线跟踪过程，使传统预测方法的计算复杂度大大降低。利用射线跟踪技术，综合考虑了隧道表面介电常数和反射系数、收发信机的工作频率和功率、以及天线增益等因素，建立了电波在拱形、圆形、矩形隧道中传播的确定预测模型，隧道中收发信机的距离与有效反射线条数的关系式、单根射线的传输损耗和传输时延随距离变化的关系式、以及多径情况下总的接收信号功率和传输衰减的表达式，为抗衰落技术的应用打下了基础。仿真结果表明：拱形隧道内两种射线跟踪法的结果比较准确，但是它们的略微有一个缺点就是仿真的工作量和计算时间比较长，对于较严谨地研究具体的某些问题它们则是首选。圆形隧道内频率越高电磁波的衰减率越小，隧道半径越大衰减率越低；隧道中的弯曲不利于电磁波的传播，曲率半径越小电磁波衰减越大。矩形隧道内隧道环境中收发天线相距越近，其接收的多径信号的平均时延扩散越大，隧道截面积越大，其接收的多径信号的平均时延扩散越大。20113
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关键词：传播特性；路劲损耗；射线跟踪；预测模型
Radio waves propagation characteristics in rail transit tunnels prediction modeling and simulation
Abstract：It is important to predict characteristics of radio wave propagation．The path-loss characteristic has close correlation with coverage and layout of a radio system．The time-delay characteristic determines the maximum transmission rate of a radio digital system．In this paper，a new model is presented to predict wave propagation in tunnels with a rectangular section．In an rectangular tunnel，paths between transmitter and receiver can be determined analytically using geometric optics．The new method avoids complicated ray tracing calculation．Using ray tracing technique，synthetically considering the tunnel dielectric constant and reflectance，the frequency and power of transceiver，and the gain of antennas，etc，a certain prediction model and simulating of the propagation of electromagnetic wave in tunnel is built up，the relationship between the transmission distance and the valid number of multipath，the relationship between the transmission distance and single path transmission attenuation and time delay，and the expressions of total power and transmission attenuation of multipath signals in three dimensions are deduced．It is the base of the application of anti-decline technique．The simulation results show that：In arch tunnel，the results of two kinds of ray tracing method is accurate，but they have a slightly is the workload and calculation time is longer，the simulation for more rigorous study some specific problems they are preferred．In circular tunnel frequency is higher，the smaller the attenuation of electromagnetic wave，the radius of tunnel，the greater the attenuation rate is lower；Bend in the tunnel of electromagnetic wave propagation，the smaller the radius of curvature，the greater the electromagnetic wave attenuation．In rectangular tunnel，the less the separation between transmitter and receiver，the larger the root mean square mean excess delay．The larger the dimension of cross section，the larger the mean excess delay．
Key Words：propagation characteristics；path-loss；ray tracing；prediction model
目 录
1 绪论 1
1.1 前言 1
1.2 铁路隧道环境电波传播路径损耗特性的历史与现状 2
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