本論文探討都市地區之行動通信電波傳播特性，其中主要乃發展曲面物體之三維射線追蹤模擬程式與高效率之三維廣射線柱追蹤模擬方法，來分析行動通信基地台發射訊號在隧道內或建築物間的傳播特性，並進行現場實測，以供市區通訊場強涵蓋區預測及發射基地台規劃之用，來提高都市地區無線通訊系統的效率與功能。
所發展之曲面物體三維射線追蹤模擬程式乃應用均勻幾何繞射理論與射線追蹤法建立電波傳播模擬程式，來計算曲面物體對無線電波的反射及繞射效應。為了驗證此射線追蹤模擬程式的正確性，本研究實地測量了GSM 900/1800基地台所發射的無線電波在曲面隧道內之傳播特性，並與模擬結果比較，兩者變化趨勢大致吻合，此外，也比較不同曲率半徑之弧形隧道與矩形隧道之電波傳播特性，以及各種頻率與不同隧道截面對場強分佈的影響。本研究所發展之模擬方法能正確地預測曲面隧道內之場強分佈，可供隧道內場強涵蓋區預測及基地台天線建置規劃之用。
另外，本論文提出廣射線柱追蹤法，其中乃是追蹤整體射向建築物表面之輻射電波，有別於一般射線追蹤法將發射天線的輻射電波以多個小射線柱來模擬。對於市區行動通信基地台發射訊號傳播特性之模擬，可大為提升程式效率與實用性。因此，非常適合用來計算市區建築物體對無線通訊電波的多次反射及繞射效應，以分析行動通信在特定環境下之訊號分佈。本研究使用千分之一電子地圖並結合地理資訊系統應用程式，以取得市區建築物主體輪廓、行動通信基地台位置及電波場強分佈路徑資料，同時應用時域有限差分套裝模擬軟體XFDTD，計算了行動通信基地台天線之3D輻射場型與周遭電磁場強分佈特性並且實測之，其中所獲得基地台天線3D輻射場型可以提供射線追蹤程式進行模擬之用。此外，亦測量了都市地區GSM行動通信基地台發射訊號於所涵蓋區域街道上之分佈特性，而所得實測與模擬結果之變化趨勢大致吻合。

In this dissertation, wave propagation properties in urban areas for mobile communications are studied. A ray-tracing program is developed to simulate waves reflected and diffracted from curved objects for evaluating field distributions in curved tunnels. Also, a high-efficient ray-tube tracing method is presented, which can be applied to determine waves propagating around buildings for signals from cellular base stations.
A ray-tube tracing method to simulate waves propagating in curved road tunnels from base stations for mobile communications had been presented in this dissertation. Ray tubes are traced by including multiple reflections in the curved tunnels and diffractions from wedges of the tunnel structures, together with the direct path. To verify this ray-tube tracing approach, field measurements of 900/1800MHz signals in two curved road tunnels from GSM base stations were performed for comparisons with the ray-tube tracing simulations. By tracing ray tubes reflected and diffracted from the curved structures of the tunnels, the effects of the curvature on wave propagations in large guiding structures can be evaluated. Good agreements between simulations and measurements in the trends of the field distributions are obtained. A parametric study of the influence of the tunnel geometry and the signal frequency on the path loss is also presented by applying this ray-tube tracing method. Curved tunnels for different radii of curvature in the tunnel cross-section and horizontal plane, and also lengths of the curved part are compared, together with rectangular tunnels. Simulations of the field distribution over the cross-section of the curved tunnel away from the transmitting antenna are demonstrated too. The ray-tube tracing program can be applied to determine the deployment of the base-station antennas for improving signal coverage in tunnels, which may have curved structures.
Besides, a global ray-tube tracing method is presented, which is to trace the global wave tubes instead of the many small ray tubes for simulating wave propagations in urban areas. Therefore, simulation efficiency can be improved significantly so that site-specific signal distributions in cities may be determined more easily and practically by considering multiple reflections and diffractions. To find building exterior geometries, base-station locations, and field distribution paths, 1:1000 digital city maps and a geographic information system software package are applied. Also, a finite difference time domain software package, XFDTD is used to evaluate the 3D antenna patterns and fields adjacent to the antenna, and measurements are performed too. Those 3D antenna patterns are needed in the ray-tracing simulations. The field measurements on streets in Taipei city are also performed, and the results are compared with those obtained from the global ray-tube tracing program. Good agreements between simulations and measurements in the trends of the field distributions are obtained.

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