| Summary: | 博士 === 國立臺灣科技大學 === 電機工程系 === 92 === In this thesis, wave propagation models with digital maps, based on heuristic uniform theory of diffraction (UTD), are developed to analyze the propagation characteristics over hilly terrain and in urban environments. Those approaches can be applied to predict signal coverage and deploy base-stations, so that the coverage qualities of the terrestrial broadcasting and urban mobile communications may be improved.
For the site-specific model determining wave propagation over hilly terrain, vertical terrain profiles between the transmitting and receiving antennas are obtained from digital maps, having a resolution of along the longitudinal and latitudinal directions. A profile linearization method is developed to simplify those terrain profiles into 2-D wedges and trapezoids, and a sequence arrangement algorithm is developed to search all forward propagation paths. Thus, computation time in finding propagation paths and evaluating field distributions may be significantly reduced. A heuristic UTD approach including multiple-edge transition zone diffractions is then applied to determine path losses for waves propagating through those 2-D structures. Entire forward diffracting contributions plus a ground reflection near the receiving antenna are included to evaluate the field distributions.
As to the site-specific model for determining wave propagation in urban environments, the contours and heights of main building structures between the transmitting and receiving antennas are obtained from 1:1000 digital city maps. A method using vertical and transverse profiles is applied to simplify those building structures into 2-D wedge combinations in two perpendicular profiles, and a sequence arrangement algorithm is developed to search all forward propagation paths. All the forward scattering contributions are computed by including multiple-wedge diffractions and reflections, based on the UTD. Thus, field distributions for mobile communications in urban may be obtained efficiently.
Some of the simulations are compared with measurements of the VHF TV signals in northern Taiwan and also GSM signals from base-stations in Gong-Guan area of Taipei city to evaluate the accuracy of the simulations. Good agreements are obtained, considering the complexity of wave propagation through irregular terrains and urban environments.
|
|---|
