微細胞無線電空時通道模型之建構與量測

Abstract

本論文提出混合式空時通道模型，研究在微細胞(都會區)環境中，無線電波之TOA、AOA與平均場強。它是由二維適應環境式模型(Site-specific Model)和統計模型組合而成，適應環境式模型可計算直接波、地面反射波與牆壁的散射波。而散射模型則可用來描述微細胞傳播環境中隨機擺放的散射體如汽車、機車、街燈等所造成的散射場。該模式能同時可精確地預估電波的TOA、DOA、延遲擴展、角度擴展與平均場強值，並藉由散射體個數 N 有效地量化微細胞傳播環境中之散射體的貢獻。由空時通道量測實驗數據（2.44-GHz於微細胞）我們發現(1)延遲擴展與角度擴展會隨距離增加而逐漸下降，而其範圍分別分佈於20ns~70ns 與2°~20°之間(2) 分佈街道上的汽車、機車、路燈等所造成的散射效應是不可忽略的; (3)在微細胞(都會區)環境中,我們設定N=10,則混合模式可以得到較好的預估結果。

This thesis presents a hybrid spatio-temporal model to predict TOA、AOA and signal strength of microcellular radio channel in urban environment. First, it is found that delay spread and angle spread decrease gradually with the increase of propagation distance. The ranges of delay spread and angle spread are 20ns~70ns and 2°~20°, respectively. Second, the hybrid model combines a deterministic model with a statistical model. The former model that is a site-specific model can calculate direct wave, ground-reflected wave and the field scattered from the street walls. The latter one employs statistical approach to calculate the scattered fields due to randomly positioned scatterers along the streets, which includes vehicles, pedestrians, trees, lampposts, motorcycles and et al. A spatio-temporal channel measurement using a high performance radio channel sounder helps us to develop the statistical model. It is found that number of randomly positioned scatterers (N) is equal to 10, which is a reasonable value for both sites #1 and site #2 and seem to be irrelevant the street width. We validate the hybrid model by comparing the computed result with measured ones. It is found that the hybrid model is reasonably accurate.