在行動通訊環境下適應性波束場型分集及信號源定位之研究

Abstract

在本論文中，吾人提出一適應性波束場型分集法，用來減輕在行動通訊環 境下衰退現象之影響。此法之主要觀念在於形成兩波束來接收入射之衰退 信號。藉由最小化兩輸出信號之互相關係數，便能建構出最佳波束合成器 。此最佳波束合成器之波束場型具有低旁波瓣和相互對稱之特性，它們的 作用分別是抑制干擾及使兩分集信號有相同功率。為了獲得較準確之指向 角，本研究中也提出一信號源定位法。首先，信號源方位角之估測能藉由 比較兩個適當波束之輸出功率來完成。其次，當基地台接收到不同次細胞 發送之信號後，便可著手來訓練曲線記憶單元，進而達成距離估測之目的 。此曲線記憶單元能記憶不同入射角、信號源距離及其對應之波束空間互 相關係數平方值之關係。它完成了波束空間互相關係數平方值與信號源距 離間之映射工作。電腦模擬結果顯示，在一具有多干擾源及衰退現象之傳 播環境下，結合吾人所提之最佳適應性波束場型分集法及信號源定位法， 將是一適當之解決方案。 An adaptive beam pattern diversity scheme for reducing the fading effects in a mobile environment is presented. The main concept of the proposed diversity technique is to form two reception beams encompassing the incoming fading signals. The optimum beamformers are then constructed so as to minimize the crosscorrelation coefficient between two beam outputs. The beam patterns should possess low sidelobes for interference rejection and mutual symmetry for equal power diversity signals. To maintain an accurate look direction, a localization method is also proposed. First, the source angle estimate is obtained by comparing two sets of fixed Chebyshev beams for equal output power. Second, range estimation is accomplished by training a curve fitting unit (CFU) with the data emitted from different subcells in the field of interest. The CFU is constructed to memorize the relationship among various incoming angles, ranges, and the corresponding squared magnitudes of beam space crosscorrelation coefficients (BSCCC). Specifically,it is used as a mapping from the squared magnitude of BSCCC to the range estimate. We demonstrate that the proposed adaptive beam patten diversity scheme working in conjunction with the location estimator provides an appropriate solution for fading phenomenon in the presence of complicated interference.