在行動通訊環境下以陣列天線擷取目標訊號之研究

Abstract

在本論文中，吾人提出一種針對於行動通訊環境下之適應性波束合成法。 此法係源於傳統單波追蹤器中所用之和╱差技巧。吾人藉由一線性限制最 小功率法則推得最佳之加權向量。此波束合成法表現出良好的干擾抑制能 力及些許的目標信號消除。在效能分析方面，吾人推導出和波束合成器輸 出之信號干擾雜訊比及比次誤碼率，並以電腦模擬結果來驗證所提之方法 。為了獲得一較準確之指向角，吾人使用一放射式基底函數架構之類神經 網路來估測在蜂巢式通訊環境下各通訊單元的訊號入射角。吾人利用一組 天線陣列波束合成器來擷取目標範圍內子細胞中送出的資料，藉以訓練該 神經網路，進而得到一組基於最小平方誤差法之加權向量。電腦模擬結果 顯示，在一存在多重反射路徑傳播環境下，結合吾人所提出之最佳波束合 成器及方位估測子將是一個適當的解決方案。 An adaptive beamforming scheme for signal acquisition in a mobile environment is presented. The scheme is developed based on sum-and-difference technique employed in conventional monopulse radars. The optimum weight vector is so constructed as to minimize the output power of the difference beamformer subject to a constraint on the sum beamformer response. The beamformer exhibits good interference suppression capability and insignificant desired signal cancellation. Performance analysis is conducted for the proposed beamformer in terms of signal-to-interference-plus-noise ratio and bit error probability. The results are confirmed by computer simulations. To maintain an accurate look direction, a novel beamspace radial basis function neural network for the estimation of the angle-of-arrival (AOA) of a mobile unit in cellular communication is proposed. By training the network with the data emitted from different sub-cells in the field of interest, and then collected by a set of antenna array beamformers, optimum weights which lead to the best approximation of the desired response in least-square can be obtained. It is demonstrated the optimum beamformer working in conjunction with the proposed angle estimator provides that an appropriate solution for signal acquisition in the presence of complicated multipath propagation.