在智慧型天線系統中使用圓柱形陣列之波束成形設計

Abstract

在一個智慧型天線系統(smart antenna system)下使用波束成形技術(beamforming)是一個有效增加系統效能之方法。本論文研究圓柱形陣列(cylindrical array)之波束成形設計。當一個訊號從特定方位入射陣列，部分天線會收不到訊號。因此，吾人提出一子陣列選擇架構來選出最佳執行波束成形之子陣列。另一方面，當執行波束成形來抑制干擾影響的同時，降低使用之天線個數可以降低系統之成本及複雜度。吾人首先提出一個可以在抑制干擾能力及使用天線個數之間取得平衡之演算法。然而，此演算法之效能可能在某些情況下降低。吾人進而提出另一兩階段式演算法，並結合輸出訊號對干擾加雜訊比之限制來改善上述問題。如此一來，系統在不同環境下能保持穩定效能。最後，模擬結果顯示基於吾人所提出之子陣列選擇架構及波束成形設計，本系統之圓柱形陣列基地台能在同一資源下同時服務多個行動台，進而增加系統之容量且降低系統之成本及複雜度。

Beamforming is an effective technique to enhance the system performance in smart antenna systems. This thesis investigates beamforming design using a cylindrical array. Since not all the antennas can receive an incident signal from a specific direction, we propose a subarray selection scheme to find a best subarray to perform beamforming. On the other hand, it is economical to use as few antennas as possible in beamforming to suppress interference automatically so as to reduce the system cost and complexity. We firstly propose an algorithm which strikes the balance between interference suppression and number of used antennas. However, the system performance may degrade in some circumstances. To mitigate this problem, we secondly propose a two-stage algorithm with an output SINR constraint which further guarantees the system performance in different environments. Finally, simulation results show that based on the proposed subarray selection scheme and beamforming designs, the cylindrical array base station can serve multiple mobile stations effectively to increase the system capacity while reducing the system cost and complexity.