CDMA系統二維犁耙式接收機架構下,關於到達方向尋找,下鏈波束形成與發射機定位的研究

Abstract

本論文所採用的接收機架構是一種以快速傅利葉轉換為基礎的匹配濾波器的二維犁耙式接收器。其策略是將通道的空間及時間響應一併考慮在同一個接收機中，即在空間與頻率的領域裡處理信號。此接收機可以估計多重路徑到達的角度、時間、強度及相位，並將接收信號以空間及時間的最大比相加。而藉由選擇強度最大的路徑，根據所估計的到達角度、時間，即可進一步的完成下鏈波束形成與發射機的定位。 為了增加系統容量與提高頻譜使用效率，下鏈波束形成已經在分碼多工進接系統中被提出。它可降低多重進接干擾、自我干擾以及細胞內部干擾的效應。在本論文中我們將以已知的信號到達方向參數來完成下鏈波束形成。 在分碼多工進接系統中，發射機定位的技術已經廣泛的在研究當中。定位技術所採用的兩種參數為：量測路徑的到達時間與方向。到達時間的取得是利用CDMA二維犛耙式接收機的架構；到達方向的取得則是利用空間訊號處理技術，假設在基地台有一組陣列天線。當改變不同的傳輸條件與不同的基地台數目來作定位的估計時，所採用定位方法效能的評估都是根據距離誤差且為二維的定位。

In this thesis we adopt a FFT based matching filter 2D rake receiver. Its characteristic is considering spatial-temporal impulse response of channel in the same receiver that is doing signal process in both spatial-temporal domains. This receiver can estimate multipath angle, timing, amplitude and phase, and then combine the receive signal using maximum ratio combining. We can choose the strongest path by estimating its angle of arrival, timing of arrival, and then downlink beamforming and transmitter positioning can be easily achieved. Downlink beamforming has been proposed for high capacity and spectrally-efficient CDMA system. It mitigates the effects of multiple access interference, self-interference and inter-cell interference. In this paper we use the DOA parameter to form downlink beamforming. Subscriber radiolocation techniques are invested for CDMA cellular networks. Two paremeters are considered for radiolocation: measured times of arrival (ToA) and angles of arrival (DoA). The ToA measurements can be obtained from CDMA 2D rake receiver and the AoA measurements at a base station are assumed to be made with an antenna array. The performance of the two methods is evaluated for both ranging and two dimension (2-D) location, while varying the propagation conditions and the number of BS’s used for the location estimate.