基於二維犁耙器接收機架構在寬頻分碼多重進接系統方面應用之研究

Abstract

對於寬頻分碼多重進接系統之二維犁耙器接收機架構，我們提出兩種實現上鏈接收機的方法，並研究其效能。這兩種方式分別為：基於波束之二維犁耙器接收機及基於空間分集之二維犁耙器接收機。當多重路徑衰弱從相同時間但不同方向抵達接收機時，基於波束之二維犁耙器接收機會在不同方向產生主瓣來結合不同方向之路徑，以減少多重路徑衰弱之效應。另一種有效對抗多重路徑衰弱之方法為基於空間分集之二維犁耙器接收機。此接收機不同於前者，其不會改變各個天線之場形，而只會結合在不同天線之基頻訊號，以提高訊號接收之強度。當訊號到達接收機的擴散角度增加時，基於波束之二維犁耙器接收機的效能有非常顯著的改進。當效能的錯誤率為10$^{-3}$時，兩者所需的訊號雜訊比幾乎相同。然而，對於十六支天線的基於波束之二維犁耙器接收機而言，其總天線之距離只需7.5$\lambda$。反觀基於空間分集之二維犁耙器接收機，其各個天線之距離就需10$\lambda$才可在各天線間獲得相當低的關聯性，此種情況則不適用在密集的都市區。對於提高基於波束之二維犁耙器接收機之效能，我們 只需提高一些運算的複雜度。如此，為了提高在密集都會區之系統容量及效能，則基於波束之二維犁耙器接收機是一種可靠性佳的方案。

In this thesis, we propose two approaches of a 2D-RAKE receiver for a wideband CDMA uplink transmission system and study their performances. A beamformer-based 2D-RAKE receiver combats multipath fading through forming multiple beams at different directions when multipath signals are received at the same time. Another approach of a 2D-RAKE receiver to combat multipath fading is a diversity-based 2D-RAKE receiver. Unlike the beamformer-based 2D-RAKE receiver, the diversity-based 2D-RAKE receiver combines signals at baseband to increase the signal level without computing individual antenna beam pattern. With a large angle of spread (AOS), the performance of the beamformer-based 2D-RAKE receiver is significantly better than the performance of the diversity-based 2D-RAKE receiver at BER=$10^{-3}$. Total antenna separation is only $7.5\lambda$ for a sixteen-antenna beamformer-based 2D-RAKE receiver, while at least $10\lambda$ of each antenna spacing is needed for the diversity-based 2D-RAKE receiver to achieve sufficiently low fading correlation. Therefore, the diversity-based 2D-RAKE receiver is not very practical in a dense urban area. The performance improvement of the beamformer-based 2D-RAKE receiver is achieved at the expense of a moderate increase in computational complexity. To improve the system capacity and performance in the dense urban area, the beamformer-based 2D-RAKE receiver is a reliable solution.