以垂直正交分頻分碼多工調變為基礎之下鏈接收機架構之設計

Abstract

下一代的蜂巢式行動通訊系統必須提供高速資訊傳輸之無線網路應用。而最可能使用之無線多重進階方式為OFDM/CDMA。這篇論文將介紹OFDM/CDMA下鏈接收機之基頻架構設計以期達到高資料傳輸速率之要求並探討OFDM/CDMA系統效能。這套系統除了具有基頻訊號偵測功能，還包含以領航訊號(pilot signal)來實現通道估計之功能。訊號偵測的部分需要設計一個通道等化器與決策器。其中通道等化器主要有最大比例合併等化器（Maximum ratio combination）、強制歸零等化器（Zero forcing）、部份等化器(Partial equalizer)、最小均方差等化器（MMSE）與相同增益合併等化器（Equal gain combination）等五種。本論文將研究各種等化器之效能以應用在下鏈接收機之架構。在通道估計方面我們是使用一已知的領航訊號，利用FFT匹配濾波器(FFT Match filter)觀念與移動平均的技術來完成。本論文另外會再比較OFDM/CDMA下鏈接收機與CDMA下鏈接收機之異同並以電腦模擬此二系統在數種通道下的效能。

The next generation cellular mobile communication system will provide high data rate for internet service. One of the most promising multiple access methods in the next generation system is the OFDM/CDMA. This thesis proposes an OFDM/CDMA downlink baseband receiver architecture for high data rate transmission and discusses the system performance. This receiver architecture includes a baseband signal detection and a channel estimation. We use a pilot signal to estimate the channel. For signal detection, we design a channel equalizer and a signal decision method. The channel equalizer has five methods: Maximum ration combining, Zero forcing, Partial equalizer, MMSE(Minimum mean square error) and Equal gain combining. The performances of these five kinds of channel matching methods are shown in the thesis. Furthermore, we use a pilot signal with FFT based matched filters and moving average unit to estimate channel response. We also compare the OFDM/CDMA downlink baseband receiver architecture with a CDMA downlink baseband receiver architecture. The performance of the systems are simulated by computer under several channel models.