MC-CDMA與MC-DS-CDMA在多路徑通道下之系統效能比較

Abstract

下一代的蜂巢式行動通訊系統需提供高速傳輸之無線通訊網路，目前以OFDM/CDMA之多重進接方式最受重視，本篇論文將介紹並比較兩種不同的OFDM/CDMA系統: 多載波分碼多重進接(MC-CDMA)與多載波直接序列分碼多重進接(MC-DS-CDMA)。在下鏈的傳輸中，MC-CDMA在接收端需具備通道等化器以補償通道效應並抑制干擾與雜訊，主要有最大比例合併等化器(Maximum ratio combination)、等增益合併等化器(Equal gain combination)、強制歸零等化器(Zero forcing)與最小均方差等化器(MMSE)，我們也將比較各等化器效能。對MC-DS-CDMA系統我們提供一個低複雜度的改良方式，改善效能的同時也完全抑制多用戶干擾。在通道估計方面我們以指標式通道估計搭配線性內插來完成。本論文最後將模擬比較MC-CDMA與MC-DS-CDMA在數種通道狀況下的效能。

The next generation cellular mobile communication system will provide high data rate for internet and digital broadcasting. OFDM/CDMA is one of the most promising multiple access method. This thesis introduces and compares two different OFDM/CDMA systems: MC-CDMA and MC-DS-CDMA. For downlink MC-CDMA system, we design a channel equalizer to compensate the channel effect and suppress interference and noise at the receiver. There are mainly four kinds of channel matching methods: Maximum ratio combining, Equal gain combining, Zero forcing combining, and MMSE combining. We also compare the performance of these methods. We propose an improved MC-DS-CDMA system with low complexity and null interference. We use pilot based channel estimation to estimate the channel frequency response. The performance of MC-CDMA and MC-DS-CDMA is simulated by the computer under several channel models.