正交分頻多工系統之傳送端分集技術

Abstract

本論文介紹兩種利用傳送端分集技術之OFDM系統，分別為以空時方塊碼及差分空時方塊碼編碼之OFDM系統。空時方塊碼編碼之OFDM系統在發射機端使用空時方塊碼編碼，在接收機端最佳化地結合信號處理。利用空間上分離的兩根天線發射信號，使得接收機端達到分集增益的效果且不需大幅增加接收機的複雜度。此系統在接收機端需要知道通道資訊以便做信號偵測。我們傳送在時間領域的互補碼領航信號以便做通道估計。領航信號以特別次序傳送，以確保在接收機端經過碼匹配處理後，領航信號仍擁有良好的自相關及互相關特性。差分空時方塊碼編碼之OFDM系統在發射機端使用差分空時方塊碼編碼。相似地，系統可以獲得非常大的分集增益好處。然而，傳送端並不需要傳送領航信號去估計通道狀態資訊。最後，我們使用電腦模擬去評估兩種系統之效能。

The thesis introduces two transmitter diversity techniques for Orthogonal Frequency Division Multiplexing (OFDM) systems. One is a space-time block coded OFDM system. The other one is a differential space-time block coded OFDM system. The space-time block coded OFDM system uses a space-time block coding scheme at the transmitter and combine signals optimally at the receiver. Diversity gain can be achieved by using two spatially separated transmitter antennas to transmit signals with only a small increase in the complexity of the receiver. The system requires the knowledge of the channel at the receiver for the purpose of the signal detection. Complementary code based pilot signals are transmitted in the time domain for the purpose of the channel estimation. The pilot signals are transmitted in a special order to ensure that they have good auto-correlation and cross-correlation properties in the code matching process at the receiver. The differential space-time coded OFDM system uses a differential space-time block coding scheme at the transmitter. The system can obtain a great benefit in the diversity gain without transmitting pilot signals. Computer simulations are used to evaluate the performance of both systems.