具發射/接收分集之空間時間編碼正交分頻多工系統之研究

A Study on Space-Time Coded OFDM System with Transmit/Receive Diversity

黃崇益(Chung-Yi Huang)

指導教授 ： 黃正光

元智大學/工程學院/電機工程學系/碩士(2001年)

摘要

在本篇論文中，吾人考慮在正交分頻多工（OFDM）的系統架構上，探討結合多根發射/接收天線與空間時間編碼技術(Space-Time Coding,STC), 使其在頻率選擇性Rayleigh衰減通道的環境下，提升系統之性能。一般而言，使用2根發射天線與M根接受天線的系統，可以提供2M 的分集增益，而其中目前以2ISO STC-OFDM及2I2O STC-OFDM 兩種方式最具實用性，如此不僅可有效地提升系統容量，也讓OFDM 系統更適合應用在未來無線通訊的高速傳輸上。此外，由於利用了天線分集之觀念，吾人需再進一步探討STC-OFDM 通道估測與內插技術，首先利用最小平方法及前導符碼(pilot symbol) 得到前導子載波(pilot subcariers) 之通道估測值，然後再分別比較三種通道內插法,即：1）升餘弦內插法 2）快速傅利葉轉換內插法,及3）線性內插法，最後，我們利用電腦模擬來評估此一STC_OFDM在系統在各種狀況下的性能表現。

關鍵字

正交分頻多工 ； 空間時間編碼 ； 發射分集 ； 接收分集 ； 通道估測

並列摘要

In this thesis, we consider using multiple transmit/receive antennas with orthogonal space-time coding (STC) in OFDM transmission system over frequency selective fading environment. Generally speaking, the space-time coding and associated diversity combining technique can provides a diversity gain of 2M by exploiting two transmit antennas and M receive antennas. In this thesis, we especially study two simple but most practical configurations is obtained for M=1 and 2, namely, the 2ISO and 2I2O STC-OFDM systems. It is shown that the STC-OFDM system ideally combines the major advantages of both techniques: It can not only offer robustness against large delay spread in high rate data transmission, but can also combat deep fading with a diversity gain of 2M. Furthermore, we consider the channel estimation/interpolation problem inherent to the STC-OFDM system. We first use pilot-symbol-assisted-modulation (PSAM) and the least squares (LS) approach to find the channel estimates at pilot subcarriers. Then we study three different channel interpolating methods : 1) Raised cosine interpolator, 2) FFT-based interpolator, and 3) Linear interpolator, for subsequent channel interpolation along the frequency axis. Finally, computer simulations are conducted to demonstrate and compare the performances of the STC-OFDM systems.

並列關鍵字

OFDM ； Space Time Coding ； transmit diversity ； receive diversity ； channel estimation

參考文獻

[1] Bingham, J.A.C , "Multicarrier modulation for data transmission: an idea whose time has come," IEEE Communications Magazine, May 1990, Page(s): 5 -14

[2] Zhendao Wang, Giannakis, G.B., "Wireless multicarrier communications," IEEE Signal Processing Magazine, May 2000, Page(s): 29 -48

[5] Leonard J. Cimini, JR., "Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing," IEEE Transactions on Communications, July. 1985, Page(s):665 -675

[6] Cavers, J.K., "An analysis of pilot symbol assisted modulation for Rayleigh fading channels," Vehicular Technology, IEEE Transactions on , Volume: 40 Issue: 4 , Nov. 1991, Page(s): 686 -693

[7] Ye Li, "Pilot-symbol-aided channel estimation for OFDM in wireless systems," Vehicular Technology, IEEE Transactions on , Volume: 49 Issue: 4 , July 2000, Page(s): 1207 -1215