以適應性濾波器估計多輸入多輸出正交分頻多工系統通道特性之應用研究

Channel Estimation for MIMO-OFDM Systems Using Adaptive Filters

陳信宏(Hsin-Hung Chen)

指導教授 ： 譚旦旭

國立臺北科技大學/電資學院/電機工程系研究所/碩士(2009年)

https://doi.org/10.6841/NTUT.2009.00258

摘要

本論文在多輸入多輸出正交分頻多工(MIMO-OFDM)系統下使用適應性濾波器估計通道特性。無線通訊系統中MIMO-OFDM架構是一個重要的技術，為了提升系統效能，精確估計通道狀態 (Channel State Information, CSI)是必要的。估計通道的方法繁多，例如最小平方 (Least Square, LS)、最小均方誤差(Minimum Mean Square Error, MMSE)與適應性濾波器(Adaptive Filter)，其中MMSE雖然有最好的效能，但它必須事先知道通道狀態且運算複雜度高，因此常作為比較的基準。LS在高度干擾或多雜訊的環境下其效能並不理想，因此本論文使用適應性濾波器與領航符碼(Pilot symbol)估計通道特性。但因傳統適應性濾波器會有收斂速度過慢的問題，因此我們進一步提出結合LS與適應性濾波器的方法，包括LS結合最小均方(LS+LMS)與LS結合遞迴式最小均方(LS+RLS)兩種，以提升適應性濾波器的收斂速度。模擬結果顯示我們提出的方法之收斂速度遠優於適應性濾波器，且其均方誤差(Mean Square Error, MSE)與適應性濾波器相當。

關鍵字

多輸入多輸出 ； 正交分頻多工 ； 空時區塊碼 ； 適應性濾波器 ； 領航符碼

並列摘要

In this study the application of adaptive filter for channel estimation in MIMO-OFDM system is investigated. During the years, MIMO-OFDM has been adopted in various wireless communication systems due to its many advantages. However, accurate channel estimation is essential for such systems to achieve good performance. Many channel estimation schemes have been presented, such as least square (LS), minimum mean square error (MMSE), and adaptive filtering. While MMSE has the best performance among them, it needs to know the channel state in advance. In addition, its computational complexity is the highest. Therefore, MMSE is commonly used as a benchmark for performance comparison. On the other hand, performance of LS degrades as channel interference or noise increase. Hence, adaptive filter and pilot symbol are employed in this study for channel estimation. To overcome the problem of slow convergence rate in conventional adaptive filter, two estimation approaches that combine LS and adaptive filters with least mean square (LMS) and recursive least square (RLS) are proposed. Experimental result indicates that the proposed schemes achieve mean square error (MSE) performance similar to the conventional adaptive filter with a faster convergence rate.

並列關鍵字

Multiple-Input Multiple-Output (MIMO) ； Orthogonal Frequency Division Multiplexing (OFDM) ； Space-Time Block Codes (STBC) ； Adaptive Filter ； Pilot Symbol

參考文獻

[3]ETSI, “Broadband Radio Access Networks; Hiperlan type 2 Technical Spec; Physical Layer,” Dec. 2001.

[5]K. F. Lee and D. B. Williams, “A Space-Time Coded Transmitter Diversity Technique for Frequency Selective Fading Channels,” in Proceedings of IEEE Sensor Array and Multichannel Signal Processing Workshop, pp. 149-152, 2000.

[9]M. Enescu and V. Koivunen, “Time-Varying Channel Tracking for Space-Time Block Coding,” in Proceedings of IEEE Vehicular Technology Conference, pp. 294-297, 2002.

[13]W. Zou and Y. Wu, “COFDM: an Overview,” IEEE Transactions on Broadcasting, pp. 1-8, 1995.

[14]S. Weinstein and P. Ebert, “Data Transmission by Frequency-Division Multiplexing Using the Discrete Fourier Transform,” IEEE Transactions on Communication Technology, pp. 628-634, 1971.