利用華氏碼進行OFDM系統通道估測

A Channel Estimation Scheme for OFDM System with WHT

孟慶瑞(Ching-Jui Meng)

指導教授 ： 涂世雄

中原大學/工學院/電機工程研究所/碩士(2005年)

https://doi.org/10.6840/cycu200500460

摘要

摘要
在本論文中，我們提出利用華氏碼來改善OFDM系統在選擇衰減通道的估測效能，避免使用線性放大器來降低頻率選擇衰減和高均峰比。
研究步驟分成3個部分︰首先，我們提出一個通道模型只進行白色高斯雜訊來模擬理論並比較估測結果。其次，利用標準OFDM系統在傳送端使用前置等化器以及在接收端使用均方錯誤(MSE)方式進行通道估測作為參考。第三，我們提出修改WHT/OFDM系統去改進適應等化器性能並取代最佳但是複雜的通道估測辦法。最後，利用模擬來證明我們提出的通道估測的性能。
我們研究主要貢獻有下列幾點:
(1)OFDM系統使用華氏碼相較於使用前置等化器的之調變模式有較高之訊雜比。
(2)OFDM系統在低調變和低訊雜比使用華氏碼優於等化器調變模式。
(3)由於通道模型不標準或其它理由，OFDM系統應用華氏碼可不需要使用回饋通道。
我們相信在這篇論文裡的研究結果對未來在無線通訊系統的通道估測研究範圍將非常有幫助。

關鍵字

白色高斯雜訊 ； 均方錯誤 ； 華氏碼 ； 峰均值功率比

並列摘要

Abstract
In this thesis, we present a method of channel estimator with the Walsh Hadamard Transform (WHT) to combat the influence of selective fading channel estimation performance on the OFDM system. It can avoid low immunity against frequency selective fading and a high peak-to-average power ratio (PAPR) which necessitates the usage of a highly linear amplifier.

This schemes can be divided into third parts as follows: First, we consider a channel modeling and estimation that is subject to AWGN only, and verify the simulation results by comparing them with the theoretical results of the modulation scheme. Second, a standard OFDM system with an adaptive Mean Square Error (MSE) equalizer at the receiver and pre-equalization at the transmitter. is used as the reference in our performance simulations. Third, we propose modification of the WHT/OFDM system to improve adaptive equalization performance istead of the optimal but complex solutions. Finally, the performance of the proposed channel estimation is demonstrated by computer simulations.

The contributions of our proposed schemes are as follows:
(1)The OFDM system with the WHT offers better performance than the system with the pre-equalization for the moderate and high SNR in all cases.
(2)The OFDM system with the WHT outperforms the system with the pre-equalization for low modulation orders and for low SNR.
(3)The OFDM system application of with WHT does not require the feedback channel due to channel nonstationarity or due to other reasons.

It is believed that the results of our study in this thesis will be much helpful to future research in the scope of the channel estimation for wireless communciation system.

並列關鍵字

PAPR ； WHT ； MSE ； AWGN

參考文獻

[2] IEEE 802.11 Standard for Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, November 1997

[4] ANSI T1.413-1995, Network and Customer Installation Interfaces: Asymmetrical Digital Subscriber Line (ADSL) Metallic Interface, American National Standards Institute, Inc.

[5] Z. Dlugaszewski, K. Wesolowski, “WHT/OFDM– an Improved OFDM Transmission Method for Selective Fading Channels,” Proceeding of the Symposium on Communications and Vehicular Technology SCVT-2000, Leuven, October 19th, 2000

[6] T. Keller, L. Hanzo, Sub-Band Adaptive Preequalised OFDM Transmission, Proceedings of VTC’99 – Fall, Amsterdam 1999, pp. 334-338

[8] M. C. Jeruchim, P. Balaban, and K. S. Shanmugan, “Simulation of Communication Systems”,Plenum Press, 1992, 731 p.