利用卡爾曼濾波器結合通道估測及最大似然資料檢測技術應用於時變通道正交分頻多工系統研究

Joint Channel Estimation and Maximum Likelihood Data Detection using Kalman Filter for OFDM system in Time-Variant Channels

陳又維(Yu-Wei Chen)

指導教授 ： 蔡育仁

國立清華大學/電機資訊學院/通訊工程研究所/碩士(2009年)

https://doi.org/10.6843/NTHU.2009.00589

摘要

正交分頻多工技術是利用正交的頻率子載波來做無線傳輸，利用不同的正交頻率，其資料傳輸量比單頻的無線傳輸系統要來的高，並且可以有效且簡單的抵抗多重路徑干擾，目前已成為通訊系統的關鍵技術，例如數位音訊廣播、數位視訊廣播和數位高畫質電視。但是隨著使用者的移動，都普勒效應的影響以及多重路徑的干擾都會使得子載波之間的正交性消失，造成資料偵測時會有嚴重的錯誤現象發生。為了改善在時變通道下正交分頻多工系統的表現，我們使用了卡爾曼濾波器及最大似然資料檢測技術來執行資料偵測。我們利用卡爾曼濾波器來偵測通道在一個正交分頻多工符號時間內不同子載波上的變化情形，一般使用卡爾曼濾波器來追蹤通道變化通常是在利用時間上的相關性，而我們則是利用了頻率域上面的相關性來進行通道估計。從模擬上可以看見，在高都普勒的環境下，我們的方法一樣可以表現的不錯，這對於要提供服務給快速移動的使用者來說，是非常重要的一件事。

關鍵字

正交分頻多工系統 ； 通道估測 ； 卡爾曼濾波器 ； 時變 ； 資料偵測 ； 通訊

並列摘要

For orthogonal frequency division multiplexing (OFDM) systems in wireless mobile application, the orthogonality between subcarriers is very important. Nevertheless, user mobility induce a time-varying channel, it will destroy the orthogonality between subcarriers and caused intercarrier interference (ICI), degrades data detection performance. To enhance the performance of OFDM systems in a time-varying channel, we use Kalman filter and Maximum-Likelihood data detection algorithm to detect data symbol. We use Kalman filter to track channel variation between subcarriers in frequency domain within an OFDM symbol period while lots of study focus on using the time correlation in channel variation instead of frequency correlation. Although the statistic method of finding channel correlation coefficients failed, we find an optimal coefficient for our scheme. Simulation results show that our method works well in high Doppler scenario. This is very important for the service provider that needs to service the user that moving very fast.

並列關鍵字

OFDM ； channel estimation ； Kalman filter ； time-varying ； data detection ； communication

參考文獻

[1] Y. Li and L. J. Cimini, “Bounds in the interchannel interference of OFDM in time-varying impairments,” IEEE Trans. Wireless Commun., vol. 49,pp.401-404, Mar. 2001

[2] P. Schniter, “Low-complexity equalization of OFDM in doubly selective channels,” IEEE Trans. Signal Process., vol. 52, no. 4, pp. 1002-1011, April 2004.

[3] M. Russell and G. Stuber, “Interchannel interference analysis of OFDM in a mobile environment,” in Proc. IEEE Vehicular Technology Conf., vol. 2, pp. 820-824, 1995.

[4] A. A. Hutter, E. de Carvalho, J. M. Cioffi, “On the impact of channel estimation for multiple antenna diversity reception in mobile OFDM systems,” in Proc. 34th Asilomar, vol. 2, pp. 1820-1824, Nov. 2000.

[5] Wei Chen, Ruifeng Zhang, “Estimation of Time and Frequency Selective Channels in OFDM Systems: A Kalman filter Structure”, in Proc. Global Telecommunication Conf., vol. 2, pp. 800-803, Nov. 2004