Performance Analysis of the Blind Minimum Output Variance Estimator for Carrier Frequency Offset in OFDM Systems
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Performance Analysis of the Blind Minimum Output Variance Estimator for Carrier Frequency Offset in OFDM Systems Feng Yang, Kwok H. Li, and Kah C. Teh School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore Received 18 November 2004; Revised 13 July 2005; Accepted 29 December 2005 Recommended for Publication by Alexei Gorokhov Carrier frequency offset (CFO) is a serious drawback in orthogonal frequency division multiplexing (OFDM) systems. It must be estimated and compensated before demodulation to guarantee the system performance. In this paper, we examine the performance of a blind minimum output variance (MOV) estimator. Based on the derived probability density function (PDF) of the output magnitude, its mean and variance are obtained and it is observed that the variance reaches the minimum when there is no frequency offset. This observation motivates the development of the proposed MOV estimator. The theoretical mean-square error (MSE) of the MOV estimator over an AWGN channel is obtained. The analytical results are in good agreement with the simulation results. The performance evaluation of the MOV estimator is extended to a frequency-selective fading channel and the maximal-ratio combining (MRC) technique is applied to enhance the MOV estimator’s performance. Simulation results show that the MRC technique significantly improves the accuracy of the MOV estimator. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
Orthogonal frequency division multiplexing (OFDM) has been considered as a promising modulation scheme for the next generation wireless communication systems. OFDM signals are transmitted in parallel subchannels, which are frequency-nonselective and overlapped in spectra. Hence, OFDM systems are robust to frequency-selective fading and enjoy high bandwidth efficiency. As the symbol duration is extended, the OFDM scheme reduces the normalized delay spread and avoids intersymbol interference (ISI). Because of these excellent characteristics, OFDM has been suggested and standardized for high-speed communications in Europe for digital audio broadcasting (DAB) [1] and terrestrial digital video broadcasting (DVB) [2]. Furthermore, OFDM is standardized for broadband wireless local area networks, for example, ETSI-BRAN High-performance local area networks (Hiperlan/2) [3], IEEE 802.11a [4], and for broadband wireless access, for example, IEEE 802.16 [5]. One drawback of OFDM systems is that carrier frequency offset (CFO) between the transmitter and receiver may degrade system performance severely [6]. CFO causes a number of impairments, including the attenuation and phase rotation of each of the subcarriers and intercarrier interference
(ICI). Many estimation techniques have been proposed to estimate and correct the CFO before demodulation. Moose proposed a scheme to estimate CFO by repeating a data symbol and comparing the phase of each of the subcarriers between successive symbols [7]. However, this scheme adds more overh
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