Orthogonal frequency division multiplexing, Electrical Engineering

CURRENTLY, orthogonal frequency division multiplexing (OFDM) is emerging as the preferred modulation technique in modern high data rate broadband wireless mobile communication systems. In OFDM, the entire spectrum is divided into subcarriers which are narrow-banded with respec to the coherence bandwidth of the channel. This provides resistance against frequency-selectivity of the channel for wideband data transmission. However, the well known problem in OFDM system is its vulnerability to the frequency offset errors causedby oscillator inaccuracies or the Doppler frequency shift due to mobility. In high mobility scenarios, the orthogonality of the subcarriers is no longer maintained that results in inter-carrier interference (ICI). Hence, the transmission performance of the mobile OFDM system is degraded severely.

ICI cancellation techniques are essential in improving the per formance of OFDM system in an environment which induces frequency offset error. A lot of ICI mitigation methods have been extensively investigated to combat the ICI, including fre- quency-domain equalization, time-domain windowing and the self-cancellation schemes, frequency offset estimation and tracking techniques and so on. Among the methods, the ICI self-cancellation method is a simple way to suppress ICI that uses redundant modulation. Several selfcancellation methods have been exploited, including data conversion, data conjugate and symmetric data-conversion/conjugate methods. Windowing methods reduce the SNR but they need redundant information. That is, the performances of the windowing methods and self-cancellation methods degrade signi?cantly with the increase of frequency offset. Besides, maximum likelihood estimation and extended Kalman

Posted Date: 3/8/2013 12:34:44 AM | Location : United States

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