Conference Paper

Approximate ber expression of ML equalizer for OFDM over doubly selective channels

Dept. of ACSE, Hiroshima Univ., Higashi-Hiroshima
DOI: 10.1109/ICASSP.2008.4518293 Conference: Acoustics, Speech and Signal Processing, 2008. ICASSP 2008. IEEE International Conference on
Source: IEEE Xplore


Maximum Likelihood (ML) equalization for Orthogonal Frequency Division Multiplexing (OFDM) over time- and frequency- selective channels is analyzed in this paper. An approximate expression for bit error rate (BER) performance of the ML equalizer with a limited number of taps is developed, which subsumes the matched filter bound (MFB) equalization performance as a special case, and which saves on intensive time-consuming empirical simulations. Numerical simulations validate our approximate expression.

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    • "The techniques proposed in these works range from linear equalizers , based on the zero-forcing (ZF) or the minimum mean-squared error (MMSE) criterion [4] [5] [6] [7] [8] [9] [10] [11] [12] [13], to nonlinear equalizers based on decision-feedback or ICI cancelation [9] [10] [11] [12] [13] [14]. Also near maximumlikelihood approaches have been proposed [16]. It has been shown that nonlinear equalizers based on ICI cancelation generally outperform linear approaches [10] [11] [12] [13]. "
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    ABSTRACT: We study the application of turbo equalization in orthogonal frequency division multiplexing (OFDM) system over doubly-selective channel. Maximum A Posteriori (MAP) equalization that exploits characteristics of the banded channel structure in OFDM is used in our turbo equalization. In settings similar to Japan's ISDB-T standards, we find that banded channel structure that accounts for only 1 neighboring subcarrier (on one side) is sufficient to ensure a good equalization performance. At moderate Doppler frequency, turbo equalization does not enhance the system performance significantly. Furthermore, the effects of 1) initial channel estimation with turbo equalization; 2) channel re-estimation with turbo equalization are investigated, with the latter conferring greater bit error-rate (BER) enhancement than the former. Channel estimation has a more prominent effect on performance than turbo equalization, as verified by numerical simulations.
    Proceedings of the IEEE International Conference on Wireless Communications, Networking and Information Security, WCNIS 2010, 25-27 June 2010, Beijing, China; 01/2010
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