Time-domain equalizer

Multicarrier modulation has been employed in wireline and wireless communication systems due to its robustness against frequency selective channels [1], [2]. The implementation of multicarrier modulation, such as orthogonal frequency division multiplexing (OFDM) and discrete multitone (DMT), utilizes the inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) algorithm to create orthogonal subchannels.

However, a spectrally shaped channel destroys the orthogonality between subchannels, giving rise to inter-carrier interference (ICI) as well as inter-symbol interference (ISI) which degrades the system performance. One way to prevent ICI/ISI is to append a cyclic prefix (CP) to each symbol block. In particular, ISI is eliminated when Nb ≥ L – 1 where Nb and L denote the length of the CP and channel impulse response, respectively. For channels where Nb < L – 1, a channel shortener, commonly known as a time-domain equalizer (TEQ) [3], [4], [5], [6], [7] can be placed at the receiving end to shorten the channel. Therefore, a TEQ is useful for mitigating ISI and improving system performance.

References
[1] J. A. C. Bingham, “Multicarrier modulation for data transmission: An idea whose time has come,” IEEE Commun. Mag., vol. 28, no. 5, pp. 5-14, May 1990.
[2] Z. Wang and G.B. Giannakis, “Wireless multicarrier communications,” IEEE Signal Processing Mag., vol. 17, pp. 29–48, May 2000.
[3] N. Al-Dhahir and J. M. Cioffi, “Efficiently computed reduced-parameter input-aided MMSE equalizers for ML detection: A unified approach,” IEEE Trans. Inform. Theory, vol. 42, pp. 903-915, May 1996.
[4] P. J. W. Melsa, R. C. Younce, and C. E. Rohrs, “Impulse response shortening for discrete multitone transceivers,” IEEE Trans. Commun., vol. 44, pp.1662-1672, Dec. 1996.
[5] G. Arslan, B. L. Evans, and S. Kiaei, “Equalization for discrete multitone receivers to maximize bit rate,” IEEE Trans. Signal Processing, vol. 49, pp. 3123-3135, Dec. 2001.
[6] B. Farhang-Boroujeny and M. Ding, “Design methods for time-domain equalizer in DMT transceivers,” IEEE Trans. Communications, vol. 49, no. 3, pp. 554–562, 2001.R. K. Martin, J. Balakrishnan,W. A. Sethares, and C. R. Johnson Jr., “A blind, adaptive TEQ for multicarrier systems,” IEEE Signal Processing Letters, vol. 9, no. 11, pp. 341-343, 2002.
[7] R. K. Martin, J. Balakrishnan,W. A. Sethares, and C. R. Johnson Jr., “A blind, adaptive TEQ for multicarrier systems,” IEEE Signal Processing Letters, vol. 9, no. 11, pp. 341-343, 2002.


(From my paper.)