On the Symbol Based Decision Feedback Equalizer

Decision Feedback equalizers (DFEs) usually outperform linear equalizers for channels with intersymbol interference. However, the DFE performance is highly dependent on the availability of reliable past decisions. Hence, in coded systems, where reliable decisions are only available after decoding the full block, the performance of the DFE will be affected. A symbol based DFE is a DFE that only uses the decision after the block is decoded. In this paper we derive the optimal settings of both the feedforward and feedback taps of the symbol based equalizer. We present a novel symbol based DFE filterbank, and derive its taps optimal settings. We also show that it outperforms the classic DFE in terms of complexity and/or performance.

Authors:

• Mohammed Nafie

Keywords:

• Coding
• DFE
• Equalization
• Exponential Channelmodels.

References:

[1] N. Al-Dhahir, and J. Cioffi, "MMSE Decision-Feedback Equalizers:
Finite-Length Results," IEEE Trans. On Info. Theory, vol. 41, No. 4, pp.
961-975, July 1995.
[2] D. George, R. Bowen, and J. Storey, "An Adaptive Decision-Feedback
Equalizer," IEEE Trans. On Commun. Tech., vol. 19, pp. 283-293, June 1971.
[3] P. Monsen, "Feedback Equalization for Fading Dispersive Channels,"
IEEE Trans. On Info. Theory, vol. 17, pp. 56-64, Jan. 1971.
[4] R. Lucky, "Techniques for Adaptive Equalization of Digital
Communications," Bell Systems Technical Journal, Vol. 45, pp. 255-
286, April 1965.
[5] B. Widrow, "Adaptive Filters, I: Fundamentals," Technical Report No. 6764-6, Stanford University, CA, Dec. 1966.
[6] M. Nafie, M. Khairy and K. Shawky, "Equalizer Training in IEEE
802.11b Standard," IEEE Midwest Symposium on Circuits and Systems,
Cairo, Egypt, Dec. 2003.
[7] S. Lin, and D. Costello, "Error Control Coding, Fundamentals and
Applications," Prentice Hall, 1983.
[8] J. Proakis, Digital Communications, 4th Edition, McGraw-Hill, New
York, 1999.
[9] A. Gatherer, "The Effect of Microreflections on Decision Feedback
Equalization," IEEE Trans. On Sig. Proc, vol. 45, No. 1, pp. 228-231,
Jan. 1997.
[10] A. Duel-Hallen, "Equalizers for Multiple Input/Multiple Output
Channels and PAM Systems with Cyclostationary Input Sequences,"
IEEE J-SAC, vol. 10, pp. 630-639, April 1992.
[11] M. Nafie, A. Gatherer and A. Dabak, "Decision Feedback Equalization
for Bluetooth Systems," Proc. Int. Conf. on Acoustics, Speech and Sig.
Proc., Salt Lake City, UT, May 2001