Pulse or digital communications – Equalizers – Automatic
Reexamination Certificate
1999-06-24
2002-12-03
Pham, Chi (Department: 2631)
Pulse or digital communications
Equalizers
Automatic
C375S230000, C375S233000
Reexamination Certificate
active
06490318
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communications equipment, and, more particularly, to blind equalization in a receiver.
BACKGROUND OF THE INVENTION
In blind equalization, the adaptive filters of a receiver are converged without the use of a training signal. As known in the art, there are two techniques for blind equalization: one is referred to herein as the “reduced constellation algorithm” (RCA) (e.g., see Y. Sato, “A Method of Self-Recovering Equalization for Multilevel Amplitude-Modulation Systems,”
IEEE Trans. Commun.,
pp. 679-682, June 1975; and U.S. Pat. No. 4,227,152, issued Oct. 7, 1980 to Godard); and the other technique is the so-called “constant modulus algorithm” (CMA) (e.g., see D. N. Godard, “Self-Recovering Equalization and Carrier Tracking in Two-Dimensional Data Communications Systems,”
IEEE Trans. Commun.,
vol. 28, no. 11, pp. 1867-1875, November 1980; and N. K Jablon, “Joint Blind Equalization, Carrier Recovery, and Timing Recovery for High-Order QAM Signal Constellations”
IEEE Trans. Signal Processing,
vol. 40, no. 6, pp. 1383-1398, 1992.) Further, U.S. Pat. No. 5,793,807, issued Aug. 11, 1998 to Werner et al., and entitled “Blind Equalization,” presents a new blind equalization technique—the multimodulus algorithm (MMA)—as an alternative to the above-mentioned RCA and CMA approaches.
However, for all blind equalization approaches the most fundamental performance issue is the ability to achieve reliable initial convergence—else the adaptive filter may converge to a wrong solution such as the well-known “diagonal solution.”
SUMMARY OF THE INVENTION
We have discovered a technique for use in blind equalization of an adaptive equalizer that reduces the rate of occurrence of a diagonal solution. In particular, and in accordance with the invention, a receiver performs blind equalization by using a tap updating algorithm that includes a phase-compensating term.
In an embodiment of the invention, a receiver comprises an adaptive filter having a two-filter structure. The receiver uses a modified form of the CMA algorithm to perform blind equalization. This modified form of CMA is referred to herein as phase compensating CMA (PC-CMA). PC-CMA includes a phase-compensating term in the tap updating algorithm of the equalizer such that convergence to a straight constellation is achieved without the need of a rotator.
REFERENCES:
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U.S. Patent Application of Larsson, entitled “System and Method for Training A Plurality of Equalizers And A Modem Employing the System Or Method”, Ser. No. 08/855,086, filed May 13, 1997.
U.S. Patent Application of Werner et al., entitled Blind Equalization Algorithm with Joint Use of the Constant Modulus Algorithm and the MultiModulus Algorithm, Ser. No. 09/066189, filed Apr. 24, 1998.
U.S. Patent Application of Werner et al., entitled “The Blind Equalization Algorithm with the Joint Use of the Constant R and the Sliced Symbols”, Ser. No. XXX, filed on XXX.
Yang, J., Werner, J.J., and G. A. Dumont “The Multimodulus Blind Equalization Algorithm”, Proceedings of DSP97, Santorini, Greece, 1997.
Larsson Patrik
Werner Jean-Jacques
Yang Jian
Agere Systems Inc.
Al-Beshrawi Tony
Mendelsohn Steve
Pham Chi
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