Automatic equalization method and automatic equalizer

Details Automatic equalization method and automatic equalizer Automatic equalization method and automatic equalizer

1999-02-19

2001-09-18

Chin, Stephen (Department: 2734)

Pulse or digital communications

Equalizers

Automatic

C375S350000, C708S323000

Reexamination Certificate

active

06292510

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an automatic equalization method and an automatic equalizer for automatically equalizing the signal distorted due to intersymbol interference.
A well-known type of automatic equalizers adapted to perform maximum likelihood sequence estimation is those using a Viterbi algorithm. The automatic equalizers using the Viterbi algorithm are disclosed in, for example, Japanese Patent Laid-open No. 7-22970 and Proakis, “Digital Communications”, McGraw-Hill, N.Y. 1983, page 410. These automatic equalizers perform the maximum likelihood sequence estimation by using the Viterbi algorithm. However, the automatic equalizer of the type described has a disadvantage that the number of arithmetic operations increases due to the complex Viterbi calculation.
Therefore, an object of the present invention is to provide an automatic equalization method that can provide the maximum likelihood sequence estimation with simple arithmetic operations.
Another object of the present invention is to provide an automatic equalizer which is suitable for the above-mentioned automatic equalization method.
SUMMARY OF THE INVENTION
An automatic equalization method according to the present invention is used to receive and equalize a digital data signal comprising transmission symbols adapted to have k levels.
According to an aspect of the present invention, the method comprises the steps of receiving a channel impulse response having a length of M (where M is a natural number), a k
m−j
number of transmission symbol sequences each having a length of (M−j) (0≦j≦M−1, where j is an integer), and a discrimination result, to produce a (k
k−j
+k
(M−j−1
)+ . . . +k
(M−j−N+1)
) number of estimated received signals (N≦(M−j), where N is a natural number); subtracting the (k
(M−j)
+k
(M−j−1)
+ . . . +k
(M−j−N+1)
) number of estimated received signals from an N number of delayed received signals r (m), r(m−1), . . . , (m−(N−1), respectively, the N number of delayed received signals being between a received signal at a time instant m and a received signal at a time instant (m−(N−1)), to produce a (k
(M−j)
+k
(M−j−1)
+ . . . +k
(M−j−N+1)
) number of estimated error signals; squaring the (k
(M−j)
+k
(M−j−1)
+ . . . +k
(M−j−N+1)
) number of estimated error signals to produce a (k
(M−j)
+k
(m−j−1)
+ . . . +k
(m−j−N+1)
) number of square error signals; receiving the (k
(M−j)
+k
(m−j−1)
+ . . . +k
(m−j−N+1)
) number of square error signals to add thereto the square error signals, respectively, obtained from the (k
(M−j)
+k
(M−j−1)
+ . . . +k
(M−j−N+1)
) number of square error signals in accordance with an N number of estimated received signals having the same previous transmission symbol sequence, thereby to produce a k
(M−j)
number of added error signals; and producing, as the discrimination result, a portion of the transmission symbol sequence that corresponds to the minimum one of the k
(M−j)
number of added error signals.
An automatic equalizer according to the present invention is supplied with and equalizes a digital data signal comprising transmission symbols adapted to have k levels.
According to an aspect of the present invention, the automatic equalizer comprises a parallel received signal estimation circuit that is supplied with a channel impulse response having a length of M (where M is a natural number), a k
(M−j)
number of transmission symbol sequences each having a length of (M−j) (0≦j≦(M−1), where j is an integer), and a discrimination result and that produces a (k
(M−j)
+k
(M−j−1)
+ . . . +k
(M−j−N+1)
) number of estimated received signals (N≦M−j, where N is a natural number). The automatic equalizer further comprises a group of a plurality of estimated error output circuits that are supplied with at least one of an N number of delayed received signals r(m), r(m−1), . . . , r(m−(N−1), and supplied with the estimated received signals, respectively, the delayed received signals being between a received signal at a time instant m and a received signal at a time instant (m−(N−1)), and that produce a (k
(M−j)
+k
(M−j−1)
+ . . . +k
(M−j−N+1)
) number of estimated error signals. The automatic equalizer still further comprises a group of a plurality of absolute value squaring arithmetic circuits that are supplied with the (k
(M−j)
+k
(M−j−1)
+ . . . +k
(M−j−N+1)
) number of estimated error signals and that produce a plurality of square error signals by carrying out absolute value squaring arithmetic operation. The automatic equalizer yet further comprises a group of a k
(M−j)
number of adders that are supplied with the (k
(M−j)
+k
(M−j−1)
+ . . . +k
(M−j−N+1)
) number of square error signals to add thereto the square error signals, respectively, obtained from the (k
(M−j)
+k
(M−j−1)
+ . . . +k
(M−j−N+1)
) number of square error signals in accordance with an N number of estimated received signals having the same previous transmission symbol sequence, thereby to produce a k
(M−j)
number of added error signals, and a discriminator that is supplied with the k
(M−j)
number of added error signals and that produces, as the discrimination result, a portion of the transmission symbol sequence that corresponds to the minimum one of the k
(M−j)
number of added error signals.


REFERENCES:
patent: 5272726 (1993-12-01), Furuya et al.
patent: 5287385 (1994-02-01), Sugawara et al.
patent: 5303263 (1994-04-01), Shoji et al.
patent: 5596607 (1997-01-01), Larsson et al.
patent: 5844946 (1998-12-01), Nagayasu
patent: 7-22970 (1995-01-01), None
Mourot, C. “A High Bit Rate Transmission Technique in mobile Radio Cellular Environment” IEEE Vehicular Technology Society Conference, May 10-13, 1992, p. 740-743.
Guren, H. and N. Holte, “Decision Feedback Sequence Estimation for Continuous Phase Modulation on a Linear Multipath Channel” IEEE transactions on Communications, vol. 41, No. 2, Feb. 1993, p. 280-284.
Proakis, “Digital Communications”, McGraw-Hill, New York, 1983, p. 410.

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