Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Patent
1995-07-20
1998-07-21
Pham, Chi H.
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
375350, 371 43, 360 65, H03D 100, H03M 1312
Patent
active
057844151
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concerns a method and apparatus for digital information transmission over channels with spectral nulls or near nulls, making use of a novel adaptive noise-predictive partial-response equalization scheme. Typical channels exhibiting spectral nulls or near nulls are wire transmission and magnetic recording channels.
BACKGROUND OF THE INVENTION
In many practical digital information transmission systems including magnetic recording systems, the frequency response of the channel exhibits spectral nulls and/or near nulls. For example, wire pair or twisted-pair subscriber loops terminated by transformers exhibit a spectral null at dc and strong attenuation at high frequencies, i.e. the corresponding frequency response 10 has a null at dc (f=0) and a near null at high frequencies, as shown in FIG. 1. The frequency response of the magnetic recording channel has similar characteristics due to the magnetic head. It is known in the art, that receivers which employ nonlinear decision-feedback equalizers (DFE) cope more effectively with channels having spectral nulls than receivers employing linear transversal Nyquist equalizers. Furthermore, a decision-feedback equalizer compensates more easily for the postcursor intersymbol-interference (ISI) such as the one caused by the presence of bridged taps in the subscriber loop plant. Examples of test loops with bridged taps can be found in the American National Standard for Telecommunications "Integrated Services Digital Network (ISDN)--Basic Access Interface for Use on Metallic Loops for Application on the Network Side of the NT (Layer 1 Specification)", ANSI Document T1.601, 1988.
A multiplication-free compromise decision-feedback equalizer with fixed forward and adaptive feedback sections has been described in "Full-Duplex Data Over Local Loops", N.-S. Lin et al., IEEE Communications Magazine, Vol. 26, No. 2, pp. 31-42, 1988. Another decision-feedback equalizer whose coefficients are updated by the sign algorithm has been proposed in "A Long Reach Digital Subscriber Loop Transceiver", P. F. Adams et al., Br. Telecommunications Journal, Vol. 5, No. 1, pp. 25-31, 1987.
The application of adaptive decision-feedback equalization in the magnetic recording channel has been discussed in the tutorial article "Adaptive Equalization in Magnetic-Disk Storage Channels", J. M. Cioffi et al., IEEE Commmunications Magazine, Vol. 28, No. 2, pp. 14-29, 1990.
Linear partial response (PR) equalization followed by Viterbi detection is an alternative to DFE and symbol-by-symbol detection. A partial response maximum likelihood (PRML) system for the magnetic recording channel has been described in "A PRML System for Digital Magnetic Recording", R. D. Cideciyan et al., IEEE Journal on Selected Areas in Communications, Vol. 10, No. 1, pp. 38-56, January 1992.
In U.S. Pat. No. 4,571,734 with title "Method and Apparatus for Decoding the Output of a Partial-Response Signal of a Partial-Response Class-IV Communication or Recording Device Channel", issued 18 Feb. 1986, the implementation of PR Viterbi detectors for partial response systems is described.
In U.S. Pat. No. 5,031,195, with title "Fully Adaptive Modem Receiver Using Whitening Matched Filtering", issued 9 Jul. 1991, a modem (modulator-demodulator) receiver is disclosed which comprises a whitened-matched filter (WMF) 20, a Viterbi decoder 21, and an intersymbol interference (ISI) coefficient estimator 22, as illustrated in FIG. 2. Some details of the operation of said modem receiver when receiving TCM (Trellis Coded Modulation) signals are described below with reference to FIG. 2.
An analytic passband signal y.sub.k, which is sampled with a sample rate s/T, is fed into said WMF 20. The WMF 20 mainly consists of a minimum mean-squared error linear equalizer 23, with fractional-T spaced coefficients {c.sub.i }, whose output signal z.sub.k is input to multiplication means 26 for the correction of the carrier phase offset. The signal z.sub.k ' after carrier phase offset correction is fed into a linear pre
REFERENCES:
patent: 4571734 (1986-02-01), Dolivo et al.
patent: 4888779 (1989-12-01), Karabed et al.
Lou, H., "Implementing the Viterbi Algorithm", IEEE Signal Processing Magazine, pp. 42-52, Sep. 1995.
Forney, Jr., G.D., "The Viterbi Algorithm", IEEE Proceedings, Vol IT-61, No. 3 pp. 268-279, Mar. 1973.
Chevillat Pierre
Eleftheriou Evangelos
Maiwald Dietrich
International Business Machines - Corporation
Luther William
Pham Chi H.
Ray-Yarletts Jeanine S.
LandOfFree
Adaptive noise-predictive partial-response equalization for chan does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Adaptive noise-predictive partial-response equalization for chan, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Adaptive noise-predictive partial-response equalization for chan will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1654503