Pulse or digital communications – Repeaters – Testing
Patent
1992-02-04
1994-01-25
Kuntz, Curtis
Pulse or digital communications
Repeaters
Testing
3647242, H03H 730
Patent
active
052822257
DESCRIPTION:
BRIEF SUMMARY
dynamically such that its output attains the same variance as that of transmitted data. The scaled equalizer output is received by a standard QAM decision module that produces so-termed eye patterns. Essentially, the decision module determines where to place each signal point in the eye pattern based on the scaled equalizer output. The signal constellation can be a 16 16, 8.times.8, 4.times.4, or 2.times.2 array of signal points, or even a pulse amplitude modulation signal with only two signal points.
All of the modules herein described can be implemented in software and executed on a general purpose computer or microprocessor. Alternatively, one or more modules can be implemented as a specialized computational element in cooperation with other specialized hardware for implementing the functionality of the modules.
DESCRIPTION OF THE DRAWING
The invention will be more fully understood from the following detailed description, in conjunction with the accompanying figures in which:
FIG. 1 is a block diagram of two modems communicating over a channel;
FIG. 2 is a schematic diagram of a prior art channel equalizer;
FIG. 3 is a block diagram of a multipoint communications network;
FIG. 4 is a block diagram of a communications channel and an equalizer;
FIG. 5A is a block diagram of an embodiment of the blind equalizer of the invention;
FIG. 5B is a block diagram of an adaptive weight module of the embodiment of FIG. 5A;
FIGS. 6A and 6C are a 3-D plot and corresponding contour map of a conventional cost function with a single term;
FIGS. 6B and 6D are a 3-D plot and corresponding contour map of a second version of the CRIMNO cost function;
FIGS. 7A and 7B are graphs of the characteristics of the simulated communications channel, showing magnitude and phase response, respectively;
FIGS. 8A and 8b are equalizer eye patterns prior to the operation of a scaling module and after the operation of the scaling module, respectively;
FIGS. 9A, 9B, and 9c are graphs of the MSE, SER, and ISI performance parameters of the first and second versions of the CRIMNO cost function, an adaptive weight CRIMNO cost function, and a cost function with a single term;
FIGS. 10A-10D are equalizer eye patterns of the cost functions of FIGS. 9A-9C at the 20,0000.sup.th iteration;
FIGS. 11A, 11B, and 11C are graphs of the performance of the adaptive weight CRIMNO cost function for different memory sizes; and
FIGS. 12A-12D are equalizer eye patterns corresponding to the cost functions of FIGS. 11A-11C.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 4, the task of blind equalization can be stated as follows: a random sequence a.sub.n of statistically independent and identically distributed data symbols, selected from a finite discrete set, is transmitted through an unknown channel 32 characterized by parameters h.sub.n and is thereby transformed into a distorted received sequence y.sub.n ; at a receiver that includes an equalizer 34 characterized by a plurality of equalizer coefficients c.sub.n, recover a sequence z.sub.n substantially equivalent to the sequence an using only the distorted received sequence y.sub.n.
The channel 32 can be, for example, a linear shift-invariant system with unknown impulse response h.sub.n. Also, the equalizer 34 restores the sequence a.sub.n in the practical sense, i.e. the probability of error is below a practical threshold value when decisions are made using the output sequence z.sub.n from the equalizer. Such sequence restoration can be attained in both noiseless and noisy environments.
Since most practical communication channels are nonminimum phase, the blind equalization problem cannot be solved using second order statistics. Instead, higher-order statistics, or a nonlinear performance cost function must be used.
If the channel impulse response, i.e., the parameters h.sub.n, can be uniquely identified, the blind equalization problem is solved. However, the converse is not true; solving the blind equalization problem does not require that the channel be uniquely identified. For example, wh
REFERENCES:
patent: 4709374 (1987-11-01), Farrow
patent: 4718073 (1988-01-01), Takaoka
patent: 4985900 (1991-01-01), Rhind et al.
J. E. Mazo, "Analysis of Decision-Directed Equalizer Convergence," The Bell System Technical Journal, vol. 59, No. 10, Dec. 1980, pp. 1857-1876.
S. Bellini, F. Rocca, "Blind Deconvolution: Polyspectra or Bussgang Techniques?" Digital Communications, 1986, pp. 251-262.
C. L. Nikias, "Blind Deconvolution Using Higher-Order Statistics," Proceedings, Intern. Workshop on Higher-Order Statistics, France, Jul. 1991, pp. 155-162.
C. L. Nikias, M. R. Raghuveer, "Bispectrum Estimation: A Digital Signal Processing Framework," Proc. IEEE, vol. 75, No. 7, Jul. 1987, pp. 869-891.
A. Bessios, C. L. Nikias, "POTEA: The Power Cepstrum and Tricoherence Equalization Algorithm," IEEE Trans. Signal Processing, submitted Oct. 1990, pp. 1-30, under review.
R. Godfrey, F. Rocca, "Zero Memory Non-Linear Deconvolution," Geophysical Prospecting, vol. 29, 1981, pp. 189-228.
S. Bellini, "Bussgang Techniques for Blind Equalization," IEEE Trans., (CH2298-9/86/0000-1634), 1986, pp. 1634-1640.
A. Benveniste, M. Goursat "Blind Equalizers," IEEE Trans. Comm., vol. COM-32, Aug. 1987, pp. 871-883.
A. Benveniste, M. Goursat, and G. Ruget, "Robust Indentification of a Nonminimum Phase System: Blind Adjustment of a Linear Equalizer in Data Communications," IEEE Trans. Automat. Contr., vol. AC-25, No. 3, 1980, pp. 385-398.
Y. Chen, C. L. Nikias, and J. G. Proakis, "Blind Equalization with CRIMNO: Criterion with Memory Nonlinearity," [To appear in Jun. 1992 Issue of Optical Engineering], pp. 1-27.
Y. Chen, C. L. Nikias, and J. G. Proakis, "CRIMNO: Criterion with Memory Nonlinearity for Blind Equalization," 25th Asilomar Conference on Signals, Systems & Computers, Nov. 4-6, 1991, Pacific Grove, Calif., 5 pages.
H-H. Chiang and C. L. Nikias, "Adaptive Deconvolution and Identification of Nonminimum Phase FIR Systems Based on Cumulants," IEEE Trans. Automatic Control, vol. AC-35, No. 1, Jan. 1990, pp. 36-47.
Z. Ding, R. A. Kennedy, B. Anderson, and C. R. Johnson, Jr., "Ill-Convergence of Godard Blind Equalizers in Data Communication Systems," IEEE Trans. Comm., vol. 39, No. 9, Sep. 1991, pp. 1313-1327.
G. J. Foschini, "Equalizing Without Altering or Detecting Data," AT&T Tech. Journal, vol. 64, No. 8, Oct. 1985, pp. 1885-1909.
D. N. Godard, "Self-Recovering Equalization and Carrier Tracking in Two-Dimensional Data Communication Systems," IEEE Trans. Comm., vol. COM-28, No. 11, Nov. 1980, pp. 1867-1875.
D. Hatzinakos and C. L. Nikias, "Blind Equalization Using a Tricepstrum-Based Algorithm," IEEE Trans. Comm., vol. COM-29, No. 5, May 1991, pp. 669-682.
O. Macchi and E. Eweda, "Convergence Analysis of Self-Adaptive Equalizers," IEEE Trans. Inform. Theory, vol. IT-30, No. 2, Mar. 1984, pp. 161-176.
G. Picchi and G. Prati, "Blind Equalization and Carrier Recovery Using a `Stop-and-Go` Decision-Directed Algorithm," IEEE Trans. Comm., vol. COM-35, No. 9, Sep. 1987, pp. 877-887.
M. R. Raghuveer and C. L. Nikias, "Bispectrum Estimation: A Parametric Approach," IEEE Trans. Acoust., Speech, Signal Processing, vol ASSP-33, No. 4, Oct. 1985, pp. 1213-1230.
Y. Sato, "A Method of Self-Recovering Equalization for Multilevel Amplitude-Modulation Systems," IEEE Trans. Comm., vol. COM-23, Jun. 1975, pp. 679-682.
O. Shalvi and E
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract No. 8433 awarded by the US Air Force.
Nikias Chrysostomos L.
Proakis John G.
Bocure Tesfaldet
Kuntz Curtis
Northeastern University
LandOfFree
Adaptive blind channel equalizer system 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 blind channel equalizer system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Adaptive blind channel equalizer system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-733621