Non-invasive digital cable test system
First Claim
1. In a digital communication system wherein digital data to be communicated over a channel is represented by sequential selection of components of a modulated signal, a method of estimating system margin comprising the steps of:
- a) receiving said modulated signal as corrupted by said channel;
b) estimating an error signal between said modulated signal as transmitted and said received modulated signal;
c) estimating a cluster variance of said error signal; and
d) estimating system margin based on said cluster variance and a required system signal to noise ratio (SNR).
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Accused Products
Abstract
Method and apparatus for non-invasive testing of digital communications systems. Amplitude measurements are made for multiple frequencies of a multi-frequency communication system, converted to the time domain. An adaptive filter output is matched to the time domain representation to characterize the channel. Impedance mismatches may be precisely located using this technique. An error signal representing a difference between a signal transmitted through the channel and a received signal is estimated and analyzed. The error signal is separated into components corresponding to contributions by wide band noise, residual phase modulation, and residual amplitude modulation. Identification and removal of narrow-band interferers may occur prior to this separation. Bit error rate and system margin computations employ a Monte Carlo simulation of the various error sources. This provides a well refined estimate of bit error rate and system margin.
64 Citations
20 Claims
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1. In a digital communication system wherein digital data to be communicated over a channel is represented by sequential selection of components of a modulated signal, a method of estimating system margin comprising the steps of:
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a) receiving said modulated signal as corrupted by said channel;
b) estimating an error signal between said modulated signal as transmitted and said received modulated signal;
c) estimating a cluster variance of said error signal; and
d) estimating system margin based on said cluster variance and a required system signal to noise ratio (SNR). - View Dependent Claims (2, 3, 4)
equalizing a digitized version of the received modulated signal to produce an equalized modulated signal; and
using symbol decision on the equalized modulated signal to estimate the error signal between said modulated signal as transmitted and said received modulated signal.
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3. The method of claim 1 wherein step c) further comprises:
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estimating a power of the modulated signal;
estimating a power of the error signal; and
estimating the cluster variance based upon the power of the modulated signal and the power of the error signal.
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4. The method of claim 1 wherein step d) further comprises employing a processor to estimate system margin based on said cluster variance and a required system SNR.
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5. A computer program product that controls a processor to estimate a system margin in a digital communication system in which digital data is communicated over a channel as sequential selection of components of a modulated signal, the computer program product comprising:
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code for estimating an error signal between said modulated signal as transmitted and a received modulated signal, said received modulated signal comprising said modulated signal corrupted by said channel;
code for estimating a cluster variance of said error signal; and
code estimating system margin based on said cluster variance and a required system signal to noise ratio (SNR). - View Dependent Claims (6, 7, 8)
code for equalizing a digitized version of the received modulated signal to produce an equalized modulated signal; - and
code for using symbol decision on the equalized modulated signal to estimate the error signal between said modulated signal as transmitted and said received modulated signal.
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7. The computer program product of claim 6 further comprising code for:
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estimating a power of the modulated signal;
estimating a power of the error signal; and
estimating the cluster variance based upon the power of the modulated signal and the power of the error signal.
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8. The computer program product of claim 5 further comprising code for:
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estimating a power of the modulated signal;
estimating a power of the error signal; and
estimating the cluster variance based upon the power of the modulated signal and the power of the error signal.
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9. An arrangement for estimating system margin for use in connection with a digital communication system for communicating digital data to be communicated over a channel as sequential selection of components of a modulated signal, said arrangement comprising:
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a sampling stage configured to receive the modulated signal and generate a digital signal synchronized to a plurality of symbol boundaries in said received modulated signal;
an equalizer configured to received the digital signal and generate an equalized modulated signal based on the digital signal;
a symbol decision stage configured to received the equalized modulated signal and generate a plurality of constellation points corresponding thereto, said symbol decision stage further configured to estimate an error signal between the received modulated signal and the modulated signal as transmitted; and
a processor configured to estimate a cluster variance of said error signal, and estimate a system margin responsive to said cluster variance. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
estimate a power of the modulated signal;
estimate a power of the error signal; and
estimate the cluster variance based upon the power of the modulated signal and the power of the error signal.
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18. The arrangement of claim 17 wherein the processor is further operable to estimate the power of the modulated signal based on the equalized modulated signal generated by the equalizer.
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19. The arrangement of claim 9 wherein the processor is further operable to estimate the system margin based on the cluster variance and a required system SNR.
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20. The arrangement of claim 9 wherein the processor is further operable to estimate the system margin by:
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estimating a current SNR responsive to said cluster variance; and
subtracting a required system SNR from said current SNR to obtain said system margin.
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Specification