Detecting nonlinearity in a cable plant and determining a cable length to a source of the nonlinearity
First Claim
1. An apparatus for determining a cable length between a test point and a source of nonlinearity in a cable plant for propagating upstream and downstream signals, the apparatus comprising:
- a peak detector for providing a triggering signal upon detection of a downstream signal peak at the test point of the cable plant;
a waveform acquisition unit coupled to the peak detector, for acquiring, upon receiving the triggering signal from the peak detector, a waveform of the upstream signal at the test point; and
a processing unit coupled to the waveform acquisition unit, for averaging upstream waveforms acquired by the waveform acquisition unit upon triggering by the peak detector, to obtain an averaged waveform of the upstream signal;
for detecting an upstream signal peak in the averaged waveform of the upstream signal, wherein the upstream signal peak is an average of common path distortion upstream signal peaks induced at the source of nonlinearity by downstream signal peaks detected by the peak detector; and
for determining the cable length between the test point and the source of nonlinearity, from a position of the upstream signal peak in the averaged waveform of the upstream signal.
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Abstract
An apparatus and a method for detecting a nonlinearity in a cable plant and for determining cable length to a source of the nonlinearity are disclosed. Upstream signal peaks are detected by averaging upstream signal waveforms. The upstream signal peaks are generated at the source of the nonlinearity from naturally occurring downstream signal peaks propagating in the cable plant. The downstream signal peaks occur due to constructive superposition of the downstream channel signals. Acquisition of the upstream signal waveforms is triggered by the downstream signal peaks. The cable length to the source of nonlinearity is determined from a time delay between the downstream signal peaks and the upstream signal peaks.
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Citations
20 Claims
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1. An apparatus for determining a cable length between a test point and a source of nonlinearity in a cable plant for propagating upstream and downstream signals, the apparatus comprising:
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a peak detector for providing a triggering signal upon detection of a downstream signal peak at the test point of the cable plant; a waveform acquisition unit coupled to the peak detector, for acquiring, upon receiving the triggering signal from the peak detector, a waveform of the upstream signal at the test point; and a processing unit coupled to the waveform acquisition unit, for averaging upstream waveforms acquired by the waveform acquisition unit upon triggering by the peak detector, to obtain an averaged waveform of the upstream signal;
for detecting an upstream signal peak in the averaged waveform of the upstream signal, wherein the upstream signal peak is an average of common path distortion upstream signal peaks induced at the source of nonlinearity by downstream signal peaks detected by the peak detector; and
for determining the cable length between the test point and the source of nonlinearity, from a position of the upstream signal peak in the averaged waveform of the upstream signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An apparatus for detecting a common path distortion signal in a cable plant for propagating downstream channel signals in a downstream spectral band and upstream channel signals in an upstream spectral band, the apparatus comprising:
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a comparator for providing trigger pulses upon detecting high-magnitude downstream electrical pulses due to a constructive superposition of the downstream channel signals in the downstream spectral band, by comparing an electrical signal amplitude in the downstream spectral band to a pre-defined threshold value, and by generating a trigger pulse when the signal amplitude in the downstream spectral band exceeds the pre-determined threshold value; an analog to digital converter (ADC) for digitizing, at a clock frequency, an electrical signal in the upstream spectral band; a memory buffer coupled to the ADC, for storing, upon receiving the trigger pulses from the comparator, waveforms of the digitized electrical signal; and an averaging unit coupled to the memory buffer, for averaging the waveforms stored in the memory buffer, so as to obtain an averaged waveform of the electrical signal in the upstream spectral band, wherein in operation, the averaged waveform has a peak corresponding to common-path distortion signals induced by the high-magnitude downstream electrical pulses detected by the comparator. - View Dependent Claims (10, 11, 12, 13)
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14. A method for detecting a common path distortion signal in a cable plant for propagating upstream signals in an upstream spectral band and downstream signals in a downstream spectral band, the method comprising:
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(a) using a peak detector to compare a signal amplitude in the downstream spectral band to a pre-determined threshold value, and generating a triggering pulse when the signal amplitude exceeds the pre-determined threshold value; (b) using a waveform acquisition unit to acquire a waveform of a signal in the upstream spectral band, upon triggering by the triggering pulse generated in step (a); (c) repeating steps (a) and (b); (d) using an averaging unit to average the waveforms acquired, to obtain an averaged waveform of the signal in the upstream signal band; and (e) using a waveform peak detector to detect a common path distortion signal, by detecting a peak in the averaged waveform. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification