US 9,414,126 B1 · Passive time domain reflectometer for HFC network

Abstract

Detecting a linear impairment in a cable under test by using a random signal transmitted down the cable. The impairment causes a reflected signal to be combined with the random signal. The combined signal extends over a plurality of sub-bands. A method and apparatus perform the steps of: (a) receiving the combined signal from a test point upstream from the impairment; (b) tuning to each sub-band and receiving a part of the combined signal within each sub-band; (c) determining an autocorrelation function of each part of the combined signal of each sub-band, to produce a plurality of autocorrelation functions; (d) combining the autocorrelation functions to form a combined function; (e) detecting the reflected signal from the combined function; and (f) determining, from the combined function, a time delay associated with the reflected signal and the distance from the test point to the impairment.

Claims20

Dependent claims

A time domain reflectometry apparatus for detecting a linear impairment in a cable under test carrying RF signals including random and unwanted narrowband signals in a downstream direction, the linear impairment causing a reflection of the RF signals in an upstream direction, said apparatus comprising:

(a) an input, to be coupled to the cable under test at a test point upstream from the linear impairment, for receiving the RF signals and the reflection of the RF signals as a received signal, the received signal having a frequency spectrum including a plurality of sub-bands at a plurality of RF frequencies, respectively, each of the sub-bands containing a part of the received signal as a sub-band signal;
(b) a tunable receiver, coupled to said input, for tuning to the plurality of sub-bands and receiving the sub-band signals, one sub-band at a time;
(c) a filter, coupled to said tunable receiver, for filtering the sub-band signals, one sub-band at a time, said filter adapting to each sub-band signal to substantially remove any unwanted narrowband signal from the sub-band signal to produce a filtered sub-band signal;
(d) an autocorrelation processor, coupled to said filter, for determining an autocorrelation function of each of the filtered sub-band signals, one sub-band at a time, to produce a plurality of sub-band autocorrelation functions;
(e) an accumulator, coupled to said autocorrelation processor, for combining the plurality of sub-band autocorrelation functions together to form a combined autocorrelation function;
and
(f) detection means, coupled to said accumulator, for detecting the reflection of the RF signals from the combined autocorrelation function.

4 more elements

A method of detecting a linear impairment in a cable under test carrying RF signals including random and unwanted narrowband signals in a downstream direction, the linear impairment causing a reflection of the RF signals in an upstream direction, said method comprising the steps of:

(a) at a test point upstream from the linear impairment, receiving the RF signals and the reflection of the RF signals as a received signal, the received signal having a frequency spectrum including a plurality of sub-bands at a plurality of RF frequencies, respectively, each of the sub-bands containing a part of the received signal as a sub-band signal;
(b) tuning to the plurality of sub-bands and receiving the sub-band signals, one sub-band at a time;
(c) filtering each sub-band signal, one sub-band at a time, by substantially removing any unwanted narrowband signal from the sub-band signal to produce a filtered sub-band signal;
(d) determining an autocorrelation function of each of the filtered sub-band signals, one sub-band at a time, to produce a plurality of sub-band autocorrelation functions;
(e) combining the plurality of sub-band autocorrelation functions together to form a combined autocorrelation function;
(f) detecting the reflection of the RF signals from the combined autocorrelation function;
and
(g) determining from the combined autocorrelation function a time delay associated with the reflection of the RF signals and with the distance from the test point to the linear impairment.

5 more elements

A method of detecting a linear impairment in an HFC network carrying a plurality of substantially random signals in a downstream direction, the linear impairment causing the plurality of substantially random signals to be reflected in an upstream direction as a reflected signal, said method comprising the steps of:

(a) at a test point upstream from the linear impairment, receiving the plurality of random signals and the reflected signal as a received signal, the received signal having a frequency spectrum including a plurality of sub-bands at a plurality of RF frequencies, respectively, each of the sub-bands containing a part of the received signal as a sub-band signal;
(b) for each sub-band, converting the sub-band signal to a digital sub-band signal at a first sampling rate;
(c) for each sub-band, down-converting the digital sub-band signal to an in-phase baseband signal and a quadrature baseband signal;
(d) for each sub-band, determining a baseband autocorrelation function of the in-phase baseband signal and a baseband cross-correlation function of the in-phase and the quadrature baseband signals, at a second sampling rate substantially lower than the first sampling rate;
(e) for each sub-band, up-sampling the baseband autocorrelation function and the baseband cross-correlation function to an up-sampled autocorrelation function and an up-sampled cross-correlation function, respectively;
(f) for each sub-band, up-converting the up-sampled autocorrelation function and the up-sampled cross-correlation function to a frequency band corresponding to the RF frequency of the sub-band;
(g) for each sub-band, constructing a sub-band autocorrelation function from the up-converted up-sampled autocorrelation function and the up-converted up-sampled cross-correlation function;
(h) accumulating the sub-band autocorrelation functions constructed in step (g) to form a combined autocorrelation function, the combined autocorrelation function including a correlation peak associated with the reflected signal and the linear impairment;
(i) detecting the reflected signal from the correlation peak of the combined autocorrelation function;
and
(j) determining from the correlation peak a time delay associated with the reflected signal and the distance from the test point to the linear impairment.

8 more elements

Dependencies are inferred from the claim text.

Passive time domain reflectometer for HFC network

Life of this patent

Passive time domain reflectometer for HFC network

Life of this patent

Abstract

Claims20