Methods and apparatus for locating leakage of digital signals

• US 8,904,460 B2
• Filed: 02/06/2013
• Issued: 12/02/2014
• Est. Priority Date: 08/18/2009
• Status: Active Grant

• Current Assignee: Arcom Digital Patent, LLC
• Original Assignee: Arcom Digital, LLC
• Inventors: Zinevich, Victor M.
• Primary Examiner(s): Kumar, Pankaj
• Assistant Examiner(s): Hicks, Charles N
• Application Number:
  US13/760,219
• Publication Number:
  US 20130147969A1
• Time in Patent Office: 664 Days
• Field of Search: 725/107, 725/111, 725/124, 725/129
• US Class Current: 725/107
• CPC Class Codes: G01R 31/08 Locating faults in cables, transmission lines, or networks
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04H 20/12 Arrangements for observation, testing or troubleshooting
• CPC Class Codes: H04N 17/004 for digital television systems
• CPC Class Codes: H04N 21/2383 Channel coding or modulation of digital bit-stream, e.g. QPSK modulation arrangements for detecting or preventing errors in the information received by adapting the channel coding H04L1/0009; analogue front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002
• CPC Class Codes: H04N 21/4382 Demodulation or channel decoding, e.g. QPSK demodulation analog front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002
• CPC Class Codes: H04N 21/6118 involving cable transmission, e.g. using a cable modem

Abstract

A leak defined by coordinates is located in a network. A signal emitted from the leak is detected at first, second and third points having first, second and third sets of coordinates, respectively. Propagation delays t1, t2 and t3 of the signal are measured, which include the propagation delays between the leak and the first, second and third points, respectively. The time difference Δt12 between delays t1 and t2 and the time difference Δt23 between delays t2 and t3 are calculated. The approximate location of the leak is determined by solving for the coordinates of the leak in at least two hyperbolic equations, where the equations are defined by the time differences Δt12 and Δt23, and by the first, second and third sets of coordinates.

Claims

1. A method of locating a leakage source in a coaxial cable portion of an HFC network, the HFC network including a reference point and a number of network points, the number of network points being located in the coaxial cable portion of the HFC network and each being characterized in a network database by a set of geographic coordinates and a network time delay value, the network time delay value of each network point representing a predetermined propagation delay between the reference point and the network point, said method comprising the steps of:

(a) receiving, at a detection point, a digital signal emitted into free space from the leakage source, the signal passing through the HFC network between the reference point and the leakage source, the detection point being defined by geographic coordinates;

(b) performing a coherent cross-correlation between the signal sampled at the reference point and the signal sampled at the detection point, the coherent cross-correlation generating a correlation function having an amplitude peak and a time delay associated with the peak;

(c) obtaining a measured propagation delay, Tm, from the time delay associated with the peak of the correlation function, Tm being a measured propagation delay between the reference point and the detection point and including a network propagation delay between the reference point and the leakage source and a free-space propagation delay between the leakage source and the detection point;

(d) retrieving the sets of geographic coordinates of the number of network points from the network database;

(e) calculating a distance between the detection point and each of the number of network points, using the geographic coordinates of the detection point and the sets of geographic coordinates of the number of network points;

(f) calculating a free-space propagation delay between the detection point and each of the number of network points, using the distances calculated in step (e) and the velocity of propagation of an electric wave in free space;

(g) retrieving the network time delay value of each of the number of network points from the network database;

(h) calculating a number of propagation delays, Tc_n, between the reference point and the detection point, via the number of network points, respectively, by adding together the free-space propagation delay calculated in step (f) and the network time delay value retrieved in step (g), for each network point;

(i) comparing the propagation delays Tc_n calculated in step (h) with the measured propagation delay Tm obtained in step (c), and selecting a delay Tc_k from the calculated delays Tc_n that substantially matches, within a tolerance value, the measured delay Tm; and

(j) identifying a network point from the delay Tc_k selected in step (i), as a candidate for the leakage source.

2. The method of claim 1, further comprising the step of:

(k) identifying the location of the candidate of the leakage source by retrieving the geographic coordinates of the network point identified in step (j).

3. The method of claim 2, further comprising the step of:

(l) representing the location of the candidate identified in step (k) on an electronic map of the HFC network by use of a marker or other symbol.

4. The method of claim 1, wherein at least one of the number of network points is a network device connected in the coaxial cable portion of the HFC network.

5. The method of claim 1, wherein steps (a) through (j) are performed in substantially real-time at or in the vicinity of the detection point.

6. The method of claim 1, wherein the coherent cross-correlation performed in step (b) includes sampling the signal at the reference point over a first sampling interval and sampling the signal at the detection point over a second sampling interval, the second sampling interval being greater than the first sampling interval.

7. The method of claim 1, wherein the digital signal is a digital TV signal normally transmitted to subscribers of the HFC network and step (a) includes receiving, at the detection point, the digital TV signal emitted into free space from the leakage source.

8. A method of locating a leakage source in a coaxial cable portion of an HFC network, the HFC network including a reference point, said method comprising the steps of:

(a) receiving, at a first detection point, a digital signal emitted into free space from the leakage source, the signal passing through the HFC network between the reference point and the leakage source, the first detection point being defined by a first set of geographic coordinates;

(b) performing a coherent cross-correlation between the signal sampled at the reference point and the signal sampled at the first detection point, the coherent cross-correlation generating a correlation function having an amplitude peak and a time delay associated with the peak;

(c) obtaining a first propagation delay of the signal, t1, from the time delay associated with the peak of the correlation function, t1 including at least a free-space propagation delay between the leakage source and the first detection point;

(d) repeating steps (a) through (c) at a second detection point defined by a second set of geographic coordinates, the coherent cross-correlation being between the signal sampled at the reference point and the signal sampled at the second detection point, wherein a second propagation delay of the signal, t2, is obtained, t2 including at least a free-space propagation delay between the leakage source and the second detection point;

(e) repeating steps (a) through (c) at a third detection point defined by a third set of geographic coordinates, the coherent cross-correlation being between the signal sampled at the reference point and the signal sampled at the third detection point, wherein a third propagation delay of the signal, t3, is obtained, t3 including at least a free-space propagation delay between the leakage source and the third detection point;

(f) calculating the difference, Δ

t12, between the first propagation delay t1 and the second propagation delay t2 and the difference, Δ

t23, between the second propagation delay t2 and the third propagation delay t3; and

(g) determining an approximate location of the leakage source by solving for a set of geographic coordinates of the leakage source in at least two hyperbolic equations, the at least two hyperbolic equations being defined by the differences Δ

t12 and Δ

t23 and by the first, second and third sets of geographic coordinates of the first, second and third detection points, respectively.

9. The method of claim 8, further comprising the step of:

(h) representing the approximate location of the leakage source determined in step (g) on an electronic map of the HFC network by use of a marker or other symbol.

10. The method of claim 8, further comprising the steps of:

(h) retrieving the first set of geographic coordinates from a GPS system at the first detection point;

(i) retrieving the second set of geographic coordinates from the GPS system at the second detection point; and

(j) retrieving the third set of geographic coordinates from the GPS system at the third detection point.

11. The method of claim 8, wherein the coherent cross-correlation performed in step (b) includes sampling the signal at the reference point over a first sampling interval and sampling the signal at the first detection point over a second sampling interval, the second sampling interval being greater than the first sampling interval.

12. The method of claim 8, wherein the coherent cross-correlation performed in steps (b), (d) and (e) includes sampling the signal at the reference point over a first sampling interval and sampling the signal at the first, second and third detection points, respectively, over a second sampling interval, the second sampling interval being greater than the first sampling interval.

13. The method of claim 8, wherein the HFC network includes a headend and the reference point of the HFC network is located at the headend.

14. The method of claim 8, wherein the HFC network includes a fiber optic node and the reference point of the HFC network is located at the fiber optic node.

15. The method of claim 8, wherein steps (a) through (g) are performed in substantially real-time in the vicinity of the first, second and third detection points.

16. The method of claim 8, wherein the digital signal is a digital TV signal normally transmitted to subscribers of the HFC network and step (a) includes receiving the digital TV signal emitted into free space from the leakage source.

17. A method of locating a low-frequency ingress source in a coaxial cable portion of an HFC network, the HFC network having forward path and return path frequency spectrums, the forward path spectrum including a VHF Low Band and the return path spectrum being lower in frequency than the forward path spectrum, the ingress source admitting ingress into the return path spectrum, the HFC network including a number of network points and a reference point coupled to the forward path spectrum, the number of network points being located in the coaxial cable portion of the HFC network and each being characterized in a network database by a set of geographic coordinates and a network time delay value, the network time delay value of each network point representing a predetermined propagation delay between the reference point and the network point, said method comprising the steps of:

(a) receiving, at a detection point, a digital signal emitted into free space from the ingress source, the signal passing through the HFC network between the reference point and the ingress source and having a center frequency in the VHF Low Band of the forward path spectrum, the detection point being defined by geographic coordinates;

(b) performing a coherent cross-correlation between the signal sampled at the reference point and the signal sampled at the detection point, the coherent cross-correlation generating a correlation function having an amplitude peak and a time delay associated with the peak;

(c) obtaining a measured propagation delay, Tm, from the time delay associated with the peak of the correlation function, Tm being a measured propagation delay between the reference point and the detection point and including a network propagation delay between the reference point and the ingress source and a free-space propagation delay between the ingress source and the detection point;

(d) retrieving the sets of geographic coordinates of the number of network points from the network database;

(e) calculating a distance between the detection point and each of the number of network points, using the geographic coordinates of the detection point and the sets of geographic coordinates of the number of network points;

(f) calculating a free-space propagation delay between the detection point and each of the number of network points, using the distances calculated in step (e) and the velocity of propagation of an electric wave in free space;

(g) retrieving the network time delay value of each of the number of network points from the network database;

(h) calculating a number of propagation delays, Tc_n, between the reference point and the detection point, via the number of network points, respectively, by adding together the free-space propagation delay calculated in step (f) and the network time delay value retrieved in step (g), for each network point;

(i) comparing the propagation delays Tc_n, calculated in step (h) with the measured propagation delay Tm obtained in step (c), and selecting a delay Tc_k from the calculated delays Tc_n that substantially matches, within a tolerance value, the measured delay Tm; and

(j) identifying a network point from the delay Tc_k selected in step (i), as a candidate for the ingress source.

18. The method of claim 17, wherein steps (a) through (j) are performed in substantially real-time at or in the vicinity of the detection point.

19. The method of claim 17, wherein the coherent cross-correlation performed in step (b) includes sampling the signal at the reference point over a first sampling interval and sampling the signal at the detection point over a second sampling interval, the second sampling interval being greater than the first sampling interval.

20. The method of claim 17, wherein the digital signal is a digital TV signal normally transmitted to subscribers of the HFC network and step (a) includes receiving, at the detection point, the digital TV signal emitted into free space from the leakage source.

21. A method of locating a low frequency ingress source in a coaxial cable portion of an HFC network having forward path and return path frequency spectrums, the forward path spectrum including a VHF Low Band and the return path spectrum being lower in frequency than the forward path spectrum, the ingress source admitting ingress into the return path spectrum, the HFC network including a reference point coupled to the forward path spectrum, said method comprising the steps of:

(a) receiving, at a first detection point, a digital signal emitted into free space from the ingress source, the signal passing through the HFC network between the reference point and the ingress source and having a center frequency in the VHF Low Band of the forward path spectrum, the first detection point being defined by a first set of geographic coordinates;

(b) performing a coherent cross-correlation between the signal sampled at the reference point and the signal sampled at the first detection point, the coherent cross-correlation generating a correlation function having an amplitude peak and a time delay associated with the peak;

(c) obtaining a first propagation delay of the signal, t1, from the time delay associated with the peak of the correlation function, t1 including at least a free-space propagation delay between the ingress source and the first detection point;

(d) repeating steps (a) through (c) at a second detection point defined by a second set of geographic coordinates, the coherent cross-correlation being between the signal sampled at the reference point and the signal sampled at the second detection point, wherein a second propagation delay of the signal, t2, is obtained, t2 including at least a free-space propagation delay between the ingress source and the second detection point;

(e) repeating steps (a) through (c) at a third detection point defined by a third set of geographic coordinates, the coherent cross-correlation being between the signal sampled at the reference point and the signal sampled at the third detection point, wherein a third propagation delay of the signal, t3, is obtained, t3 including at least a free-space propagation delay between the ingress source and the third detection point;

(f) calculating the difference, Δ

t12, between the first propagation delay t1 and the second propagation delay t2 and the difference, Δ

t23, between the second propagation delay t2 and the third propagation delay t3; and

(g) determining an approximate location of the ingress source by solving for a set of geographic coordinates of the ingress source in at least two hyperbolic equations, the at least two hyperbolic equations being defined by the differences Δ

t12 and Δ

t23 and by the first, second and third sets of geographic coordinates of the first, second and third detection points, respectively.

22. The method of claim 21, wherein the coherent cross-correlation performed in step (b) includes sampling the signal at the reference point over a first sampling interval and sampling the signal at the first detection point over a second sampling interval, the second sampling interval being greater than the first sampling interval.

23. The method of claim 21, wherein the coherent cross-correlation performed in steps (b), (d) and (e) includes sampling the signal at the reference point over a first sampling interval and sampling the signal at the first, second and third detection points, respectively, over a second sampling interval, the second sampling interval being greater than the first sampling interval.

24. The method of claim 21, wherein steps (a) through (g) are performed in substantially real-time in the vicinity of the first, second and third detection points.

25. The method of claim 21, wherein the digital signal is a digital TV signal normally transmitted to subscribers of the HFC network and step (a) includes receiving the digital TV signal emitted into free space from the leakage source.

26. A method of locating a plurality of leakage sources in a coaxial cable portion of an HFC network, the HFC network including a reference point and a number of network points, the number of network points being located in the coaxial cable portion of the HFC network and each being characterized in a network database by a set of geographic coordinates and a network time delay value, the network time delay value of each network point representing a predetermined propagation delay between the reference point and the network point, said method comprising the steps of:

(a) receiving, at a detection point, a digital signal emitted into free space from the plurality of leakage sources, the signal passing through the HFC network between the reference point and the plurality of leakage sources, the detection point being defined by geographic coordinates;

(b) performing a coherent cross-correlation between the signal sampled at the reference point and the signal sampled at the detection point, the coherent cross-correlation generating a correlation function having a plurality of amplitude peaks and a plurality of time delays associated with the peaks, respectively, the plurality of peaks representing detections of the signal from the plurality of leakage sources, respectively;

(c) obtaining a plurality of measured propagation delays, Tm_p, from the plurality of time delays of the correlation function, Tm_p being a plurality of measured propagation delays between the reference point and the detection point, via the plurality of leakage sources, respectively, each of the plurality of measured propagation delays Tm_p including a network propagation delay between the reference point and a respective leakage source and a free-space propagation delay between the respective leakage source and the detection point;

(d) retrieving the sets of geographic coordinates of the number of network points from the network database;

(e) calculating a distance between the detection point and each of the number of network points, using the geographic coordinates of the detection point and the sets of geographic coordinates of the number of network points;

(f) calculating a free-space propagation delay between the detection point and each of the number of network points, using the distances calculated in step (e) and the velocity of propagation of an electric wave in free space;

(g) retrieving the network time delay value of each of the number of network points from the network database;

(h) calculating a number of propagation delays, Tc_n, between the reference point and the detection point, via the number of network points, respectively, by adding together the free-space propagation delay calculated in step (f) and the network time delay value retrieved in step (g), for each network point;

(i) comparing the propagation delays Tc_n calculated in step (h) with the measured propagation delays Tm_p obtained in step (c), and selecting a plurality of calculated delays Tc_p from the number of calculated delays Tc_n that substantially match, within a tolerance value, the plurality of measured delays Tm_p, respectively; and

(j) identifying a plurality of network points from the plurality of calculated delays Tc_p selected in step (i), as candidates for the plurality of leakage sources, respectively.

27. The method of claim 26, wherein the digital signal is a digital TV signal normally transmitted to subscribers of the HFC network and step (a) includes receiving, at the detection point, the digital TV signal emitted into free space from the leakage source.

28. A method of locating a plurality of leakage sources in a coaxial cable portion of an HFC network, the HFC network including a reference point, said method comprising the steps of:

(a) receiving, at a first detection point, a digital signal emitted into free space from the plurality of leakage sources, the signal passing through the HFC network between the reference point and the plurality of leakage sources, the first detection point being defined by a first set of geographic coordinates;

(b) performing a coherent cross-correlation between the signal sampled at the reference point and the signal sampled at the first detection point, the coherent cross-correlation generating a correlation function having a plurality of amplitude peaks and a plurality of time delays associated with the peaks, respectively, the plurality of peaks representing detections of the signal from the plurality of leakage sources, respectively;

(c) obtaining a first plurality of propagation delays of the signal, t1_p, from the plurality of time delays of the correlation function, each t1_p including at least a free-space propagation delay between a respective leakage source and the first detection point;

(d) repeating steps (a) through (c) at a second detection point defined by a second set of geographic coordinates, the coherent cross-correlation being between the signal sampled at the reference point and the signal sampled at the second detection point, wherein a second plurality of propagation delays of the signal, t2_p, is obtained, each t2_p including at least a free-space propagation delay between a respective leakage source and the second detection point;

(e) repeating steps (a) through (c) at a third detection point defined by a third set of geographic coordinates, the coherent cross-correlation being between the signal sampled at the reference point and the signal sampled at the third detection point, wherein a third plurality of propagation delays of the signal, t3_p, is obtained, each t3_p including at least a free-space propagation delay between a respective leakage source and the third detection point;

(f) calculating a plurality of differences, Δ

t12_p, between the first plurality of propagation delays t1_p and the second plurality of propagation delays t2_p, respectively, and calculating a plurality of differences, Δ

t23_p, between the second plurality of propagation delays t2_p and the third plurality of propagation delays t3_p, respectively; and

(g) determining a plurality of approximate locations of the plurality of leakage sources, respectively, by calculating, for each leakage source, a set of geographic coordinates of the leakage source using at least two hyperbolic equations, the at least two hyperbolic equations being defined by (i) an associated one of the differences Δ

t12_p, (ii) an associated one of the differences Δ

t23_p, and (iii) the first, second and third sets of geographic coordinates of the first, second and third detection points, respectively.

29. The method of claim 28, wherein the digital signal is a digital TV signal normally transmitted to subscribers of the HFC network and step (a) includes receiving the digital TV signal emitted into free space from the leakage source.