Low-cost leakage detector for a digital HFC network

• US 8,650,605 B2
• Filed: 04/26/2012
• Issued: 02/11/2014
• Est. Priority Date: 04/26/2012
• 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:
  US13/456,950
• Publication Number:
  US 20130291044A1
• Time in Patent Office: 656 Days
• Field of Search: 725/107, 725/111, 348/180, 348/192
• US Class Current: 725/111
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details
• CPC Class Codes: H04N 21/44209 Monitoring of downstream path of the transmission network originating from a server, e.g. bandwidth variations of a wireless network arrangements for maintenance or administration in data switching networks involving bandwidth and capacity management H04L41/0896
• CPC Class Codes: H04N 21/6118 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 21/6168 involving cable transmission, e.g. using a cable modem

Abstract

A handheld leakage detector for finding digital QAM signal leaks in a HFC network, comprises a radio receiver, a leakage receiver, leakage sampler, a correlator, and a display. The radio receiver receives samples of the QAM signal taken from the HFC network, called “reference samples.” The leakage receiver receives a QAM leakage signal, which is related to the QAM signal from the HFC network. The leakage sampler samples the leakage signal to form leakage samples. The correlator performs a coherent cross-correlation of the reference samples and the leakage samples, to produce a correlation peak. A value is determined from the correlation peak and displayed on the display. The value generally becomes more optimized as the detector approaches the leak. The leak is sought by iteratively changing the position of the detector until the displayed value becomes substantially optimized or the leak is found.

Claims

1. An improved apparatus for finding a leak in a HFC network carrying a digital signal having a signal part, where the leak emits the digital signal including the signal part into free space as a leakage signal, said apparatus being of the type in which

a reference subsystem includes a first navigation receiver, a reference receiver, a reference sampler, and a communications interface, the first navigation receiver being adapted to receive from a navigation system a reference clock signal having a frequency, the reference receiver being adapted to receive the digital signal from a reference point in the HFC network, the reference sampler being adapted to sample in synchronism with the reference clock signal the signal part of the digital signal received by the reference receiver, to form reference samples, and the communications interface being adapted to deliver the reference samples to a first communications link that includes a mobile wireless network, and in which

a field subsystem includes a second navigation receiver and a wireless modem, the second navigation receiver being adapted to receive the reference clock signal from the navigation system, and the wireless modem being adapted to receive the reference samples from the mobile wireless network of the first communications link, wherein the improvement comprises:

(a) a communications bridge, associated with said field subsystem, including—

(i) a phase lock loop frequency divider, coupled to the second navigation receiver, for dividing the frequency of the reference clock signal down to a lower frequency, to form a slower clock signal that is substantially phase-locked to the reference clock signal, and

(ii) a radio transmitter, coupled to the frequency divider and the wireless modem, for transmitting the reference samples and the slower clock signal over a second communications link consisting essentially of a relatively short-range, radio communications path; and

(b) a handheld leakage detector, excluding a receiver for a navigation system and including—

(i) a radio receiver for receiving the reference samples and the slower clock signal from the radio communications path of the second communications link,

(ii) a phase lock loop clock generator, coupled to the radio receiver, for generating a local clock signal from the slower clock signal, the local clock signal being substantially phase-locked to the slower clock signal and, in turn, to the reference clock signal and having a frequency substantially equal to the frequency of the reference clock signal,

(iii) a leakage receiver for receiving from free space, at a detection position, the leakage signal including the signal part,

(iv) a leakage sampler, coupled to the leakage receiver and the local clock generator, for sampling the leakage signal including the signal part in synchronism with the local clock signal, to form leakage samples,

(v) a correlator, coupled to the radio receiver and the leakage sampler, for performing a coherent cross-correlation of the reference samples and the leakage samples, to produce a correlation peak characterized by a parameter,

(vi) a detector processor, associated with the correlator, for determining a value related to the parameter of the correlation peak, and

(vii) means for indicating the value, the value generally becoming more optimized as the detection position of the leakage signal approaches the leak,

whereby the leak is sought by iteratively changing the detection position relative to the leak while operating said apparatus, in an effort to optimize the value.

2. The apparatus of claim 1, wherein:

the first navigation receiver of said reference subsystem is adapted to receive from the navigation system a first sync pulse, the reference sampler of said reference subsystem forming the reference samples in response to the first sync pulse;

the second navigation receiver of said field subsystem is adapted to receive a second sync pulse from the navigation system, the radio transmitter of said communications bridge being coupled to the second navigation receiver to receive the second sync pulse and being adapted to transmit the second sync pulse over the radio communications path of the second communications link; and

the radio receiver of said handheld leakage detector is adapted to receive the second sync pulse from the radio communications path of second communications link, the leakage sampler of said leakage detector forming the leakage samples in response to the second sync pulse.

3. The apparatus of claim 2, wherein:

said reference subsystem further includes a first processor coupled to the first navigation receiver, the reference sampler and the communications interface, the first navigation receiver being adapted to receive from the navigation system a first timestamp associated with the first sync pulse, the first processor being programmed to associate the first timestamp with the reference samples and to assemble a reference data packet containing the first timestamp and the reference samples, the communication interface being adapted to deliver the reference data packet to the first communications link;

the wireless modem of said field subsystem being adapted to receive the reference data packet from the mobile wireless network, the second navigation receiver of said field subsystem being adapted to receive a second timestamp from the navigation system, the radio transmitter of said field subsystem being adapted to transmit the reference data packet and the second timestamp over the radio communications path of the second communications link; and

the radio receiver of said leakage detector is adapted to receive the reference data packet and the second timestamp from the radio communications path of the second communications link, the detector processor being coupled to the radio receiver and the leakage sampler and being programmed to associate the second timestamp with the leakage samples, the detector processor being further programmed to deliver the reference samples of the reference data packet and the leakage samples to the correlator for cross-correlation if the first timestamp of the reference data packet is the same as the second timestamp.

4. The apparatus of claim 2, wherein the signal part of the digital signal spans a reference time interval and propagates between the reference point in the HFC network and said leakage detector within a propagation time interval, and wherein

the leakage sampler of said leakage detector forms the leakage samples over a leakage time interval, the start of the leakage time interval being delayed by a delay interval triggered by the second sync pulse, the leakage time interval having a duration of at least the reference time interval plus the propagation time interval minus the delay interval.

5. The apparatus of claim 1, wherein the navigation system is a satellite navigation system and the first and the second navigation receivers are satellite navigation receivers.

6. The apparatus of claim 1, wherein the HFC network includes a fiber optic node, the reference point in the HFC network being located at about the fiber optic node.

7. The apparatus of claim 1, wherein the lower frequency of the slower clock signal is between about 9 KHz and about 385 KHz.

8. The apparatus of claim 1, wherein the radio transmitter of said communications bridge is a FSK transceiver that transmits the reference samples and the slower clock signal over an ISM band of frequencies, and wherein the radio receiver of said leakage detector is a FSK transceiver that receives the reference samples and the slower clock signal over the ISM band of frequencies.

9. The apparatus of claim 8, wherein the ISM band of frequencies is within a range selected from the group consisting of 902 MHz to 928 MHz, 862 MHz to 870 MHz, and 431 MHz to 464 MHz.

10. The apparatus of claim 1, wherein the parameter characterizing the correlation peak is an amplitude of the correlation peak, and wherein the value is a relative strength of the leakage signal.

11. The apparatus of claim 1, wherein the parameter characterizing the correlation peak is an amplitude of the correlation peak, and wherein the value is a field strength of the leakage signal.

12. The apparatus of claim 1, wherein the parameter characterizing the correlation peak is a time delay, and wherein the value is a relative distance between the detection position of the leakage signal and the leak.

13. The apparatus of claim 1, wherein the digital signal is a QAM television signal.

14. The apparatus of claim 1, wherein said handheld leakage detector excludes a wireless modem for a mobile wireless network.

15. The apparatus of claim 14, wherein the radio transmitter of said communications bridge and the radio receiver of said leakage detector are FSK transceivers that communicate with each other in an ISM band of frequencies over the radio communications path of the second communications link.

16. A system for finding a leak in a coaxial cable portion of a HFC network carrying a digital QAM television signal having a signal part, where the leak emits the QAM signal including the signal part into free space as a leakage signal, said system comprising:

(a) a reference subsystem, including

(i) a first satellite receiver for receiving from a satellite navigation system a first sync pulse, a first timestamp, and a reference clock signal having a frequency,

(ii) a reference receiver, adapted to be coupled to a reference point in the HFC network, for receiving the QAM signal carried on the HFC network,

(iii) a reference sampler, coupled to the first satellite receiver and the reference receiver, for sampling the signal part of the QAM signal, to form reference samples, the reference sampler sampling the signal part in response to the first sync pulse and in synchronism with the reference clock signal,

(iv) a reference processor, coupled to the first satellite receiver and the reference sampler and programmed to assemble a reference data packet containing the first time-stamp and the reference samples, and

(v) a communications interface, coupled to the reference processor, for delivering the reference data packet to a first communications link including a mobile wireless network;

(b) a field-deployable subsystem including—

(i) a second satellite receiver for receiving from the satellite navigation system a second sync pulse, a second timestamp, and the reference clock signal, and

(ii) a phase lock loop frequency divider, coupled to the second satellite receiver, for dividing the frequency of the reference clock signal down to a lower frequency, to form a slower clock signal that is substantially phase-locked to the reference clock signal,

(iii) a wireless modem for receiving the reference data packet from the mobile wireless network of the first communications link, and

(iv) an FSK transmitter, coupled to the second satellite receiver, the frequency divider and the wireless modem, for transmitting in an ISM band the second sync pulse, the second timestamp, the slower clock signal, and the reference data packet, over a relatively short-range, radio communications path; and

(c) a handheld leakage detector, excluding a satellite receiver for a satellite navigation System and including—

(i) an FSK receiver, tuned to the ISM band, for receiving from the radio communications path the second sync pulse, the second timestamp, the slower clock signal, and the reference data packet,

(ii) a phase lock loop clock generator, coupled to the FSK receiver, for generating a local clock signal from the slower clock signal, the local clock signal being substantially phase-locked to the slower clock signal and, in turn, to the reference clock signal and having a frequency substantially equal to the frequency of the reference clock signal,

(iii) a detector processor, coupled to the FSK receiver, for receiving the second sync pulse, the second timestamp, and the reference data packet,

(iv) a leakage receiver for receiving from free space, at a detection position, the leakage signal including the signal part,

(v) a leakage sampler, coupled to the leakage receiver, the detector processor, and the local clock generator, for sampling the leakage signal including the signal part in response to the second sync pulse and in synchronism with the local clock signal, to form leakage samples, the detector processor being programmed to associate the second timestamp with the leakage samples,

(vi) a correlator associated with the detector processor, the detector processor being further programmed to deliver to the correlator the reference samples of the reference data packet and the leakage samples if a condition is met that the first timestamp of the reference data packet is the same as the second timestamp, the correlator performing a coherent cross-correlation of the reference samples and the leakage samples if the condition is met, to produce a correlation peak characterized by a parameter,

(vii) means, associated with the correlator, for determining a value related to the parameter of the correlation peak, and

(viii) means for indicating the value, the value generally becoming more optimized as the detection position of the leakage signal approaches the leak,

whereby the leak is sought by iteratively changing the detection position relative to the leak while operating said system, in an effort to optimize the value.

17. The apparatus of claim 16, wherein said handheld leakage detector excludes a wireless modem for a mobile wireless network.

18. A method of finding a leak in a coaxial cable portion of a HFC network carrying a digital signal having a signal part, where the leak emits the digital signal including the signal part into free space as a leakage signal, said method comprising the steps of:

(a) at a local position, receiving from a reference point in the HFC network the signal part of the digital signal;

(b) at the local position, receiving from a navigation system a reference clock signal having a frequency;

(c) sampling in synchronism with the reference clock signal the signal part received in step (a), to form a set of reference samples;

(d) at the local position, transmitting the set of reference samples over a first communications link that includes a mobile wireless network;

(e) at a remote position along the HFC network, receiving the set of reference samples from the mobile wireless network;

(f) at the remote position, receiving the reference clock signal from the navigation system;

(g) dividing the frequency of the reference clock signal received in step (f) to a lower frequency, to form a slower clock signal that is substantially phase locked to the reference clock signal received in step (f);

(h) at the remote position, transmitting the set of reference samples and the slower clock signal over a second communications link consisting essentially of a relatively short-range, radio communications path;

(i) at a detection position, receiving from free space the leakage signal including the signal part;

(j) at the detection position, receiving the set of reference samples and the slower clock signal from the radio communications path of the second communications link;

(k) at the detection position, generating from the slower clock signal a local clock signal having a frequency substantially equal to the frequency of the reference clock signal received in step (f) and being substantially phase-locked to the slower clock signal and, in turn, to the reference clock signal received in step (f);

(l) at the detection position, sampling the leakage signal including the signal part in synchronism with the local clock signal, to form a set of leakage samples;

(m) at the detection position, performing a coherent cross-correlation of the set of reference samples and the set of leakage samples, to produce a correlation peak characterized by a parameter;

(n) at the detection position, determining a value related to the parameter of the correlation peak, the value generally becoming more optimized as the detection position of the leakage signal approaches the leak; and

(o) at the detection position, indicating the value,

whereby the leak is sought by iteratively changing the detection position relative to the leak while repeating steps (a) through (o), in an effort to optimize the value.

19. The method of claim 18, further comprising the steps of:

(p) moving to a second detection position and repeating steps (a) through (n) with respect to the second detection position and a second signal part of the digital signal;

(q) indicating any change in the value between what was originally determined in step (n) and what was determined in step (p);

(r) moving to a third detection position and repeating steps (a) through (n) with respect to the third detection position and a third signal part of the digital signal;

(s) indicating any change in the value between what was determined in step (p) and what was determined in step (r); and

(t) if necessary, moving to successive detection positions and successively repeating steps (a) through (n), with respect to the successive detection positions and successive signal parts of the digital signal, respectively, until a substantially optimized value is obtained or the leak is found.

20. The method of claim 18, wherein steps (b) and (f) include receiving the reference clock signal from a satellite navigation system.

21. The method of claim 20, wherein step (i) includes receiving the leakage signal using a leakage detector that does not include a satellite receiver for a satellite navigation system or a wireless modem for a mobile wireless network.

22. The method of claim 18, wherein:

step (b) further includes receiving a first sync pulse from the navigation system;

step (c) includes forming the set of reference samples in response to the first sync pulse;

step (f) further includes receiving a second sync pulse from the navigation system;

step (h) includes transmitting the second sync pulse over the radio communications path of the second communications link;

step (j) includes receiving the second sync pulse from the radio communications path of the second communications link; and

step (l) includes forming the set of leakage samples in response to the second sync pulse received in step (j).

23. The method of claim 22, wherein:

step (b) includes receiving from the navigation system a first timestamp associated with the sync pulse;

step (c) includes associating the first timestamp with the set of reference samples;

step (d) includes transmitting the first timestamp together with the set of reference samples over the first communications link;

step (e) includes receiving the first timestamp together with the set of reference samples from the mobile wireless network;

step (f) includes receiving a second timestamp from the navigation system;

step (h) includes transmitting the first timestamp together with the set of reference samples and the second timestamp over the radio communications path of the second communications link;

step (j) includes receiving the first timestamp together with the set of reference samples and the second timestamp from the radio communications path;

step (l) includes associating the second timestamp with the set of leakage samples; and

step (m) is performed if the first and the second timestamps are the same.

24. The method of claim 22, wherein the signal part of the digital signal spans a reference time interval and the signal part propagates between the reference point in the HFC network and the detection position during a propagation time interval;

and

wherein step (l) includes forming the leakage samples over a leakage time interval, the start of the leakage time interval being delayed by a delay interval triggered by the second sync pulse, the leakage time interval having a duration of at least the reference time interval plus the propagation time interval minus the delay interval.

25. The method of claim 18, wherein the leak in the coaxial cable portion of the HFC network is located at the subscriber premises.

26. The method of claim 18, wherein step (h) includes transmitting the set of reference samples and the slower clock signal in an ISM band of frequencies, and wherein step (j) includes receiving the set of reference samples and the slower clock signal over the ISM band of frequencies.

27. The method of claim 18, wherein the parameter characterizing the correlation peak is an amplitude of the correlation peak, and wherein step (n) includes determining a relative strength of the leakage signal based the amplitude of the correlation peak.

28. The method of claim 18, wherein the parameter characterizing the correlation peak is an amplitude of the correlation peak, and wherein step (n) includes determining a field strength of the leakage signal based the amplitude of the correlation peak.

29. The method of claim 18, wherein the parameter characterizing the correlation peak is a time delay, and wherein step (n) includes determining a relative distance between the detection position of the leakage signal and the leak based on the time delay.

30. The method of claim 18, wherein the digital signal is a QAM television signal.

31. A handheld leakage detector for finding a leak in a coaxial cable portion of a HFC network carrying a digital QAM television signal having a signal part, the leak emitting the QAM signal including the signal part into free space as a QAM leakage signal, said leakage detector excluding a receiver for a navigation system and comprising:

(a) a housing configured and dimensioned to be conveniently held in the hand by a user;

(b) a radio receiver, mounted in said housing, for receiving a radio data packet over a relatively short-range radio communications path in an ISM band of frequencies, the radio data packet containing reference samples, a first timestamp associated with the reference samples, a second timestamp, a sync pulse, and a data clock signal, the reference samples being digital samples of the QAM signal carried in the HFC network and being formed in synchronism with a reference clock signal received from a navigation system, the data clock signal being phase locked to the reference clock signal;

(c) a phase lock loop clock generator, mounted in said housing and coupled to said radio receiver, for generating from the data clock signal a local clock signal having substantially the same frequency as the reference clock signal and being substantially phase locked to data clock signal and, in turn, to the reference clock signal;

(d) a leakage receiver, mounted in said housing, for receiving from free space, at a detection position, the QAM leakage signal including the signal part;

(e) a leakage sampler, mounted in said housing and coupled to said leakage receiver, for sampling the QAM leakage signal including the signal part, to form leakage samples, the leakage samples being formed in synchronism with the local clock signal;

(f) a processor, mounted in said housing and coupled to said radio receiver, said clock generator, and said leakage sampler, for receiving the first timestamp and the associated reference samples, the second timestamp, the sync pulse, and the leakage samples, said processor being programmed to associate the second timestamp with the leakage samples;

(g) a correlator associated with the processor, said processor being further programmed to deliver to said correlator the reference samples and the leakage samples if a condition is met that the first and the second timestamps are the same, said correlator performing a coherent cross-correlation of the reference samples and the leakage samples if the condition is met, to produce a correlation peak characterized by a parameter;

(h) means, associated with the correlator, for determining a value related to the parameter of the correlation peak, the value generally becoming more optimized as the detection position of the QAM leakage signal approaches the leak; and

(i) means for indicating the value,

whereby the leak is sought by iteratively changing the detection position relative to the leak while operating said leakage detector until the value becomes substantially optimized or the leak is found.

32. The leakage detector of claim 31, wherein said radio receiver is an FSK receiver.

33. The leakage detector of claim 31, wherein the ISM band of frequencies is within a range selected from the group consisting of 902 MHz to 928 MHz, 862 MHz to 870 MHz, and 431 MHz to 464 MHz.

34. The leakage detector of claim 31, further excluding a wireless modem for a mobile wireless network.

35. The leakage detector of claim 31, wherein the parameter characterizing the correlation peak is an amplitude of the correlation peak, and wherein the value is a relative strength of the QAM leakage signal.

36. The leakage detector of claim 31, wherein the parameter characterizing the correlation peak is an amplitude of the correlation peak, and wherein the value is a field strength of the QAM leakage signal.

37. The leakage detector of claim 31, wherein the parameter characterizing the correlation peak is a time delay, and wherein the value is a relative distance between the detection position of the QAM leakage signal and the leak.