Low-cost leakage detector for a digital HFC network

• US 9,038,119 B2
• Filed: 02/11/2014
• Issued: 05/19/2015
• 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:
  US14/177,771
• Publication Number:
  US 20140165126A1
• Time in Patent Office: 462 Days
• Field of Search: 725/107, 725/111, 348/180, 348/192
• US Class Current: 725/107
• 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 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 digital signal taken from the HFC network, called “reference samples.” The leakage receiver receives a leakage signal, which is a leaked version of the digital signal from the HFC network. The leakage sampler samples the leakage signal to form leakage samples. The correlator performs a cross-correlation of the reference samples and the leakage samples, to produce a correlation function. An optimizable value is determined from the correlation function. 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 value becomes substantially optimized or the leak is found.

Claims

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

(a) a reference subsystem, including

(i) a first navigation receiver for receiving from a 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 digital signal carried on the HFC network,

(iii) a reference sampler, coupled to the first navigation receiver and the reference receiver, for sampling the signal part of the digital 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 navigation receiver and the reference sampler and programmed to assemble a reference data packet containing the first timestamp and the reference samples, and

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

(b) a field-deployable subsystem including—

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

(ii) a frequency divider, coupled to the second navigation receiver, for lowering the frequency of the reference clock signal to a lower frequency, to form a slower clock signal,

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

(iv) a radio transmitter, coupled to the second navigation receiver, to the frequency divider, and to the wireless modem, for transmitting 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, including—

(i) a radio receiver 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 clock generator, coupled to the radio receiver, for generating a local clock signal from the slower clock signal, the local clock signal having a frequency substantially equal to the frequency of the reference clock signal,

(iii) a detector processor, coupled to the radio 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 cross-correlation of the reference samples and the leakage samples if the condition is met, to produce a correlation function characterized by a parameter,

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

(viii) means for indicating the value, the value generally becoming more optimized as the detection position 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.

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

3. The system 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.

4. The system of claim 1, wherein the radio transmitter of said field-deployable subsystem is a FSK transceiver, and wherein the radio receiver of said handheld leakage detector is a FSK transceiver.

5. The system of claim 1, wherein the parameter characterizing the correlation function is amplitude of a correlation peak, and wherein the value is a relative strength of the leakage signal.

6. The system of claim 1, wherein the parameter characterizing the correlation function is amplitude of a correlation peak, and wherein the value is a field strength of the leakage signal.

7. The system of claim 1, wherein the parameter characterizing the correlation function is time delay, and wherein the value is a relative distance between the detection position and the leak.

8. The system of claim 1, wherein the digital signal is a QAM signal.

9. The system of claim 1, wherein said handheld leakage detector does not include a navigation receiver or a wireless modem for a mobile wireless network.

10. The system of claim 1, wherein the slower clock signal and the local clock signal are substantially phased locked to the reference clock signal.

11. 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) receiving from a reference point in the HFC network the signal part of the digital signal;

(b) 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) transmitting the set of reference samples over a communications link that includes a mobile wireless network;

(e) at a remote position, 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;

(h) at the remote position, transmitting the set of reference samples and the slower clock signal over 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;

(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);

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

(m) performing a cross-correlation of the set of reference samples and the set of leakage samples, to produce a correlation function characterized by a parameter; and

(n) determining a value related to the parameter of the correlation function, the value generally becoming more optimized as the detection position approaches the leak,

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

12. The method of claim 11, further comprising the steps of:

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

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

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

13. The method of claim 11, wherein step (i) includes receiving the leakage signal using a leakage detector that does not include a receiver for a satellite navigation system or a wireless modem for a mobile wireless network.

14. The method of claim 11, 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;

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

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

15. The method of claim 14, 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 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;

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.

16. A handheld leakage detector for finding a leak in a coaxial cable portion of a HFC network carrying a digital signal having a signal part, the leak emitting the digital signal including the signal part into free space as a leakage signal, said handheld leakage detector 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 data packet over a relatively short-range radio communications path, the 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 samples of the digital signal carried in the HFC network and being formed in synchronism with a reference clock signal, the data clock signal being related to the reference clock signal;

(c) a 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;

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

(e) a leakage sampler, mounted in said housing and coupled to said leakage receiver, for sampling the 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 cross-correlation of the reference samples and the leakage samples if the condition is met, to produce a correlation function characterized by a parameter; and

(h) means, associated with the correlator, for determining a value related to the parameter of the correlation function, the value generally becoming more optimized as the detection position approaches the leak,

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.

17. The handheld leakage detector of claim 16, wherein said handheld leakage detector does not include a navigation receiver or a wireless modem for a mobile wireless network.

18. The handheld leakage detector of claim 16, wherein the parameter characterizing the correlation function is amplitude of a correlation peak, and wherein the value is a relative strength of the leakage signal.

19. The handheld leakage detector of claim 16, wherein the parameter characterizing the correlation function is amplitude of a correlation peak, and wherein the value is a field strength of the leakage signal.

20. The leakage detector of claim 16, wherein the parameter characterizing the correlation function is time delay, and wherein the value is a relative distance between the detection position and the leak.