Method and apparatus for pinpointing common path distortion

• US 20060248564A1
• Filed: 01/03/2006
• Published: 11/02/2006
• Est. Priority Date: 02/22/2005
• Status: Active Grant

• Current Assignee: Arcom Digital Patent, LLC
• Original Assignee: Arcom Digital, LLC
• Inventors: Zinevitch, Victor M.
• Granted Patent: US 7,584,496 B2
• Time in Patent Office: Days
• US Class Current: 725/121
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details

Abstract

A system for pinpointing CDP sources in a two-way HFC CATV network comprises a headend CPD radar unit, a return path switch, and a computer. The radar unit is coupled to a headend combiner. The return path switch is coupled between the nodes of the CATV network and the radar unit. The computer is connected to the radar unit and the return path switch. The computer controls the radar unit and switch and causes them to perform constant sequential CPD monitoring of the nodes of the network. The system further comprises a portable radar-calibrator unit that is carried into the field and connected to various points along the coaxial cable portion of the network. The portable radar unit is used to detect CPD sources in the field and to calibrate the network as to time delay. The portable unit communicates with the headend radar unit through the CATV network.

Claims

1. A system for pinpointing CDP sources in a two-way HFC CATV network, comprising;

(a) a headend CPD radar unit coupled to a headend combiner;

(b) a return path switch coupled between the nodes of the CATV network and the headend radar unit; and

(c) a headend computer for controlling the headend radar unit and return path switch, for constant sequential CPD monitoring of the nodes of the network.

2. The system as claimed in claim 1, further comprising

a portable radar-calibrator unit that is carried into the field and connected to various points along the coaxial cable portion of the CATV network, for field detection of CPD sources and for calibrating the CATV network as to time delay, said portable radar-calibrator unit communicating with the headend radar unit through the CATV network.

3. A method of locating a CPD source in a CATV network, comprising the steps of:

(a) using a double sideband probing signal to determine an approximate time delay associated with the CPD source;

(b) cross-correlating CPD distortion products of the forward path TV program signals, received in the return path, with a locally produced replica of the CPD distortion products;

(c) guiding the cross-correlation in step (b) by delaying the replica of the CPD distortion products by the approximate time delay determined in step (a); and

(d) determining the time delay of the CPD source based on the cross-correlation in steps (b) and (c).

4. The method as claimed in claim 3, further comprising the step of:

(f) suppressing the return path service signals before performing the cross-correlation in step (b).

5. The method as claimed in claim 3, further comprising the step of:

(f) employing a portable radar-calibrator unit at a plurality of connection points along the CATV network to locate the CPD source.

6. A method of calibrating a CATV network employing a portable radar-calibrator unit, comprising the steps of:

(a) connecting said portable unit to the CATV network at a calibration point;

(b) generating a simulated CPD distortion product as a calibration signal in the return path frequency spectrum, where the calibration signal has a pulse train;

(c) altering the pulse train of the calibration signal to distinguish it from a distortion product from a CPD source located near the calibration point;

(d) transmitting the calibration signal with the altered pulse train back to the headend in the return path;

(e) detecting the calibration signal at the headend substantially independent of the CPD distortion product; and

(f) determining the time delay between the headend and the calibration point to establish a calibrated time delay associated with the location of the calibration point.

7. The method as claimed in claim 6, wherein the pulse train of said calibration signal is altered in step (c) by blanking every other pulse in the pulse train.

8. The method as claimed in claim 7, wherein said calibration signal is detected in step (e) by inverting every other pulse of a pulse train of the CPD distortion product and performing coherent accumulation of the calibration signal and CPD distortion product, such that the pulse train of the CPD distortion product cancels itself out and the pulse train of the calibration signal is accumulated.

9. An apparatus for detecting a CPD source in a CATV network that carries forward path signals in a forward path and return path signals in a return path, said apparatus comprising:

(a) a first input coupled to the forward path of the CATV network to receive the forward path signals;

(b) a CPD generator, coupled to said first input, that generates a plurality of intermodulation products from the forward path signals for use as a reference signal;

(c) a second input coupled to the return path of the CATV network to receive the return path signals, the return path signals including a plurality of distortion products of the forward path signals created by the CPD source; and

(d) a processor, coupled to said CPD generator and to said second input, that determines a time delay associated with the CPD source based on said reference signal and the plurality of distortion products created by the CPD source, the time delay being a function of the propagation time of the forward path signals from a reference point to the CPD source and the propagation time of the distortion products from the CPD source to the reference point.

10. The apparatus of claim 9, wherein said processor includes a correlator having one input coupled to said CPD generator for receiving the reference signal and another input for receiving the plurality of distortion products created by the CPD source, the reference signal being correlated with the plurality of distortion products to determine the time delay.

11. The apparatus of claim 9, wherein the return path signals of the CATV network include service signals, said apparatus further comprising a filter coupled between said second input and said processor, said filter being adapted to substantially suppress the service signals such that the service signals do not substantially interfere with the processing of the plurality of distortion products in said processor.

12. The apparatus of claim 9, wherein the forward path signals include a plurality of digital QAM television signals and wherein the plurality of intermodulation products generated by said CPD generator includes intermodulation products between said plurality of digital QAM signals.

13. The apparatus of claim 12, wherein the forward path signals further include a plurality of analog television signals and wherein the plurality of intermodulation products generated by said CPD generator includes intermodulation products between said plurality of analog signals and said plurality of digital QAM signals.

14. A method of detecting a CPD source in a CATV network that carries forward path signals in a forward path and return path signals in a return path, said method comprising the steps of:

(a) receiving the forward path signals from the forward path of the CATV network;

(b) generating a plurality of intermodulation products from the forward path signals for use as a reference signal;

(c) receiving the return path signals from the return path of the CATV network, the return path signals including a plurality of distortion products of the forward path signals created by the CPD source; and

(d) determining a time delay associated with the CPD source based on said reference signal and the plurality of distortion products created by the CPD source, the time delay being a function of the propagation time of the forward path signals from a reference point to the CPD source and the propagation time of the distortion products from the CPD source to the reference point.

15. The method of claim 14, wherein said step (d) includes correlating the reference signal with the plurality of distortion products created by the CPD source to determine the time delay.

16. The method of claim 14, wherein the return path signals of the CATV network include service signals, said method further comprising the step of substantially suppressing the service signals such that the service signals do not substantially interfere with the time delay determination in step (d).