Distortion monitoring system for CATV transmission networks

• US 6,556,239 B1
• Filed: 04/10/2000
• Issued: 04/29/2003
• Est. Priority Date: 04/10/2000
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Al-Araji, Saleh R., Quesenberry, Paul E., Kruse, Herman A.
• Primary Examiner(s): Lee, Michael
• Application Number:
  US09/545,650
• Time in Patent Office: 1,114 Days
• Field of Search: H04/N 1.700, H04/N.716, 348/192, 348/193, 348/607, 725/143, 725/148, 725/127
• US Class Current: 348/192
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details
• CPC Class Codes: H04N 7/10 Adaptations for transmission by electrical cable H04N7/12 takes precedence

Abstract

Systems and methods for a distortion monitoring system that detects an abnormal amount of signal distortion occurring in a transmission system. The distortion monitoring system includes a system amplifier section for amplifying and coupling an input signal to provide first and second outputs and a distortion monitoring section for processing the second output. The amount of distortion present is represented by an output from the distortion monitoring section of the system. In one embodiment, the distortion monitoring section can include an envelope detector for receiving the second output signal, a lowpass filter coupled to the envelope detector for cutting off frequencies below the Nyquist rate, and a voltage amplifier coupled to the lowpass filter for amplifying the signal. An analog to digital converter coupled to the voltage amplifier digitizes the signal, a memory buffer coupled to the analog to digital converter captures the digital data from the analog to digital converter, and a digital signal processor extracts the converted signal. In yet another embodiment, the digital signal processor includes an on-chip memory. A status monitor coupled to the output of the distortion monitoring section provides for monitoring the output signal.

Claims

1. A distortion monitoring system, comprising:

a system amplifier section for amplifying and coupling an input signal to provide a first and second output; and

a distortion monitoring section for processing the second output to provide a third output representing an amount of distortion present, wherein the distortion monitoring section comprises;

an envelope detector for receiving the second output signal;

a lowpass filter coupled to the envelope detector for cutting off frequencies below a Nyquist rate and for outputting a signal;

a voltage amplifier coupled to the lowpass filter for amplifying the signal;

an analog to digital converter coupled to the voltage amplifier for digitizing the signal;

a memory buffer coupled to the analog to digital converter for capturing digital data from the analog to digital converter; and

a digital signal processor for extracting a converted signal.

2. The distortion monitoring system of claim 1, wherein the system amplifier section includes at least one system amplifier for receiving the input signal and a directional coupler at an output of the system amplifier.

3. The distortion monitoring system of claim 1, wherein the input signal comprises a radio frequency.

4. The distortion monitoring system of claim 2, wherein the system amplifier comprises a forward amplifier in a coaxial transmission system.

5. The distortion monitoring system of claim 2, wherein the system amplifier comprises an optical receiver in a fiber transmission system.

6. The distortion monitoring system of claim 1, wherein the digital signal processor further comprises:

a Fast Fourier Transform for isolating the converted signal and for indicating the power of the converted signal; and

an averager for averaging the amplitude of the beats around the converted signal.

7. The distortion monitoring system of claim 1, wherein the distortion monitoring section further comprises:

a digital to analog converter coupled to the digital signal processor for converting the digital signal to analog and providing an analog output signal.

8. The distortion monitoring system of claim 1, wherein the digital signal processor further comprises:

a digital filter coupled to the memory buffer and adapted to provide a narrow digital band pass filter centered at a nominal beat frequency;

a squarer coupled to the digital filter for squaring the output;

a summer coupled to the squarer for summing the output; and

an averager coupled to the summer for averaging the output and providing the beat level and distortion level of the output.

9. The distortion monitoring system of claim 1, wherein the digital signal processor further comprises a sliding Fast Fourier Transform coupled to the memory buffer for processing the digital output and providing an output representing a signal level in a narrow band centered around the selected beat frequency.

10. The distortion monitoring system of claim 1, further comprising a status monitoring system coupled to the third output.

11. The distortion monitoring system of claim 1, further comprising a status monitoring system coupled to the third output.

12. The distortion monitoring system of claim 8, further comprising a status monitoring system coupled to the analog output signal.

13. A communications system, comprising:

a headend section for transmitting a cable signal over a communications medium;

a system amplifier section for amplifying the cable signal and providing at least main and auxiliary outputs;

a distortion monitoring section for processing the auxiliary output to provide a third output representing an amount of distortion present; and

taps coupled to the main output of the system amplifier section for routing the main output to subscribers,

wherein the distortion monitoring section further comprises;

an envelope detector for receiving the auxiliary output signal;

a lowpass filter coupled to the envelope detector for cutting off frequencies below a Nyquist rate and for outputting a signal;

a voltage amplifier coupled to the lowpass filter for amplifying the signal;

an analog to digital converter coupled to the voltage amplifier for digitizing the signal;

a memory buffer coupled to the analog to digital converter for capturing digital data from the analog to digital converter; and

a digital signal processor for extracting a converted signal.

14. The communications system of claim 13, wherein the system amplifier section includes at least one system amplifier for receiving the cable signal and a directional coupler at an output of the system amplifier.

15. The communications system of claim 13, wherein the cable signal comprises a radio frequency.

16. The communications system of claim 14, wherein the system amplifier comprises a forward amplifier in a coaxial transmission system.

17. The communications system of claim 14, wherein the system amplifier comprises an optical receiver in a fiber transmission system.

18. The communications system of claim 13, wherein the digital signal processor further comprises:

a Fast Fourier Transform for isolating the converted signal and for indicating the power of the converted signal; and

an averager for averaging the amplitude of the beats around the converted signal.

19. The communications system of claim 13, wherein the digital signal processor further comprises:

an averager for averaging the amplitude of the beats around the converted signal; and

a spectral estimation algorithm selected from the group consisting of a maximum entropy method, an all poles method and other spectral estimation algorithms for isolating the converted signal and for indicating the power of the converted signal.

20. The communications system of claim 13, wherein the distortion monitoring section further comprises:

a digital to analog converter coupled to the digital signal processor for converting the digital signal to analog and providing an analog output signal.

21. The communication system of claim 13, wherein the digital signal processor further comprises

a digital filter coupled to the memory buffer and adapted to provide a narrow digital band pass filter centered at a nominal beat frequency;

a squarer coupled to the digital filter for squaring the output;

a summer coupled to the squarer for summing the output; and

an averager coupled to the summer for averaging the output and providing the beat level and distortion level of the output.

22. The distortion monitoring system of claim 13, wherein the digital signal processor further comprises a sliding Fast Fourier Transform coupled to the memory buffer for processing the digital output and providing an output representing a signal level in a narrow band centered around the selected beat frequency.

23. The communications system of claim 13, further comprising a status monitoring system coupled to the third output.

24. The communications system of claim 13, further comprising a status monitoring system coupled to the third output.

25. The distortion monitoring system of claim 21, further comprising a status monitoring system coupled to the analog output signal.