System and method for characterizing undesirable noise of a signal path within a selected frequency band

• US 6,151,559 A
• Filed: 06/21/1997
• Issued: 11/21/2000
• Est. Priority Date: 06/21/1997
• Status: Expired due to Term

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Thomas H. Williams
• Inventors: Williams, Thomas H.
• Primary Examiner(s): Swann, Tod R.
• Assistant Examiner(s): Smithers, Matthew
• Application Number:
  US08/897,494
• Time in Patent Office: 1,249 Days
• Field of Search: 702/58, 702/57, 702/66, 702/67, 702/77, 702/78, 315/393, 315/364, 315/392, 455/1, 455/4.1, 455/67.3, 455/454, 348/193, 348/181, 348/192
• US Class Current: 702/58
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 7/102 Circuits therefor, e.g. noise reducers, equalisers, amplifiers H04N7/108 takes precedence

Abstract

A test (600) system for characterizing the nature and the severity of the impairments affecting a radio frequency signal path (148) which may be an upstream or a downstream channel in a cable system. Testing is done by monitoring the output of an unused signal path (614) with a filter (608) and a totaling counter (612). The filter passes impairment energy from the signal path to the counter in a frequency band of interest, thereby increasing the count value on the counter. The bandpass filter limits the ability of impairments or signals from other frequency bands to increase the counter'"'"'s count value. The counter'"'"'s input threshold voltage level (404) is set to trigger on impairments that are sufficiently strong to cause data errors. The count value may be used to determine the time duration of an impairment by dividing the count accumulated in one second by the center frequency of the filter. An optional digital time trace acquisition unit (710), connected to the broadband signal path output (614), may be employed to capture time traces (734) to help identify the source and the nature of the impairment. The time traces can be stored, retrieved, and analyzed by conversion into the frequency domain, by digital filtering, by plotting as a histogram, and by plotting as a waterfall display.

Claims

1. A test system for characterizing an impairment affecting a signal path comprising:

a signal path output with a vacant frequency band;

a filter passing said vacant frequency band;

a filter input;

a filter output;

a digital time trace acquisition unit;

a digital time trace acquisition unit input;

a digital time trace acquisition unit trigger input;

a time trace, said filter input connected to the signal path output, said filter output connected to the digital time trace acquisition unit trigger input and said signal path output connected to said digital time trace acquisition unit input, and

wherein impairments from the signal path pass through the filter and trigger said digital time trace acquisition unit and said digital time trace acquisition unit acquires said time trace of said impairments upon triggering.

2. A test system for characterizing an impairment affecting a signal path claim, as per claim 1, further comprising a histogram plot whereby the time trace is processed into the histogram plot.

3. A test system for characterizing an impairment affecting a signal path claim, as per claim 1, further comprising:

a filtered time domain trace;

a software digital filter, and

whereby the time trace is processed with the software digital filter for display as the filtered time domain trace.

4. A test system for characterizing an impairment affecting a signal path claim, as per claim 1, further comprising:

a waterfall plot, and

whereby multiple time traces are processed with a fast Fourier transform for display as the waterfall plot.

5. A test system for characterizing an impairment affecting a signal path, as per claim 1, further comprising:

a spectral plot obtained by processing the time trace.

6. A test system for characterizing impairments affecting a signal path with a vacant frequency band comprising:

a filter connected to said signal path and passing said vacant frequency band;

a totaling counter connected to the output of said filter, said totaling counter having a threshold value, and

wherein signal path impairments having a value in excess of said threshold value increment said totaling counter.

7. A test system for characterizing impairments affecting a signal path, as per claim 6, further comprising:

a circuit to detect block errors, and

wherein an impairment that would cause a block of data to be corrupted is counted and an impairment that would not corrupt the block of data is not counted.

8. A test system for characterizing impairments affecting a signal path, as per claim 6, further comprising:

a digital time trace acquisition unit;

a digital time trace acquisition unit trigger input;

a digital time trace acquisition unit input;

a time trace;

said signal path output is connected to the digital time trace acquisition unit input and said filter output is connected to said digital time trace acquisition unit trigger input, and

said trigger input is set such that impairments of sufficient amplitude to increment said totaling counter trigger said digital time trace acquisition unit and said digital time trace acquisition unit acquires said time trace of said impairments upon triggering.

9. A test system for characterizing impairments affecting a signal path, as per claim 6, further comprising:

a digital time trace acquisition unit;

a digital time trace acquisition unit trigger input;

a digital time trace acquisition unit input;

a time trace;

a trigger output associated with said totaling counter;

said signal path output is connected to the digital time trace acquisition unit input and said trigger output is connected to said digital time trace acquisition unit trigger input, and

wherein incrementing said totaling counter causes said trigger output to trigger said digital time trace acquisition unit and said digital time trace unit acquires said time trace of said impairments upon triggering.

10. A test system for characterizing impairments affecting a signal path, as per claim 6, further comprising:

a plurality of bandpass filters connected to a plurality of totaling counters whereby the severity of impairments can be counted in multiple frequency bands.

11. A test system for characterizing impairments affecting a signal path, as per claim 6, further comprising:

said filter with a bandwidth matching a data carrier and said threshold value of said totaling counter set to a level that would cause a data carrier to make an error, and

whereby the error rate said impairment could cause in a data carrier can be determined.

12. A test system for characterizing impairments affecting a signal path, as per claim 11, further comprising the steps of:

dividing a count value accumulated on the counter by the product of the filter'"'"'s center frequency and the duration of the test, and

whereby the fraction of the test time that the signal path was impaired can be determined.

13. A test system for characterizing impairments affecting a signal path, as per claim 6, wherein said signal path is one of either an upstream or downstream path of a CATV distribution system, rf, wireless or microwave distribution system.

14. A test system for characterizing impairments affecting a signal path, as per claim 6 further comprising:

a plurality of totaling counters with multiple threshold levels connected to the filter output whereby the severity of impairments can be counted for multiple threshold levels.

15. A test system for characterizing impairments affecting a signal path, as per claim 6 further comprising an adjustable threshold value wherein multiple count values may be obtained at multiple threshold levels.

16. A test system for characterizing impairments affecting a signal path, as per claim 6, further comprising a down converter connected between said signal path and said filter.

17. A test system for characterizing impairments affecting a signal path, as per claim 6 further comprising:

an agile downconverter connected between the signal path and the filter wherein a test channel is selected by tuning the agile downconverter.

18. A test system for characterizing impairments affecting a signal path, as per claim 17 wherein said threshold value is adjusted to determine a peak signal level.

19. A system for characterizing impairments affecting a signal path comprising:

a filter connected to said signal path via a frequency converter providing a frequency converted and filtered output of said impairments;

a totaling counter which maintains a count value representative of the number of times said filtered output traverses a predetermined threshold value during a test duration time, and

wherein said count value characterizes said impairment.

20. A system for characterizing impairments affecting a signal path, as per claim 19, wherein said threshold value is chosen such that a filtered output amplitude which traverses said threshold value is sufficient to cause a data error in a signal.

21. A system for characterizing impairments affecting a signal path, as per claim 19, wherein said threshold value is adjustable.

22. A test system for characterizing impairments affecting a signal path, as per claim 19, wherein said signal path is one of either an upstream or downstream path of a CATV distribution system, rf, wireless or microwave distribution system.

23. A system for characterizing impairments affecting a signal path, as per claim 19, wherein at least one of said impairments, a peak signal level of a signal passing through said filter, data traffic, or test signals passing through said filter are determined.

24. A system for characterizing impairments affecting a signal path, as per claim 19, further comprising:

a digital time trace acquisition unit and associated trigger input and signal input;

wherein said signal input is connected to said signal path and said trigger input is connected to said filtered output, and

impairments of sufficient amplitude to cause said count value of said totaling counter to change trigger said digital time trace acquisition unit causing digital time trace acquisition unit to record a time trace of said impairments.

25. A system for characterizing impairments affecting a signal path, as per claim 24, further comprising:

a microprocessor based device connected to the outputs of said counter and digital time trace acquisition unit, and

wherein said microprocessor device stores and performs processing operations on said count value or said time trace.

26. A system for characterizing impairments affecting a signal path, as per claim 19, further comprising:

a digital time trace acquisition unit and associated trigger input and signal input;

a trigger output associated with said counting means, said signal input operatively connected to said signal path and said trigger input connected to said trigger output;

impairments of sufficient amplitude to cause said count value of said totaling counter to change cause said trigger output to trigger said digital time trace acquisition unit and digital time trace unit acquires said time trace of said impairments upon triggering.

27. A system for characterizing impairments affecting a signal path, as per claim 19, further comprising a block error detector connected to said filtered output, and

wherein block error detector means maintains a count value representative of the number of data blocks which would have uncorrectable errors.

28. A system for characterizing impairments affecting a signal path, as per claim 19, further comprising a plurality of bandpass filters connected to a plurality of totaling counters whereby the severity of impairments can be counted in multiple frequency bands.

29. A system for characterizing impairments affecting a signal path, as per claim 19, further comprising the steps of:

dividing a count value accumulated on the counter by the product of the filter'"'"'s center frequency and the duration of the test, and

whereby the fraction of the test time that the signal path was impaired can be determined.

30. A test system for characterizing undesirable energy of a signal path within a selected frequency band comprising:

a signal path comprising a plurality of data channels and at least one test channel wherein said test channel is in said frequency band;

a filter for selecting said test channel from the plurality of said data channels;

a counter responsive to the test channel signal amplitude which maintains a count of the number of times said test channel amplitude traverses a threshold value, and

wherein said test channel signal consists substantially of said undesirable energy and said threshold value is the value at which said undesirable energy could cause a data error in a signal.

31. A method for characterizing undesirable energy of a signal path within a frequency band comprising:

determining a threshold value at which said undesirable energy could cause a data error;

selecting a test channel within said frequency band wherein said test channel consists primarily of said undesirable energy, and

maintaining a count of the number of times said undesirable energy traverses said threshold value during a test duration.