Method and apparatus for adaptive cancellation of responses in cabling

• US 6,522,152 B1
• Filed: 11/15/2000
• Issued: 02/18/2003
• Est. Priority Date: 05/13/1999
• Status: Expired due to Term

• Current Assignee: Microtest, Inc. (NetScout Systems Incorporated)
• Original Assignee: Microtest, Inc. (NetScout Systems Incorporated)
• Inventors: Patterson, James A., Tonti, James G., Sciacero, James R.
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): Nguyen, Vincent Q.
• Application Number:
  US09/713,383
• Time in Patent Office: 825 Days
• Field of Search: 324/628, 324/535, 324/543, 324/617, 324/539
• US Class Current: 324/628
• CPC Class Codes: G01R 31/083 in cables, e.g. underground
• CPC Class Codes: G01R 31/11 using pulse reflection methods

Abstract

An Adaptive Vector Cancellation method which uses time domain data for an instrument connection to estimate magnitude, phase, and time position of a signal response such as NEXT or Return Loss associated with the connection. Based on the estimate of the amplitude and time of the connection response, a suitable full-bandwidth frequency response that corresponds to a point source of NEXT or Return Loss is determined. This calculated connector response is then scaled to an appropriate magnitude, phase and time shifted to the estimated position of the actual connection. The scaled/shifted response is then vectorially combined with the measured sweep data to suitably cancel the connection contribution to NEXT and/or Return Loss. Thus, the amount of NEXT or return loss existing in the user'"'"'s patch cord is preserved, while the NEXT or return loss due to the instrument connection is suitably suppressed. Correction is done in the frequency domain, over the full bandwidth of the measured data.

Claims

1. A method for improving performance characteristic testing, comprising the steps of:

(a) sending a test signal through a channel;

(b) obtaining a time domain impulse response corresponding to said test signal;

(c) searching said time domain impulse response for a connector response signature;

(d) estimating an amplitude and a location of said connector response signature;

(e) generating an ideal frequency response corresponding to said connector response signature at said amplitude and said location; and

(f) canceling said connector response signature with said ideal frequency.

2. The method of claim 1, further comprising the steps of:

(g) searching said time domain response for an N^th connector response 3 signature; and

(h) estimating an N^th amplitude and an N^th location of said N^th connector response signature;

(i) generating an N^th ideal frequency response corresponding to said N^th connector response signature at said N^th amplitude and said N^th location; and

(j) canceling said N^th connector response signature with said N^th ideal frequency response.

3. The method of claim 1, wherein said connector response signature is a NEXT response.

4. The method of claim 1, wherein said connector response signature is a Return Loss response.

5. The method of claim 1, wherein said estimating step further comprises the step of determining a peak response and a zero crossing point.

6. The method of claim 1, wherein said generating step comprises determining a polynomial curve corresponding to said connector response signature.

7. The method of claim 1, wherein said searching step is performed about a predetermined range of time or distance.

8. The method of claim 1, wherein said searching step is performed near zero time or distance.

9. A method for removing an undesirable performance characteristic measured by cable field testers, comprising the steps of:

(a) sending a test signal through a channel;

(b) obtaining an impulse frequency response corresponding to said test signal;

(c) converting said impulse frequency response to a time domain response;

(d) searching said time domain response for a connector response signature;

(e) estimating an amplitude and a location of said connector response signature;

(f) generating an ideal frequency response corresponding to said connector response signature at said amplitude and said location; and

(g) canceling said connector response signature with said ideal frequency response.

10. The method of claim 9, further comprising the steps of:

(h) searching said time domain response for an N^th connector response signature; and

(i) estimating an N^th amplitude and an N^th location of said N^th connector response signature;

(j) generating an N^th ideal frequency response corresponding to said N^th connector response signature at said N^th amplitude and said N^th location; and

(k) canceling said N^th connector response signature with said N^th ideal frequency response.

11. The method of claim 9, wherein said connector response signature is a NEXT response.

12. The method of claim 9, wherein said connector response signature is a Return Loss response.

13. The method of claim 9, wherein said searching step is performed about a predetermined range of time or distance.

14. The method of claim 9, wherein said searching step is performed near zero time or distance.

15. The method of claim 9, wherein said estimating step further comprises the step of determining a peak response and a zero crossing point.

16. The method of claim 9, wherein said generating step comprises determining a polynomial curve corresponding to said connector response signature.

17. A method for removing an undesirable performance characteristic measured by cable field testers, comprising the steps of:

(a) sending a test signal through a channel;

(b) obtaining a time domain impulse response corresponding to said test signal;

(c) searching said time domain impulse response for a connector response signature;

(d) estimating an amplitude and a location of said connector response signature;

(e) determining a peak response and a zero crossing point of said connector response signature;

(f) generating a polynomial curve of an ideal frequency response corresponding to said connector response signature; and

(g) canceling said connector response signature with said polynomial curve.

18. The method of claim 17, further comprising the steps of:

(h) searching said time domain response for a second connector response signature; and

(i) estimating a second amplitude and a second location of said second connector response signature;

(j) determining a second peak response and a second zero crossing point of said second connector response signature;

(i) generating a second polynomial curve of a second ideal frequency response corresponding to said second connector response signature; and

(j) canceling said second connector response signature with said second polynomial curve.

19. The method of claim 17, wherein said connector response signature is a NEXT response.

20. The method of claim 17, wherein said connector response signature is a Return Loss response.

21. The method of claim 17, wherein said searching step is performed about a predetermined range of time or distance.

22. The method of claim 17, wherein said searching step is performed near zero time or distance.