System and method for phone line characterization by time domain reflectometry

• US 6,534,996 B1
• Filed: 03/23/2001
• Issued: 03/18/2003
• Est. Priority Date: 03/27/2000
• Status: Expired due to Fees

• Current Assignee: Conexant Incorporated (Synaptics Incorporated)
• Original Assignee: GlobespanVirata, Inc. (Synaptics Incorporated)
• Inventors: Amrany, Daniel, Delvaux, Marc
• Primary Examiner(s): Oda, Christine K
• Application Number:
  US09/816,506
• Time in Patent Office: 725 Days
• Field of Search: 324/533, 324/534, 324/532, 324/527, 702/108
• US Class Current: 324/533
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data

Abstract

A system and method for characterizing a transmission line in a digital subscriber line (DSL) system. Broadly, the method uses DSL system components, which are configured to perform time domain reflectometry (TDR), in order to determine transmission line characteristics.

Claims

1. A test logic circuit in a digital subscriber line (DSL) modem configured to perform time domain reflectometry (TDR) measurements on a transmission line, the test logic circuit comprising:

means for preparing the transmission line for the TDR measurements;

means for creating a predetermined test signal;

means for transmitting the predetermined test signal to the transmission line at a predetermined repetition rate;

means for receiving reflected signals;

means for accumulating the received reflected signals;

means for measuring a time interval between transmission of the test signals and reception of the reflected signals;

means for identifying the location of disruptions from the measured time intervals;

means for deconvolving known effects of the DSL modem from the accumulated signal to produce a deconvolved signal;

means for determining changes in shape between the transmitted test signal and the deconvolved signal;

means for determining changes in phase between the transmitted test signal and the deconvolved signal; and

means for deriving an impedance profile of the transmission line from the differences in the shape and phase between the test signal and the deconvolved signal.

2. A system for characterizing transmission lines, comprising:

a transmission line; and

a digital subscriber line (DSL) modem configured to perform time domain reflectometry (TDR) measurements on the transmission line, wherein the TDR measurements of the DSL modem are performed by an analog front end configured to perform TDR measurements within the DSL modem, wherein the analog front end further comprises;

a transceiver configured to transmit a TDR test signal to a transmission line, the transceiver further configured to receive a reflected signal from the transmission line; and

a test logic circuit configured to produce the TDR test signal and send the test signal to the transceiver, the test logic circuit further configured to receive the reflected signal from the transceiver, the test logic circuit further configured to process the reflected signal, wherein the test logic circuit is further configured to deconvolve known system effects from the reflected signal to produce a deconvolved signal.

3. The system of claim 2, further configured to derive an impedance profile of the transmission line from the processed reflected signal.

4. The system of claim 2, wherein the TDR test signal is an impulse function.

5. The system of claim 2, wherein the TDR test signal is a step function.

6. The system of claim 2, wherein the test logic circuit is further configured to measure a time interval between transmission of the test signal and reception of the reflected signal.

7. The system of claim 6, wherein the test logic circuit is further configured to identify a reflection point from the measured time interval.

8. The system of claim 2, wherein the test logic circuit is further configured to determine a change in signal shape between the transmitted signal and the deconvolved signal.

9. The system of claim 8, wherein the test logic circuit is further configured to determine a change in phase between the transmitted signal and the deconvolved signal.

10. The system of claim 9, wherein the test logic circuit is further configured to calculate reflection coefficients from the change in signal shape and the change in signal phase.

11. The system of claim 10, wherein the test logic circuit is further configured to calculate an impedance ratio from the calculated reflection coefficients.

12. The system of claim 11, wherein the test logic circuit is further configured to calculate an impedance of the transmission line beyond the location of the reflection point.

13. The system of claim 12, wherein the test logic circuit is further configured to derive an impedance profile from the calculated impedance coefficients using deconvolution techniques.

14. The system of claim 2, wherein the test logic circuit is further configured to determine a change in phase between the transmitted signal and the deconvolved signal.

15. A system for characterizing transmission lines, comprising:

means for transmitting a predetermined test signal from a DSL modem to a transmission line;

means for receiving a reflected signal from the transmission line at the DSL modem;

means for determining transmission line characteristics as a function of the reflected signal and the transmitted signal, the means for determining transmission line characteristics being disposed within the DSL modem;

means for preparing the transmission line for TDR measurements, wherein the means for preparing the transmission line further comprises means for transmitting a predetermined preamble for a predetermined sample period to the transmission line; and

means for creating the predetermined test signal.

16. The system of claim 15, wherein the predetermined preamble comprises a sequence of null signals.

17. The system of claim 15, wherein the means for creating the predetermined test signal further comprises:

means for determining desired characteristics of the test signal; and

means for preparing a line buffer of data values from the determined desired characteristics of the test signal.

18. The system of claim 15, wherein the means for transmitting the predetermined test signal further comprises:

means for determining a pulse repetition rate; and

means for transmitting the test signal at the predetermined pulse repetition rate.

19. The system of claim 15, wherein the means for determining transmission line characteristics further comprises:

means for accumulating the received signal;

means for processing the accumulated signal; and

means for determining the impedance profile from the processed signal.

20. The system of claim 19, wherein the means for processing the accumulated signal further comprises means for measuring a time interval between transmission of the test signal and reception of the reflected signal.

21. The system of claim 20, wherein the means for processing the accumulated signal further comprises means for identifying a reflection point from the measured time interval.

22. The system of claim 19, wherein the means for processing the accumulated signal further comprises means for deconvolving known system effects from the accumulated signal to produce a deconvolved signal.

23. The system of claim 22, wherein the means for processing the accumulated signal further comprises means for determining a signal shape difference between the transmitted signal and the deconvolved signal.

24. The system of claim 22, wherein the means for processing the accumulated signal further comprises means for calculating a phase difference between the transmitted test signal and the deconvolved signal.

25. The system of claim 23, wherein the means for processing the accumulated signal further comprises means for calculating a phase difference between the transmitted test signal and the deconvolved signal.

26. The system of claim 25, wherein the means for processing the accumulated signal further comprises means for calculating reflection coefficients from the signal shape difference and the phase difference.

27. The system of claim 26, wherein the means for processing the accumulated signal further comprises means for calculating an impedance ratio from the calculated reflection coefficients.

28. The system of claim 27, wherein the means for processing the accumulated signal further comprises means for calculating an impedance of the transmission line beyond the location of the reflection point using the calculated impedance ratio.

29. The system of claim 28, wherein the means for processing the accumulated signal further comprises means for deriving an impedance profile using deconvolution techniques.

30. A method for characterizing a DSL transmission line using a DSL modem, comprising the steps of:

transmitting a predetermined test signal from the DSL modem to a transmission line;

receiving a reflected signal from the transmission line at the DSL modem;

determining within the DSL modem transmission line characteristics as a function of the reflected signal and the transmitted signal;

preparing the transmission line for TDR measurements, wherein the step of preparing the transmission line further comprises;

generating a disable command at a test logic circuit, the disable command configured to disable a timing recovery circuit in the DSL modem; and

transmitting a predetermined preamble for a predetermined sample period to the transmission line; and

creating the predetermined test signal.

31. The method of claim 30, wherein the preamble comprises a series of null signals.

32. The method of claim 30, wherein the creating step further comprises the steps of:

determining desired characteristics of the test signal; and

preparing a line buffer of data values from the determined desired characteristics of the test signal.

33. The method of claim 30, wherein the transmitting step further comprises the steps of:

determining a pulse repetition rate; and

transmitting the test signal at the determined pulse repetition rate.

34. The method of claim 30, wherein the determining step further comprises the steps of:

accumulating the received signal;

processing the accumulated signal; and

determining the impedance profile from the processed signal.

35. The method of claim 34, wherein the processing step comprises the step of measuring a time interval between transmission of the test signal and reception of the reflected signal.

36. The processing step of claim 35, further comprising the step of identifying a reflection point from the measured time interval.

37. The processing step of claim 34, further comprising the step of deconvolving known system effects from the accumulated signal to produce a deconvolved signal.

38. The processing step of claim 37, further comprising the step of determining a signal shape difference between the transmitted test signal and the deconvolved signal.

39. The processing step of claim 37, further comprising the step of calculating a phase difference between the transmitted test signal and the deconvolved signal.

40. The processing step of claim 38, further comprising the step of calculating a phase difference between the transmitted test signal and the deconvolved signal.

41. The processing step of claim 40, further comprising the step of calculating reflection coefficients from the signal shape difference and the phase difference.

42. The processing step of claim 41, further comprising the step of calculating an impedance ratio from the calculated reflection coefficients.

43. The processing step of claim 42, further comprising the step of calculating an impedance in the transmission line beyond the location of the reflection point using the calculated impedance ratio.

44. The processing step of claim 43, further comprising the step of deriving an impedance profile using deconvolution techniques.