DMT test method for determining ADSL capability of cables

• US 6,445,773 B1
• Filed: 06/14/2000
• Issued: 09/03/2002
• Est. Priority Date: 06/14/2000
• Status: Expired due to Fees

• Current Assignee: EXFO Electro-Optical Engineering Incorporated (11172239 Canada, Inc.)
• Original Assignee: Consultronics Ltd. (11172239 Canada, Inc.)
• Inventors: Liang, Ronald Y. R., Layton, Robert
• Primary Examiner(s): NGUYEN, DUC MINH
• Application Number:
  US09/593,371
• Time in Patent Office: 811 Days
• Field of Search: 379/1.01, 379/1.03, 379/1.04, 379/15.03, 379/22.01, 379/22.02, 379/22.04, 379/26.01, 379/27.01, 379/27-2-, 379/28, 379/30, 375/224-228, 370/241, 370/248-249, 370/251, 370/252-253
• US Class Current: 379/1.04
• CPC Class Codes: H04M 3/30 for subscriber's lines , for the local loop
• CPC Class Codes: H04Q 1/45 using multi-frequency signalling H04Q1/46 takes precedence

Abstract

A DMT (Discrete Multi-Tone) test method is provided. The test method is employed by two test devices to estimate the theoretical and practical data rates of a cable under test for a pair of target ADSL (Asymmetric Digital Subscriber Line) DMT modems. The present DMT test can also be used to analyze the cause of, or to predict a problem, whereby a pair of ADSL DMT modems could fail to synchronize. The method includes (a) synchronizing two devices at lower frequencies; (b) measuring the frequency characteristics of the cable with test signals; (c) measuring the cable noise and interference for every sub-channel of the ADSL bandwidth; (d) determining the theoretical and practical data rates for every sub-channel, based on the measured frequency characteristics and noise characteristics, as well as modem parameters selected by the user; (e) estimating the theoretical and practical data rates for the ADSL bandwidth based on the ADSL DMT standard selected by the user.

Claims

1. A method for performing a DMT test to determine cable data rates using two test devices, without employing ADSL modems, on a telephone cable or a local loop cable for ADSL application, whereby an available frequency bandwidth is divided into sub-channels, the method comprising the steps of:

(a) synchronizing a transmitter and receiver in each of the two test devices at lower frequency signals;

(b) measuring the frequency characteristics of the cable with test signals;

(c) measuring cable noise and interference for every sub-channel;

(d) determining a theoretical and practical data rate for every sub-channel based on the measured frequency and noise characteristics, and modem parameters selected by a user; and

(e) determining the theoretical and practical data rates for the ADSL bandwidth based on an ADSL DMT standard selected by the user.

2. The method of claim 1, wherein the test signals and cable noise are converted into digital form at the receivers for processing.

3. The method of claim 1, wherein coded or modulated signals are employed for passing information between the two test devices for test parameters, such as ADSL standard and selected modem parameters, and test results.

4. The method of claim 1, wherein the step of synchronizing the two test devices at lower frequencies comprises the steps of:

(i) synchronizing two test devices in a tone, or a modulated signal, of voice band frequencies;

(ii) sending a synchronization signal at up to the maximum power allowable for the cable under test; and

(iii) adjusting the AGC setting of the receiver for synchronization signal.

5. The method of claim 1, wherein the step of synchronizing the two test devices at lower frequencies comprises the steps of:

(iv) synchronizing two test devices in a tone, or a modulated signal, of frequencies close to voice band, or lower frequencies in the ADSL frequency band;

(v) sending a synchronization signal at up to the maximum power allowable for the cable under test; and

(vi) adjusting the AGC setting of the receiver for the synchronization signal.

6. The method of claim 4, wherein a time-domain or frequency-domain analysis method is used for detecting and receiving the synchronization signal.

8. The method of claim 1, wherein the step of measuring the frequency characteristics of the cable with discrete tones comprises the steps of:

(vii) sending individual test tones, one tone at a time, at up to the maximum power allowable for the cable under test;

(viii) adjusting the AGC setting of the receivers for each sub-channel accordingly;

(ix) measuring the attenuation characteristics of the cable for each sub-channel; and

(x) calculating the frequency characteristics of the cable for each sub-channel.

9. The method of claim 1, wherein the step of measuring the frequency characteristics of the cable with discrete tones comprises the steps of:

(xi) sending individual test tones, a few tones at a time, at up to the maximum power allowable for the cable under test;

(xii) adjusting the AGC setting of the receivers for the few sub-channels accordingly;

(xiii) measuring the attenuation characteristics of the cable for each sub-channel; and

(xiv) calculating the frequency characteristics of the cable for each sub-channel.

10. The method of claim 8, wherein a time-domain or frequency-domain analysis method is used for detecting and receiving the test signals.

11. The method of claim 9, wherein a time-domain or frequency-domain analysis method is used for detecting and receiving the test signals.

12. The method of claim 1, wherein the step of measuring the cable noise and interference for every sub-channel comprises the steps of:

(xv) measuring the level or energy level of the cable noise and interference for sub-channels of upstream and downstream respectively at the two test devices connected for the test; and

(xvi) adjusting the AGC setting of the receivers when required.

13. The method of claim 1, wherein the step of measuring the cable noise and interference for every sub-channel comprises the steps of:

(xvii) measuring the level or energy level of the cable noise and interference for all sub-channels of the whole ADSL bandwidth at the one or two test devices connected for the test; and

(xviii) adjusting the AGC setting of the receivers when required.

14. The method of claim 12, wherein a time-domain or frequency-domain analysis method is used for measuring the cable noise and interference.

15. The method of claim 13, wherein a time-domain or frequency-domain analysis method is used for measuring the cable noise and interference.

16. The method of claim 1, wherein the step of determining the theoretical and practical data rates for every sub-channel based on the measured frequency and noise characteristics, and modem parameters selected by the user comprises the steps of:

(xix) converting the measured signal level at the receiver input of the test devices to the signal level of an ADSL modem receiver for each sub-channel;

(xx) calculating the optimum signal-to-noise ratio (SNR_o) of each sub-channel,

(xxi) calculating the practical signal-to-noise ratio (SNR_p) of each sub-channel according to the ADC resolution selected by the user for the target ADSL modem;

(xxii) determining the theoretical data rates from the calculated SNR_o for every sub-channel for the modem parameters selected by the user; and

(xiii) determining the practical data rates from the calculated SNR_p for every sub-channel for the modem parameters selected by the user.

17. The method of claim 1, wherein the step of determining the theoretical and practical data rates for the ADSL bandwidth based on an ADSL DMT standard selected by the user comprises the steps of:

(xxiv) estimating the theoretical and practical data rates of upstream ATU-C according to the ADSL DMT standard selected by the user;

(xxv) estimating the theoretical and practical data rates of downstream ATU-R according to the ADSL DMT standard selected by the user; and

(xxvi) estimating the theoretical and practical data rates of the whole ADSL bandwidth according to the ADSL DMT standard selected by the user.

18. The method of claim 1, wherein the step of determining the theoretical and practical data rates for the ADSL bandwidth based on an ADSL DMT standard selected by the user comprises the step of estimating the theoretical and practical data rates of upstream and downstream ATU-C or U-R or both sides according to the ADSL DMT standard selected by the user.

19. The method of claim 1, wherein steps (d) and (e) further include predicting any possible failure of a potential ADSL service and/or an ADSL modem test on a cable when a pair of ADSL modems would fail to synchronize over it.

20. The method of claim 1, wherein steps (d) and (e) further include analyzing the failure of an ADSL service and/or an ADSL modem test by showing, in text or graphic format, the converted measured signal levels, measured cable noise levels, and/or the bits allocated, for each sub-channel of ADSL bandwidth or for those sub-channels used by a pair of ADSL modems for synchronization purposes.

7. The method of claim, wherein a time-domain or frequency-domain analysis method is used for detecting and receiving the synchronization signal.