Modeling and calibrating a three-port time-domain reflectometry system
View Patent ↗A three-port TDR front end comprises numerous components. An exemplary three-port TDR front end is a DSL modem. Information-bearing TDR signals are distorted as they pass through these components. With a perfect model of the response of its front-end, a TDR system usually can compensate for the effects of its front-end. In reality, however, the electrical characteristics of each component vary from design-to-design, board-to-board, and slowly over time The result is imperfect knowledge about the true response of the front-end, errors in the model of the front-end, and degraded TDR performance. At least for this reason it is important to precisely calibrate the response of the TDR front-end through the use of a TDR modeling system.
1. A method of calibrating a DSL transceiver front-end for operation as a TDR system, the method comprising:
connecting a first predetermined impedance to the DSL transceiver front-end;
transmitting a first waveform and receiving a first echo response of the first waveform in the DSL transceiver;
connecting a second predetermined impedance to the DSL transceiver front-end;
transmitting a second waveform and receiving a second echo response of the second waveform in the DSL transceiver;
connecting a third predetermined impedance to the DSL transceiver front-end;
transmitting a third waveform and receiving a third echo response of the third waveform in the DSL transceiver;
determining three independent parameters that characterize the DSL transceiver front-end;
connecting the DSL transceiver to a transmission line; and
determining a length of the transmission line using the three independent parameters.
2. The method of claim 1 , wherein the three predetermined impedances are each a different value.
3. The method of claim 1 , further comprising:
connecting additional predetermined impedances to the DSL transceiver front-end; and
transmitting a waveform and receiving an echo response in the DSL transceiver for each of the additional predetermined impedances.
4. The method of claim 1 , wherein the first, second and third waveforms are the same waveform.
5. The method of claim 1 , wherein the first, second and third waveforms are different waveforms.
6. The method of claim 1 , further comprising determining a location of a bridged tap.
7. The method of claim 1 , further comprising determining a length of a bridged tap.
8. The method of claim 1 , wherein length the determining step is performed after the transceiver is not performing as expected.
9. The method of claim 1 , wherein the length determining step is performed when the DSL transceiver data rate is low.
10. The method of claim 1 , wherein the length determining step is performed when a data link is not possible.
11. The method of claim 1 , wherein the length determining step is performed when the DSL transceiver has too many bit errors.
12. A system to calibrate a DSL transceiver front-end for operation as a TDR system comprising:
a DSL transceiver capable of:
transmitting a first waveform and receiving a first echo response of the first waveform in the DSL transceiver when a first predetermined impedance is connected to the DSL transceiver front-end;
transmitting a second waveform and receiving a second echo response of the second waveform in the DSL transceiver when a second predetermined impedance is connected to the DSL transceiver front-end;
transmitting a third waveform and receiving a third echo response of the third waveform in the DSL transceiver when a third predetermined impedance is connected to the DSL transceiver front-end; and
a parameter determination module capable of determining three independent parameters that characterize the DSL transceiver front-end, wherein the DSL transceiver is connected to a transmission line and a length of the transmission line is determined using the three independent parameters.
13. The system of claim 12 , wherein the three predetermined impedances are each a different value.
14. The system of claim 12 , wherein additional predetermined impedances are connected to the DSL transceiver front-end and a waveform transmitted and an echo response received in the DSL transceiver for each of the additional predetermined impedances.
15. The system of claim 12 , wherein the first, second and third waveforms are the same waveform.
16. The system of claim 12 , wherein the first, second and third waveforms are different waveforms.
17. The system of claim 12 , wherein the DSL transceiver determines a location of a bridged tap.
18. The system of claim 12 , wherein the DSL transceiver determines a length of a bridged tap.
19. The system of claim 12 , wherein length the determining is performed after the transceiver is not performing as expected.
20. The system of claim 12 , wherein the length determining step is performed when the DSL transceiver data rate is low.
21. The system of claim 12 , wherein the length determining step is performed when a data link is not possible.
22. The system of claim 12 , wherein the length determining step is performed when the DSL transceiver has too many bit errors.