Granted Patent B2

US 6,934,655 · App. 09/810,932 · Granted Aug 23, 2005

Abstract

Claims (44)

1. A method for utilizing a modem to perform time domain reflectometry on a communication channel comprising:

connecting a modem to a communication channel;

generating a maximal length sequence signal utilizing the modem;

transmitting the sequence signal over the communication channel;

receiving a reflection signal from the communication channel in response to the transmitting of the sequence signal;

correlating the reflection signal within the modem with the sequence signal to generate a correlated signal;

retrieving a template signal;

aligning the template signal and the correlated signal to determine a point of alignment;

subtracting the template signal from the correlated signal to remove near-end echo from the correlated signal;

measuring a time interval between the point of alignment and a subsequent peak in the correlated signal;

multiplying the time interval by a rate of propagation of the sequence signal through the communication channel to obtain distance information regarding a line anomaly;

performing a circular rotation of the sequence signal to create a rotated sequence signal;

transmitting the rotated sequence signal over the communication channel;

receiving a rotated reflection signal;

correlating the rotated reflection signal with the rotated sequence signal to create a rotated correlated signal;

aligning the rotated correlated signal with the correlated signal; and

adding the rotated correlated signal to the correlated signal to reduce or remove correlation artifacts on the correlated signal.

2. The method of claim 1 , wherein the template signal is a correlated version of a reflection created by a line interface.

3. The method of claim 1 , wherein a subsequent peak in the reflection signal is caused by a bridge tap.

4. The method of claim 1 , wherein the communication channel comprises a twisted pair conductor.

5. The method of claim 1 , wherein transmitting the sequence signal is at a power level that does not introduce crosstalk into other communication channels.

6. A method for processing a reflection signal within a communication modem generated by transmission of a test signal onto a channel to determine a location of a line anomaly comprising:

correlating the reflection signal with the test signal to create a correlated reflection signal, wherein the test signal is a signal that has autocorrelation properties;

analyzing the correlated reflection signal to determine a time difference between transmission of the test signal and a point of correlation;

multiplying the time difference by a rate of propagation of the test signal through the channel to obtain information regarding the location of a line anomaly;

subtracting a template signal from the reflection signal or the correlated reflection signal to more clearly define a point of correlation; and

adding a rotated signal to the correlated reflection signal to reduce correlation artifacts, wherein the rotated signal comprises a signal resulting from correlating a rotated test signal with a reflection of a rotated test signal.

7. The method of claim 6 , wherein analyzing the correlated reflection signal comprises determining a time difference between receipt of a near-end echo of the correlated reflection signal and a peak in the correlated reflection signal.

8. The method of claim 6 , wherein the method is performed by an integrated circuit that is part of the communication modem.

9. The method of claim 6 , wherein the test signal is a sequence signal with good autocorrelation properties.

10. A digital subscriber line modem for performing sequence time domain reflectometry to determine a location of impedance mismatches on a channel being configured to communicate data using a digital subscriber line standard, the digital subscriber line modem comprising:

a sequence generator configured to generate a sequence signal, wherein the sequence generator is further configured to operate as part of the digital subscriber line modem during communication of data using a digital subscriber line standard;

a transmitter configured to transmit the sequence signal on a channel causing the sequence signal to propagate through the channel, the channel being analyzed to determine the location of impedance mismatches that may affect data transmission, wherein the transmitter is further configured to operate as part of the digital subscriber line modem during communication of data using a digital subscriber line standard;

a receiver configured to receive one or more reflections that result from the sequence signal encountering impedance mismatches as it propagates through the channel, wherein the receiver is further configured to operate as part of the digital subscriber line modem during communication of data using a digital subscriber line standard;

a correlator configured to correlate the one or more reflections with the sequence signal to generate an output having one or more peaks;

a processor, that is also configured to perform processing to achieve communication using a digital subscriber line standard, the processor further configured to:

subtract a template signal from the one or more reflections or the output having one or more peaks to more clearly define a point of correlation; and

add a rotated signal to the one or more reflections to reduce correlation artifacts, wherein the rotated signal comprises a signal resulting from correlating a rotated test signal with a reflection of a rotated test signal;

time a period between a beginning of the sequence signal transmission by the transmitter and at least one of the one or more peaks; and

calculate a value corresponding to a channel length between the digital subscriber line modem and an impedance mismatch.

11. The system of claim 10 , wherein the digital subscriber line modem is embodied in an integrated circuit configured to communicate data using a digital subscriber line standard.

12. The system of claim 10 , wherein the sequence generator comprises a tapped delay line.

13. The system of claim 10 , wherein the channel comprises a channel selected from the group consisting of twisted pair conductor and fiber optic cable.

14. The system of claim 10 , wherein the correlator comprises a tapped delay line.

Assignments (8)