Systems and Methods for Single End Loop Testing
Systems and methods for performing single-end line testing (SELT) are described. At least one embodiment includes a method for SELT to determine loop characteristics for a loop. The method for performing SELT comprises generating a test signal through a loop to be tested and receiving an echo response. The method further comprises subtracting predetermined near end echo response from the received echo to derive a far end echo response, performing time-dependent scaling on the far end echo response to compensate for loop attenuation, comparing the time-scaled far end echo response to a set of predefined templates, and providing an estimate of loop characteristics by identifying a matching template within the set of predefined templates, wherein the matching template contains information relating to loop characteristics comprising loop length and loop termination.
1 . A method for single-end line testing (SELT) to determine loop characteristics for a loop, the method comprising:
generating a test signal through the loop to be tested, wherein the test signal is a pseudo-random sequence;
receiving an echo response;
subtracting a predetermined near end echo response from the received echo to derive a far end echo response;
performing time-dependent scaling on the far end echo response to compensate for loop attenuation;
comparing the time-scaled far end echo response to a set of predefined templates; and
providing an estimate of loop characteristics by identifying a matching template within the set of predefined templates, wherein the matching template contains information relating to loop characteristics comprising loop length and loop termination.
2 . The method of claim 1 , wherein the predetermined near end echo response is derived by measuring echo response for a loop length of 18 kft, wherein the predetermined near end echo is an average of the echo response measured for a plurality of xDSL modems.
3 . The method of claim 1 , further comprising returning a flag indicating an invalid estimate if the loop is not a straight-loop configuration, wherein the loop is determined to be a non-straight loop configuration if no matching templates are found.
4 . The method of claim 1 , further comprising returning a flag indicating an invalid estimate if the loop length exceeds 9 kft in length.
5 . The method of claim 1 , wherein the set of templates comprises four templates, wherein the four templates correlate with Home Wiring Model 1, Home Wiring Model 2, an open termination on the loop, and a closed termination on the loop.
6 . The method of claim 1 , wherein the loop is comprised of 26 AWG (American Wire Gauge).
7 . The method of claim 1 , wherein the time-dependent scaling comprises multiplying the far end echo response by the expressions 10 t/0.009 , wherein t represents time in milliseconds.
8 . The method of claim 1 , wherein subtracting the predetermined near end echo response from the received echo to derive a far end echo response further comprises curve fitting the difference to a 6 th order polynomial.
9 . The method of claim 1 , wherein identifying a matching template comprises:
determining whether a mean squared error associated with the far end response exceeds a predetermined threshold value; and
determining that the loop is not straight if the threshold value is exceeded.
10 . An apparatus for performing single-end line testing (SELT), the apparatus comprising:
a transmitter adapted to transmit a test signal through a loop to be tested;
a receiver having an input that receives an echo response signal resulting from the transmission of the test signal;
a processing unit configured to subtract a predetermined near end echo response from the received echo response signal in order to derive a far end echo response;
a time scaler configured to perform time-dependent scaling on the far end echo response to compensate for loop attenuation; and
a comparison module configured to compare the time-scaled far end echo response to a set of predefined templates and provide an estimate of loop characteristics by identifying a matching template within the set of predefined templates, wherein the matching template contains information relating to loop characteristics comprising loop length and loop termination.
11 . The apparatus of claim 10 , wherein the predetermined near end echo response is derived by measuring echo response for a loop length of 18 kft, wherein the predetermined near end echo is an average of the echo response measured for a plurality of xDSL modems.
12 . The apparatus of claim 10 , further comprising an error indicator configured to return a flag indicating an invalid estimate if the loop is not a straight-loop configuration, wherein the loop is determined to be a non-straight loop configuration if no matching templates are found.
13 . The apparatus of claim 12 , wherein the error indicator is further configured to return a flag indicating an invalid estimate if the loop length exceeds 9 kft in length.
14 . The apparatus of claim 10 , wherein the set of templates comprises four templates, wherein the four templates correlate with Home Wiring Model 1, Home Wiring Model 2, an open termination on the loop, and a closed termination on the loop.
15 . The apparatus of claim 10 , wherein the loop is comprised of 26 AWG (American Wire Gauge).
16 . The apparatus of claim 10 , wherein the time-dependent scaling comprises multiplying the far end echo response by the expressions 10 t/0.009 , wherein t represents time in milliseconds.
17 . The apparatus of claim 10 , wherein subtracting the predetermined near end echo response from the received echo to derive a far end echo response further comprises curve fitting the difference to a 6 th order polynomial.
18 . The apparatus of claim 10 , wherein the comparison module identifies a matching template by first determining whether a mean square error associated with the far end response exceeds a predetermined threshold value and determining that the loop is not straight if the threshold value is exceeded.
19 . A program stored on a computer readable medium for performing single-end line testing (SELT) to determine loop characteristics for a loop, the program comprising:
logic for generating a test signal through a loop to be tested, wherein the test signal is a pseudo-random sequence;
logic for receiving an echo response;
logic for subtracting predetermined near end echo response from the received echo to derive a far end echo response;
logic for performing time-dependent scaling on the far end echo response to compensate for loop attenuation;
logic for comparing the time-scaled far end echo response to a set of predefined templates; and
logic for providing an estimate of loop characteristics by identifying a matching template within the set of predefined templates, wherein the matching template contains information relating to loop length and loop termination.
20 . The program of claim 19 , wherein the program is embodied in at least one of the following: customer premise equipment (CPE) and a central office (CO).