Method and apparatus for detecting and locating loop impairments
View Patent ↗According to certain aspects, the present invention relates to methods and apparatuses to identify and locate a line-cuts in a loop that may or may not also contain bridgetaps. In embodiments, different bands of SELT signal data are analyzed separately using a TDR method, to effectively detect any potential bridgetaps. In these and other embodiments, by combining information from the separate bands, bridgetap locations and lengths are determined. Methodology is also established to distinguish legitimate line cut or bridgetap signal data from spurious data. According to certain aspects, embodiments of the invention also incorporate baselining, which includes tests to make sure that there are no inconsistencies or imperfections that can corrupt the SELT data.
1. A method, implemented by a computer processor, for examining a line coupled to a modem in a communications system, comprising:
receiving test signal data from the line for two or more separate frequency bands;
separately converting the test signal data to at least first and second different sets of time domain data corresponding to first and second ones of the separate frequency bands; and
analyzing, using the computer processor, the first and second sets of time domain data to identify impairments in the line.
2. The method according to claim 1 , wherein the test signal data comprises frequency domain S 11 data.
3. The method according to claim 1 , wherein the impairment is a bridgetap, and analyzing includes determining one or both of a location relative to the modem and length of the bridgetap.
4. The method according to claim 1 , wherein the impairment is a line cut, and analyzing includes determining a location relative to the modem of the line cut.
5. The method according to claim 1 , wherein analyzing includes identifying peaks in one or both of the first and second different sets of time domain data.
6. The method according to claim 5 , wherein analyzing further includes comparing identified peaks to a threshold, and declaring identified peaks exceeding the threshold as legitimate peaks.
7. The method according to claim 5 , wherein the first one of the separate frequency bands is higher in frequency than the second one of the separate frequency bands, and wherein the identified peaks in the first set of time domain data are used to detect a bridgetap in the line.
8. The method according to claim 7 , wherein analyzing includes analyzing a pair of identified peaks to determine a length of the detected bridgetap.
9. The method according to claim 5 , wherein the first one of the separate frequency bands is lower in frequency than the second one of the separate frequency bands, and wherein the identified peaks in the first set of time domain data are used to detect a cut in the line.
10. The method according to claim 1 , further comprising, before receiving the test signal data, baselining the modem.
11. The method according to claim 10 , wherein baselining includes repeatedly capturing test signal data with power cycling to determine capture repeatability.
12. The method according to claim 10 , wherein baselining includes obtaining transfer function characteristics of one or both of a transmit and receive processing chains of the modem and determining whether the characteristics are spectrally flat across a usable frequency spectrum.
13. The method according to claim 10 , wherein baselining includes determining a signal level consistency of the modem.
14. The method according to claim 1 , wherein the modem is a CPE modem and the first and second separate frequency bands are separate first and second upstream bands in a xDSL system frequency band plan.
15. The method according to claim 14 , wherein the test signal data is associated with symbols constructed using tones in only the first and second upstream bands.
16. An apparatus for examining a line coupled to a modem in a communications system, comprising:
a capture block that receives test signal data from the line for two or more separate frequency bands;
first and second Inverse Fast Fourier Transforms (IFFTs) that respectively convert the test signal data to at least first and second different sets of time domain data corresponding to first and second ones of the separate frequency bands; and
a Time Domain Reflectometry analysis engine that analyzes the first and second time domain data to identify impairments in the line.
17. The apparatus according to claim 16 , wherein the test signal data comprises frequency domain S 11 data.
18. The apparatus according to claim 16 , wherein the first one of the separate frequency bands is higher in frequency than the second one of the separate frequency bands, and wherein identified peaks in the first set of time domain data are used to detect a bridgetap in the line.
19. The apparatus according to claim 16 , wherein the first one of the separate frequency bands is lower in frequency than the second one of the separate frequency bands, and wherein identified peaks in the first set of time domain data are used to detect a cut in the line.
20. The apparatus according to claim 16 , wherein the modem is a CPE modem and the first and second separate frequency bands are separate first and second upstream bands in a xDSL system frequency band plan.
21. The method according to claim 1 , wherein separately converting includes splitting the received test signal into frequency domain data corresponding to first and second ones of the separate frequency bands.
22. The apparatus according to claim 16 , further comprising a band splitter that splits the received test signal into frequency domain data corresponding to first and second ones of the separate frequency bands before the test signal data is respectively converted by the first and second IFFTs.