Crosstalk identification for spectrum management in broadband telecommunications systems
Crosstalk between subscriber loops used to transmit different broadband services through the same bundled telephone cable is a significant limitation to providing digital subscriber line services. A method for estimating the crosstalk, identifying the sources of the crosstalk and predicting additional sources of crosstalk are disclosed. The crosstalk sources are identified in the frequency domain by maximizing the correlation with a “basis set” of received crosstalk PSDs which consist of the cascade of a finite set of known transmit PSDs types times a representative set of crosstalk couplings. Multiple crosstalk types are identified with a technique of successive spectral subtraction. This information can be used to perform crosstalk cancellation and spectrum management for DSL systems.
1. A method for identifying the source of crosstalk disturbance in a subscriber loop comprising the steps of:
measuring the power spectral density of the noise present on a subscriber loop;
correlating the power spectral density for said subscriber loop with a predetermined set of power spectral densities for a group of possible crosstalk disturbers;
selecting the crosstalk disturber having the most closely correlated power spectral density;
subtracting the power spectral density for the selected crosstalk disturber from the measured power spectral density of said subscriber loop using spectral subtraction to generate a residual power spectral density;
correlating the residual power spectral density with the predetermined set of power spectral densities for the group of possible crosstalk disturbers; and,
selecting the crosstalk disturber having the most closely correlated power spectral density.
2. The method of claim 1 wherein the steps of subtracting, correlating and selecting are iteratively performed until the correlation coefficient for the most closely correlated power spectral density falls below a predetermined correlation threshold.
3. The method of claim 2 wherein the predetermined correlation threshold is between approximately 0.7 to approximately 0.99.
4. The method of claim 2 wherein the predetermined correlation threshold is approximately 0.9.
5. The method of claim 1 wherein negative power spectrum densities resulting from said subtracting step are mapped into a non-negative value.
6. The method of claim 5 wherein the mapping function, T, is defined as:
T
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=
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wherein |{tilde over (C)} i+l (f)| 2 is the residual power spectral density and Φ└|C i (f)| 2 ┘ is a non-negative function equal to a pre-determined noise floor.
7. The method of claim 1 further comprising the step of sending the identity of the selected crosstalk disturber to a system for spectrum management of a system having a plurality of bundled subscriber loops.
8. An apparatus for identification of the source of crosstalk disturbance in a subscriber loop comprising:
a means for inputting a signal indicative of the power spectral density of the noise present on a subscriber loop;
a means for correlating the signal indicative of the power spectral density for said subscriber loop with a predetermined set of power spectral densities for a group of possible crosstalk disturbers;
a means for selecting the crosstalk disturber having the most closely correlated power spectral density;
a means for subtracting the power spectral density for the selected crosstalk disturber from the signal indicative of the measured power spectral density of said subscriber loop using spectral subtraction to generate a residual power spectral density; and, a means for mapping negative residual power spectral densities into a non-negative value wherein the mapping function, T, is defined as:
T
[
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~
i
+
1
(
f
)
2
]
=
{
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~
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+
1
(
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2
,
if
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+
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(
f
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>
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i
(
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2
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i
(
f
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2
]
,
otherwise
wherein |{tilde over (C)} i+l (f)| 2 is the residual power spectral density and Φ└|C i (f)| 2 ┘ is a non-negative function equal to a pre-determined noise floor.