System and method for decreasing cross-talk effects in time-domain-modulation (TDM) digital subscriber line (DSL) systems
View Patent ↗A communications system may be characterized by a system error variance because the error variance provides an indication of signal corruption in the system. By strategically adding a secondary sensor to the communications system, system characteristics may be altered so that the system error variance is reduced. A system and method are presented, wherein a secondary sensor is configured to receive a disturbance effect and produce a filtered slave signal as a function of the disturbance effect. The filtered slave signal is configured to alter the characteristics of the communications system and thereby reduce system error variance.
1. A system for reducing signal corruption in a communications system, comprising:
a receiver having a frequency gain of (ν) at a normalized frequency of ν, wherein the receiver is configured to receive a main signal having a variance σ main 2 , wherein the receiver is further configured to receive a master-perturbation signal through a master coupling filter, wherein the master coupling filter has a filter coefficient of (ν), wherein the master-perturbation signal is characterized by a master channel white noise variance σ WM 2 and a disturbance signal spectral density σ dist 2 (ν), wherein the receiver has a signal-to-noise ratio (SNR) of:
SNR
(
v
)
=
σ
main
2
(
v
)
2
σ
WM
2
+
σ
dist
2
(
v
)
;
and
a secondary sensor coupled to the receiver, wherein the secondary sensor is configured to receive a slave-perturbation signal through a slave-coupling filter having a filter coefficient of (ν), wherein the slave-perturbation signal is characterized by a slave channel white noise variance of σ WS 2 and a disturbance signal variance σ dist 2 , wherein the secondary sensor is configured to decrease the disturbance spectral density from σ dist 2 (ν) to
σ
dist
2
(
v
)
1
+
{
(
σ
dist
2
(
v
)
)
(
(
v
)
2
σ
WS
2
)
}
.
2. A system for reducing signal corruption in a communications system, comprising:
a receiver having a master frequency gain, wherein the receiver is configured to receive a main signal, wherein the main signal has a variance σ main 2 , wherein the receiver is further configured to receive a master-perturbation signal, wherein the receiver has an error variance:
V
=
σ
main
2
(
exp
{
∫
[
1
]
log
(
1
+
SNR
(
v
)
)
ⅆ
v
}
)
,
wherein V represents the error variance, ν represents a normalized frequency, and SNR(ν) represents a signal-to-noise ratio (SNR) of the receiver at the normalized frequency; and
a secondary sensor having a slave frequency gain, wherein the secondary sensor is coupled to the receiver, wherein the secondary sensor is configured to receive a portion of the main signal, wherein the secondary sensor is further configured to receive a slave-perturbation signal, wherein the secondary sensor is further configured to alter the error variance from
V
=
σ
main
2
(
exp
{
-
∫
[
1
]
log
(
1
+
SNR
(
v
)
)
ⅆ
v
}
)
to
V
new
=
σ
main
2
(
exp
{
-
∫
[
1
]
log
(
1
+
σ
main
2
(
v
)
(
v
)
(
v
)
)
ⅆ
v
}
)
,
wherein V new represents the altered error variance due to the secondary sensor, (ν) represents a vector characterization of both the master frequency gain and the slave frequency gain and (ν) represents a corresponding transposed vector, (ν) represents a spectral covariance matrix of both the master-perturbation signal and the slave-perturbation signal.
3. A method for reducing signal corruption in a communications system, comprising the steps of:
generating a filtered slave signal;
decreasing a system variance using the filtered slave signal; and
recursively updating the slave feedforward filter coefficient;
wherein the step of generating the filtered slave signal comprises the steps of:
receiving a disturbance signal;
receiving a slave-perturbation signal having slave channel white noise and the disturbance signal; and
filtering the slave-perturbation signal using a slave feedforward filter to produce the filtered slave signal; and
wherein the step of decreasing the system variance comprises the steps of:
receiving a main signal;
producing a master-composite signal from the main signal by adding a master-perturbation signal to the main signal, wherein the master-perturbation signal is the disturbance signal in the presence of master channel white noise; and
subtracting the filtered slave signal from the master-composite signals.
4. The method of claim 3 , wherein the step of generating the filtered slave signal comprises the steps of:
receiving a disturbance signal and a portion of a main signal;
receiving a slave-perturbation signal having slave channel white noise and the disturbance signal;
generating a slave-composite signal by adding the slave-perturbation signal to the portion of the main signal; and
filtering the slave-composite signal using a slave feedforward filter to produce the filtered slave signal.
5. The method of claim 4 , further comprising the step of recursively updating the slave feedforward filter coefficient.
6. The method of claim 5 , wherein the step of decreasing the system variance comprises the steps of:
receiving a main signal;
producing a master-composite signal from the main signal by adding a master-perturbation signal to the main signal, wherein the master-perturbation signal is the disturbance signal in the presence of master channel white noise; and
subtracting the filtered slave signal from the master-composite signal.
7. A system for reducing signal corruption in a communications system, comprising:
means for generating a filtered slave signal;
means for decreasing a system variance using the filtered slave signal; and
means for recursively updating the slave feedforward filter coefficient;
wherein the means for generating the filtered slave signal comprises:
means for receiving a disturbance signal;
means for receiving a slave-perturbation signal having slave channel white noise and the disturbance signal; and
means for filtering the slave-perturbation signal using a slave feedforward filter to produce the filtered slave signal; and
wherein the means for decreasing the system variance comprises:
means for receiving a main signal;
means for producing a master-composite signal from the main signal by adding a master-perturbation signal to the main signal, wherein the master-perturbation signal is the disturbance signal in the presence of master channel white noise; and
means for subtracting the filtered slave signal from the master-composite signals.
8. The system of claim 7 , further comprising means for recursively updating the slave feedforward filter coefficient.
9. The system of claim 8 , wherein the means for decreasing the system variance comprises:
means for receiving a main signal;
means for producing a master-composite signal from the main signal by adding a master-perturbation signal to the main signal, wherein the master-perturbation signal is the disturbance signal in the presence of master channel white noise; and
means for subtracting the filtered slave signal from the master-composite signal.