System and method for canceling crosstalk
First Claim
1. A telecommunication system having reduced crosstalk comprising:
- a modem disposed at a customer premises;
a local loop terminating at the customer premises and connected to the modem, the local loop for carrying modem communications;
a first circuit disposed to sense the signal received on the local loop;
a second circuit configured to obtain a common mode signal from the local loop; and
a processor circuit disposed within the modem, the processor configured to reduce crosstalk on the local loop through computations based upon both the signal received on the local loop and the common mode signal, wherein the processor circuit is configured to process a signal that takes in the time domain, after digitization, the following forms;
p[n]=(f{circle around (x)}u)[n]+(l{circle around (x)}e)[n]+w[n], common mode signal and
r[n]=(h{circle around (x)}e)[n]+(g{circle around (x)}u)[n]+v[n], differential mode signal,where w[n] and v[n] are independent white noise quantities, r[n] is the signal received on the local loop, p[n] is the common mode signal, h[n] is an impulse response of the first local loop, l[n] is a cross-coupling measure between the local loop and the common mode, u[n] is a signal carried on a disturber line, f[n] is a cross-coupling measure between the disturber line and the common mode signal, e[n] is the signal transmitted from a remote transmitter on the local loop, g[n] is a cross-coupling measure between the disturber line and the local loop, and wherein the {circle around (x)} symbol represents a convolution operation.
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Accused Products
Abstract
A method and apparatus are disclosed for reducing crosstalk in a telecommunication system. Broadly, the present invention utilizes a common mode signal to obtain additional information that can be used to better approximate the transmitted signal (by approximating and canceling crosstalk or otherwise). In accordance with one embodiment of the invention, a modem is provided having improved crosstalk cancellation circuitry for canceling crosstalk received on a local loop (or otherwise estimating the remotely transmitted signal) carrying modem communications. The modem includes a first input for receiving a signal carried on the local loop and a second input for receiving a signal obtained from the common mode. The modem further includes processing circuitry configured to either reduce crosstalk present in the signal carried on the local loop, or to otherwise closely approximate the remotely transmitted signal. Using both the first and second signals allows the processing circuitry of the modem to obtain more accurate results.
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Citations
29 Claims
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1. A telecommunication system having reduced crosstalk comprising:
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a modem disposed at a customer premises; a local loop terminating at the customer premises and connected to the modem, the local loop for carrying modem communications; a first circuit disposed to sense the signal received on the local loop; a second circuit configured to obtain a common mode signal from the local loop; and a processor circuit disposed within the modem, the processor configured to reduce crosstalk on the local loop through computations based upon both the signal received on the local loop and the common mode signal, wherein the processor circuit is configured to process a signal that takes in the time domain, after digitization, the following forms;
p[n]=(f{circle around (x)}u)[n]+(l{circle around (x)}e)[n]+w[n], common mode signal and
r[n]=(h{circle around (x)}e)[n]+(g{circle around (x)}u)[n]+v[n], differential mode signal,where w[n] and v[n] are independent white noise quantities, r[n] is the signal received on the local loop, p[n] is the common mode signal, h[n] is an impulse response of the first local loop, l[n] is a cross-coupling measure between the local loop and the common mode, u[n] is a signal carried on a disturber line, f[n] is a cross-coupling measure between the disturber line and the common mode signal, e[n] is the signal transmitted from a remote transmitter on the local loop, g[n] is a cross-coupling measure between the disturber line and the local loop, and wherein the {circle around (x)} symbol represents a convolution operation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. In a telecommunications system having a local loop terminating at a customer premises, a method of reducing crosstalk on the local loop comprising the steps of:
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sensing a first signal received on the local loop; obtaining a common mode signal from the local loop; using the first signal and the common mode signal to compute a measure of crosstalk present on the first local loop, wherein the step of using the first signal and the common mode signal to compute a measure of crosstalk includes processing equations for signals in the following form;
p[n]=(f{circle around (x)}u)[n]+(l{circle around (x)}e)[n]+w[n], and
r[n]=(h{circle around (x)}e)[n]+(g{circle around (x)}u)[n]+v[n],where w[n] and v[n] are independent white noise quantities, r[n] is the signal received on the local loop, p[n] is the common mode signal, h[n] is an impulse response of the first local loop, l[n] is a cross-coupling measure between the local loop and the common mode, u[n] represents at least one signal carried on a disturber line, f[n] is a cross-coupling measure between the disturber line and the common mode signal, e[n] is the signal transmitted from a remote transmitter on the local loop, g[n] is a cross-coupling measure between the disturber line and the local loop, and wherein the {circle around (x)} symbol represents a convolution operation; and subtracting the measure of crosstalk from the first signal. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25)
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26. In a telecommunications system having a local loop terminating at a customer premises, a method of reducing the effects of crosstalk on the local loop comprising the steps of:
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sensing a first signal received on the local loop; obtaining a common mode signal from the local loop; computing a Discrete Fourier Transform of both the first signal and the common mode signal; using both the first signal and the common mode signal to compute a transmitted signal, wherein the step of using the first signal and the common mode signal to compute a measure of crosstalk includes solving equations in the following form;
q is the bin rank, and t is the time symbol index where E[q, t] is the emitted complex constellation point for the bin q and the symbol t, the superscript (i), 0≦
i≦
1, refers to the path, V(i)[q, t] stands for the whole perturbation of bin q of symbol t on path i, i.e. crosstalk and the Additive White Gaussian Noise(AWGN) gain per bin q, on path i.- View Dependent Claims (27)
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28. In a customer premises, a modem having improved crosstalk cancellation circuitry for canceling crosstalk received on a local loop carrying modem communications comprising:
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a first input for receiving a signal carried on the local loop; a second input for receiving a common mode signal obtained from the local loop; logic for computing a Discrete Fourier Transform of both the first signal and the common mode signal; processing circuitry configured to reduce crosstalk present in the signal carried on the first local loop through computations based upon the signals carried on both the first signal and the common mode signal, wherein the processor circuit is configured to compute equations in the following form;
q is the bin rank, and t is the time symbol index where E[q, t] is the emitted complex constellation point for the bin q and the symbol t, the superscript (i), 0≦
i≦
1, refers to the path, V(i)[q, t] stands for the whole perturbation of bin Q of symbol t on path i, i.e. crosstalk and the Additive White Gaussian Noise(AWGN) gain per bin q, on path i.- View Dependent Claims (29)
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Specification