Method and system for filtering a signal and providing echo cancellation using an adaptive length filter
First Claim
1. An adaptive filter, comprising:
- a filter input for receiving a first signal;
a filter output for outputting a second signal based upon said first signal;
an error input for receiving an error signal;
a plurality of first coefficients, each having an associated energy, wherein said first coefficients are modified based upon the error signal; and
a plurality of second coefficients having a start coefficient and an end coefficient, the second coefficients being a subset of the first coefficients, wherein the start coefficient and end coefficient are determined by applying at least one threshold value to an energy value, said energy value being a function of the energy of a plurality of first coefficients.
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Abstract
The present invention provides for adaptive filters that have improved convergence, computational, and memory bandwidth proprieties. When applied to telecommunication applications, the present invention additionally provides for improved methods and systems of canceling echoes. In one embodiment of the adaptive filter of the present invention, a filter, preferably an adaptive finite impulse response (FIR) filter, of an appropriate length, N, is chosen. Once the filter is chosen, convergence is achieved using a convergence process. With convergence complete, the total energy of the filter coefficients is computed and two energy thresholds, a first energy threshold and a second energy threshold, are set relative to the computed total energy. Using the set energy thresholds, new filter coefficients are determined by relating the starting filter coefficient with the first energy threshold and the end filter coefficient with the second energy threshold. A first filter delay, in accordance with the determined start coefficient, is incorporated into the filter operation.
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Citations
46 Claims
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1. An adaptive filter, comprising:
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a filter input for receiving a first signal;
a filter output for outputting a second signal based upon said first signal;
an error input for receiving an error signal;
a plurality of first coefficients, each having an associated energy, wherein said first coefficients are modified based upon the error signal; and
a plurality of second coefficients having a start coefficient and an end coefficient, the second coefficients being a subset of the first coefficients, wherein the start coefficient and end coefficient are determined by applying at least one threshold value to an energy value, said energy value being a function of the energy of a plurality of first coefficients. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A process for filtering a signal, comprising the steps of:
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deriving a plurality of second coefficients having a start coefficient and an end coefficient, the second coefficients being a subset of a plurality of first coefficients, wherein the start coefficient and end coefficient are determined by applying at least one threshold value to an energy value, said energy value being a function of the energy of a plurality of first coefficients;
receiving a first signal;
outputting a second signal wherein the second signal is a function of the second coefficients and the first signal;
receiving an error signal; and
updating the first coefficients based upon said error signal. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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39. An echo cancellation system for canceling echo within a second signal generated by the transmittal of a first signal through a cross-coupling pathway, comprising:
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a device for summing a third signal and the second signal to produce an error signal; and
an adaptive filter comprising a filter input for receiving the first signal, a filter output for outputting the second signal based upon said first signal, an error input for receiving the error signal, a plurality of first coefficients, each having an associated energy, wherein said first coefficients are updated based upon the error signal, and a plurality of second coefficients having a start coefficient and an end coefficient, the second coefficients being a subset of the first coefficients, wherein the start coefficient and end coefficient are determined by applying at least one threshold value to an energy value, said energy value being a function of the energy of a plurality of first coefficients. - View Dependent Claims (40, 41, 42, 43)
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44. A method for canceling an echo wherein the echo is generated by transmitting a first signal through an echo-causing system, comprising the steps of:
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deriving a plurality of second coefficients having a start coefficient and an end coefficient, the second coefficients being a subset of a plurality of first coefficients, wherein the start coefficient and end coefficient are determined by applying at least one threshold value to an energy value, said energy value being a function of the energy of a plurality of first coefficients;
receiving a first signal;
outputting a second signal wherein the second signal is a function of the second coefficients and the first signal;
receiving an error signal; and
updating the first coefficients based upon said error signal.
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45. A gateway operative to transmit signals between a circuit switched network and a packet based network, comprising:
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a plurality of digital to analog encoders and decoders; and
an echo cancellation device wherein said device comprises an adaptive filter having a plurality of second coefficients having a first coefficient and a second coefficient, the second coefficients being a subset of the first coefficients, wherein the first coefficient and second coefficient are determined by applying at least one threshold value to an energy value, said energy value being a function of the energy of a plurality of first coefficients.
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46. A method for equalizing a channel, comprising the steps of:
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deriving a plurality of second coefficients having a start coefficient and an end coefficient, the second coefficients being a subset of a plurality of first coefficients, wherein the start coefficient and end coefficient are determined by applying at least one threshold value to an energy value, said energy value being a function of the energy of a plurality of first coefficients;
receiving a first signal;
outputting a second signal wherein the second signal is a function of the second coefficients and the first signal;
receiving an error signal; and
updating the first coefficients based upon said error signal.
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Specification