Digital adaptive filter and method of convergence therein
First Claim
1. A digital adaptive filter for cancelling an echo component generated by a partial return of a transmission signal, comprising:
- main tap group means for sequentially shifting the transmission signal and outputting the shifted signal in parallel;
at least one subtap group means, operatively connected to said main tap group means, for sequentially shifting the transmission signal and outputting the shifted signal in parallel;
main tap group memory means, operatively connected to said main tap group means, for storing a first echo replica which can be stored or read by using the parallel signal from said main tap group means as an address signal;
at least one subtap group memory means, operatively connected to said at least one subtap group means, for storing a second echo replica which can be stored or read by using the parallel signal from said at least one subtap group means as an address signal and which has a greater precision than the first echo replica stored in said main memory means;
adding means, operatively connected to said main tap group memory means and said at least one subtap group memory means, for adding the first echo replica read from said main tap group memory means and the second echo replica read from said at least one subtap group memory means.
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Abstract
Disclosed is a digital adaptive filter and a method of cancelling an echo component generated by a partial return of a transmission signal to a receiving side. The digital adaptive filter comprises: a main memory unit for storing a first echo replica which can be stored or read by using the parallel signal from a main tap unit as an address signal, at least one submemory unit for storing a second echo replica which can be stored or read by using the parallel signal from said subtap unit as an address signal, and an adding circuit for adding the first echo replica and the second echo replica. The second echo replica stored in the at least one submemory unit has a greater precision than the precision of the first echo replica stored in the main memory unit, and thus the accumulated error due to memory division can be reduced. Instead of or accompanied by the greater precision, the contents of the main memory are updated directly based on the error between the pseudo signal and an input signal or based on a step size corresponding to the error, depending on whether the error is relatively large or relatively small, respectively.
21 Citations
28 Claims
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1. A digital adaptive filter for cancelling an echo component generated by a partial return of a transmission signal, comprising:
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main tap group means for sequentially shifting the transmission signal and outputting the shifted signal in parallel; at least one subtap group means, operatively connected to said main tap group means, for sequentially shifting the transmission signal and outputting the shifted signal in parallel; main tap group memory means, operatively connected to said main tap group means, for storing a first echo replica which can be stored or read by using the parallel signal from said main tap group means as an address signal; at least one subtap group memory means, operatively connected to said at least one subtap group means, for storing a second echo replica which can be stored or read by using the parallel signal from said at least one subtap group means as an address signal and which has a greater precision than the first echo replica stored in said main memory means; adding means, operatively connected to said main tap group memory means and said at least one subtap group memory means, for adding the first echo replica read from said main tap group memory means and the second echo replica read from said at least one subtap group memory means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A digital adaptive filter for cancelling an echo component generated by a partial return of a transmission signal to a receiving side, characterized by comprising:
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a tap unit for sequentially shifting the transmission signal and outputting the shifted signal in parallel, said tap unit being divided into a main tap unit and at least one subtap unit; a main memory unit, operatively connected to said main tap unit, for storing an echo replica which can be stored or read by using the parallel signal from said main tap unit as an address signal; at least one transversal filter, operatively connected to said at least one subtap unit, for setting tap coefficients based on a residual echo component obtained upon detection of a specific pattern from said main tap unit; and adding means, operatively connected to said main memory unit and said at least one transversal filter for adding the echo replica read from said main memory unit and the output signal from said at least one transversal filter; the output signal of said at least one transversal filter having a greater precision than the precision of the echo replica stored in said main memory unit. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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20. A digital adaptive filter for cancelling an echo component generated by a partial return of a transmission signal, comprising:
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main tap group means for sequentially shifting the transmission signal and outputting the shifted signal in parallel; at least one subtap group means, operatively connected to said main tap group means, for sequentially shifting the transmission signal and outputting the shifted signal in parallel; main tap group memory means, operatively connected to said main tap group means, for storing a first echo replica which can be stored or read by using the parallel signal from said main tap group means as an address signal; at least one subunit memory means, operatively connected to said at least one subtap group means, having one of a memory arrangement and a transversal filter arrangement, for setting a second echo replica which can be written or read by using the parallel signal from said at least one subtap group means and which has greater precision than the first echo replica stored in said main tap group memory means; adding means, operatively connected to said main tap group memory means and said at least one subunit memory means, for adding the first echo replica read from said main tap group memory means and the second echo replica read from subunit memory means. - View Dependent Claims (21, 22, 23)
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24. A digital adaptive filter for cancelling an echo component generated by a partial return of a transmission signal, comprising:
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main tap group means for sequentially shifting the transmission signal and outputting the shifted signal in parallel; at least one subtap group means, operatively connected to said main tap group means, for sequentially shifting the transmission signal and outputting the shifted signal in parallel; main tap group memory means, operatively connected to said main tap group means, for storing a first echo replica which can be stored or read by using the parallel signal from said main tap group means as an address signal; at least one subtap group memory means, operatively connected to said at least one subtap group means, for storing a second echo replica which can be stored or read by using the parallel signal from said subtap group means as an address signal and for providing a first output having an error signal; adding means, operatively connected to said main tap group memory means and said at least one subtap group memory means, for adding the first echo replica read from said main tap group memory means and the second echo replica read from said at least one subtap group memory means; monitoring means, operatively connected to said main tap group memory means and said at least one subtap group memory means, for comparing an absolute value of the error signal with a predetermined positive value; first replica updating means, operatively connected between said monitoring means and said main tap group memory means, for updating, by means of step size corresponding to the error signal when the error signal is relatively large, the first echo replica in said main tap group memory means; second replica updating means, operatively connected between said adding means and said at least one subtap group memory means, for updating, by means of step size corresponding to the error signal the second echo replica; the first echo replica in said main tap group memory means when the error signal is relatively small. - View Dependent Claims (25, 26)
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27. A method of converging in a digital adaptive filter comprising a main filter portion, including first contents, for generating main component of a pseudo signal, a subfilter portion, including second contents, for generating a subcomponent of the pseudo signal, and a synthesizing portion for synthesizing the main component and the subcomponent to generate the pseudo signal, said method comprising the steps of:
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(a) receiving an input signal; (b) updating the first contents according to a calculation based on an error between the pseudo signal and the input signal if the error is relatively large, and if the error is relatively small, updating the first contents based on a step size corresponding to the error; and (c) updating the second contents based on a step size corresponding to the error. - View Dependent Claims (28)
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Specification