Method and apparatus for cancelling echo originating from a mobile terminal
First Claim
1. A method for use in an echo canceler, comprising a plurality of adaptive filters, for controlling an echo signal originating from a digital mobile terminal, comprising the steps of:
- determining if an adaptive filter sample histogram maximum value associated with said echo signal is greater than a first predetermined value;
determining if said adaptive filter sample histogram maximum value associated with said echo signal is greater than a second value;
and inserting a non-linearity in an output signal from a network echo canceller in communication with said digital mobile terminal if the following inequalities hold;
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Abstract
A novel method and apparatus are disclosed for cancelling echoes originating from a digital mobile handset using an echo canceller located in the network. The method and apparatus thus solve a practical echo problem that many mobile telephone operators have long been faced with. The method includes an algorithm that differs significantly from a conventional network echo canceller algorithm, because of the following basic considerations that influenced a solution to the echo problem: (1) the algorithm should not worsen speech quality for digital mobiles that do not generate echoes; and (2) the echo path is non-linear due to two speech coder/decoder pairs in the echo path and a low echo level.
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Citations
14 Claims
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1. A method for use in an echo canceler, comprising a plurality of adaptive filters, for controlling an echo signal originating from a digital mobile terminal, comprising the steps of:
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determining if an adaptive filter sample histogram maximum value associated with said echo signal is greater than a first predetermined value;
determining if said adaptive filter sample histogram maximum value associated with said echo signal is greater than a second value;
and inserting a non-linearity in an output signal from a network echo canceller in communication with said digital mobile terminal if the following inequalities hold;
- View Dependent Claims (3, 4, 5, 6, 7, 8, 9)
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2. An echo canceller found in a mobile services switching center for canceling echo originating from a mobile station, comprising:
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a plurality of adaptive filters, each of said adaptive filters for modeling an impulse response of an echo path so that said plurality of adaptive filters span an entire sample;
means for controlling an independent adaptation of each of said plurality of adaptive filters;
a histogram logic unit coupled to an output of each of said plurality of adaptive filters, for determining whether a mobile terminal in communication with said echo canceller is generating echo; and
a non-linear processor responsive to said histogram logic unit, for introducing non-linearity to an output signal from said echo canceller if said mobile terminal is generating echo.
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10. A method for use in an echo canceler, comprising a plurality of adaptive filters, for controlling a high frequency echo signal originating from a mobile terminal, comprising the steps of
estimating, in a network echo canceller in communication with said mobile terminal, a power level of said echo signal; - and
inserting a non-linearity in an output signal from said network echo canceller if an adaptive filter sample histogram maximum value associated with said echo signal is greater than a predetermined value. - View Dependent Claims (11, 12, 13, 14)
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13. The method of claim 12, wherein said estimating step comprises estimating said power level as:
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wherein ĥ
max(t) is said vector of sub-filter coefficients selected by said histogram, and xmax(t) is said vector of input signal samples in said sub-filter.
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14. The method of claim 10, wherein said predetermined value is 4096.
Specification