Echo canceller with dynamically positioned adaptive filter taps
First Claim
1. A method of allocating filter taps in an echo canceller for a transmission line comprising the steps of:
- storing a plurality of samples of a signal representative of said transmission line'"'"'s impulse response in a memory;
examining said plurality of stored samples to find variable sized ranges of samples of said impulse response having at least a predetermined amount of echo energy, said examining step including computing a center of echo of each of said ranges of said samples in order to find the approximate center of each of said ranges of samples of impulse response containing echo energy; and
allocating a variable total number of filter taps of said echo canceller by turning on only those taps corresponding to said ranges of samples having at least said predetermined amount of echo energy.
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Abstract
An echo canceller according to the present invention includes means for storing an impulse response in a memory, the impulse response being indicative of the characteristics of a transmission line. It also includes a detector for detecting ranges of samples within the impulse response having relatively large distribution of echo energy, these ranges of samples of relatively large distribution of echo energy being indicative of echoes on the transmission line. An echo canceller includes a digital filter having a plurality of weighted taps, each of the weighted taps having an associated tap weight value. A tap allocation circuit establishes the tap weight values in response to said detecting means so that only taps within the regions of relatively large distributions of echo energy are turned on. The ranges of echo energy are detected coarsely by detecting ranges of samples having relatively high estimated average echo power. The echo is more finely located by computing the terms analogous to the mechanical computation of the center of gravity type calculation referred to as a `center of echo` and radius of gyration type calculation referred to as `radius of echo` of the echo energy within the coarsely located ranges of samples.
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Citations
19 Claims
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1. A method of allocating filter taps in an echo canceller for a transmission line comprising the steps of:
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storing a plurality of samples of a signal representative of said transmission line'"'"'s impulse response in a memory; examining said plurality of stored samples to find variable sized ranges of samples of said impulse response having at least a predetermined amount of echo energy, said examining step including computing a center of echo of each of said ranges of said samples in order to find the approximate center of each of said ranges of samples of impulse response containing echo energy; and allocating a variable total number of filter taps of said echo canceller by turning on only those taps corresponding to said ranges of samples having at least said predetermined amount of echo energy. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An echo canceller comprising in combination:
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means for storing an impulse response in a memory, said impulse response being indicative of the characteristics of a transmission line; means for detecting variable sized ranges of samples within said impulse response having echo energy, by locating a central sample of an echo and computing a radius of echo about said central sample in order to define said variable sized ranges; an echo canceller means including a digital filter having a plurality of weighted taps, each of said weighted taps having an associated tap weight value; and tap allocation means for activating and deactivating variable numbers of said taps in response to said detecting means so that only taps within said ranges of samples are turned on within said echo canceller and taps outside said ranges of samples are turned off. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of locating taps for allocation to an echo canceller, comprising the steps of:
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storing a plurality of samples representative of a transmission line'"'"'s impulse response; estimating the average power in said stored samples; comparing said estimated average power to a predetermined threshold in order to coarsely locate samples containing echo energy; computing the center of echo of said coarsely located samples in order to estimate the center of the echo energy; and computing a radius of echo about said center of echo in order to estimate the spread of the echo energy.
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19. An echo canceller comprising in combination:
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means for storing an impulse response in a memory, said impulse response being indicative of the characteristics of a transmission line; an echo canceller means including a digital filter having a plurality of weighted taps, each of said weighted taps having an associated tap weight value; means for estimating the average power of ranges of samples of said impulse response; means for comparing said estimated average power with a predetermined threshold to coarsely locate ranges of samples containing echo energy; means for computing a center of echo of each of said ranges of samples of said impulse response; means for computing a radius of echo about each said center of echo; tap allocation means for activating a variable number of echo canceller taps within a range of 2.5 to 3.5 times the radius of echo about each said center of echo.
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Specification