Estimating delay of an echo path in a communication system
Methods and corresponding systems for reducing an echo signal include assigning a subsegment delay to each of a plurality of subsegment adaptive filters. A send signal and a delayed receive signal are coupled to each of the subsegment adaptive filters, wherein the delayed receive signal is delayed according to a respective subsegment delay. A set of filter coefficients in each of the subsegment adaptive filters are adapted, in parallel, to correspond to a respective subsegment impulse response of a connected system. Each set of filter coefficients is analyzed to produce a pure delay, and the pure delay is used to delay the receive signal for a main adaptive filter. An echo signal replica is produced using the main adaptive filter and an error signal. The echo signal replica is subtracted from the send signal to produce the error signal.
1. A method for estimating a delay of an echo signal comprising:
partitioning an echo path coverage time into a first subsegment and a second subsegment;
adapting a first filter having first coefficients to estimate a response of a connected system with respect to the first subsegment;
adapting a second filter having second coefficients to estimate a response of the connected system with respect to the second subsegment; and
in response to the first coefficients and the second coefficients, estimating a pure delay of the echo signal for use in echo reduction.
2. The method for estimating the delay of an echo signal according to claim 1 wherein the adapting the second filter comprises adapting the second filter in parallel with the adapting the first filter.
3. The method for estimating the delay of an echo signal according to claim 1 wherein the first subsegment partially overlaps the second subsegment.
4. The method for estimating the delay of an echo signal according to claim 1 wherein the first and second filters are adaptive finite impulse response (FIR) filters.
5. The method for estimating the delay of an echo signal according to claim 1 wherein the adapting the first filter comprises adapting the first filter to estimate the response of the connected system with respect to the first subsegment using reduced rate data.
6. The method for estimating the delay of an echo signal according to claim 1 wherein the estimating the pure delay comprises:
selecting one or more selected coefficients of the first coefficients and the second coefficients that indicate an echo; and
estimating a pure delay associated with the selected coefficients.
7. The method for estimating the delay of an echo signal according to claim 6 wherein the estimating the pure delay associated with the selected coefficients comprises
estimating a first pure delay associated with first selected coefficients that indicate a first echo; and
estimating a second pure delay associated with second selected coefficients that indicate a second echo.
8. The method for estimating the delay of an echo signal according to claim 6 wherein the estimating the pure delay associated with the selected coefficients comprises subtracting an offset from a delay correlated with the selected coefficients.
9. The method for estimating the delay of an echo signal according to claim 8 wherein the subtracting an offset comprises subtracting an offset related to values of the first coefficients and the second coefficients.
10. A system for reducing an echo signal comprising:
a first subsegment adaptive filter coupled to a receive signal delayed by a first delay and a send signal, wherein the first subsegment adaptive filter adapts a first set of coefficients in response to the receive signal delayed by the first delay and the send signal;
a second subsegment adaptive filter coupled to the receive signal delayed by a second delay and the send signal, wherein the second subsegment adaptive filter adapts a second set of coefficients in response to the receive signal delayed by the second delay and the send signal;
a filter coefficient analysis system coupled to the first and second subsegment adaptive filters for estimating a pure delay in response to the first and second sets of coefficients;
a dynamic pure delay coupled to the filter coefficient analysis system and the receive signal, wherein the dynamic pure delay delays the receive signal in response to the pure delay to produce a delayed receive signal;
a main adaptive filter having an input coupled to the dynamic pure delay for receiving the delayed receive signal, an input coupled to an error signal, and having an estimated echo output; and
an adder having an input coupled to the estimated echo output and an input coupled to the send signal, and having an output for outputting the error signal, wherein the main adaptive filter adapts to reduce an echo signal in the error signal.
11. The system for reducing an echo signal according to claim 10 further comprising a first subsegment delay and a second subsegment delay, wherein the first and second subsegment delays each have an input coupled to the receive signal, wherein the first subsegment delay has an output coupled to the first subsegment adaptive filter for providing the receive signal delayed by the first delay, and wherein the second subsegment delay has an output coupled to the second subsegment adaptive filter for providing the receive signal delayed by the second delay.
12. The system for reducing an echo signal according to claim 10 wherein the first subsegment adaptive filter has a first length and the second subsegment adaptive filter has a second length, and wherein the first length and the first delay define a first subsegment of an echo path impulse response domain, and the second length and the second delay define a second subsegment of the echo path impulse response domain, and wherein the first subsegment of the echo path impulse response domain partially overlaps the second subsegment of the echo path impulse response domain.
13. The system for reducing an echo signal according to claim 10 wherein the first subsegment adaptive filter coupled to the receive signal delayed by the first delay and the send signal comprises a first subsegment adaptive filter coupled to a send signal decimator for providing a decimated send signal, and coupled to a first receive signal delay that is coupled to a receive signal decimator for providing a decimated receive signal delayed by the first delay, and wherein the second subsegment adaptive filter coupled to the receive signal delayed by the second delay and the send signal comprises a second subsegment adaptive filter coupled to the send signal decimator, and coupled to a second receive signal delay that is coupled to the receive signal decimator for providing a decimated receive signal delayed by the second delay.
14. The system for reducing an echo signal according to claim 10 wherein the second adaptive filter comprises two subsegment adaptive filters, each coupled to the receive signal delayed by different delays, and each having an input coupled to a subsegment error signal, and wherein outputs of the two subsegment adaptive filters are added together to produce the subsegment error signal.
15. A method for reducing an echo signal comprising:
assigning a subsegment delay to each of a plurality of subsegment adaptive filters;
coupling a send signal and a delayed receive signal to each of the plurality of subsegment adaptive filters, wherein the delayed receive signal is delayed according to a respective subsegment delay;
in parallel, adapting a set of filter coefficients in each of the plurality of subsegment adaptive filters to correspond to a respective subsegment impulse response of a system having an input coupled to the receive signal and an output coupled to the send signal;
analyzing each set of filter coefficients and producing a pure delay;
using the pure delay to delay the receive signal for a main adaptive filter;
producing an echo signal replica using the main adaptive filter and an error signal; and
subtracting the echo signal replica from the send signal to produce the error signal.
16. The method for reducing an echo signal according to claim 15 wherein the assigning the subsegment delay to each of the plurality of subsegment adaptive filters comprises assigning a subsegment delay to each of a plurality of subsegment adaptive filters, wherein selected pairs of the subsegment delays partially overlap.
17. The method for reducing an echo signal according to claim 15 wherein the coupling the send signal and the delayed receive signal to each of the plurality of subsegment adaptive filters comprises coupling a decimated send signal and a decimated delayed receive signal to each of the plurality of subsegment adaptive filters.
18. The method for reducing an echo signal according to claim 15 wherein the adapting the set of filter coefficients in each of the plurality of subsegment adaptive filters comprises adapting a set of filter coefficients in each of a plurality of subsegment finite impulse response (FIR) adaptive filters, wherein each subsegment FIR adaptive filter has a length corresponding to a respective subsegment of an echo path impulse response.
19. The method for reducing an echo signal according to claim 15 wherein the analyzing each set of filter coefficients and producing a pure delay comprises distinguishing selected coefficients adapted to the echo signal and producing a pure delay in response to the selected coefficients.
20. The method for reducing an echo signal according to claim 15 wherein the analyzing each set of filter coefficients and producing a pure delay comprises:
distinguishing selected coefficients adapted to a first echo signal;
distinguishing selected coefficients adapted to a second echo signal;
producing a first pure delay in response to the selected coefficients adapted to the first echo signal; and
producing a second pure delay in response to the selected coefficients adapted to the second echo signal.