Systems and methods for echo cancellation and echo suppression
View Patent ↗Traditionally, echo cancellation has employed linear adaptive filters to cancel echoes in a two way communication system. The rate of adaptation is often dynamic and varies over time. Disclosed are novel rates of adaptation that perform well in the presence of background noise, during double talk and with echo path changes. Additionally, the echo or residual echo can further be suppressed with non-linear processing performed using joint frequency-time domain processing.
1. A method of cancelling an echo comprising: approximating the echo by applying a transfer function to a far-end signal to generate an approximate echo, said transfer function having an impulse response and an order; adapting the transfer function by modifying the impulse response based on an adaptation coefficient, by dividing a value generated by an estimator function by a sum of a total energy of the far-end signal over a first observation window and a predetermined constant number; and wherein the estimator function generates a value on the basis of the received signal, an output signal from an echo canceller, the far-end signal and/or the approximate echo.
2. The method of claim 1 wherein the output signal is generated by subtracting the approximate echo from a received signal.
3. The method of claim 2 wherein the received signal comprises a near-end signal.
4. The method of claim 2 wherein the received signal comprises the echo.
5. The method of claim 1 where the total energy is calculated as an average of |x(n)| 2 over the first observation window times the order of the transfer function.
6. The method of claim 5 , wherein the average is an arithmetic average or a smooth average.
7. The method of claim 5 , wherein the first observation window has a size equal to the order of the transfer function.
8. The method of claim 5 , wherein x(n) is the far-end signal and n is a sampling time index.
9. The method of claim 1 further comprising: synthesizing a synthetic echo; and adding the synthetic echo to the received signal.
10. A system with echo cancellation comprising: an echo approximator configured to apply a transfer function, having an impulse response and an order, to a far-end signal and produce an approximate echo; a subtractor configured to subtract the approximate echo from a received signal comprising a near-end signal and an echo of the far-end signal to produce an output signal; an adaption coefficient generator configured to generate an adaptation coefficient, by dividing a value generated by an estimator by a sum of a total energy of the far-end signal over a first observation window and a predetermined constant number; wherein the impulse response of the transfer function is modified based on the adaptation coefficient.
11. The system of claim 10 wherein the estimator function is configured to generate a value on the basis of the received signal, the output signal, the far-end signal and/or the approximate echo.
12. The system of claim 10 further comprising an echo synthesizer configured to generate a synthetic echo from the far-end signal.
13. The echo cancellation system of claim 12 further comprising an adder configured to add the synthetic echo to the received signal.