28-07-2014, 11:56 AM
ACOUSTIC ECHO CANCELLATION
[attachment=66315]
ABSTRACT
This scheme identifies the frequency response of the echosystem so that the adaptive filter generates an estimate of the echo and subtracts it from a distorted signal so that the original signal can be recovered. The LMS algorithm design is used extensively in communication networks to correct for the echoes created by line impedance mismatches and is useful to compensate for the imperfection in telephony networks. This shows how the LMS algorithm is useful to solve echo problems
Introduction
A significant problem in communications is the generation of echoes. The echoes arise for a number of reasons, with the primary reason being an impedance mismatch. The impedance mismatch occurs when the two-wire network meets the four-wire network, this interface is known as the hybrid. This impedance mismatch causes some of the signal energy to be returned to the source as an echo
A sinusoid will be used as the input signal. The DSP board will create an echo of the sinusoid and add the echo to the original sinusoidal signal, thus creating a distorted version of the input signal. The DSP will then use LMS adaptive filtering to estimate the echo, and remove the echo from the distorted signal creating a reconstructed signal. The LMS algorithm seeks to minimize the excess mean-square error (MSE) between the echo signal and the estimated echo. The excess MSE refers to the LMS algorithm fluctuations about the adaptive filter coefficients after a large number of iterations
Design Procedure
A sinusoid wave is be used as the test signal in simulation and in experiments. The m value in the LMS algorithm is an important value in determining the performance of the echo cancellation. m must be chosen between zero and twice the inverse total input power
Conclusion
The LMS algorithm successful cancelled the echo and returned a reconstruction of the original signal.
Echo cancellation works well if one can estimate the echo delays so that the m values and adaptive filter length are chosen properly.
[attachment=66315]
ABSTRACT
This scheme identifies the frequency response of the echosystem so that the adaptive filter generates an estimate of the echo and subtracts it from a distorted signal so that the original signal can be recovered. The LMS algorithm design is used extensively in communication networks to correct for the echoes created by line impedance mismatches and is useful to compensate for the imperfection in telephony networks. This shows how the LMS algorithm is useful to solve echo problems
Introduction
A significant problem in communications is the generation of echoes. The echoes arise for a number of reasons, with the primary reason being an impedance mismatch. The impedance mismatch occurs when the two-wire network meets the four-wire network, this interface is known as the hybrid. This impedance mismatch causes some of the signal energy to be returned to the source as an echo
A sinusoid will be used as the input signal. The DSP board will create an echo of the sinusoid and add the echo to the original sinusoidal signal, thus creating a distorted version of the input signal. The DSP will then use LMS adaptive filtering to estimate the echo, and remove the echo from the distorted signal creating a reconstructed signal. The LMS algorithm seeks to minimize the excess mean-square error (MSE) between the echo signal and the estimated echo. The excess MSE refers to the LMS algorithm fluctuations about the adaptive filter coefficients after a large number of iterations
Design Procedure
A sinusoid wave is be used as the test signal in simulation and in experiments. The m value in the LMS algorithm is an important value in determining the performance of the echo cancellation. m must be chosen between zero and twice the inverse total input power
Conclusion
The LMS algorithm successful cancelled the echo and returned a reconstruction of the original signal.
Echo cancellation works well if one can estimate the echo delays so that the m values and adaptive filter length are chosen properly.