Telephonic communications – Echo cancellation or suppression – Using digital signal processing
Reexamination Certificate
2001-09-06
2004-03-02
Mei, Xu (Department: 2643)
Telephonic communications
Echo cancellation or suppression
Using digital signal processing
C379S406010
Reexamination Certificate
active
06700978
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates to signal processing. In particular, the invention relates to echo cancellation.
2. Description of Related Art
Echo is generally undesirable in telephony. Echo is caused a number of sources. These include multiple reflections of the signal from the loudspeaker back to the microphone, direct acoustic coupling between the loudspeaker and the telephone, and ambient noise. Echo cancellation is a technique to reduce the undesirable effects of the echo. The echo canceller estimates the impulse response of the echo path and generates an estimate of the echo. The estimated echo is then subtracted from the near-end signal. Typically, an adaptive filter is used to estimate the echo because the echo path is usually unknown and randomly time-varying.
An existing technique for echo cancellation is the normalized least mean squares (NLMS) method. This method attempts to minimize the expected value of the squared error. However, the NLMS method has a number of disadvantages. One significant disadvantage is its slow convergence rate for colored inputs.
Therefore, there is a need to have an efficient technique to perform echo cancellation having a convergence rate faster than the NLMS method.
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Tomas Gansler, et. al., A Robust Proportionate Affine Projection Algorithm For Network Echo Canellation, IEEE, 2000, 4 pages.
Yang-Won Jung, et. al., A New Adaptive Algorithm For Stereophonic Acoustic Echo Canceller, IEEE, 2000, 4 pages.
Bershad Neil
Bist Anurag
Hsieh Stan
Harold Jefferey
Mei Xu
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