Communication Engineering

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Browsing Communication Engineering by Subject "Acoustic echo"

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    Convex Combination of Adaptive Linear Finite Impulse Response and Nonlinear Volterra Filters for Acoustic Echo Cancellation
    (Addis Ababa University, 2011-10) Labena, Tagel; Adugna, Eneyew(PhD)
    We all know how much joy and freedom hands-free communication system has brought to our daily life. But associated with this is the problem of acoustic echo which degrades the quality of communication. A number of researches have been conducted in order to eliminate acoustic echo. Most of the acoustic echo cancellers are made on the assumptions of the linearity of the echo. However, this assumption is no longer valid when the nonlinearity along the echo path is taken into account. This led to the invention of Nonlinear Acoustic Echo Cancellation (NLAEC) techniques such as Volterra filters. However, in some situations, NLAEC is inferior to a linear Acoustic Echo Cancellation (AEC), especially when the channel generates a negligible (or no) nonlinear echo. In general, the ratio of the linear to nonlinear echo signal power is unknown a priori, and will vary over time, thus making it difficult to know if NLAEC would improve or degrade the cancellation. Therefore, in this thesis a convex combination of the linear and the nonlinear Volterra filters is studied. Simulation has been carried out and the results indicate the combination scheme follows the best contributing filter regardless of the nature of the echo. Another important problem of AEC is the problem of double talk (DT) which occurs when both parties talk at the same time. If DT is not controlled it results in diverging of the adaptive filter coefficients and as a result audible echoes pass without being cancelled. In order to alleviate this problem most DT controllers have been studied based on correlation of the available signals. Since correlation is valid only for linear relationship; this assumption doesn’t hold when the nonlinearity along the echo path is considered. Therefore, in this thesis mutual information (MI) based DT detection has been studied together with AEC. Simulation is carried out by introducing a DT region and the results obtained indicate performance improvement of 97.06% in terms of algorithm misalignment error (AME). Key words: Acoustic echo, In general, Convex Combination, Volterra, adaptive filters