Echo Cancellation

(Under Construction-more to come)

Background and Overview

At the onset, Greg Lenihan has extensive experience with echo cancellation, multi-path, and
adaptive filtering. Lenihan's Master's Thesis, "Controlling Echo on Multiple Communication
Paths," is part of this knowledge and experience. This thesis presents a novel approach for
estimating multi-path tails and placing the dispersion coefficients accordingly, which is
essentially a correlation enhancement algorithm. The advantage of such an algorithm is that
it mitigates mis-adjustment in a Least Mean Squares (LMS) based algorithm. Mis-adjustment
becomes a problem when the echo impulse response is quite long--as is the case for Satellite
or terretrial hops across oceans. This mis-adjustment leads to positive feedback, or open
instability in the case of the classic "split" canceller configuration.

Figure 1.0: Model for Typical Echo Impulse Response.

Figure 2.0: Block diagram of typical "Split Canceller" configuration.

Some NLMS Plots

Desired Signal ("white"), Error Signal ("blue"), Replica Signal ("red"), Decorrelation (10 samples), Sampling Rate (125 us), ERLE Suppression Threshold (50 dB)

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mu = .05, tap length=2

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mu = .05, tap length=5

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mu = .05, tap length=10

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mu = .05, tap length=20