Post on 10-Apr-2016
description
Applications of adaptive filters
Echo Cancellation System identification or direct modelling
configuration. Hybrid leakage path is the plant. To match characteristics of hybrid leakage
path Adaptation is disabled when local caller is on
line on the phone.
Equalization, Inverse modelling and Deconvolution
Used at the start of transmission only. Recovery of delayed version of s (original
signal) from x. Signal x -> certain plant followed by
addition of noise. The noise may represent communication
channel Delay included to allow propagation of
signals through plant and adaptive filter. Adaptive filter takes on inverse
characteristics of plant.
Noise or Interference Calculations To improve Signal to Noise ratio, the
arrangement subtracts an estimate of the noise in the received signal.
Assume n0 is correlated with n1 and s is uncorrelated with either of them.
S and n0 is detected by primary sensor. Reference sensor only used for detection
of noise n1. Since the paths between noise source
are different, the nature of correlation is unknown.
Adaptive filter acts in such way by acting on n1 to approximately replicated n0 followed by subtraction from primary sensor signal.
To make (s+n0)-y best fit with s. Noise cancellation configuration resembles following figure when s is
ignored and n0 is viewed as output of n1.
To provide noise free signal s by estimation of n0 at noise canceller output.
Examples of application of adaptive noise cancellation Aircraft Cockpit Noise
Reason: Engine noise interference with pilot speech. Noise may consist similar frequency content to pilot’s speech.
Intensity of noise and frequency will vary with engine speed and altitude of pilots head.
Solution: Adaptive noise filtering can be used. Primary sensor is microphone of pilot.
Reference sensor is another microphone located somewhere in cockpit