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