28-03-2014, 04:28 PM
Adaptive Noise Cancelling: Principles and Applications
INTRODUCTION
THE USUAL method of estimating a signal corrupted by
additive noise’ is to pass it through a fiiter that tendsto
suppress the noise while
leaving the signal relatively
unchanged. The design of such filtersis the domain of optimal
filtering, which originated with .the pioneering work of Wiener
and was extendedand enhanced by the work of Kalman,
Bucy, and others [ 11-[ 51.
Filters used for the above purpose can be fixed or adaptive.
The design of fixed filters is based on prior knowledge of both
the signal and the noise. Adaptive filters, on the other hand,
have the ability to adjust their own parameters automatically,
andtheir design requires littleor no u priori knowledge of
signal or noise characteristics.
Noisecancellingis variation of optimal filtering thatis
highly advantageous in many applications. It makes use of an
auxiliary or reference input derived from one or more sensors
located at points in the noise field where the signal is weak or
undetectable. This input is filtered andsubtractedfrom
a primary input containing bothsignal and noise. As a result the
primary noise is attenuated or eliminated by cancellation.
At first glance, subtracting noise from a received
signal. If done improperly
it could result in an increase in output noise power. If, how-
ever, filtering and subtraction are controlled by an appropriate
adaptive process, noise reduction can beaccomplished with
little risk of distorting thesignal or increasing the output noise
level.would be difficult or impossible to achieve by direct filtering.
The purpose of thispaper is to describe the concept of
adaptive noise cancelling, t o provide a theoretical treatment of
its advantages and limitations, and to describe some of the ap-
plications where it is most useful.
APPLICATIONS
The principles of adaptive noise cancelling,
including a description of the concept and theoretical
analyses of per- formancewith various kinds of signal and noise,
have been presented in the preceding pages. This section describes a
variety of practical applications of the technique. These
applications include the cancellingofseveral kinds of inter-
ference in electrocardiography, of noise in speech signals, of
antenna sidelobe interference, and of periodic or broad-band
interference for which there is no external reference source.
CONCLUSION
Adaptive noisecancelling is a method of optimal filtering
that can be applied whenever a suitable 'reference input is
available. The principal advantages of the
method are its
adaptivecapability,itslowoutput
noise, and itslow signal
distortion.The adaptive capability allows the processing of
inputs whose properties are unknown and in some cases non-
stationary. It leads to a stable system that automatically turns
itself off when no improvement in signal-to-noise ratio can be
achieved. Output noise and signal distortion are generally
lower than can be achieved with conventional optimal filter
configurations.
INTRODUCTION
THE USUAL method of estimating a signal corrupted by
additive noise’ is to pass it through a fiiter that tendsto
suppress the noise while
leaving the signal relatively
unchanged. The design of such filtersis the domain of optimal
filtering, which originated with .the pioneering work of Wiener
and was extendedand enhanced by the work of Kalman,
Bucy, and others [ 11-[ 51.
Filters used for the above purpose can be fixed or adaptive.
The design of fixed filters is based on prior knowledge of both
the signal and the noise. Adaptive filters, on the other hand,
have the ability to adjust their own parameters automatically,
andtheir design requires littleor no u priori knowledge of
signal or noise characteristics.
Noisecancellingis variation of optimal filtering thatis
highly advantageous in many applications. It makes use of an
auxiliary or reference input derived from one or more sensors
located at points in the noise field where the signal is weak or
undetectable. This input is filtered andsubtractedfrom
a primary input containing bothsignal and noise. As a result the
primary noise is attenuated or eliminated by cancellation.
At first glance, subtracting noise from a received
signal. If done improperly
it could result in an increase in output noise power. If, how-
ever, filtering and subtraction are controlled by an appropriate
adaptive process, noise reduction can beaccomplished with
little risk of distorting thesignal or increasing the output noise
level.would be difficult or impossible to achieve by direct filtering.
The purpose of thispaper is to describe the concept of
adaptive noise cancelling, t o provide a theoretical treatment of
its advantages and limitations, and to describe some of the ap-
plications where it is most useful.
APPLICATIONS
The principles of adaptive noise cancelling,
including a description of the concept and theoretical
analyses of per- formancewith various kinds of signal and noise,
have been presented in the preceding pages. This section describes a
variety of practical applications of the technique. These
applications include the cancellingofseveral kinds of inter-
ference in electrocardiography, of noise in speech signals, of
antenna sidelobe interference, and of periodic or broad-band
interference for which there is no external reference source.
CONCLUSION
Adaptive noisecancelling is a method of optimal filtering
that can be applied whenever a suitable 'reference input is
available. The principal advantages of the
method are its
adaptivecapability,itslowoutput
noise, and itslow signal
distortion.The adaptive capability allows the processing of
inputs whose properties are unknown and in some cases non-
stationary. It leads to a stable system that automatically turns
itself off when no improvement in signal-to-noise ratio can be
achieved. Output noise and signal distortion are generally
lower than can be achieved with conventional optimal filter
configurations.