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This module develops the matched filter detector, including its mathematical justification based on the Cauchy-Scwarz inequality, its practical implementation via convolution, and several example applications.


A great many applications in signal processing, image processing, and beyond involve determining the presence and location of a target signal within some other signal. A radar system, for example, searches for copies of a transmitted radar pulse in order to determine the presence of and distance to reflective objects such as buildings or aircraft. A communication system searches for copies of waveforms representing digital 0s and 1s in order to receive a message.

Two key mathematical tools that contribute to these applications are inner products and the Cauchy-Schwarz inequality . As is shown in the module on the Cauchy-Schwarz inequality, the expression x | | x | | , y | | y | | attains its upper bound, which is 1, when y = a x for some scalar a in a real or complex field. The lower bound, which is 0, is attained when x and y are orthogonal. In informal intuition, this means that the expression is maximized when the vectors x and y have the same shape or pattern and minimized when x and y are very different. A pair of vectors with similar but unequal shapes or patterns will produce relatively large value of the expression less than 1, and a pair of vectors with very different but not orthogonal shapes or patterns will produce relatively small values of the expression greater than 0. Thus, the above expression carries with it a notion of the degree to which two signals are “alike”, the magnitude of the normalized correlation between the signals in the case of the standard inner products.

This concept can be extremely useful. For instance consider a situation in which we wish to determine which signal, if any, from a set X of signals most resembles a particular signal y . In order to accomplish this, we might evaluate the above expression for every signal x X , choosing the one that results in maxima provided that those maxima are above some threshold of “likeness”. This is the idea behind the matched filter detector, which compares a set of signals against a target signal using the above expression in order to determine which is most like the target signal.

Matched filter detector theory

Signal comparison

The simplest variant of the matched filter detector scheme would be to find the member signal in a set X of signals that most closely matches a target signal y . Thus, for every x X we wish to evaluate

m ( x , y ) = x | | x | | , y | | y | |

in order to compare every member of X to the target signal y . Since the member of X which most closely matches the target signal y is desired, ultimately we wish to evaluate

x m = argmax x X x | | x | | , y | | y | | .

Note that the target signal does not technically need to be normalized to produce a maximum, but gives the desirable property that m ( x , y ) is bounded to [ 0 , 1 ] .

The element x m X that produces the maximum value of m ( x , y ) is not necessarily unique, so there may be more than one matching signal in X . Additionally, the signal x m X producing the maximum value of m ( x , y ) may not produce a very large value of m ( x , y ) and thus not be very much like the target signal y . Hence, another matched filter scheme might identify the argument producing the maximum but only above a certain threshold, returning no matching signals in X if the maximum is below the threshold. There also may be a signal x X that produces a large value of m ( x , y ) and thus has a high degree of “likeness” to y but does not produce the maximum value of m ( x , y ) . Thus, yet another matched filter scheme might identify all signals in X producing local maxima that are above a certain threshold.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
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Source:  OpenStax, Signals and systems. OpenStax CNX. Aug 14, 2014 Download for free at http://legacy.cnx.org/content/col10064/1.15
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