# 0.3 Modelling corruption  (Page 4/11)

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Thus, filtering in the receiver can be used to reshape the received signal within the frequency band of the transmissionas well as to remove unwanted out-of-band frequencies.

Another kind of corruption that a signal may encounter on its journey from the transmitter to the receiver is called“fading,” where the frequency response of the channel changes slowly over time. This may be caused because the transmission pathchanges. For instance, a reflection from a cloud might disappear when the cloud dissipates, an additional reflection mightappear when a truck moves into a narrow city street, or in a mobile device such as a cell phone the operatormight turn a corner and cause a large change in the local geometry of reflections. Fading may also occurwhen the transmitter and/or the receiver are moving. The Doppler effect shifts the frequencies slightly,causing interferences that may slowly change.

Such time-varying problems cannot be fixed by a single fixed filter; rather, the filter must somehow compensatedifferently at different times. This is an ideal application for the adaptive elements of [link] , though results from the study of linear filters will becrucial in understanding how the time variations in the frequency response can be represented as time-varyingcoefficients in the filter that represents the channel.

## Linear systems: linear filters

Linear systems appear in many places in communication systems. The transmission channel is often modeled as a linear systemas in [link] . The bandpass filters used in the front end toremove other users (and to remove noises) are linear. Lowpass filters are crucial to the operation of the demodulatorsof Chapter  [link] . The equalizers of Chapter  [link] are linear filters that are designed during the operation of the receiveron the basis of certain characteristics of the received signal.

Time invariant linear systems can be described in any one of three equivalent ways:

• The impulse response $h\left(t\right)$ is a function of time that defines the output of a linear system when the input is an impulse (or $\delta$ ) function. When the input to the linear system is more complicated than a single impulse, the output can becalculated from the impulse response via the convolution operator.
• The frequency response $H\left(f\right)$ is a function of frequency that defines how the spectrum of the input is changed into the spectrum of the output. The frequency responseand the impulse response are intimately related: $H\left(f\right)$ is the Fourier transform of $h\left(t\right)$ .
• A linear difference equation with constant coefficients (such as [link] ) shows explicitly how the linear system can be implemented and canbe useful in assessing stability and performance.

This chapter describes the three representations of linear systems and shows how they interrelate. The discussion beginsby exploring the $\delta$ -function, and then showing how it is used to define the impulse response. The convolution property of theFourier transform then shows that the transform of the impulse response describes how the system behaves in termsof the input and output spectra, and so it is called the frequency response. The final step is to show how the action of the linear system can be redescribedin the time domain as a difference (or as a differential) equation. This is postponed to Chapter  [link] .

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
how did you get the value of 2000N.What calculations are needed to arrive at it
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