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Beam me up, Scotty.

—attributed to James T. Kirk, Starship Enterprise , “Star Trek”

Several parts of a communication system modulate the signal and change the underlyingfrequency band in which the signal lies. These frequency changes must be reversible; after processing, the receiver must beable to reconstruct (a close approximation to) the transmitted signal.

The input message w ( k T ) in [link] is a discrete-time sequence drawn from a finite alphabet.The ultimate output m ( k T ) produced by the decision device (or quantizer) is also discrete-time and is drawnfrom the same alphabet. If all goes well and the message is transmitted, received,and decoded successfully, then the output should be the same as the input,although there may be some delay δ between the time of transmission and the time when theoutput is available. Though the system is digital in terms of the message communicatedand the performance assessment, the middle of the system is inherently analog from the (pulse-shaping)filter of the transmitter to the sampler at the receiver.

At the transmitter in [link] , the digital message has alreadybeen turned into an analog signal by the pulse shaping (whichwas discussed briefly in [link] and is considered in detail in [link] ). For efficient transmission, the analog version of the messagemust be shifted in frequency, and this process of changing frequencies is called modulation or upconversion.At the receiver, the frequency must be shifted back down, and this is called demodulation or downconversion.Sometimes the demodulation is done in one step (all analog) and sometimes the demodulation proceeds in twosteps; an analog downconversion to the intermediate frequency and then a digital downconversion to thebaseband. This two step procedure is shown in [link] .

There are many ways that signals can be modulated. Perhaps the simplest is amplitude modulation , which is discussed in two forms (large and small carrier) in the nexttwo sections. This is generalized to the simultaneous transmission of twosignals using quadrature modulation in "Quadrature Modulation" , and it is shown that quadrature modulation uses bandwidth more efficiently than amplitude modulation.This gain in efficiency can also be obtained using single sideband and vestigial sideband methods, which are discussed in the document titled Other Modulations , available on the website.Demodulation can also be accomplished using sampling as discussed in [link] , and amplitude modulation can also be accomplished witha simple squaring and filtering operation as in Exercise  [link] .

A complete digital communication system has many parts. This chapter focuses on the upconversion and the downconversion, which can done in many ways including large carrier AM as in Section 5-1, suppressed carrier AM as in Section 5-2, and quadrature modulation as in Section 5-3.
A complete digital communication system has many parts. This chapter focuses on the upconversion and the downconversion,which can done in many ways including large carrier AM as in "Amplitude Modulation with Large Carrier" , suppressed carrier AM as in "Amplitude Modulation with Suppressed Carrier" , and quadrature modulation as in "Quadrature Modulation" .

Throughout, the chapter contains a series of exercises that prepare readers to create their own modulationand demodulation routines in M atlab . These lie at the heart of the software receiver that will beassembled in [link] and [link] .

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
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
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Software receiver design. OpenStax CNX. Aug 13, 2013 Download for free at http://cnx.org/content/col11510/1.3
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