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The next layer encompasses [link] through [link] . This gives a closer look at the idealized receiver—how things work when everythingis just right: when the timing is known, when the clocks run at exactly the right speed, when there are no reflections,diffractions, or diffusions of the electromagnetic waves. This layer also introduces a few M atlab tools that are needed to implement the digital radio.The order in which topics are discussed is precisely the order in which they appear in the receiver:

channel C h a p t e r 4 frequency translation C h a p t e r 5 sampling C h a p t e r 6
receive filtering equalization C h a p t e r 7 decision device decoding C h a p t e r 8
Channel impairments and linear systems Chapter 4 Frequency translation and modulation Chapter 5 Sampling and gain control Chapter 6 Receive (digital) filtering Chapter 7 Symbols to bits to signals Chapter 8

Chapter  [link] provides a complete (though idealized) software-defined digital radio system.

From there to here, from here to there, funny things are everywhere.

—Dr. Seuss, One Fish, Two Fish, Red Fish, Blue Fish, 1960

If every signal that went from here to there arrived at its intended receiver unchanged, the life of a communications engineerwould be easy. Unfortunately, the path between here and there can be degraded in several ways, including multipath interference,changing (fading) channel gains, interference from other users, broadband noise, and narrowband interference.

This chapter begins by describing these problems, which are diagrammed in [link] . More important than locating the sources of the problems isfixing them. The received signal can be processed using linear filters to help reduce the interferencesand to undo, to some extent, the effects of the degradations. The central question is how to specify filters that can successfullymitigate these problems, and answering this requires a fairly detailed understanding of filtering.Thus, a discussion of linear filters occupies the bulk of this chapter, which also provides a background for other uses of filtersthroughout the receiver, such as the lowpass filters used in the demodulators of Chapter  [link] , the pulse shaping and matched filters of Chapter  [link] , and the equalizing filters of Chapter  [link] .

When bad things happen to good signals

The path from the transmitter to the receiver is not simple, as [link] suggests. Before the signal reaches the receiver, it is subjectto a series of possible “funny things,” events that may corrupt the signal and degrade the functioning of the receiver.This section discusses five kinds of corruption that are used throughout the chapter to motivate and explain the various purposesthat linear filters may serve in the receiver.

Other users

Many different users must be able to broadcast at the same time. This requires that there be a way for areceiver to separate the desired transmission from all the others (for instance, to tune to a particular radio or TV station among a largenumber that may be broadcasting simultaneously in the same geographical region). One standard method is to allocate different frequencybands to each user. This was called frequency division multiplexing (FDM) in Chapter  [link] , and was shown diagrammatically in [link] . The signals from the different users can be separatedusing a bandpass filter, as in [link] . Of course, practical filters do not completely remove out-of-bandsignals, nor do they pass in-band signals completely without distortions. Recall the three filters in [link] .

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, Software receiver design. OpenStax CNX. Aug 13, 2013 Download for free at http://cnx.org/content/col11510/1.3
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