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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

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
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industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
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scanning tunneling microscope
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Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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
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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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