# 0.1 A telecommunication system  (Page 8/15)

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Even within the frequency range of the message signal, the medium can affect different frequencies in different ways. (These are called frequency selective effects .) For example, a signal may arrive at the receiver, and a momentlater a copy of the same signal might arrive after having bounced off a mountain or a nearby building.This is called multipath interference , and it can be viewed as a sum of weighted and delayed versions

of the transmitted signal. This may be familiar to the (analog broadcast) TV vieweras “ghosts,” misty copies of the original signal that are shifted and superimposed over the main image.In the simple case of a sinusoid, a delay corresponds to a phase shift,making it more difficult to reassemble the original message. A special filter called the equalizer is often added to the receiver to help improve the situation.An equalizer is a kind of “deghosting” circuit, We refrain from calling these ghost busters. and equalization is addressed in detail in [link] .

Because of the proliferation of inexpensive and capable digital processors, receivers often contain chipsthat are essentially special purpose computers. In such receivers, many of the functions that are traditionally handled bydiscrete components (such as analog oscillators and filters) can be handled digitally.Of course, this requires that the analog received signal be turned into digital information (a series of numbers) that acomputer can process. This analog-to-digital conversion (A/D) is known as sampling .

Sampling measures the amplitude of the waveform at regular intervals, and thenstores these measurements in memory. Two of the chief design issues in a digital receiverare the following:

• Where should the signal be sampled?
• How often should the sampling be done?

The answers to these questions are intimately related to each other.

When taking samples of a signal, they must be taken fast enough so that important information is not lost.Suppose that a signal has no frequency content above ${f}^{*}$ Hz. The widely known Nyquist reconstruction principle (see [link] ) says that if sampling occurs at a rate greater than $2{f}^{*}$ samples per second, it is possible to reconstruct the original signal fromthe samples alone. Thus, as long as the samples aretaken rapidly enough, no information is lost. On the other hand, when samples are taken too slowly,the signal cannot be reconstructed exactly from the samples, and the resulting distortion is called aliasing .

Accordingly, in the receiver, it is necessary to sample at least twice as fast as the highest frequency present in the analog signal being sampledin order to avoid aliasing. Because the receiver contains modulators that change thefrequencies of the signals, different parts of the system have different highest frequencies.Hence the answer to the question of how fast to sample is dependent on where the samples will be taken.

The sampling

1. could be done at the input to the receiver at a rate proportional to the carrier frequency,
2. could be done after the downconversion, at a rate proportional to the rate of the symbols, or
3. could be done at some intermediate rate.

where we get a research paper on Nano chemistry....?
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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
how did you get the value of 2000N.What calculations are needed to arrive at it
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