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A Gray code has the property that the binaryrepresentation for each symbol differs from its neighbors by exactly one bit.A Gray code for the translation of binary into 4-PAM is

01 + 3 11 + 1 10 - 1 00 - 3

Mimic the code in naivecode.m to implement this alternative and plot the number of errors as a function ofthe noise variance v . Compare your answer with [link] . Which code is better?

Symbols to signals

Even though the original message is translated into the desired alphabet, it is not yet ready for transmission:it must be turned into an analog waveform. In the binary case, a simple method is to use a rectangular pulseof duration T seconds to represent + 1 , and the same rectangular pulse inverted (i.e., multiplied by - 1 ) to represent the element - 1 . This is called a polar non-return-to-zero line code.The problem with such simple codes is that they use bandwidth inefficiently.Recall that the Fourier transform of the rectangular pulse in time is the sinc ( f ) function in frequency [link] , which dies away slowly as f increases. Thus, simple codes like the non-return-to-zeroare compact in time, but wide in frequency, limiting the number of simultaneous nonoverlapping users ina given spectral band.

More generally, consider the four-level signal of [link] . This can be turned into an analog signal for transmission by choosinga pulse shape p ( t ) (that is not necessarily rectangular and not necessarily of duration T ) and then transmitting

p ( t - k T ) if the k th symbol is 1 - p ( t - k T ) if the k th symbol is - 1 3 p ( t - k T ) if the k th symbol is 3 - 3 p ( t - k T ) if the k th symbol is - 3

Thus, the sequence is translated into an analog waveform by initiating a scaled pulse at the symbol time k T , where the amplitude scaling is proportional to the associated symbolvalue. Ideally, the pulse would be chosen so that

  • the value of the message at time k does not interfere with the value of the message at other sample times(the pulse shape causes no intersymbol interference ),
  • the transmission makes efficient use of bandwidth, and
  • the system is resilient to noise.

Unfortunately, these three requirements cannot all be optimized simultaneously, and so the design of thepulse shape must consider carefully the tradeoffs that are needed. The focus in Chapter [link] is on how to design the pulse shape p ( t ) , and the consequences of that choice in terms of possible interference betweenadjacent symbols and in terms of the signal-to-noise properties of the transmission.

For now, to see concretely how pulse shaping works, let's pick a simple nonrectangular shape and proceedwithout worrying about optimality. Let p ( t ) be the symmetrical blip shape shown in the top part of [link] , and defined in pulseshape.m by the hamming command. The text string in str is changed into a 4-level signal as in Example [link] , and then the complete transmitted waveform is assembled by assigning an appropriatelyscaled pulse shape to each data value. The output appears in the bottom of [link] . Looking at this closely, observe that the first letter T is represented by the four values - 1 - 1 - 1 - 3 , which corresponds exactly to the first four negative blips, three small and one large.

Questions & Answers

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
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.
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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