# 0.7 Bits to symbols to signals  (Page 2/8)

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$...000010110101...\to ...00\phantom{\rule{4pt}{0ex}}00\phantom{\rule{4pt}{0ex}}10\phantom{\rule{4pt}{0ex}}11\phantom{\rule{4pt}{0ex}}01\phantom{\rule{4pt}{0ex}}01....$

Then the pairs might be encoded as

$\begin{array}{ccc}11\hfill & \to \hfill & +3\hfill \\ 10\hfill & \to \hfill & +1\hfill \\ 01\hfill & \to \hfill & -1\hfill \\ 00\hfill & \to \hfill & -3\hfill \end{array}$

to produce the symbol sequence

$...00\phantom{\rule{4pt}{0ex}}00\phantom{\rule{4pt}{0ex}}10\phantom{\rule{4pt}{0ex}}11\phantom{\rule{4pt}{0ex}}01\phantom{\rule{4pt}{0ex}}01...\to ...-3,\phantom{\rule{4pt}{0ex}}-3,\phantom{\rule{4pt}{0ex}}+1,\phantom{\rule{4pt}{0ex}}+3\phantom{\rule{4pt}{0ex}},-1,\phantom{\rule{4pt}{0ex}}-1....$

Of course, there are many ways that such a mapping between bits and symbols might be made, and [link] explores one simple alternative called the Gray code.The binary sequence may be grouped in many ways: into triplets for an 8-level signal, intoquadruplets for a 16-level scheme, into “in-phase” and “quadrature” parts for transmission through aquadrature system. The values assigned to the groups ( $±1,±3$ in (8.2)) are called the alphabet of the given system.

Text is commonly encoded using ASCII, and M atlab automatically represents any string file as a list of ASCII numbers.For instance, let str='I am text' be a text string. This can be viewed in its internal form bytyping real(str) , which returns the vector $73\phantom{\rule{4pt}{0ex}}32\phantom{\rule{4pt}{0ex}}97\phantom{\rule{4pt}{0ex}}109\phantom{\rule{4pt}{0ex}}32\phantom{\rule{4pt}{0ex}}116\phantom{\rule{4pt}{0ex}}101\phantom{\rule{4pt}{0ex}}120\phantom{\rule{4pt}{0ex}}116$ , which is the (decimal) ASCII representation of this string.This can be viewed in binary using dec2base(str,2,8) , which returns the binary (base 2) representation of thedecimal numbers, each with 8 digits.

The M atlab function letters2pam.m , provided on the website,changes a text string into the 4-level alphabet $±1,±3$ . Each letter is represented by a sequence of 4 elements, for instance the letter $I$ is $-1\phantom{\rule{4pt}{0ex}}-3\phantom{\rule{4pt}{0ex}}1\phantom{\rule{4pt}{0ex}}-1$ . The function is invoked with the syntax letters2pam(str) . The inverse operation is pam2letters.m . Thus pam2letters(letters2pam(str)) returns the original string.

One complication in the decoding procedure is that the receiver must figure out when the groups begin in order to parse thedigits properly. For example, if the first element of the sequence in [link] was lost, then the message would be mistranslated as

$\begin{array}{ccc}\hfill ...00010110101...& \to & ...00\phantom{\rule{4pt}{0ex}}01\phantom{\rule{4pt}{0ex}}01\phantom{\rule{4pt}{0ex}}10\phantom{\rule{4pt}{0ex}}10...\hfill \\ & \to & ...-3,\phantom{\rule{4pt}{0ex}}-1,\phantom{\rule{4pt}{0ex}}-1,\phantom{\rule{4pt}{0ex}}1,\phantom{\rule{4pt}{0ex}}1,....\hfill \end{array}$

Similar parsing problems occur whenever messages start or stop. For example, if the message consistsof pixel values for a television image, it is important that the decoder be able to determine precisely when the image scan begins. These kinds of synchronization issues are typically handledby sending a special “start of frame” sequence that is known to both the transmitter and the receiver.The decoder then searches for the start sequence, usually using some kind of correlation (pattern matching) technique.This is discussed in detail in "Correlation" .

There are many ways to translate data into binary equivalents. Example  "Bits to Symbols" showed one way to convert text into 4-PAM and then into binary. Another way exploits theM atlab function text2bin.m and its inverse bin2text.m , which use the 7-bit version of the ASCII code (rather than the 8-bit version). This representationis more efficient, since each pair of text letters can be represented by 14 bits (or seven 4-PAM symbols) rather than16 bits (or eight 4-PAM symbols). On the other hand, the 7-bit version can encode only half as many charactersas the 8-bit version. Again, it is important to be able to correctly identify the start of each letterwhen decoding.

The M atlab code in naivecode.m , which is on the website, implements the translation from binary to 4-PAM(and back again) suggested in [link] . Examine the resiliency of this translation to noiseby plotting the number of errors as a function of the noise variance v . What is the largest variance for which no errors occur? At what varianceare the errors near 50%?

how can chip be made from sand
are nano particles real
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
no can't
Lohitha
where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
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
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
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
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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
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