<< Chapter < Page Chapter >> Page >
... 000010110101 ... ... 00 00 10 11 01 01 ... .

Then the pairs might be encoded as

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

to produce the symbol sequence

... 00 00 10 11 01 01 ... ... - 3 , - 3 , + 1 , + 3 , - 1 , - 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 32 97 109 32 116 101 120 116 , 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 - 3 1 - 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

... 00010110101 ... ... 00 01 01 10 10 ... ... - 3 , - 1 , - 1 , 1 , 1 , ... .

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%?

Questions & Answers

Application of nanotechnology in medicine
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.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
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?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
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
what is Nano technology ?
Bob Reply
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?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Software receiver design. OpenStax CNX. Aug 13, 2013 Download for free at http://cnx.org/content/col11510/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Software receiver design' conversation and receive update notifications?

Ask
Rylee Minllic
Start Quiz
Subramanian Divya
Start Quiz
Caitlyn Gobble
Start Exam