<< Chapter < Page Chapter >> Page >
Explains what happens in constellation mapping in DMT.

Constellation mapping

In the constellation mapping process, length B segments of the bitstreams are assigned a single complex value in a constellation . This is similar to quadrature ampliture modulation (QAM), because the IFFT of these complex points maps to various sinusoids with amplitudes proportional to the real part and phase shifts proportional to the complex part. We mostly used 2-bit (4 point) and 4-bit (16 point) constellations in our system, but we also coded a function that generates a mapping with an arbitrary number of points. In comparison, constellations used in actual DMT systems can have as many as 240 points. Important characteristics of these constellations include the area occupied by the points and the spacing between points. The power neccessary to transmit the actual signal is proportional to the area, so it is key not to let the points be too far apart. However, the channel introduces noise which results in the constellation points being recieved with error. If the points are too close together, it is impossible to correctly match the received points with the correct value in the constellation. We implemented constellation mapping with a home-cooked parser: it would examine every 2 or 4 bits (depending on the mapping), look up the current segment in a table and assign the next element in a new vector the corresponding constellation point.

4-bit constellation mapping

Got questions? Get instant answers now!
16-point mapping
Bit Sequence Value Bit Sequence Value
0000 .354+.354j 1000 1
0001 .707 1001 .707+.707j
0010 .707j 1010 j
0011 -.354+.354j 1011 -.707+.707j
0100 -.707j 1100 -1
0101 .354-.354j 1101 -.707-.707j
0110 -.354-.354j 1110 -j
0111 -.707 1111 .707-.707j

16-point constellation

This is the 16-point constellation we used. It is an approximation of the V.29 16-QAM constellation (4 amplitudes, 8 phases).

Our related MATLAB functions: constmap.m , deconstmap.m

Home | Previous: Implementation | Next: Mirror/IFFT, De-Mirror/FFT

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
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
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
absolutely yes
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
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, Ece 301 projects fall 2003. OpenStax CNX. Jan 22, 2004 Download for free at http://cnx.org/content/col10223/1.5
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Ece 301 projects fall 2003' conversation and receive update notifications?