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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

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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 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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