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This module shows the results and conclusions for our DMT project.


In order to test our DMT system, we investigated how the probability of bit error changed with the signal-to-noise ratio of the transmitted signal in our channel. In particular, we compared how these PE - SNR curves changed as the cyclic pad length was varied. As a comparison, we also looked at how DMT stacked up with a simple model of single-carrier modulation in these same regards.

Dmt vs single - carrier (sc)

We ran our tests of the system with the following constraints:

  • Bitstream length: 512
  • Block-size: 128 (DMT), 1 (SC)
  • AWGN amplitude: .00001 - 1
  • Channel impulse response length: 1 (wire), 16
  • Cyclic prefix length (DMT): 0, 8, 16
  • Impulse noise: 0
  • Constellation size: 16-point
The results of our tests were as expected. For wire channel, SC and DMT were comparable. They both demonstrated a Q-function behavior, dropping to zero error once the SNR was high enough and leveling off to about 0.5 (i.e. a coin flip) for very low SNR. For impulse response length L less than cyclic prefix C , DMT dropped to a error fell from 0.5 as SNR increased, but leveled off once ISI began to have a more prominent effect. Single-carrier also demonstrated this same behavior, though there was no cyclic prefix involved. This was a little strange, but this project's goal was to study DMT, not SC. Once the cyclic pad length was larger than the impulse response length, DMT again displayed Q-function behavior as ISI was no longer a problem.

L = 1

This is shows how bit error probabilities compare for DMT (red) and SC (blue) with a wire channel impulse response (length L = 1).


This is shows how bit error probabilities compare for DMT (red) and SC (blue) with a length L = 16 channel impulse response and a DMT cyclic prefix of length C = 8.


This is shows how bit error probabilities compare for DMT (red) and SC (blue) with a length L = 16 channel impulse response and a DMT cyclic prefix of length C = 16.


From our results and experience implementing our DMT system, we reached the following conclusions:

  • It is possible to implement a working DMT system in MATLAB. It looks as though a more complicated extension of the system, possibly involving variable frequency allocation, a time-varying channel freq. response, more complicated constellations or a transmitter-receiver synchronization process, should also be quite feasible.
  • DMT's advantages over other modulation schemes are difficult to see with such a simple system; they would be more apparent in a system including a more realistic model of data assignment to the various frequencies (instead of evenly distributing all data over the first 256).
  • The need for a cyclic prefix is readily verifiable; as soon as the prefix length is correct, bit error drops to zero at high SNR.
  • Communications engineering and DSP are fun (except when you have to stay up all night writing connexions modules)! Looking forward to 431 next semester!

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Questions & Answers

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.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
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Source:  OpenStax, Ece 301 projects fall 2003. OpenStax CNX. Jan 22, 2004 Download for free at http://cnx.org/content/col10223/1.5
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