# 0.7 Bits to symbols to signals  (Page 7/8)

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If all has gone well, the quantized output mprime should be identical to the original message string.The function pam2letters.m rebuilds the message from the received signal. The final line of the programcalculates how many symbol errors have occurred (how many of the $±1,±3$ differ between the message m and the reconstructed message mprime ).

% first run pulseshape.m to create x y=xcorr(x,ps);                     % correlate pulse with received signalz=y(N*M:M:N*M)/(pow(ps)*M);       % downsample to symbol rate and normalize mprime=quantalph(z,[-3,-1,1,3])';  % quantize to +/-1 and +/-3 alphabet pam2letters(mprime)               % reconstruct messagesum(abs(sign(mprime-m)))          % calculate number of errors recfilt.m undo pulse shaping using correlation (download file) 

In essence, pulseshape.m is a transmitter, and recfilt.m is the corresponding receiver. Many of the details of this simulation can be changedand the message will still arrive intact. The following exercises encourage exploration of some of the options.

Other pulse shapes may be used. Try

1. a sinusoidal shaped pulse ps=sin(0.1*pi*(0:M-1));
2. a sinusoidal shaped pulse ps=cos(0.1*pi*(0:M-1));
3. a rectangular pulse shape ps=ones(1,M);

What happens if the pulse shape used at the transmitter differs from the pulse shape used at the receiver? Try using theoriginal pulse shape from pulseshape.m at the transmitter, but using

1. ps=sin(0.1*pi*(0:M-1)); at the receiver. What percentage errors occur?
2. ps=cos(0.1*pi*(0:M-1)); at the receiver. What percentage errors occur?

The received signal may not always arrive at the receiver unchanged. Simulate a noisy channelby including the command before the xcorr command in recfilt.m . What percentage errors occur? What happens as you increase or decrease the amount ofnoise (by changing the 1.0 to a larger or smaller number)?

## Frame synchronization: from symbols to bits

In many communication systems, the data in the transmitted signal is separated into chunks called frames.In order to correctly decode the text at the receiver, it is necessary to locate the boundary (the start) of each chunk.This was done by fiat in the receiver of recfilt.m by correctly indexing into the received signal y . Since this starting point will not generally be known beforehand,it must somehow be located. This is an ideal job for correlation and a marker sequence.

The marker is a set of predefined symbols embedded at some specified location within eachframe. The receiver can locate the marker by cross-correlating it with the incoming signal stream.What makes a good marker sequence? This section shows that not all markers are created equally.

Consider the binary data sequence

$...+1,-1,+1,+1,-1,-1,-1,+1,\mathcal{M},+1,-1,+1,...,$

where the marker $\mathcal{M}$ is used to indicate a frame transition. A seven-symbol marker is to be used.Consider two candidates:

• marker A: $1,\phantom{\rule{4pt}{0ex}}1,\phantom{\rule{4pt}{0ex}}1,\phantom{\rule{4pt}{0ex}}1,\phantom{\rule{4pt}{0ex}}1,\phantom{\rule{4pt}{0ex}}1,\phantom{\rule{4pt}{0ex}}1$
• marker B: $1,\phantom{\rule{4pt}{0ex}}1,\phantom{\rule{4pt}{0ex}}1,\phantom{\rule{4pt}{0ex}}-1,\phantom{\rule{4pt}{0ex}}-1,\phantom{\rule{4pt}{0ex}}1,\phantom{\rule{4pt}{0ex}}-1$

The correlation of the signal with each of the markers can be performed as indicated in [link] .

For marker A, correlation corresponds to a simple sum of the last seven values.Starting at the location of the seventh value available to us in the data sequence (two data points before the marker), marker A producesthe sequence

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
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?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
how did you get the value of 2000N.What calculations are needed to arrive at it
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