# 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

I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
what is the stm
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Rafiq
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Damian
How we are making nano material?
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What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
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Rafiq
what is Nano technology ?
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?
what king of growth are you checking .?
Renato
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Kyle
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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
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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
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How can I make nanorobot?
Lily
how did you get the value of 2000N.What calculations are needed to arrive at it
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