# 0.7 Bits to symbols to signals  (Page 6/8)

 Page 6 / 8

One way that the correlation might fail to find the correct location of the header is if the header string accidently occurredin the data values. If this happened, then the correlation would be as large at the “accidental” location as at the intendedlocation. This becomes increasingly unlikely as the header is made longer, though a longer header also wastes bandwidth.Another way to decrease the likelihood of false hits is to average over several headers.

Rerun correx.m with different length data vectors (try l=100 , r=100 and l=10 , r=10 ). Observe how the location of the peak changes.

Rerun correx.m with different length headers. Does the peak in the correlation become more or less distinct asthe number of terms in the header increases?

Rerun correx.m with different amounts of noise. Try sd=0, .1, .3, .5, 1, 2 . How large can the noise be made if the correlation is still to find the true location of the header?

The code in corrvsconv.m explores the relationship between the correlation and convolution. The convolution of twosequences is essentially the same as the cross-correlation of the time-reversed signal, except that the correlation is padded with extra zeroes.(The M atlab function fliplr carries out the time reversal.) If h is made longer than x , what needs to be changed so that yconv and ycorr remain equal?

h=[1 -1 2 -2 3 -3];                 % define sequence h[k]x=[1 2 3 4 5 6 -5 -4 -3 -2 -1];     % define sequence x[k]yconv=conv(x,h)                     % convolve x[k]*h[k]ycorr=xcorr(h,fliplr(x))            % correlation of flipped x and h corrvsconv.m comparing correlation and convolution (download file) 

## Receive filtering: from signals to symbols

Suppose that a message has been coded into its alphabet, pulse shaped into an analog signal, and transmitted.The receiver must then “un–pulse-shape” the analog signal back into the alphabet, which requires finding wherein the received signal the pulse shapes are located. Correlation can be used to accomplishthis task, because it is effectively the task of locating a known sequence (in this case the sampled pulse shape) within a longersequence (the sampled received signal). This is analogous to the problem of finding the header within thereceived signal, although some of the details have changed. While optimizing this procedure is somewhat involved (and istherefore postponed until Chapter  [link] ), the gist of the method is reasonably straightforward,and is shown by continuing the example begun in pulseshape.m .

The code in recfilt.m below begins by repeating the pulse shaping code from pulseshape.m , using the pulse shape ps defined in the top plot of [link] . This creates an “analog” signal x that is oversampled by a factor $M$ . The receiver begins by correlating the pulse shapewith the received signal, using the xcorr function. Because of the connections between cross-correlation, convolution, and filtering, this process is often called pulse-matched filtering because the impulse response of the filter is matched to the shape of the pulse. After appropriate scaling, this is downsampled to the symbol rate by choosing one out of each $M$ (regularly spaced) samples. These values are then quantized to thenearest element of the alphabet using the function quantalph (which was introduced in Exercise  [link] ). The function quantalph has two vector arguments; the elements of the first vector are quantized to the nearest elementsof the second vector (in this case quantizing z to the nearest elements of $\left[-3,-1,1,3\right]$ ).

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
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
yes that's correct
Professor
I think
Professor
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
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
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
hi
Loga
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
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