# 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 $\left[-3,-1,1,3\right]$ ).

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
Got questions? Join the online conversation and get instant answers!