<< Chapter < Page Chapter >> Page >
- 1 , - 1 , 1 , 1 , 1 , 3 , 5 , 7 , 7 , 7 , 5 , 5 .

For marker B, starting at the same point in the data sequence and performing the associated moving weighted sum, produces

1 , 1 , 3 , - 1 , - 5 , - 1 , - 1 , 1 , 7 , - 1 , 1 , - 3 .

With the two correlator output sequences shown, started two values prior to the start of the seven-symbol marker, we want theflag indicating a frame start to occur with point number 9 in the correlator sequences shown.Clearly, the correlator output for marker B has a much sharper peak at its ninthvalue than the correlator output of marker A. This should enhance the robustness of the use of marker Brelative to that of marker A against the unavoidable presence of noise.

The binary signal from Equation 8 is shown with a seven symbol embedded marker m_1, m_2, ..., m_7. The process of correlation multiples successive elements of the signal by the marker, and sums. The marker shifts to the right and the process repeats. The sum is largest when the marker is aligned with itself because all the terms are positive, as shown in the bottom part of the diagram. Thus the shift with the largest correlation sum points towards the embedded marker in the data sequence. Correlation can often be useful even when the data is noisy.
The binary signal from [link] is shown with a seven symbol embedded marker m 1 , m 2 , . . . , m 7 . The process of correlation multiples successive elementsof the signal by the marker, and sums. The marker shifts to the right and the process repeats. The sum is largest when the marker is aligned with itselfbecause all the terms are positive, as shown in the bottom part of the diagram. Thus the shift with the largest correlation sum pointstowards the embedded marker in the data sequence. Correlation can often be useful even when the data is noisy.

Marker B is a “maximum-length pseudonoise (PN)” sequence. One property of a maximum-length PN sequence { c i } of plus and minus ones is that its autocorrelation is quite peaked:

R c ( k ) = 1 N n = 0 N - 1 c n c n + k = 1 , k = N - 1 N , k N .

Another technique that involves the chunking of data and the need to locate boundaries between chunksis called scrambling . Scrambling is used to “whiten” a message sequence(to make its spectrum flatter) by decorrelating the message.The transmitter and receiver agree on a binary scrambling sequence s that is repeated over and over to form a periodic string S that is the same size as the message. S is then added (using modulo 2 arithmetic) bit by bit to the message m at the transmitter, and then S is added bit by bit again at the receiver.Since both 1 + 1 = 0 and 0 + 0 = 0 ,

m + S + S = m

and the message is recaptured after the two summing operations.The scrambling sequence must be aligned so that the additions at the receiver correspond to theappropriate additions at the transmitter. The alignment can be accomplishedusing correlation.

Redo the example of this section, using M atlab .

Add a channel with impulse response 1 , 0 , 0 , a , 0 , 0 , 0 , b to this example. (Convolve the impulse response of the channel with the data sequence.)

  1. For a = 0 . 1 and b = 0 . 4 , how does the channel change the likelihood that the correlation correctly locatesthe marker? Try using both markers A and  B .
  2. Answer the same question for a = 0 . 5 and b = 0 . 9 .
  3. Answer the same question for a = 1 . 2 and b = 0 . 4 .

Generate a long sequence of binary random data with the marker embedded every 25 points. Check that marker Ais less robust (on average) than marker B by counting the number of times marker A misses the frame start comparedwith the number of times marker B misses the frame start.

Create your own marker sequence, and repeat the previous problem. Can you find one that does better thanmarker B?

Use the 4-PAM alphabet with symbols ± 1 , ± 3 . Create a marker sequence, and embed it in a long sequenceof random 4-PAM data. Check to make sure it is possible to correctly locate the markers.

Add a channel with impulse response 1 , 0 , 0 , a , 0 , 0 , 0 , b to this 4-PAM example.

  1. For a = 0 . 1 and b = 0 . 4 , how does the channel change the likelihood that the correlation correctly locatesthe marker?
  2. Answer the same question for a = 0 . 5 and b = 0 . 9 .

Choose a binary scrambling sequence s that is 17 bits long. Create a message that is 170 bits long, andscramble it using bit-by-bit mod 2 addition.

  1. Assuming the receiver knows where the scrambling begins, add s to the scrambled data and verify that the output is the same as the original message.
  2. Embed a marker sequence in your message. Use correlation to find the marker and toautomatically align the start of the scrambling.

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
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
Brian Reply
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?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
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 ?
Bob Reply
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?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
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?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
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
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Software receiver design. OpenStax CNX. Aug 13, 2013 Download for free at http://cnx.org/content/col11510/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Software receiver design' conversation and receive update notifications?

Ask