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The problem of reducing the sensitivity to noise is addressed in [link] using the idea of linear block codes , which cluster a number of symbols together, and then add extra bits.A simple example is the (binary) parity check, which adds an extra bit to each character. If there are aneven number of ones then a 1 is added, and if there are an odd number of ones, a 0 is added.The receiver can always detect that a single error has occurred by counting the number of 1's received.If the sum is even, then an error has occurred, while if the sum is odd then no single error can have occurred.More sophisticated versions can not only detect errors, but can also correct them.

Like good equalization and proper synchronization, coding is an essential part of the operation of digital receivers.

A telecommunication system

The complete system diagram, including the digital receiver that will be built in this text, is shown in [link] . This system includes the following:

  • A source coding that reduces the redundancy of the message.
  • An error coding that allows detection and/or correction of errors that may occur during the transmission.
  • A message sequence of T -spaced symbols drawn from a finite alphabet.
  • Pulse shaping of the message, designed (in part) to conserve bandwidth.
  • Analog upconversion to the carrier frequency (within specified tolerance).
  • Channel distortion of transmitted signal.
  • Summation with other FDM users, channel noise, and other interferers.
  • Analog downconversion to intermediate frequency (including bandpass prefiltering aroundthe desired segment of the FDM passband).
  • A/D impulse sampling (preceded by antialiasing filter) at a rate of 1 T s with arbitrary start time. The sampling rate is assumed to be at least asfast as the symbol rate 1 T .
  • Downconversion to baseband (requiring carrier phase and frequency synchronization).
  • Lowpass (or pulse-shape-matched) filtering for the suppression of out-of-band users and channel noise.
  • Downsampling with timing adjustment to T -spaced symbol estimates.
  • Equalization filtering to combat intersymbol interference and narrowband interferers.
  • Decision device quantizing soft decision outputs of equalizer to nearest memberof the source alphabet (i.e. the hard decision).
  • Source and error decoders.

Of course, permutations and variations of this system are possible, but we believe that [link] captures the essence of many modern transmission systems.

Stairway to radio

The path taken by Software Receiver Design is to break down the telecommunication system into its constituent elements:the modulators and demodulators, the samplers and filters, the coders and decoders.In the various tasks within each chapter, you are asked to build a simulation of therelevant piece of the system. In the early chapters, the parts need to operate onlyin a pristine, idealized environment, but as we delve deeper into the onion, impairments and noises inevitablyintrude. The design evolves to handle the increasingly realistic scenarios.

Throughout this text, we ask you to consider a variety of small questions, some of which aremathematical in nature, most of which are “what if” questions best answered by trial and simulation.We hope that this combination of reflection and activity will be a useful in enlarging your understandingand in training your intuition.

For further reading

There are many books about various aspects of communication systems. Here are some of our favorites.Three basic texts that utilize probability from the outset, and that also pay substantial attention to pragmatic design issues(such as synchronization) are the following:

[1] J. B. Anderson, Digital Transmission Engineering,IEEE Press, 1999. [2]J. G. Proakis and M. Salehi, Communication Systems Engineering, Prentice Hall, 1994. [This textalso has a Matlab-based companion, Introduction to Communication Systems Using Matlab, Brooks-ColePubs., 1999.] [3]S. Haykin, Communication Systems, 4th edition, John Wiley and Sons, 2001.Three introductory texts that delay the introduction of probability until the latter chapters are the following:[4] L. W. Couch III, Digital and Analog CommunicationSystems, 6th edition, Prentice Hall, 2001. [5]B. P. Lathi, Modern Digital and Analog Communica- tion Systems, 3rd edition, Oxford University Press, 1998.[6] F. G. Stremler, Introduction to CommunicationSystems, 3rd edition, Addison Wesley, 1990. These final three references are probably the mostcompatible with Software Receiver Design in terms of the assumed mathematical background.

Questions & Answers

how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
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or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
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Embra Reply
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ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
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J, combine like terms 7x-4y
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Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
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. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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Cied
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Porter
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Yasmin
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Cesar
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what is system testing?
AMJAD
preparation of nanomaterial
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
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AMJAD
what is system testing
AMJAD
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Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
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Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
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Source:  OpenStax, Software receiver design. OpenStax CNX. Aug 13, 2013 Download for free at http://cnx.org/content/col11510/1.3
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