modulation/demodulation using VHDL

[chaahatjain]

Hi all,
Can somebody tell me how we implement modulation/demodulation
techniques using VHDL. I am not able to grasp the basic idea of where
to begin. Any help in this matter, or suggestion of books/literature
will be of great help.
Thank You,
Chaahat Jain.

 

[Mike Treseler]

how we implement modulation/demodulation
techniques using VHDL.

Modulation is an analog process so VHDL synthesis is out.
Some VHDL simulators can display integers as analog waveforms.

I am not able to grasp the basic idea of where to begin.

http://www.google.com/search?q=digital+modulation

-- Mike Treseler

 

[jtw]

Is modulation inherently analog? For many types of modulation, you can do
all your waveform creation digitally, up until it enters the
"channel"--which, of course, tends to be analog. If the channel were also
[truely] digital, perhaps we could get zero BER and not need the complex
coding and modulation schemes, our SNR would be so high....

Jason

 

[Jan Panteltje]

Is modulation inherently analog? For many types of modulation, you can do
all your waveform creation digitally, up until it enters the
"channel"--which, of course, tends to be analog. If the channel were also
[truely] digital, perhaps we could get zero BER and not need the complex
coding and modulation schemes, our SNR would be so high....

Jason

Correct, 'modulation' anly implies changing some attribute of a signal.
That could be its frequency, amplitude, phase, ANYTHING.
You could even modulate its spectral noise...
Anything really.
And it can all be done digitally... and if needed converted to analog later.
JP

 

[Ray Andraka]

Really??? Modulation is analog??? Modulation is any changing of
a carrier (which in itself could be a sinusoid, noise or anything
in between) so that it can carry information. Typical radio
modulations (starting with the simple stuff) are phase and/or
amplitude modulation of a sinusoid. Although that was
traditionally done with analog circuits, there is no reason it
can't be done digitally. I've got several papers and projects on
my website referring to modulation/demodulation using FPGAs (which
are all digital). I also refer to a project implementing an
entire short wave receiver using an FPGA, an analog to digital
converter eval board, and a pair of PC speakers. Guess what. The
demodulation is done entirely in the DIGITAL FPGA. OK, so there
is a minimal low pass filter in front of the ADC, but that is the
extent of the analog electronics.

By itself, just asking how to do implement modulation/demodulation
with VHDL is akin to asking "how do I build a house with a
hammer?". VHDL is simply a tool for capturing and expressing your
design. You need to first narrow the problem: what kind of
modulation, what is the information, the data rate, what kind of
data etc.

The key is to not start by asking how to do it with VHDL, rather
the question should be how do I do it with digital hardware,
followed by OK, now how do I express that hardware using VHDL (or
some other design language or method). I suggest you pick up a
good digital communications book (Frerking's Digital Comms book is
IMHO among the best you'll find, and you can find it in the
bookstore on my website--buying it there helps to support the
website). Read and understand it, especially the chapters on
modulation and demodulation. From there, you can start thinking
about the digital design. Block out the design, fill in the
details. Now when you have a circuit pretty well nailed down,
then you can code it with VHDL or whatever other entry method you
desire.

Modulation is an analog process so VHDL synthesis is out.
Some VHDL simulators can display integers as analog waveforms.

http://www.google.com/search?q=digital+modulation

-- Mike Treseler

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email (e-mail address removed)
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
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