This is something I raised a year ago or so. I have been learned that
the very reason to use ofdm is
that the "next" carrier is located on the "previous" and the "nextnext"
NULL, i.e. there is a minimum
"right there", and that given imperfect filtering, with the integer
relation between carrier spacing
and baud rate do 2) below. Net effect, still in MY head, is that you
could either increase signalling
to 75 baud, or squeeze carriers together. Now, signalling at 75 baud
instead of 50, will burden
us CPU-wise, since all maths done in 20 mS must now be done in 13.33 mS.
I guess the answer probably
lies in 3).
One more very interested...
Gullik
On 06/05/2013 10:16 PM, Frank Palazzolo wrote:
Well, at this point I'm still experimenting, and I'm really focused on
providing the best possible HF modem for FreeDV. Of course, if I come
up with something that can be used elsewhere, all the better. Most of
the OFDM stuff has really complex synchronization and a lot of bits
per symbol. I'm starting from the FDMDV philosophy where things are a
lot simpler - for example, a single, stationary carrier for easy and
fast time and frequency sync. I doubt my implementation will end up
anywhere near as complex as the DRM stuff, for example.
The questions I am trying to answer are:
1) Will the orthogonality of the OFDM carriers be degraded
significantly by the HF channel, compared to FDM?
2) If not, can we take advantage of that spectrum 'between the
carriers' that FDMDV is not using?
3) If we keep a symbol rate of 50Hz with a carrier spacing of 75Hz,
this is equivalent to a 6.67ms guard band. Will having this guard
band in time rather than spacing between carriers be more robust to
multipath?
These questions are all very interesting to me, even if the FDMDV
modem turns out to be ideal.
-Frank
On Wed, Jun 5, 2013 at 10:52 AM, Karel Fassotte
<[email protected] <mailto:[email protected]>> wrote:
hello Frank,
I am not a programmer bur very interested in a windows application
for the OFDM modem, not necesarly Codec2 integrated.
Just a OFDM modem for SW with an easy Gui in windows for data
transmissions. Idealy I want be capable to run ip traffic through
the modem. Speed should be autobaud and 4800bs,
3600bs,2400bs,1200bs,600bs,
300bs. Do you have any material or perhaps something running?
Thanks
73
Karel
HC1AKP
PE2KFA
2013/6/5 Frank Palazzolo <[email protected]
<mailto:[email protected]>>
So, I've done some experimenting with an OFDM modem
implementation in Octave. I still think the idea has a lot of
promise, so and I've decided it's time to try to build codec2
and FreeDV.
Codec2-dev was no big deal, as it has no dependancies. I
didn't have trouble getting the mingw/MSYS toolchain going.
For FreeDV, I spent a lot of time bringing in each dependant
package one at a time and trying to build or integrate them.
I ended up getting surprised and stuck with ctb, since it
seems to not want to build in the the mingw environment, due
to slash conventions in the makefile. (even if it is ok on
Linux). Has anyone made this work on mingw?
Now I've come to realize that maybe I should have started with
cmake. Will that make it all easier? Does the cmake build
work on mingw ok?
This may be blasphemy, but when all is said and done, I am
tempted to put together a set of project files for devstudio
2010 and binaries for everything but codec2 and freedv. I
think this would make it a lot easier for developers on
windows to get their feet wet without going through a long
startup process. Nothing kills incentive like having to spend
a bunch of time building third party stuff...
Thanks,
Frank
NQ8N
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