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[Discuss-gnuradio] OFDM-Code: DC-Carriers and ofdm_mapper
From: |
Martin Braun |
Subject: |
[Discuss-gnuradio] OFDM-Code: DC-Carriers and ofdm_mapper |
Date: |
Fri, 19 Dec 2008 18:26:39 +0100 |
User-agent: |
Mutt/1.5.16 (2007-06-09) |
Hi,
I'm currently trying to get a hang of the OFDM-internals and I'm stuck
in gr_ofdm_mapper_bcv. I hope someone might be able to enlighten me...
First of all, how exactly does gr_ofdm_mapper_bcv decide which carriers
are used? I really, really hate having to ask this kind of question when
I have the source code right here, but - with all respect to the
authors - I find some of the code pretty obscure.
Say I want to use an IFFT length of 16 (for academic reasons). A call
like
gr.ofdm_mapper_bcv(constellation, 2, oc, 16)
will always throw an exception unless oc is 14 or 16. Using 8
subcarriers should not be a problem physically? What's the rule of
possible combinations of FFT-length occupied carriers?
Next, I noticed that the DC carrier(s) are left unused. Logically, this
should happen in gr_ofdm_mapper_bcv, but I can't really find where.
However, this is slightly confusing: say you set options.occupied in
ofdm_mod to 200, then what you really get are 198 occupied subcarriers,
or am I mistaken?
By the way, why can't I use try:except to catch an instance of
'std::invalid_argument'? Is this a SWIG-problem?
Thanks for any insight you may have!
Cheers,
MB
--
Dipl.-Ing. Martin Braun Phone: +49-(0)721-608 3790
Institut fuer Nachrichtentechnik Fax: +49-(0)721-608 6071
Universitaet Karlsruhe (TH) http://www.int.uni-karlsruhe.de/
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