GNU Radio OFDM Theori

GNU Radio
1

Hi every one,
i would like to know how the OFDM Library in GNU Radio is being
constructed?
what is the theory? can any body help me? Thank you very much…

adib

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2

On Wed, Mar 25, 2009 at 02:15:35AM -0700, adib_sairi wrote:

Hi every one,
i would like to know how the OFDM Library in GNU Radio is being constructed?
what is the theory? can any body help me? Thank you very much…

Assuming you understand the theory behind OFDM in general, a good place
to look is gnuradio-examples/python/ofdm/benchmark* code. You can run
the examples with a flag ‘–log’, which will dump the streams after most
intermediate steps into separate .dat-files for you to inspect.
These examples use the ‘ofdm’ python module, its source is in
gnuradio-core/src/python/gnuradio/ofdm.py. This contains a complete flow
graph starting with a message queue which takes bits ending in a I/Q
sample stream and vice versa.

Should you know nothing about OFDM, I recommend not trying to figure it
out from the GNU Radio code, but to read up on the theory first. OFDM is
covered in most of the standard books on digital wireless communication.

Have fun,
MB

3

Thank you Martin. but is there any detail on how OFDM in GNU Radio is
constructed like the documentation for FM recv …in FM recv they explain
detail on how they construct the code… what is the reson for each line
and
what references that they used… so in OFDM GNU Radio is there any
documentation like this? i thought bob is the leader for the GNU Radio
OFDM
project (if i am not mistaken)… so bob or any body, can you please help
me?
thank you…

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4

On Wed, Mar 25, 2009 at 06:47:52PM -0700, adib_sairi wrote:

Thank you Martin. but is there any detail on how OFDM in GNU Radio is
constructed like the documentation for FM recv …in FM recv they explain
detail on how they construct the code… what is the reson for each line and
what references that they used… so in OFDM GNU Radio is there any
documentation like this? i thought bob is the leader for the GNU Radio OFDM
project (if i am not mistaken)… so bob or any body, can you please help me?
thank you…

There is no documentation of that type for OFDM.

Eric

5

adib_sairi wrote:

for OFDM), can i just edit the ofdm benchmark python file? or i have to go
in detail until the IFFT and FFT? the OFDM that GNU Radio have currently i
think it already have the CP (cyclic prefix) right? eric can you please tell
me how the IFFT and FFT is being constructed? or how the OFDM is being made
in GNU Radio? what references they use?

To change the modulation per subcarrier is going to require reworking
gr_ofdm_mapper_bcv.cc.

Tom

6

Eric B. wrote:

There is no documentation of that type for OFDM.

Eric

if i want to reconfigure the modulation for each sub-carrier (bit
loading
for OFDM), can i just edit the ofdm benchmark python file? or i have to
go
in detail until the IFFT and FFT? the OFDM that GNU Radio have currently
i
think it already have the CP (cyclic prefix) right? eric can you please
tell
me how the IFFT and FFT is being constructed? or how the OFDM is being
made
in GNU Radio? what references they use?

i found this presentation slide (
http://www.nabble.com/file/p22735812/gr_ofdm.rar gr_ofdm.rar )… i hope
it
is usefull for those who are working in the same area as me. but i think
this meterial is not enough … so any body had more documentation please
help me… thank you.

–
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7

Martin B.-3 wrote:

Should you know nothing about OFDM, I recommend not trying to figure it
out from the GNU Radio code, but to read up on the theory first. OFDM is
covered in most of the standard books on digital wireless communication.

I try the benchmark_ofdm_* in the ofdm example (gnuradio trunk v10991)
but
unfortunately i always receive no data and TIMEOUT. did i need to modify
somewhere in the code? is there any ofdm example in any trunk version
that
work? thanks

adib

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8

adib_sairi wrote:

for OFDM), can i just edit the ofdm benchmark python file? or i have to go
in detail until the IFFT and FFT? the OFDM that GNU Radio have currently i
think it already have the CP (cyclic prefix) right? eric can you please tell
me how the IFFT and FFT is being constructed? or how the OFDM is being made
in GNU Radio? what references they use?

To change the modulation per subcarrier is going to require reworking
gr_ofdm_mapper_bcv.cc.

Tom