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Re: [Discuss-gnuradio] OFDM Implementation

From: Tuan (Johnny) Ta
Subject: Re: [Discuss-gnuradio] OFDM Implementation
Date: Fri, 9 Sep 2011 19:26:48 -0400

As far as I know there's no open source code for an OFDM transceiver available. I was trying to build one half a year back but wasn't successful before I had to move on to something else. The benchmark_ofdm code will give you a simplex OFDM system. Ie you can run the transmitter on 1 USRP and receiver on another. 

Ie. run this on 1 USRP
./benchmark_ofdm_tx.py -f 2.412G

And this on the other
./benchmark_ofdm_rx.py -f 2.412G

The value of the frequency depends on the daughterboards you're using. If you're using USRP1 make sure the decimation rate is 1/2 of the interpolation rate as the ADC is 2 times faster than the DAC on the USRP1 (or the other way around, you should chek that).

Watch out for the frequency offset, it killed the system for me. If the above doesn't work, run the transmitter on 1 USRP and usrp_fft.py on the other. Check the center frequency of the FFT plot and manually adjust the receiver center frequency. I used the RFX2400 boards and the offset for me was ~ 40kHz.

Good luck,

On Fri, Sep 9, 2011 at 2:30 AM, sumitstop <address@hidden> wrote:

see carefully....... it has a gmsk modulator in the bottom.u can make the
bottom modulator part in another pc

benchmark programs are quite good to start with...
u can type benchmark_ofdm.py -h to see all the parameters u can play with.

waqasme wrote:
> And sorry to mention in the last mail that i will be suing USRP 1 .
> waqasme wrote:
>> Hi Sumit,
>> Thank you so much for your quick response. yah i understand what your
>> saying and i am trying to understand this document but it doesnot help
>> much . As you mentioned use the same Tranceiver setup and only replace
>> OFDM blocks with that. My question is in this basic tranciver diagram the
>> used two UHD's source and sink and in the middle they use GMSK
>> Demodulator right. but they didnot use any modulator any where in the
>> design. Now i am confused what blocks i have to replace with OFDM
>> blocks??? Please try to explain in bit detail so i can design it properly
>> .
>> OR you mentioned other option that use benchmark_OFDM.py file . Somebody
>> already told me about this benchmark file. but its just C++ code . i am
>> quite new to GNU radio and dont know much about the functions how it
>> works.
>> Please let me know how to use that benchmark_OFDM.py file in order to
>> make the simulation design? do i have to download the file or what? how
>> it works ?? let me know if you know about the process how to compile and
>> run that code in GNU radio.
>> Thanks for ur help and support really appriciate that...
>> Regards,
>> Waqas.
>> sumitstop wrote:
>>> Try to understand these
>>> http://pwnhome.wordpress.com/2011/04/26/intro-to-gnuradio-and-the-usrp-part-5-simple-transceiver/
>>> here u need to put those ofdm blocks .. thats it.... also go through
>>> some modifications as written in umit,
>>> http://pwnhome.wordpress.com/2011/04/19/intro-to-gnuradio-and-the-usrp-part-4/
>>> or else work with benchmark_ofdm.py  its very easy.. :)
>>> may i know what daughter boards do you have...
>>> waqasme wrote:
>>>> Hello sumit,
>>>> Thanks for your help i went through that document that you refered to,
>>>> and i tried to implement that OFDM transmitter part. This document only
>>>> explain about OFDM flow graph or transmitter. Is there any other
>>>> document or information related to OFDM modulator and demodulator
>>>> (Transceiver)? i haver to implement OFDM transmission and reception via
>>>> USRP. i will really appriciate if you can help me that or someone else
>>>> who knows how to implement by using GNU radio companion.
>>>> Thanks in advance.
>>>> Regards,
>>>> Waq.

Sumit Kr.
Research Assistant
Communication Research center
IIIT Hyderabad
View this message in context: http://old.nabble.com/OFDM-Implementation-tp32380874p32429184.html
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