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Re: [Discuss-gnuradio] OFDM Implementation

From: sumitstop
Subject: Re: [Discuss-gnuradio] OFDM Implementation
Date: Sun, 11 Sep 2011 07:02:00 -0700 (PDT)

go to the directory /usr/local/bin
there u will find benchmark files for ofdm (both transmission and reception)
u need to type benchmark_ofdm_rx.py -h
and benchmark_ofdm_tx.py -h

these will show you the parameters u can play with.

after that u can run these files by typing ./benchmark_ofdm_tx.py -f
<frequency appropriate to ur daughter board>
and ./benchmark_ofdm_rx.py -f <frequency appropriate to ur daughter board>

also there may be drift in the center frequency of the daughter board so u
can do one thing. first run the transmitter part and see on the spectrum
analyzer for the center frequency of the ofdm signal.

after that run the receiver part with that center frequency specified in the
now run the transmitter again with the same frequency.

if u get timeouts then u need to play with the receiver gain and transmitter
amplitude as well as the receiver center frequency.

u can change the bandwidth of the ofdm signal by changing the no of occupied
tones or fft length because bw = occupied tones/ fft length

let me know ur results.


waqasme wrote:
> hello sumit,
> yah i have replaced the GMSK modulator and demodulator with OFDM modulator
> and demaodulator. but i coudlnot find message source , ,message sink,
> probe signal and probe avg mag 2 with only input .. the one i have found
> has input and output as well for probe avg mag 2 block... i couldnot able
> to find these blocks as in the simple tranceiver diagram example they used
> these blocks... can you plesase guide me where to get these blocks? 
> Also you mentioned this command ( benchmark_ofdm.py -h )   is that a
> command or what? because i have entered this command in terminal window
> but it says command not found? and if i type in google to search it opens
> a c ++ code ..what i am suppose to do with that. ?? please tell me how to
> use this benchmark_ofdm.py code.. where to put this code to make the
> simulation work. i am very new to GNU radio so i have no idea what
> functions i can play with and how to implement this. please guide me  like
> how to make this OFDM tranmission and reception  via USRP.  iam using
> Linux Ubuntu maveric and GNU Radio companion 3.2.2 version... I really
> appriciate your help because i have only few time left for my Masters
> project. Thanks in advance i am looking forward to hear from you.
> Regards,
> Waq.
> sumitstop wrote:
>> http://pwnhome.files.wordpress.com/2011/04/simple_transceiver1.png
>> 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
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