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Re: [Discuss-gnuradio] OFDM TRANSFER and RECEIVE IN GRC


From: chaitanya
Subject: Re: [Discuss-gnuradio] OFDM TRANSFER and RECEIVE IN GRC
Date: Thu, 7 Aug 2014 06:32:07 -0700 (PDT)

Hi Marcus

Thanks for reply

>Your GRCs don't work for me. With which version of GNU Radio were they
built? 
one is version 3.6.5.1 and the other one is version 3.7.2.1.
I think the device addr in usrp sink and source should be changed.And also
the file path in file sink and source should be changed according to ur
system. 


>Thinking about this, that was a bad question from my side.
>Since the ofdm_mod doesn't even *know* about the center frequency, the
>signal generated digitally is always the same, so you can only be
>looking at the rx side's abs(FFT).

yeah,at rx side only

>Would be nice if you had a description of what happens or a screenshot
uploaded somewhere! 

These are the screen shots of FFT at 2.45GHz and 2.455GHz center
frequencies.
2_45GHz.png <http://gnuradio.4.n7.nabble.com/file/n49851/2_45GHz.png>  
2_455GHz.png <http://gnuradio.4.n7.nabble.com/file/n49851/2_455GHz.png>  

These are the screen shots of FFT at 2.452GHz and 2.454GHz center
frequencies.

2_452GHz.png <http://gnuradio.4.n7.nabble.com/file/n49851/2_452GHz.png>  
2_454GHz.png <http://gnuradio.4.n7.nabble.com/file/n49851/2_454GHz.png>  


>Ok, you're seeing frequency selective behaviour. This can happen for a
>myriad of reasons, among these interference and multipath propagation.
>You're excluding interference as a reason on an ISM band, so I presume
>you're working with a direct cable between tx and rx or in an anechoic
>chamber; thus multipath can't be the reason, either.

No , I am not working with a cable between tx and  rx or not in an anechoic
chamber.But I can say there is no interference (as on ISM band) because when
I run the benchmark_tx.py and benchmark_rx.py files ,then most of the
packets are being received (i.e, n_right value is near to n_rcvd ) even at
2.452 and 2.454GHz center frequencies.  

chaitanya



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