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

[Martin Braun]

On 08/07/2014 03:32 PM, chaitanya wrote:
> 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. 

Ah, so you're using the old OFDM components, I guess. Not what I was
assuming.

What's your UHD version?

>> 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>  

Posting this earlier would have helped. Your rx spectrum is pretty
screwed up at these frequencies. I can't say why, but I'd like to get
the version issues sorted out first.

Also, I recommend using the new OFDM subsystem. Refer to the manual for
details.

Cheers,
Martin


> 
> 
>> 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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> 
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