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Re: [Discuss-gnuradio] OFDM receiver on USRP2

From: Guanbo
Subject: Re: [Discuss-gnuradio] OFDM receiver on USRP2
Date: Wed, 12 Jan 2011 16:37:16 -0800 (PST)

Hi, Tom

I am not quite understand the ofdm_sync_xx.cc in python/gnuradio/blks2impl/.

What is the difference between frequency synchronization and carrier
frequency offset. 
Why we have to do the timing and frequency synchronization before it?



Tom Rondeau wrote:
> On Tue, Feb 16, 2010 at 5:45 PM, Srinivas <address@hidden> wrote:
>> Matt,
>> Thanks for verifying the data rate calculation!
>> I tried the other solutions that you suggested, namely,
>> - increasing the data rate by a factor of 2 or 4
>> It works.
>> - modifying the OFDM code to widen the search range - How do I widen the
>> search range ?
>> Should I be looking in the "ofdm_sync_" blocks in "blks2impl" folder ? If
>> yes, which synchronizer is currently used with ofdm_examples ?
> You need to add an argument to gr.ofdm_frame_acquisition in
> ofdm_receiver.py (in python/gnuradio/blks2impl).
> In the current Git master, this is located on line 109 of
> ofdm_receiver.py. After the "ks[0]" argument, you can put in an
> integer. This is the maximum number of bins the receiver will search
> over for correlation. It defaults to 10.
>> - locking the usrps to a common reference
>> My usrp2s are located wide apart so I guess this solution is not
>> practical.
>> Besides, this confirms that the problem is somewhere in the USRP2 board,
>> right ? (as I tried swapping the daughter cards & firmware with the
>> working
>> pair)
>> Thanks,
>> Srinivas
> Nope, this is typical of radio hardware. They are always off
> frequency. If two oscillators are off frequency and then multiplied up
> to another frequency, the difference will also be magnified. So a 2.4
> GHz board will have a larger frequency offset than if you ran it just
> through the BasicTx/Rx boards (even though the ratios should be the
> same).
> Tom
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> Discuss-gnuradio mailing list
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