Re: [Discuss-gnuradio] OFDM on USRP2

[Tom Rondeau]

On Mon, Jan 17, 2011 at 2:48 PM, Josh Blum <address@hidden> wrote:
>
>
> On 01/17/2011 11:31 AM, Veljko Pejovic wrote:
>> Hi,
>>
>> I updated the OFDM example. You can find it at
>> http://www.cs.ucsb.edu/~veljko/downloads/ofdm_example.tar.gz
>>
>> It supports both USRPs and the UHD driver. I get pretty bad
>> performance with UHD receiver for some reason. Any ideas?
>>
>
> For the UHD performance issue, which model usrp? The following applies
> to usrp2:
>
> Was the bad performance on a transmit + receive application? There was
> an issue where if receive was not keeping up, the transmit flow control
> could be hampered; this is fixed on next branch.
>
> Or was it receive only? And in any case did UHD print and warnings about
> buffer sizes? Because it needs sysctl permission to allocate a large
> enough receive buffer.
>
> -josh


I found issues with the UHD code in setting the sample rates. When you
set the sample rate, the best thing to do is ask the UHD device what
the real sample rate it was actually set to. I then use a PFB arb
resampler to adjust to the actual sample rate that I want.

I was playing around with some FM signals and found that I couldn't
get anything clean out until I did this, even though I was setting
what I thought was a standard sample rate (that is, an integer
decimation of the clock) to my N210. What I asked for and what I set
were only off by a little bit, but it makes a huge difference in
performance for FM signals.

That said, we should be adjusting for this in the OFDM code, but it's
something to keep in mind.

Tom


>>
>> Cheers,
>>
>>
>> Veljko
>>
>>
>> On Tue, Jan 11, 2011 at 9:26 PM, Guanbo <address@hidden> wrote:
>>>
>>> Hi,
>>>
>>> I was looking for the source codes through the list.
>>> And I got one from Veljko from UCSB, who are very nice to share his codes,
>>> "ofdm_example.tar.gz"
>>> The codes are attached.
>>> Given the enough gain in TX and RX, you can see the output result at RX.
>>>
>>> Guanbo
>>> http://old.nabble.com/file/p30650478/ofdm_example.zip ofdm_example.zip
>>>
>>>
>>> mrahaim wrote:
>>>>
>>>>
>>>> Hi all,
>>>>
>>>> Does anyone know of any updated OFDM benchmark code that is modified to
>>>> be run on a USRP2?  I have seen previous posts of this, however the
>>>> link to the updated code is no longer available.
>>>>
>>>> Thanks,
>>>>
>>>> Michael Rahaim
>>>> Graduate Research Assistant
>>>> Smart Lighting Engineering Research Center
>>>> Boston University
>>>> address@hidden
>>>>
>>>>
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>>>>
>>>>
>>>
>>> --
>>> View this message in context: 
>>> http://old.nabble.com/OFDM-on-USRP2-tp30638994p30650478.html
>>> Sent from the GnuRadio mailing list archive at Nabble.com.
>>>
>>>
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