Re: [Discuss-gnuradio] GNU Radio Conference 2011

[Tom Rondeau]

On Tue, Aug 30, 2011 at 9:23 AM, Tuan (Johnny) Ta <address@hidden> wrote:
> Scott,
> I thought the frequency offset should be taken care of by the receiver
> synchronization? The 802.11 NIC don't have external reference but they can
> still sync to the AP.
> Thank you,
> Johnny

The standards will specify the frequency offsets required for a system
to work. With the USRPs, the accuracy of the crystal oscillators is 20
ppm (I forget the numbers for the USRP2, but I think the accuracy is
about the same while the stability is better). Most standards require
a much smaller possible offset in their frequencies (0.1 - 1 ppm in
some), so that the maximum possible frequency offset is known and
accounted for in the standard. From there, yes, the waveform
synchronizations are enough.

For large frequency offsets, there are a handful of coarse frequency
correction algorithms out there, or you could measure the difference
and compensate for it, but that's not scalable. Most things shouldn't
require an external clock, though, even though a highly accurate
reference would solve these issues.

Tom


> On Tue, Aug 30, 2011 at 9:04 AM, Scott Johnston <address@hidden>
> wrote:
>>
>> If you are having frequency offset problems, you need to synchronize the
>> USRPs with an external reference, i.e. a GPS receiver.
>>
>> Scott
>>
>> Tuan (Johnny) Ta wrote:
>>>
>>> Martin,
>>>
>>> Thanks for the suggestion! I think it's a good idea. I remember having a
>>> lot of problems with the OFDM receiver. The frequency offset between the 2
>>> oscillators screwed things up. Looking around, I don't think this issue has
>>> been resolved. Correct me if I'm wrong.
>>>
>>> Thank you,
>>> Johnny
>>>
>>> On Tue, Aug 30, 2011 at 3:25 AM, Martin Braun <address@hidden
>>> <mailto:address@hidden>> wrote:
>>>
>>>    On Mon, Aug 29, 2011 at 11:19:39PM -0400, Tuan (Johnny) Ta wrote:
>>>
>>>    Hi everyone,
>>>
>>>    I actually think doing something *with* GNU Radio is the more
>>>    interesting part, at least at the beginning. How about you start
>>>    writing
>>>    a receiver for your favourite comms standard?
>>>
>>>    That way, you can start with a fairly simple environment, use a lot of
>>>    code templates and concentrate on what you already know.
>>>
>>>    Once you start doing that, you will inevitably end up with something
>>>    that annoys you, something you feel is inefficient or whatever. Then
>>>    you've got something to discuss about at the conference :)
>>>
>>>    MB
>>>    --
>>>    Karlsruhe Institute of Technology (KIT)
>>>    Communications Engineering Lab (CEL)
>>>
>>>    Dipl.-Ing. Martin Braun
>>>    Research Associate
>>>
>>>    Kaiserstraße 12
>>>    Building 05.01
>>>    76131 Karlsruhe
>>>
>>>    Phone: +49 721 608-43790 <tel:%2B49%20721%20608-43790>
>>>    Fax: +49 721 608-46071 <tel:%2B49%20721%20608-46071>
>>>    www.cel.kit.edu <http://www.cel.kit.edu>
>>>
>>>    KIT -- University of the State of Baden-Württemberg and
>>>    National Laboratory of the Helmholtz Association
>>>
>>>
>>>    _______________________________________________
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>>>
>>>
>
>
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