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Re: [Discuss-gnuradio] Synchronizing N210 TX and RX channels

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] Synchronizing N210 TX and RX channels
Date: Tue, 22 Jul 2014 22:14:37 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

Hi Daniele,

your problem is actually harder: The latency of digital signal
processing depends on your desired decimation, and analog signal latency
depends on a ton of factors like target RF frequency, adjustable filters
(if your daughterboard has something like this), antenna and cabling
delay, and so on.
The only real way to know is to *measure* the roundtrip for each
configuration, and that's exactly what echotimer is for.

With best regards,

On 22.07.2014 19:25, Daniele Nicolodi wrote:
> Hello Stephan,
> thank for your reply.  What I would like to do is more simple than that:
> I need to synchronize tx and rx of the same USRP, not of two different
> devices.  But I need continuous streaming and not burst.
> Any help in this direction is much appreciated.
> Thanks. Best,
> Daniele
> On 22/07/2014 19:14, Stefan Wunsch wrote:
>> Hey Daniele,
>> I have done the radar toolbox and implemented a synced USRP interface
>> (USRP Echotimer).
>> You are right, the USRP Echotimer does align the timestamps of the TX/RX
>> commands on both USRPs. But if you connect them by MIMO, the time and
>> clock are pretty good in sync. Therefore I think the Echotimer can
>> provide a sync with an accuracy of at least +- 1 sample. Check out [0]
>> for a video of the sync. There is also a sync setup for testing
>> (gr-radar/examples/usrp). Unfortunately the documentation is not
>> finished yet.
>> But care: The Echotimer bursts only a packet in sync, it does not stream
>> the whole time! The packet is defined by a tagged stream.
>> Greetings,
>> Stefan
>> [0]
>> https://grradar.wordpress.com/2014/06/17/synchronisation-echotimer-usrp-interface/
>> Am 22.07.2014 18:40, schrieb Daniele Nicolodi:
>>> On 22/07/2014 18:18, Martin Braun wrote:
>>>> On top of what Marcus' has said,
>>>> the gr-radar toolbox might be helpful. It has a block that takes a
>>>> tagged stream, and outputs a signal it acquired synchronously to the
>>>> transmitted one.
>>> Thanks Martin.  This seems to imply that there is no way to actually
>>> synchronize the hardware, and that the synchronization can only be done
>>> in software aligning the timestamps of the two streams. Is that the case?
>>> Thanks. Cheers,
>>> Daniele
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