Forum: GNU Radio Synchronize USRP in which level

Hi,
My last topic "Synchronize multiple USRP-N210s"may be a big one which
gives no reply.If I want to synchronize two USRPs without cable or
GPSDO,I should design a synchronization protocol.Simply A sends some
time-stamped samples to B ,then B record local time when receiving these
samples.Knowing the distance between them,we can synchronize B with
A.Apparently the synchronization accuracy depend on we make the
timestamps in which level.Ethernet involve in 10s of microseconds jitter
shows that we should do it on FPGA.Does UHD have this function?
Any comments will be valuable to me.
Thanks.

On 01/30/2013 09:00 PM, Gong Zhang wrote:
> Thanks.
Start here, you can do this with plain UHD in C++ or with the gnuradio
gr-uhd component in python or C++:
http://code.ettus.com/redmine/ettus/projects/uhd/wiki

The sync docs should explain just about everything:
http://files.ettus.com/uhd_docs/manual/html/sync.html

Many examples of timed transmission and reception:
http://code.ettus.com/redmine/ettus/projects/uhd/w...

Awesome project/use case for these features:
https://github.com/jmalsbury/pre-cog/wiki

-josh

2013/1/31 11:51, Josh Blum wrote: On 01/30/2013 09:00 PM, Gong Zhang 
wrote:
>> Thanks.
> Awesome project/use case for these features:
> https://github.com/jmalsbury/pre-cog/wiki
>
> -josh
My target is to sample signal at the same time with two USRP connected
to different PCs placed in different place.The sync accuracy should be
within microsecond.I can not use cable and GPSDO,which gives no external
sync signal such as PPS.The only way maybe sync their local time,which
is usually unsynchronized due to the instability of oscillator.So I need
a time-stamp exchange based sync protocol.
Thank you for your time.

On 01/31/2013 12:54 AM, Gong Zhang wrote:
>>> Any comments will be valuable to me.
>>
> Thank you for your time.
Sounds feasible. Suppose you did something simple like a synchronization
pulse. Send out a pulse that all devices could detect. Record the time
the pulse was detected at each device to establish an absolute time
amongst the devices.

The precog project does stuff like this for the frequency hopping and
TDMA engines to sync up the time windows for transmission and hopping,
etc... https://github.com/jmalsbury/pre-cog/wiki

-josh