USRP2 and OsmoTRX

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Alexander Huemer alexander.huemer at xx.vu
Mon Jan 15 13:46:30 UTC 2018


Hi!

On Mon, Jan 15, 2018 at 10:07:50AM -0200, Rafael Diniz wrote:

> I'm doing some tests with an old USRP2 + RF900 daughterboard, and I get
> a very unstable system (with osmo-trx, osmo-bts-trx and osmo-nitb) -
> some phones can connect, some dont. I'd like to identify the problem -
> is it a bad GBit ethernet or the lack of a GPSDO connected to the 10MHz
> port?

According to [1] the clock accuracy of the USRP2 is 20ppm.
GSM 05.10[2] states that accuracy has to be 0.05ppm or better.
That's quite a bit off, so I don't think it's surprising that you don't 
see much stability.
I believe it makes a difference whether the MSs see other BTSs or not.
If the MSs see only the unstable BTS it is more likely to work out.
Not sure what is the case here.

> And after some time, osmo-trx stops reading samples from UHD and
> osmo-bts-trx shuts down.

Not sure if that is a possible effect of an unstable clock. I could 
imagine so, but again, I am not sure.

I guess the obvious advice is to attach a more stable clock and try 
again.

Kind regards,
-Alex

[1] http://openbts.org/w/index.php?title=Ettus_Research_USRP
[2] http://www.etsi.org/deliver/etsi_gts/05/0510/05.00.00_60/gsmts_0510v050000p.pdf
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