Thank you for your reply and for the information, Marcus.
In my setup, there are :
- 2 base stations : one b210, one x310
- 1 UE : one b210
So in OAI there is a procedure at UE side that checks for downlink offset
around a specified carrier frequency before attaching to base station.
Base stations are asked to transmit around a carrier at 2.68Ghz
When using internal clock source, UE detects an offset of :
- roughly -5.3kHz around 2.68GHz for x310 base station;
- roughly +0.9kHz around 2.68GHz for b210 base station
When using my external clock source, UE detects an offset of :
- roughly -54kHz around 2.68GHz for x310 base station;
- roughly +20kHz around 2.68GHz for b210 base station
When I sent the email yesterday, UE wasn't checking offset more than |10kHz| so
this is why it wasn't detecting base stations broadcasts.
You said that " the internal clocks are already pretty good" so I had the idea
that if mine is less good, then offset would likely be further than when using
internal clock. And it seems to be the case.
Thank you for the hint.
Now, UE cannot attach to base station, basically it doesn't decode anything
except synchronisation signals and MIB. I think it is because of the poor
quality clock.
Do you think that using the Ettus OctoClock-G can enable base station time
synchronisation while reducing carrier offset and without breaking everything
as my poor clock does?
Thank you again.
Regards,
Rodolphe
-----Message d'origine-----
De : USRP-users <usrp-users-boun...@lists.ettus.com> De la part de Marcus D.
Leech via USRP-users
Envoyé : lundi 7 décembre 2020 18:35
À : usrp-users@lists.ettus.com
Objet : Re: [USRP-users] b210 and x310 synchronisation from non-GPSDO external
clock
On 12/07/2020 11:24 AM, BERTOLINI Rodolphe via USRP-users wrote:
> Dear all,
>
> I put both mailing list (OAI and USRP) because both may have something to do
> with my problem. I apologize if it is not appropriate.
>
> I would like to synchronize a b210 and an x310 using a square signal
> generated by a function generator. It has a 10MHz ref output, so I generate a
> 1Hz square clock through a regular front output.
> Except the output voltage, is there something I should care about ? I use
> them with OAI, and they both are used as LTE base stations. When the base
> station is on external ref, UE doesn't detect the base station. When the base
> station is on internal ref, UE detects base station broadcasts and connects
> to the base station.
>
> Note 1 : PPS and REF are well detected by the USRP, when I change for example
> PPS frequency, x310 led changes respectively.
> Note 2 : only one USRP is used at the same time, I want to make it
> work first with only one base stations, and then when base stations are both
> on and synchronised Note 3 : in OAI code, there is something like :
>
> usrp_master_clock = 30.72e6;
> args += boost::str(boost::format(",master_clock_rate=%f") %
> usrp_master_clock); args += ",num_send_frames=256,num_recv_frames=256,
> send_frame_size=7680, recv_frame_size=7680" ;
>
> Is this master clock related to the sampling rate, or should it be changed to
> 10MHz?
The master clock rate is related to the available sampling rates, and not the
external reference frequency, which is 10MHz. The B210 is
quite flexible in its master clock rate, but the X310 is much more limited
in the master-clock rates it supports.
>
> Note 4 : I looked at the spectrum of signal sent by base station, I
> don't see any difference between the setup with external clock and the
> setup with internal clock
Unless you have your spectrum analyser set-up for very-fine resolution, you
likely won't see much difference--the internal clocks are
already pretty good.
>
> Any pointer would be much appreciated
> Thank you.
>
> Regards,
> Rodolphe
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> USRP-users@lists.ettus.com
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