[USRP-users] N210 + new WBX v3 daughterboard does not work, but with old WBX v2 it works (OpenBTS)

Tom Tsou tom at tsou.cc
Thu Sep 25 13:45:02 EDT 2014


On Thu, Sep 25, 2014 at 4:31 AM, Martin via USRP-users
<usrp-users at lists.ettus.com> wrote:
> I seem to have found the problem.
> I had to lower the rxgain dramaticly.
>
> With old WBX v2 an  rxgain of 47 would work fine. Even with phones as close
> as 1.5 meter from the USRP receive antenna.
> With WBX v3 I had to lower the rxgain to 10 to get it to work at this
> distance.

I can't explain the exact differences between WBX v2 and v3 and the
effect on handling different GSM signal levels, but I will say that
the default OpenBTS configuration can cause handsets to RACH at high
power levels. Depending on the operating band and device class, the
initial power level can be in excess of 30 dBm. During testing I've
measured RACH bursts through an antenna at levels around 10 dBm. With
receive gain at maximum, this is a bad combination.

Some device combinations might work better than others in the
max-rx-gain/max-tx-gain case. But, it doesn't surprise me that any
device combination might, at some point, become unpredictable in this
scenario.

  -TT




More information about the USRP-users mailing list