Re: [Openbts-discuss] OpenBTS 5.0 + USRP B200

[Tom T. <tom...@et...>]

On Thu, Sep 10, 2015 at 8:02 PM, Gerhard <ope...@gk...> wrote:
> I'm struggling to get OpenBTS 5.0 with an USRP B200 to work. After I
> have build, installed and run OpenBTS, all I get is the network showing
> up on my Android device. When I try to connect to it, it fails (even
> with open registration enabled). There are no hints in the logfiles. The
> "tmsis"-table stays empty.

Likely case is RACH bursts being missed.

Can you give OsmoTRX a try as a replacement for OpenBTS transceiver?
Note the section on compatibility with OpenBTS.

http://openbsc.osmocom.org/trac/wiki/OsmoTRX

> Another mail said that the internal clock of the B200 is way to bad for
> using it with OpenBTS.[2] Is that so? How can I find out, if the clock
> is causing the issues?

Typically, but not always, If the handset is able to detect the
network, then clocking is sufficient for test calls other basic
services.

> The OpenBTS book and several other sources state to set "rxgain" to 0-10
> for USRP devices. However, Matt Ettus said (regarding the gain of a
> B200) via the USRP-users mailing list: "0dB of gain is unusably low. You
> should be using at least 40dB unless there is a very strong signal."
> What value should I use?

The point of confusion is that gain ranges vary across different USRP
devices. For example, gain range on the RFIC based B200 is roughly
0-75 dB while the range on X300 with UBX daughterboard is 0-30 dB. The
OpenBTS book assumes a range closer to the latter, which ends up in
the low to middle part of the range.

40 dB on RFIC is close to mid-level, which is a reasonable starting
point. With GSM handsets we are dealing high transmit power levels, so
lowering the Rx gain at close range makes sense. Setting gain down to
0 dB is excessive and typically reserved for directly coupled use
cases (i.e. not OTA).

> My setup is
> * Ubuntu 12.04.05 LTS Server (32 bit)
> * OpenBTS 5.0 ($ ./switchto.sh 5.0)
> * USRP B200 (no external clock)
> * UHD 003.009.000
> * No Antennas attached (Phone is next to the USRP)

Nothing abnormal. Attaching antenna(s) with lowered gain settings is
recommended over raw SMA connectors for consistency. Also check
logging for anything unusual; INFO logging level is fine.

  -TT