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

[Alexander C. <ale...@gm...>]

Gerhard,

As an additional tip - OsmoTRX has an improved signal clipping
detection which can help you understand when you're saturating
receiver with a strong signal from your phone.

Not for the faint of heart - you can enable DEBUG logging level and
see if a transceiver decodes any bursts at all. It may generate A LOT
of output, so be prepared. By default it logs to syslog which can
quickly grow to Gbs in size. There a patch in fairwaves/master branch
not yet merger to master which disables syslog output - you can use
it. Also note, that sometimes osmo-trx detects bursts when there is
none, which is ok and is not a bug.

On Thu, Sep 10, 2015 at 6:33 PM, Tom Tsou <tom...@et...> wrote:
> 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
>
> ------------------------------------------------------------------------------
> Monitor Your Dynamic Infrastructure at Any Scale With Datadog!
> Get real-time metrics from all of your servers, apps and tools
> in one place.
> SourceForge users - Click here to start your Free Trial of Datadog now!
> http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140
> _______________________________________________
> Openbts-discuss mailing list
> Ope...@li...
> https://lists.sourceforge.net/lists/listinfo/openbts-discuss



-- 
Regards,
Alexander Chemeris.
CEO, Fairwaves, Inc.
https://fairwaves.co

Subscribe to Fairwaves news: http://eepurl.com/baL_pf