"Osmo-USRP": combining OpenBTS and Osmocom

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Thomas Cooper tacooper at vt.edu
Mon Mar 19 18:27:28 UTC 2012


Hey all,
I've been working on connecting OpenBTS and osmo-bts ever since Harald
formed the openbts-osmo repo
(http://cgit.osmocom.org/cgit/openbts-osmo) and left me with a nice
muxer framework and L1-L2 separation. I've named it Osmo-USRP but you
can call it openbts-osmo or TrueBTS or whatever; it's not a big deal.
Unfortunately I'm running short on time for completing my MS research,
so testing is nowhere near complete but I figured I'd let the public
users help me out a bit here if they want to try it out. Many thanks
to Tom Tsou for helping me weed out bugs and test too.

I've only scratched the surface of testing it with USRP1, USRP2,
single vs. multiple PCs (Ubuntu and Fedora), and multiple BTSs. I've
been able to get a stable network of 1 and 2 BTSs across 2 PCs with
multiple MSs camped, and voice calls and SMS working. There seem to be
a few fickle and unknown issues depending on which PC/Linux
flavors/time of day I tested, and of course sometimes it will work for
a certain MS but not another. Sometimes MSs won't location update to
the network, or will hit errors when establishing a call; in the usual
case, this won't even free the TCH so if resources run out the BTS
must be rebooted. Just a few issues to name here, and I'm sure there
are more out there.

The current focus of work (when I can find time) is implementing
handover between cells. I'm not even sure if osmo-bts and OpenBTS
contain all the supporting functionality for handover (OpenBSC does
though). The MSs correctly send SACCH meas reports, the BSC detects
and decides to handover, and the TCH is activated, but I think the
Handover Command is getting lost in the BTS or the MS Handover Accept
bursts are being processed. The newly activated osmo-bts instance
segfaults somewhere in LAPDm. I haven't had time lately to pinpoint
the error, but just wanted to update on the current status of that.

Also, multiple configuration files are needed because I have network
parameters hard-coded (just for ease), which is elaborated some in the
wiki. I ran into a segfault/bug trying to implement passing in config
parameters from OpenBSC, and gave up to pursue more critical aspects
of the project.

Github repo:
https://github.com/tacooper
(first release tag for Osmo-USRP = v0.1)

README/Guide:
https://github.com/tacooper/Osmo-USRP/downloads
(issues, configuration, and example setup for single/multi-BTS networks)

If you'd like to help out by testing or even working on this project,
it is much appreciated, even if only to help me grow my understanding
of GSM networks through discussion.

Thanks!
Tom Cooper




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