Bug #1617 CBCH implementation for osmo-bts-trx

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Harald Welte laforge at gnumonks.org
Fri Apr 6 08:59:05 UTC 2018


Hi Antony,

On Fri, Apr 06, 2018 at 10:36:06AM +0200, Antony Lemmens wrote:
> I have read articles about the superframe mechanism but I do not figure out
> how to advertise the CBCH functionality on the BCCH, 

The Osmocom stack should take care of this "automatically" if
the osmo-bts-trx low-level code gets the required support.

As you may have seen, CBCH operation is already supported with several other
BTS back-ends inside osmo-bts.  Unfortunately, for osmo-bts-trx nobody has
been contributing the related code so far.

> nor how to adapt the scheduler to enable the CB channel.

This boils down to the tables in osmo-bts/src/scheduler_mframe.c where
you can e.g. find "static const struct trx_sched_frame frame_bcch[51]"
which defines the 51-multiframe for the non-combined BCCH and "static
const struct trx_sched_frame frame_bcch_sdcch4[102]" for the combined
BCCH, as well as "static const struct trx_sched_frame frame_sdcch8"

AFAIR, the BCCH can be on a combined BCCH or on a SDCCH/8.  You would
have to create copies of "frame_bcch_sdcch4" and "frame_sdcch8" and edit
those copies to confirm with the way how the respective multiframe is
specified when CBCH is enabled.  As far as I remember from memory, it's
always the second sub-channel that's replaced with CBCH instead of
SDCCH.  See the related specs, I think mostly 3GPP TS 45.002

> Is it someone also interrested in this and/or working on the Bug 1617?

I'm interested but seriously have no time to work on this.  At sysmocm
we could work on it as a development project under contract, but we also
have quite a backlog so it might be best if somebody else works on this.

> Or is it someone that can me give a track to start the implementation?

My notes above should help with implementing it.

-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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