Hi Ivan,
On Wed, Nov 11, 2020 at 01:26:01AM +0300, Ivan Babanov wrote:
After it we tried to use default config from master
branch initially
created for RBS-2308.
It worked pretty fine except RF Power which was configured as 41dBm and 41
- 12 = 29 dBm. Value 29 was not acceptable for our RBS.
I checked with Ericsson BSC Doc and found that our RBS2206 has max RF
output 47dBm for DCS1800. (btw, RBS2308 has only 34dBm max output according
to the same document, maybe config needs to be corrected)
feel free to send a patch.
Looks like internal oscillator is not ready. So, the
question is how to
make internal oscillator synchronized? Could it be an E1 Sync stability
issue caused by Digium cards?
The question is not "could". Any BTS always needs a proper, stable
reference clock. So unless your BTS has a built-in GPS clock refrence (and that
reference is configured/enabled), your E1 will have to provide a stable clock
reference.
"stable" means (likely) fulfilling a clock stability that is _at the very least_
the
stability of what commercial TDM/ISDN networks used to have. It doesn't hurt to have
better stability.
Any crystal oscillator on any E1/T1 peripheral card (digium or not) is by far not stable
enough, possibly up to 1000 times worse than required.
1. Set Digium card to get Sync from RBS. Now Digium is
configured for
Internal clocking and acts as master. Maybe in case when both sides will be
configured to get sync from E1 it will decrease difference between internal
clock of RBS and E1 and RBS will get Synced state.
And what would that get you to? In the end, a BTS that transmits at a frequency that
will likely be so far off that you have serious problems connecting phones to it.
2. Theoretically I can try to use Nokia DX200 BSC as a
clock master for
Digium and deliver sync to RBS from Digium. I'm not sure if timing accuracy
is the same for Nokia and Ericsson HW.
Sure, that should work. You can use any proper clock reference. One option I'm
using
here is to use a SIU-02. It has a 1PPS input for GPS, and it clocks up to 16 E1/T1
interfaces with that clock. You can then feed that clock signal to one port of your
multi-port Digium card, and configure that as clock source, and the other ports will
use that clock when talking to your BTSs.
One more question is where can I find some info about
timing accuracy for
BTS and any possible way to check it on the existing E1 line?
You would have to use some kind of test equipment that has a much more accurate/stable
clock itself, like a rubidium oscillator or a GPS-DO. And then you can
try to measure the Allan deviation/variance. But why do that? It's
obvious that a normal crystal oscillator is way insufficient, no need to
measure it.
--
- Harald Welte <laforge(a)osmocom.org>
http://laforge.gnumonks.org/
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