19 Jun
2009
19 Jun
'09
9:13 a.m.
On Fri, Jun 19, 2009 at 12:05:47AM +0200, Harald Welte wrote:
On Thu, Jun 18, 2009 at 11:58:48PM +0200, Harald Welte
wrote:
However, what contradicts this is:
The BCCH never gets 'activated', i.e. we just set the 12.21 CHANNEL ATTRIBUTEs
and don't call a 08.58 'ACTIVATE CHANNEL'. 12.21 CHANNEL ATTRIBUTEs
don't
allow us to set any power level. Thus the TS0 should currently be instructed
to transmit at the maximum TRX power.
Since the TRX that carries TS0 cannot employ any power control but has to
operate at constant power, the BTS will have to use the highest power of any
TS on that TRX.
What we could try is to send a 'BS POWER CONTROL' 08.58 message containing a
'BS POWER' IE for TS0 and see if that further reduces the TRX power. I think
especially on the nanoBTS this is desirable, since it's nominal output can not
be reduced to 30mW like we can do for the BS-11 with lmt or bs11_config.
Cheers,
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
On Thu, Jun 18, 2009 at 11:32:55PM +0200, Harald
Welte wrote:
For the BTS I'm still puzzled. For the MS, a power level of 0xf (15) means:
13dBm (19mW) output power in GSM900 and 0dBm (1mW) in GSM1800 - which would
probably work well unless there's actual uplink interference on the respective
channel. If we use the knowledge of the behavior as
described above, we can also deduct:
* the BS-11 is configured to a NM_ATT_RF_MAXPOWR_R of 0, i.e. it will transmit
with the power level that is configured by LMT / ipaccess_config. By default
this is set to 30mW
* the nanoBTS 900 has 20dBm (1800 is 23dBm) TRX output power. bsc_hack is
configured to a NM_ATT_RF_MAXPOWR_R of 12, i.e. 24dB. This means we are
transmitting with a mere -4dBm (398uW) or -1dBm (794uW) which would be _really_
low. So either the nanoBTS are not following specs, or we're really
transmitting something that would barely be possible to receive. Or my
calculations are wrong ;)
I've now also realised that every CHANNEL ACTIVATE message contains a BS power
and MS power IE with 0x0f as value, i.e. another 30dB decrease in initial power
levels. This really makes me suspicious... at levels that low, everything
should never be working. Probably the MS and BTS cannot operate below a
certain level, and thus they choose whatever is the minimum level they support.