19 Jun
2009
19 Jun
'09
12:05 a.m.
On Thu, Jun 18, 2009 at 11:58:48PM +0200, Harald Welte wrote:
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.
--
- 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)
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.