19 Jun
2009
19 Jun
'09
12:22 a.m.
On Thu, Jun 18, 2009 at 11:32:55PM +0200, Harald Welte wrote:
12.21 also specifies a 'RF max power
reduction' value in 9.4.47. This element
can be sent as part of 'SET RADIO CARRIER ATTRIBUTE'. The value in this IE is
the 'Pn' value of 08.58. The Scale is 2dB steps, and the maximum value is 255,
so there can be a maximum value of 512dB.
08.58 defines Pn as the 'nominal power level', i.e. the level that is not yet
reduced by dynamic power control.
As I've now figured, the 'RF max power reduction' element seems to be marked
as
read-only, i.e. the BSC is not allowed to change it. This means that I was
probably reading the specs the wrong way earlier.
It's also weird that all the A-bis traces that I've seen actually try to set
that attribute (without any error message).
So if it was read-only, it might well be that this is only indicating the
'maximum possible power reduction', i.e. the limit you can specify for the
'BS
power level' IE in the CHANNEL ACTIVATION or other messages.
If we once again combine this with our knowledge, i.e.
BS-11 30mW 15dBm
BS-11 80mW 19dBm
BS-11 250mW 24dBm
BS-11 2W 33dBm
nanoBTS 900 20dBm
nanoBTS 1800 23dBm
And we set the BS power level in channel activation as 0xf (i.e. -30dB),then
we get something like -15dBm for BS-11/30mW and -10/-7dBm for the nanoBTS.
That would still be _very_ low.
05.05 Chapter 4.1.2 tells us that a BTS has to support at least six levels of
2dB each power reduction, i.e. -12dB is the minimum it has to support.
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
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