Discussion:
Question about ms max power parameter.
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Philipp Fabian Benedikt Maier
2013-04-09 20:55:04 UTC
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Hi Folks.

I have a simple and straight forward question:

in the openbsc.cfg i find a parameter "ms max power" which is set to 15
dBm (apporox 30mW) by default.

http://openbsc.osmocom.org/trac/wiki/osmo-nitb_VTY says the following:
"maximum transmit power (in dBm) to be used by MS in this BTS. This is
used in the System Information on the BCCH as well as for the MS power
level at the time a dedicated channel is activated."

My question is how low may i set ms max power level? Is 15dBm already
the lowest possible minimum or can i set it down to 1dBm if i like?

regards
Philipp
dexter
2013-04-09 20:57:38 UTC
Permalink
Hi Folks.

I have a simple and straight forward question:

in the openbsc.cfg i find a parameter "ms max power" which is set to 15
dBm (apporox 30mW) by default.

http://openbsc.osmocom.org/trac/wiki/osmo-nitb_VTY says the following:
"maximum transmit power (in dBm) to be used by MS in this BTS. This is
used in the System Information on the BCCH as well as for the MS power
level at the time a dedicated channel is activated."

My question is how low may i set ms max power level? Is 15dBm already
the lowest possible minimum or can i set it down to 1dBm if i like?

regards
Philipp
Alexander Huemer
2013-04-09 21:54:32 UTC
Permalink
Hi,
Post by Philipp Fabian Benedikt Maier
in the openbsc.cfg i find a parameter "ms max power" which is set to
15 dBm (apporox 30mW) by default.
http://openbsc.osmocom.org/trac/wiki/osmo-nitb_VTY says the
following: "maximum transmit power (in dBm) to be used by MS in this
BTS. This is used in the System Information on the BCCH as well as
for the MS power level at the time a dedicated channel is
activated."
My question is how low may i set ms max power level? Is 15dBm
already the lowest possible minimum or can i set it down to 1dBm if
i like?
I'd say it's 0..40.

Kind regards,
-Alexander Huemer

[?] http://openbsc.osmocom.org/trac/wiki/osmo-nitb_VTY#msmaxpower0-40
[?] http://cgit.osmocom.org/openbsc/tree/openbsc/src/libbsc/bsc_vty.c#n1934
Alexander Huemer
2013-04-09 22:12:10 UTC
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Andreas Eversberg
2013-04-10 20:20:25 UTC
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Post by Philipp Fabian Benedikt Maier
My question is how low may i set ms max power level? Is 15dBm already
the lowest possible minimum or can i set it down to 1dBm if i like?
hi,

set ms max power to 0 to get 1 milliwatts to start with (rach and
initial power). set it to 30 to get 1 watts (1800) or 33 to get 2 watts
(900). during dedicated channel, it is up to the bts to change the power
level up or down, depending on the uplink level/quality.

regards,

andreas
Sergey V. Efimov
2013-04-10 21:13:39 UTC
Permalink
Hello Andreas,

Does this setting has linear dependence? Or is there something like a calibration table for max_power_red value?

Thanks,
Sergey.
My question is how low may i set ms max power level? Is 15dBm already the lowest possible minimum or can i set it down to 1dBm if i like?
hi,
set ms max power to 0 to get 1 milliwatts to start with (rach and initial power). set it to 30 to get 1 watts (1800) or 33 to get 2 watts (900). during dedicated channel, it is up to the bts to change the power level up or down, depending on the uplink level/quality.
regards,
andreas
dexter
2013-04-11 18:57:56 UTC
Permalink
Hi Sergey
Post by Sergey V. Efimov
Does this setting has linear dependence? Or is there something like a calibration table for max_power_red value?
I think i can answer this (please correct my if i am wrong). To my
understanding "nominal power" is the maximum power the BTS is capable to
transmit. In the case of the nanoBTS it is 23dBm which is about 200mW.
So the "nominal power" is the calibration value you asked for.

The "max_power_red" value is the setting for the actual output power. In
my case it has been set to 20dBm. This should result in an output power
of 23dBm-20dBm=3dBm=ca. 2mW. This is the default setting. I do not know
if it is the lowest possible setting. I transmit into a dummyload anyway
which results into a cell radius of approx 1m.

The dBm scale is not linear, just look it up yourself It's easy ;-)

regards.
Philipp
Harald Welte
2013-04-11 20:55:21 UTC
Permalink
Dear Sergey,
Post by Sergey V. Efimov
Does this setting has linear dependence? Or is there something like a
calibration table for max_power_red value?
dB values are never linear, they're logarithmic. dBm is vs. Power.

The value is the absolute tranmission power of the MS (uplink) in dBm.
It has nothing to do with max_power_red, whcih is about the relative
reduction of downlink transmit power respective to the nominal transmit
power of the BTS in downlink.

The values are all specified in the relevant GSM specs.
--
- Harald Welte <laforge at gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
dexter
2013-04-11 18:41:06 UTC
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Hello Andreas,
Post by Andreas Eversberg
set ms max power to 0 to get 1 milliwatts to start with (rach and
initial power). set it to 30 to get 1 watts (1800) or 33 to get 2
watts (900). during dedicated channel, it is up to the bts to change
the power level up or down, depending on the uplink level/quality.
Thank you very much for your hint. I have set it to 0 dBm now and it
works fine. I have my phones directly next to the BTS so i think it will
not raise the power above 1 or 2 mW.

regards.
Philipp
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