BS-11 power measurement results

[Dieter Spaar]

Hello Harald,

On Sat, 20 Jun 2009 10:02:17 +0200, "Harald Welte" <laforge at gnumonks.org> wrote:
> 
> Do you get an error message (SET ATTRIBUTE NACK) if you try to set it?

I have not looked at the response, but LMT says "unrecognized value"
or something like that if I query the TRX attributes. The BS-11 seems
to use "6" if something larger than 6 is sent. The nanoBTS 1800 however
does not start if an invalid value for NM_ATT_RF_MAXPOWR_R is sent,
the green LED is just blinking.

> According to the spec, 6 steps of 2dB is the minimum a BTS has to support.

Yes, and looking at the test report of the BS-11 seems to indicate that
there are 15 steps possible for dynamic adjustment (probably used only
if BTS power control is enabled).

> sure.  Also, the BTS is 12 years old...

I think the power of the BS-11 is still rather accurate, someone
else (you know him) with much better measurment equippment has
confired a while ago that the maximum power of the BS-11 is very
accurate. Anyway, 3 dB more or less is not really a problem for
our purpose.

> MS power control (the dynamic adjustment of MS power) should be used even now,
> otherwise I would not understand my observation of the phone bursts becoming
> much lesss loud in the speakers after the initial few very loud bursts.

I can only report the results of a short test. According to LMT, the
MS power control is currently disabled when bsc_hack is used (at least
the version I use). If I enable it and additionally enable the whole
power control of the BS-11, I can see that the MS power is changed.
I guess the same is true for the BS power.

> What would be more interesting to me than dynamic BS power control is:
> How do the 'BS POWER' IE's in the ACTIVATE CHANNEL and 'BS POWER CONTROL'
> messages affect the BS transmit power.
> 
> Some things to confirm:
> 
> 1) whatever we use as BS POWER value in ACTIVATE CHANNEL on a TCH/SDCCH8
>    on the C0 does not make any changes to the acutal TX power

Difficult to measure for me with the current setup (ARFCN of the
traffic channel is the same as the BCCH channel). To find out if the
BS power of the traffic channel is modified, I have to switch to a
different ARFCN for traffic.

> 2) if we activate a channel on the second TRX, do we see the BTS power
>    adjusted according to BS POWER in ACTIVATE CHANNEL ?

Does bsc_hack already support the second TRX ?

> 3) if we use a BS POWER CONTROL message on the CCCH on C0 of an otherwise idle
>    BTS, do we see a power change on the TRX ?

I can only measure it if I switch the ARFCN to a different channel than
used by the BCCH. I don't think the BTS will modify the BCCH power.

Best regards,
  Dieter
-- 
Dieter Spaar, Germany                           spaar at mirider.augusta.de