[CUWiN-Dev] Transmit power control / RSS measurement

[Jeongkeun Lee]

> On Thu, Apr 27, 2006 at 03:16:55PM -0500, Paul Smith wrote:
> > David Young wrote:
> >
> > >Transmit power is controlled by these sysctls,
> > >
> > >hw.ath0.tpscale = 0
> > >hw.ath0.tpc = 0
> > >hw.ath0.tpack = 63
> > >hw.ath0.tpcts = 63
> >
> > So, just to ask the naive question, if you, say, turn on TPC, with:
> >
> > $ sysctl -w hw.ath0.tpc=1
> >
> > then you can turn the other knobs and have coarsed-grain (i.e., not
> > at the packet-level) control over the power output of the device? And
> > this currently works? What values should I feed to these sysctls if
> > say I wanted to make my radio quieter in a lab space?
> 
> I'm not sure.  Documentation is lacking in NetBSD.  Maybe it is better
> in FreeBSD, I haven't checked recently.  Anyway, I believe higher values
> of tpscale translate to lower power.
> 
> Dave
> 

In my CUwireless build based on the sourceforge source code distribution,
the output of '$ sysctl hw.ath0' does not contain 'hw.ath0.tpack' and
'hw.ath0.tpcts'.

And the tpcscale option accepts only five integers 0 to 4 as a valid
argument. The default is 0 and it is the highest. As I increased the
tpcscale value one by one at the transmitter, the RSSI at the receiver
(which was very close to the transmitter) showed 2~3 dB degradation.

However, the 'tx power' field of tcpdump did not show correlated changes.
It was 60dBm with tpcscale 0, and changed to 54dBm, 48 dBm, 63dBm, and
47dBm.
Another tcpdump test with a different radio card (but same CM9 model)
resulted in a similar phenomenon. 

-- JK