From: Henrique Marks <henriquemarks@gm...> - 2007-10-25 11:51:43
Following a previous discussion, i would like to post a few more
questions about transmission power and TPC.
First of all, we have a setup with one AP and one STA, connected using
one cable, and using an attenuator. In our tests, when the attenuation
is set to 10 dB or less, the signal (measured in the STA with
iwconfig) is more or less -17dBm, and we start to lose packets in the
transmission between the AP and STA, both configured as bridges. This
occurs with simple pings or using more elaborated setups, like a
In this test, we used madwifi from trunk, and tried to enable TPC. To
achieve this, we had compiled the sources with CFLAGS=-DATH_CAP_TPC,
and passed the parameter tpc=1 to insmod ath_pci. The other values
that seems important are:
txpower = 17dBm, both AP and STA
doth = 1, both AP and STA
doth_pwrtgt = 27, both AP and STA
Our understanding of this parameters are as follows: doth_pwrtgt = 27
means that the maximum transmission power used is 13.5 dBm. Because
txpower > doth_pwrtgt, this value is not used.
We were expecting that, with TPC enabled, the signal level (measured
in the STA), would start to fall when the attenuation is too low,
automatically, avoiding the problem of losing packets. We couldnt see
this behaviour, and indeed we didnt see any difference, in this setup,
with tpc enabled or not. So, the question is: what would we expect to
see with TPC enabled, what is the point of using TPC with this setup.
Also, can we set doth = 0 and rely just on txpower to control the
transmission power for the STA and AP ? ( i guess so, just to
Also about TPC, i was expecting the transmission power of the AP to be
fixed, and the txpower of the STA to be regulated automatically by the
use of TPC, but how can we measure the Txpower of the station ? We
couldnt inspect the packets yet, our monitor setup is not working ok,
but can we expect to see the transmission power for the packets that
goes from STA to AP inside the transmitted packets ?
thanks in advance, hope to give more results of this tests as soon we
figure out this problems.