2012-05-15 15:04:46

by George Nychis

Subject: AR9280 reported signal strengths are flat (comparison with bcm4322 included)

I am experiencing unexpected signal strength values reported by an
AR9280. Basically, they always tend to be flat no matter how far or
close I am from the device that is transmitting. Roughly between the
-65 and -55dBm range on average. The exact AR9280 I am using is:

Sony UWA-BR100 802.11abgn Wireless Adapter [Atheros AR7010+AR9280]

I have compared this behavior to a bcm4322 and the behavior I see with
the bcm4322 is as expected. Far away I get low signal strength
values, and close to the device I get high signal strength values
(-20dBm).

Here is a comparison of the two (taken at the same time) as I walk
closer to the transmitter. I record the signal strength from
wireshark using radiotap header field radiotap.dbm_antsignal.

http://www.flickr.com/photos/gnychis/7203437510/in/photostream

Surprisingly, the average signal strength seems to decrease with the
ar9280 as I get closer, yet remains relatively flat. The bcm4322
shows a clear increasing trend as I get closer.

Does anyone have any insight as to what might be going on? I'm using
the most recent firmware and compat-wireless as of May 14, 2012.

Thanks!
George

2012-05-16 06:08:01

by Holger Schurig

Subject: Re: AR9280 reported signal strengths are flat (comparison with bcm4322 included)

This is probably due to ANI (adapative noise immunity). I think ath9k
does too much here, in other words: it doesn't just kick in if there
are too strong signals there. Instead it seems to always adjust the
input attenuator, needed or not.