[ath9k-devel] Realtime plot of Spectral Scan in ath9k

[Gui Iribarren <gui@altermundi.net>]

On 07/26/2013 06:18 PM, Adrian Chadd wrote:
> Right. Adjacent channels can decode some CCK frames, but OFDM should
> look like garbage.
>
> Now, the $50 question - can we (ab)use the signal sizing / threshold
> parameters (like what ANI does) to make the OFDM/CCK receiver
> effectively deaf to wireless frames, so they appear as spectral
> samples? Hm!

He-he ;)
well, i actually did try the opposite: i wanted to generate/visualize 
recognizable spectral patterns, like a 5mhz bw communication, which 
would definitely appear and stand out clear, so i set a couple of 
routers with wireless.radio0.chanbw=5 ... sadly it didn't work.

/sys/kernel/debug/ieee80211/phy0/ath9k/chanbw was correctly set to 0x5
but communication used 20mhz as usual. didn't dug into it, maybe i was 
missing some other option.. who knows, didn't care much, it was just a test.

Yet, I must admit I didn't think about setting the *scanning* radio to a 
narrower bandwidth, that would definitely make the trick!
Hm, there's no code yet for sampling anything else than HT20,
But in any case, I think we would need a "spectral scan" mode, distinct 
from "normal" scan (which is currently overloaded with sampling), to be 
able to:
a) Use a narrower bandwidth like you say,
b) not send any beacon request, or wait for any beacon (which is what i 
suspect happens in "passive" scans) which would speed up the hopping

i don't know what are the implications of modifying the bw size, is it 
something that can be done just for a single scan? i.e. radio is 
operating normally on 20/40mhz, talking to peers, and for an instant 
(100ms?) makes a quick scan with 5mhz bw over 14 channels in 2.4ghz, 
then goes back to normal 20/40mhz?
maybe a reset is needed between those bw changes?
[I have *absolutely* no idea of what i'm talking about]

Thanks a lot for the feedback Adrian!

Gui

>
>
> -adrian
>