Re: State of DFS with Mac80211/ath9k

[Zefir Kurtisi <zefir.kurtisi@neratec.com>]

On 03/06/2015 09:04 AM, Henning Rogge wrote:
> [...]
> 
> Second, we are seeing a huge amount of radar events on some nodes, but
> not on a node on the same channel in the next room. What is the status
> of the DFS detector in ath9k, is it reliable or is it still
> "experimental".
> 

Henning,

the DFS detector on one hand still can be labeled as 'experimental' since it seems
to be not used / tested all too much. On the other hand, our company got it
DFS-ETSI certified for a ath9k based product - so it does what it was made for.

As for the 'false' radar detections you observe: those are inherent for the
detection method used. The ath9k's pulse detection engine reports anything that
somewhat looks like a radar pulse - besides very rare cases where those were
generated by real radar, most of them are EM-noise, WLAN traffic, other radio devices.

Reality check: let two APs operate close to each other on adjacent DFS-channels,
connect one station to one of them and generate continuous downstream traffic
(e.g. 10Mbps). It will take only seconds until the other AP will detect a radar -
simply because it is inevitable to spot some potential pattern within a lot of
random pulses.


If you performed the tests in a similar environment, your observation is what you
have to expect. And unfortunately there is nothing to be done to prevent the false
radar detections - rendering operation on DFS frequencies inapplicable under some
environmental conditions.


Cheers,
Zefir