[ath9k-devel] Several questions and observations

[Nenad Opsenica <nenad@panline.net>]

Hi everybody,

I would like to ask several questions and write some of my observations 
regarding ath9k. My testbed consists of two UBNT Routerstation boards 
with Mikrotik R52N MiniPCI card each, with OpenWRT kamikaze (trunk -  
r18131). This revision uses kernel 2.6.30.8 (or 2.6.30.9) and 
compat-wireless-2009-10-09. I'm testing  802.11n connection between AP 
and STA, both of them are on my desk, few feet apart; one UBNT RS acts 
as AP, other as STA.

Well, here are the questions:
- is there any way I could tune some of "advanced" parameters, e.g. slot 
time, ack timeout, ... etc?

- is there any way to force MCS, HT20, HT40, or SG (apart from 
"ht_capab" hostapd option which, if I understood right, only announces 
AP capability without forcing it)?

- how can one be sure what is TX power after "iwconfig wlan0 txpower 
XXX", as "iw wlan0 station dump" on other device always reports same 
signal value ? Is it even possible to change TX power?

- what are real-world performances one can expect in communication 
between ath9k AP and STA with MIMO 2x2? With both UBNT RS devices on my 
desk I was able to get stable ~90Mbps transfer when using HT20 at 130Mbps 
rate, and up to 80Mbps (not_so_stable) with HT40 at 270,300Mbps rate (AP 
patched to force HT40, see observation #2 and 
https://forum.openwrt.org/viewtopic.php?id=21544)


Observations:
- after changing AP operating channel with "iwconfig wlan0 channel XXX" 
STA is no longer able to associate, not even after STA reboot

- when hostapd is configured with "ht_capab 
'[HT40-][SHORT-GI-40][DSSS_CCK-40]'", STA is using HT40 mode for 
transfer packets to AP, but AP is still using only HT20.

- it looks like STA is not willing to automatically reassociate to AP 
when AP is restarted (in fact, it is enough to do "wifi down; wifi up" 
on OpenWRT). One have to issue "iwconfig wlan0 essid XXX" to force STA 
to associate to AP again. This behavior is really annoying.


Regards,
    Nenad