Link can't get estabilished over RB911AC boards

[Alessandro Bolletta]

Hi,

I have two Mikrotik RB911AC boards (radio based on QCA9882) in which I injected OpenWRT 15.05 and ath10k. 

I managed to get them connected in AP/STA configuration in a very short (2 meters) distance, but when I try to connect them on 5 kilometers, even if I set the distance parameter on OpenWRT's UCI config files properly, it tries to connect but after 3 retries, it declares unauthenticated.

No problem with the same firmware on ath9k, for example.
Signal is stable at -62 dbm, I also tried to change channels and push tx power, but nothing helped to do the trick.
Also tried with every firmware combination (10.2.4, CT firmware, 999.999.0.636, 10.1.467.2-1), without success.

Is there anybody who can tell me why? Could it be due to the kernel version (i'm running on 3.18.21)?

Thanks in advance,

--
Alessandro Bolletta
Mediaspot Srl