how to disable Wifi link band shrinking while idle ?

How to disable this option when wifi link shrinks it’s band when it is idle and no traffic on it ?
I need to achive stable wifi link for ospf/mpls/vpls purposes.
and i don’t like this thing when it’s idle i have ping timeouts and 300ms to Station site

disable automatic rate selection in the advanced wireless tab, and select the rates you wish the radio to negotiate

Enable Nstreme with polling or nv2, both keep the AP going even without data going across.