I replied on a similar topic to another user not so long ago, about power settings for dongles that might help
if you run iwconfig is the "power management enabled and if it is, does running iwconfig wlan0 power off make any difference to connection stability? If it works there are a couple of ways to make the change permanent.
Secondly I noticed from the replies that nobody suggested setting a “reserved” IP address for the network adaptor in the DHCP settings on your router, it does help connection stability.