Comment 30 for bug 761176

For me it was almost certainly the 802.11n problem. If you have access to the router, disable it there.
If you don't, then the situation is worse. Unfortunately, ath9k hasn't got an easy way to disable it on the device (11n_disable option as some other drivers do). You may compile your own one, though: start with http://askubuntu.com/questions/18897/enable-only-802-11b-g-in-a-802-11n-in-atheros-wireless-card .