The Atheros Wifi cards are very much used in laptops especially on portable PC Acer and Asus and then used by many users including those who also uses Linux as Operating System. For some months are giving many problems and especially with the arrival of the new Linux kernel 3.0.x found a bug that has many problems.
In fact the connection is very unstable slows down and after a few minutes up to a few kb both in download and upload. with Ubuntu 11.10 Oneiric things are worse because of the new Linux kernel 3.0.x which sends the Atheros Wifi card always power saving mode doing what our connection becomes unstable and very slow.
Solve the problem is very simple, just start the terminal and type:
sudo gedit /etc/rc.local
ifconfig wlan0 power off
save and reboot
And here is our connection back to normal.