?system log to check if ip address is settled
$ sudo vi /var/log/syslog
update linux version:
$ sudo apt-get install linux-image-generic-lts-quantal
check system version
$ sudo uname -a
check network card driver
$ sudo lshw -C network
restart wireless card driver
$ sudo service avahi-daemon restart
?>? find "ath"included driver
$ lsmod | grep ath
install "ath9k" driver
$ sudo modprobe ath9k
$ sudo modprobe -r ath9k