By Default, Ubuntu 11.10, comes with a very awkward energy management policy: when you switch off the power cable or you come from a sleep, the wireless network card turns instantly off. Besides, if your wireless card doesn’t work properly as mine (RT3090), maybe this policy can bring you some unexpected headaches.
The solution is to create a text file, located in /etc/pm/power.d/ and name it wireless:
sudo gedit /etc/pm/power.d/wireless
With the following content:
/sbin/iwconfig wlan0 power off
In addition, it is necessary to give “read” and “write” permissions to all users:
sudo chmod 777 /etc/pm/power.d/wireless
All we have to do now is to reboot. Energy Manager will not disconnect again the WIFI card.