Wireless connection with a Centrino Wireless-N 1000 won't last longer than 20 seconds

I have the same wireless device in a Lenovo x121e laptop and had similar issues.

I had to disable the Wireless 'n' network. That solved the problem for me.

Try that:

echo 'options iwlagn 11n_disable=1' | sudo tee /etc/modprobe.d/iwlagn.conf >/dev/null

Then reboot the computer. Hope this helps... ;)

Source: Linux iwlagn problems

Try the following, worked for me:

in a terminal type

sudo iwconfig wlan0 power off

in my case, the power-management was broken. if it worked, just do the following to fix the problem on startup

sudo nano /etc/rc.local

and paste "iwconfig wlan0 power off" into it upon (!) "exit0". Save the file and reboot.

I hope this helps.