Resetting wireless interface in Ubuntu

Most often in Ubuntu, the wireless stops working. Either it shows
Wireless Networks - Disconnected
and does not display any wireless connections available, or the wireless connection speed slows down drastically and resets quite frequently. This happens when the laptop wakes from a sleep or I try to unlock the screen after a brief period of inactivity.

One way to get out of this situation without rebooting is to restart the wireless lan interface (wlan0) using the commands:
sudo ifdown wlan0
sudo ifup wlan0

(or)

sudo ifconfig wlan0 down
sudo ifconfig wlan0 up

Reference:
1. http://askubuntu.com/questions/33818/lost-wireless-connection-and-detection