Restarting the wireless device

You can restart networking with:

sudo /etc/init.d/networking restart

but that's not an interface specific command, it just restarts the whole thing. If you use the graphical network tool to manage your wireless interface, I know of no way to administer it from the command line. I would suggest migrating to a conf file based set up using /etc/network/interfaces.

It sounds like router is freezing which depending on your security may require multiple steps to reconnect, such as interface authentication, security authentication and dhcp requests. Based upon the multiple steps restarting the networking service as Jinux suggested appears to be the best option. I recommend modifying your sudoers file to allow your normal user access to run the networking script as root without password authentication and creating a shortcut to run the command on your desktop.

Although you may want a script to auto-reconnect that concept can create problems by being stuck in a loop when you are not in range of the said router effectively knocking out any connections that you may have had setup, so based upon that logic I will not just give you a script or guide to accomplish the task, but if you are still interested I may work with you to make it a reality.

Before we jump to a script I recommend you lookup instructions for using wicd instead of the ubuntu network manager, wicd has a clean option to automatically reconnect that has worked well for me.