Do you really need to have your AT&T MicroCell signal booster near a window for the network extender to work? Yes initially to get a GPS location on the device. However, you don't necessarily need a GPS extender because the MicroCell should remember the location if you initially power the device on near a window when you first install it. After the device finds your GPS location you can move it to the interior portion of your house or office. You can also put it in a cabinet or location near your network or broadband router.
If you need to buy MicroCell GPS Network Extender the for $24.95 it is easy to install, just plug it into the jack on the MicroCell, no other configuring needed. It may help you prevent loss signal, in fact, this will allow you to place the MicroCell closer to the center of the house for better coverage throughout the house. Keep in mind the AT&T MicroCell drops calls so set your expectations low when you first start using the network enhancer. See also Powerline Extender.