There are no settings I know of that can affect your signal strength from your cell carrier. It's not uncommon for a 3G signal to have difficulties within a building, particularly in residential areas where it can be difficult for carriers to locate cell towers.
Since it's working outside of your house, it would not seem to be a problem with your iPad as such and you therefore may need to discuss the issue with your cell carrier, though if other 3G phones work correctly from your house with the same carrier, there could be a hardware problem with your iPad. If no device works, though, it's probably a signal problem with the carrier. Some carriers provide "microcells" that attach to a broadband Internet connection to get around these problems, but if your broadband isn't working correctly, that of course won't be a solution for you. There are also 3G signal boosters available that work in some circumstances; consult your carrier.
Regards.