The biggest element is where your wireless router is located and the type walls / floors you have. If it's a fairly new router then it would be on 802.11n.
The general rule of thumb the thicker the walls and floors, the less signal you will get.
If you have brick walls and thick carpet, you might need to get a usb adapter such as this (I do not have experience with this brand but it's the first one that came up with a fair amount of reviews):