I'm not sure what wifi adapter you're currently using, but... using a wifi adapter with an external antenna, and using a high-gain and/or directional antenna (if desirable) will do wonders.
One such card is the Alfa AWUS036NHA ($30-$40 on Amazon)
Hope that helps...
One such card is the Alfa AWUS036NHA ($30-$40 on Amazon)
Hope that helps...