Most USB dongles (particularly small ones with internal antennas) have pretty bad range unfortunately.
Can't suggest anything in particular, but a quick search on Amazon will show you the ones with external antennas and/or "high power" ones that should provide a bit more range:
http://www.amazon.co.uk/s/ref=nb_sb_...reless&x=0&y=0
This and
this look like they do what you want.