It sounds like range is not the problem because you say that the connection drops altogether, but I'd like to mention that the range on my Netvigator modem is miserable. I sometimes lose the WIFI connection when I'm in my bedroom using my iPhone/iPad; the WIFI router is very near, about four meters away in the living room.
It's my theory that concrete walls block WIFI signals but I can't seem to find any definitive info on this...