Help me choose a good wireless n usb adapter for pc

[unpossible]

I have just purchased a new wireless n router (Billion 7404VNPX), and i need some wireless adapter cards for my pcs.

I hvae already purchased a billion 3011N for my parents computer which works very well since that computer is much closer to the router.

My PC (win xp sp3) is quite a distance away from the router (router is downstairs, about 15m away, with about 4 walls between my pc and the router). - Tried 3011N with my computer, very little signal, about 30%)

Could you guys recommend a good usb wireless n adapter which would work well (2T2R) and give me good connection speeds over this distance.

Thanks