Mine does the same exact thing. I'll restart it, it'll be fine for 10-15 minutes at home. I'll leave, log on from a different computer (that I know it works and is also on a ds3) and it will be disconnected. I have no other issues with any other device (I have Linksys WRT54GL routers flashed with DD-WRT and this one is setup on a client bridge with full singnal strength).
Could this be overheating?