MacBook Pro WiFi keeps shutting down for no apparent reason
Solution 1:
I've had the exact same problem before with my Mid-2010 MacBook Pro. I took it into the Apple support people on campus and, after running quite a few tests, they found out that the cable connecting the AirPort card to the motherboard had gone bad. It sounds like this is the same thing that you're experiencing, so your best bet is to see about getting that cable replaced.