Network Help?

Hey guys, a buddy of mine is having troubles staying connected to PSN. We have tried everything we can think of but what happens is, we will start playing then his ps3 will freeze. when he restarts it he will sign in, but 30 seconds later he will get signed out again. Then he will let his system sit for about 30 minutes, and then the whole process starts again. So we are wondering if you had any ideas as to why he can't stay signed in. His internet is fine because he is on his laptop and his phone too. Also, he does have the new 'super' slim ps3 so its not too old and it does have good ventilation. Any help would be good, and I will relay the ideas to him.

Thanks in advance.