Why do I drop my personal hotspot from my iphone to ipad whenever my ipad goes to sleep?

OK, so I have the new ipad wifi only. Whenever there isn't a wifi signal around, I turn on my Personal hotspot from my iphone and sync internet via Bluetooth. First, the process to recognize pairing always seems to be sporadic. It takes a long time for my ipad to see my iphone's attempt to establish pairing. Most of the time I have to turn both Bluetooth's settings off and then on to establish pairing. Then, once I do gain a connection, if my ipad goes into Auto-Lock after 2 minutes of inactivity, my pairing is lost and I have to start the proess all over again. It's very annoying. Any suggestions would be great appreciated.