hotspot stops being detectable I have an iPhone 4 and a MacBook Pro. If I turn 'Personal Hotspot' on my iPhone to on, then I can connect with my laptop fine and everything is great. 

If on the other hand I then disconnect the laptop and leave 'Personal Hotspot' switched on, the signal appears to vannish after a while.  So if I come back later and try to connect my Mac to the network again, the Mac can't even see the network.
If I open up the settings on the iPhone and switch 'Personal Hotspot' off and then on again (good old technical training) the signal reappears and everything is fine. 

I'd like to be able to just leave the 'Personal Hotspot' available at all times because it's a extra bit of bother to switch it off and on again.  Can anyone suggest a fix or tell me what's happening here...?
Actually, this is what happens for hotspot.

If there is no active WiFi connection, and you're not in the screen that says "Personal Hotspot", it turns off WiFi hotspot feature completely.

To connect your FIRST device, you MUST be in that Personal Hotspot settings page.

After that, it won't turn off until the last device is disconnected.