Personal Hotspot
By default, Personal Hotspot is hidden. You need to activate it by the following procedure :
(a) Settings - Cellular Data - Personal Hotspot - APN Settings - Personal Hotspot
(b) Enter some information at APN, Username and Password. Those information is not required to be real data.
(c) Exit and return, you will find Personal Hotspot option on the menu.
Cellular Data and Wifi Connection Timeout
(a) Settings - Touch ID & Passcode
(b) Enable iPad Unlock, Enable Require Passcode
(c) Settings - General - Auto-Lock
(d) Set to Never. If you cannot find "Never", you need to go to Settings - General - Reset - Reset All Settings.
(e) Enable Lock/Unlock
The internet connection will not be timeout or disconnected even you close the smartcase cover, unless you quit the application.
Make sure your MacBook Air's Energy Saving setting is set to "Never" when it is using battery. Meanwhile, the Energy Saving setting is set to prevent computer sleeping when using power adapter. However, I encounter some problem when connecting the shared wifi. I think we should wait for the release of 10.10.2 for the wifi fix.
In addition, the Personal Hotspot share with Bluetooth is awesome. It is stable and fast but with the distance limitation. It is the alternative of the wifi share at the moment.
That's all! See you.