Mobile data connection lost on iPhone 5S

I have iPhone 5S with 10.1.1 iOS and sometimes happens to me that I loose mobile data connection. In other words in top left corner on my screen there is provider (operator) and right next to it I usually have LTE. This LTE disappears from unknown reason (even in places that are 100% covered by LTE, but that is ok, I can accept it) but the problem is that it doesn't come back until I restart iPhone completely. I tried to restart data connection or some other things, but nothing worked. Only turning off and on again completely. Has anyone experienced this or have suggestions? Many thanks