These are temporary fixes. is there a permanent way to maintain service since iOS 8.'

SSince iOS 8, my iPads (I have 2) consistently display "No Service" in the status bar. I have tried all the recommended Aplle "fixes" but they only provide cellular access for short periods and then goes back to "No Service". Is there a way to get my iPads back to maintaining constant service as I have experienced for the 3 plus years prior to iOS 8?