Google's broadband-in-the-sky goes TITAN-ic

20km is above jetstream

20km is above jetstream level. So it cannot hover. It has to go down to 12 km or thereabouts which means that it will enter the altitude range where it is obliged to comply with FAA (and other agencies reqs, have a flight plan and a transponder). So the idea of hover like a kestrel (into wind) is off the menu.

Otherwise, an LTE (or similar tech) network with antennas pointing downwards will work quite nicely at radio level. At higher layers it will get intresting - there are way too many places in the code in the mobiles, provisioning system, switching, etc which were written using the basic premise that a base-station does not move.

Re: s/hover/orbit/

And that's a bog standard mission profile whether you are tasking a Combat Air Patrol (CAP) with a human on-board or a drone tasked to orbit some piece of ground.