constantly keeping the cell antenna and CPU awake would probably do it. it's a BIG part of why weak cell signal and lots of noise at e.g. conventions drains your phone many times faster than normal, even when you're not using it. you could probably do that just by sending junk data to everyone occasionally, or delaying valid data to prevent going into sleep modes for longer periods.
I think it has to do with the phone constantly renegotiating with cell towers along the route.
I've seen similar behaviour when a hurricane took out power to a local tower, and it was intermittently restored.
It might be possible to emulate that in a controlled environment/area.
If a phone isn’t connecting to any towers (like on a plane) it assumes it is out of range and is blasting out max power trying to find something to connect to. During hurricanes, many towers are down, which can overburden adjacent towers as well (since each tower only has a certain number of slots/channels it can handle). It means that you may not be able to communicate with your closest tower, since it is down, but you also may not be able to communicate with the next nearest tower, since it at capacity for current users, which puts you in a longer distance higher transmit power situation.
From what I have heard, those Stingrays act as fake towers, so I would assume they could set them to always tell the phones it needs max transmit power.
