How did that ground based system solve the horizon problem ? Drones don't fly very high, so you'd need one of these systems, say at 50 meters drone height, ~ ev

How did that ground based system solve the horizon problem ? Drones don't fly very high, so you'd need one of these systems, say at 50 meters drone height, ~ every 50km. That's probably worse than those drones watching from above, seeing as you'd need actual infrastructure at every interval. And, that'd be fixed infrastructure, with fixed blind spots.