Since UAV activity is largely constrained by the see-and-avoid issues;
I though it would be appropriate to propose a solution which is compatible for every form of flight from gnat-weight to jumbojets. I've worked this out is a simulator - but here is the jist:
This requires only a single frequency and very short blips.
1. Every plane determines it's location and vector by GPS.
2. Then it transmits this information using one short blip every second or so.
a. The blip timing is based on current GPS location, so that the blips cannot interfere, and their location in Timespace tells us where they are coming from. Since GPS provides a very accurate, shared time base. So let t in microseconds = latitude\1 + longitude\1 * 100 + Alt in Km *1000 .
b. Odd seconds communicate vector (ie destination), Even seconds communicate Location.
3. There is a third variable required - which I call "Density". Each plane calculates the perceived Density of their airspace and sends that as well. Your density is your passenger count divided by the distance between you and other planes multiplied by their perceived density.
4. For manned aircraft nothing further is required - this beacon signal will ward off all unmanned vehicles.
5. For Autopilot or UAV, it is possible to chart a new safe vector by trying random vector changes and calculating their future density based on the vectors and densities of nearby airplanes. The vector which optimizes progress toward destination with lowest density is the vector chosen.
simple calculation requirements (ie Arduino), cheap transmitter/receiver requirements, and low power requirements. cheap unit cost, and no ground control.
Such a system could be demonstrated by coordinating a swarm of Ardu-Planes.