The consumer drone sector is expected to grow rapidly in the coming decades. In Europe alone, it is predicted that in excess of seven million such machines will be flying by 2050. This poses a risk of conflict in dense airspaces, with both aircraft and other drones. Such a growing market provides a need to make drones visible to ATC and other airspace users. While several passive surveillance methods exist, such as primary drone radar, a cooperative surveillance system would provide more data to airspace users and other drones to allow for features such as automatic separation. An Automatic Dependent Surveillance system concept is presented in this paper, allowing the drone to broadcast information about itself without external input. This is akin to ADS-B, from which the system inherits its format for the time being. The study's main contents are threefold. The first consists of recommendations made on the basis of literature. Then, a simulation approach to examine system capacity and related constraints through a sensitivity study is done. Finally, a hardware proof-of-concept, consisting of inexpensive and simple off-the-shelf components is built and tested. Overall, the paper demonstrates that such a system is indeed feasible. Through the literature, it was found that direct integration of the system with current ADS-B on the 1090 MHz frequency is possible, but may cause performance degradation for existing aircraft. Therefore, the carrier frequency and code allocation are changed. The simulation and capacity study shows that the system works in high-density scenarios (in excess of one drone per square kilometer), but will require additional work on hardware, format and modulation techniques to enable this. Finally, the hardware demonstrator shows that an inexpensive COTS implementation with a range of approximately 200 meters is possible, on hardware drawing less than five Watts of power.