  Unmanned Aerial Vehicles (UAVs), a.k.a. drones, are increasingly used for
different tasks. With more drones in the sky, the risk of accidents rises,
sparkling the need for conflict management solutions. Aircraft use a system
called Automatic Dependent System-Broadcast (ADS-B) to continuously broadcast
their position and speed but this system is not suitable for small drones
because of its cost, complexity and capacity limitations.
  Broadband technologies such as Wi-Fi beacons are more suited for such dense
scenarios, and they also offer the benefit of wide availability and low cost.
The main challenges for Wi-Fi are (a) the multi-channel nature of the
technology makes transmitter and receiver coordination difficult, and (b)
standard chipsets are not designed for frequent broadcast transmission and
reception. In this paper, we propose and analyze a multi-channel position
broadcast solution that is robust against jamming and achieves a reliable
location update within 125~ms. In addition, we implement the protocol on
inexpensive embedded Wi-Fi modules and analyze the hardware limitations of such
devices. Our conclusions are that even on the simplest Wi-Fi chipsets, our
protocol can be implemented to achieve a realistic location broadcast solution
that still perfectly mimics simulation and analytical results on the lab bench
and still can achieve approximately 4~message/s throughput at a distance of
900~m on flying UAVs.
