  Micro Air Vehicles (MAVs) will unlock their true potential once they can
operate in groups. To this end, it is essential for them to estimate on-board
the relative location of their neighbors. The challenge lies in limiting the
mass and processing burden needed to enable this. We developed a relative
localization method that only requires the MAVs to communicate via their
wireless transceiver. Communication allows the exchange of on-board states
(velocity, height, and orientation), while the signal-strength provides range
data. These quantities are fused to provide a full relative location estimate.
We used our method to tackle the problem of collision avoidance in tight areas.
The system was tested with a team of AR.Drones flying in a 4mx4m area and with
miniature drones of ~50g in a 2mx2m area. The MAVs were able to track their
relative positions and fly several minutes without collisions. Our
implementation used Bluetooth to communicate between the drones. This featured
significant noise and disturbances in signal-strength, which worsened as more
drones were added. Simulation analysis suggests that results can improve with a
more suitable transceiver module.
