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A Lightweight, Low-Cost ADS-B System for UAS Applications
January 2008
Robert C. Strain, The MITRE Corporation
Matthew T. DeGarmo, The MITRE Corporation
J. Chris Moody, The MITRE Corporation
ABSTRACT
Unmanned Aircraft Systems (UAS) are proliferating in the military. At the
same time, civil government, commercial entities and research organizations are looking into
unmanned aircraft for a variety of applications in domestic airspace. Despite the growing
demand and many advantages offered by the portability, low cost, and sophistication of
these systems, their use in the National Airspace System (NAS) remains limited. Safety of
other airspace users is the primary concern. Small UAS are difficult to see visually and
sense electronically (e.g., radar). The Federal Aviation Administration (FAA) and the
aviation community must ensure that the operation of small UAS in the NAS will not pose an
undue risk that degrades safety. Making small UAS more conspicuous to other aircraft
would reduce the risk of collision and facilitate their integration into the NAS. One means of
making an aircraft more "visible" is through the electronic broadcast of the aircraft's state
vector data (i.e., position and velocity). For many years, FAA surveillance radars and radar-based
technologies, such as Traffic Alert and Collision Avoidance System (TCAS), have
relied on the active interrogation of aircraft transponders to determine position and velocity.
With the advent of Automated Dependent Surveillance-Broadcast (ADS-B) and its adoption
by the FAA and other civil aviation authorities around the world, aircraft will begin
broadcasting their state vector to Air Traffic Control (ATC) and other ADS-B equipped
aircraft independent of transponder interrogators. Since many small UAS will likely
operate in airspace not covered by radar, the use of ADS-B for these operations seems to be
a promising opportunity. However, the limited payload and power generation capabilities of
small UAS make it impractical for them to equip with existing ADS-B units, not to mention
the transponder-based system available today. Without an ADS-B or transponder system, it
is difficult to imagine the widespread applications envisioned for small UAS in the NAS. In
October 2006, The MITRE Corporation began researching the use of a lightweight, low-cost,
and low-power version of ADS-B for small UAS. This system will employ the Universal
Access Transceiver (UAT) datalink and will be interoperable with existing FAA certified
UAT-based ADS-B systems operating in the NAS. A modular architecture enables the
device to be either stand-alone or integrated with other electronics or sensors. Using ADS-B
requirements as a base will enable conformance to the planned FAA system. This paper
presents progress on the feasibility of the UAT Beacon radio for small UAS having limited
power, weight, and space.
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