sUAS Sense and Avoid

In order to safely operate an aircraft of any type, it is necessary to detect incoming obstacles such as birds, buildings, other aircraft, weather, etc.  Pilots in manned aircraft are able to visually search and assess the airspace around their aircraft.  However, due to latency and unwanted breaks in communication, Unmanned Aircraft Systems (UASs) flying beyond an operator’s line of sight cannot accurately search and assess their airspace.

ICAO Cir 328, Unmanned Aircraft Systems (UAS)

Many large UASs have been outfitted with Sense and Avoid (SAA) systems to fill this gap.  “SAA functions to protect against collisions with other aircraft as well as various other hazards” (Zeitlin, 2010).  SAA in large UASs commonly use information from onboard transponders, Automatic Dependent Surveillance – Broadcast (ADS-B), optical sensors, LIDAR, and Radar to autonomously avoid threats.  However, small UASs (sUASs) (55 pounds or less) are not commonly outfitted with SAA systems due to weight and power constraints.

RADAR Based Collision Avoidance for Unmanned Aircraft Systems (2013) is a doctorate dissertation by Allistair A. Moses, from the Daniel Felix Ritchie School of Engineering and Computer Science, University of Denver, which provides insight on sUAS SAA technology.  Moses demonstrates the feasibility of a self-contained radar based collision avoidance system that weighs 304 grams (0.670205 pounds).  The SAA system was outfitted on an Align TRex450 Helicopter with a flying weight of 900 grams (1.98416 pounds).

RADAR Based Collision Avoidance for
Unmanned Aircraft Systems

The power consumption of the SAA is 5.8 W, with an input voltage of 5.6 VDC.  Its transmit frequency is 10.5 GHz with a transmit bandwidth of 5MHz.  It has a transmit power of 0.4mW and utilizes Frequency Shift Keying Continuous Wave Modulation (FSKCW).  FSKCW is a square wave modulation that is used to reduce background noise caused by terrain.   

The entire SAA system was built from scratch except for the antenna. The SAA uses a custom radar suite capable of detecting other aircraft.  The radar uses micro Doppler signal acquisition and identification consisting of quadruple transmit receive modules.  “This allows for the ready implementation of what they describe as a ‘Reactive Collision Avoidance Algorithm’ wherein the host vehicle steers away from the quadrants with the highest returned signal energy” (Moses, 2013).   

University of Denver faculty advisor Dr. Matt Rutherford stated, “in our field tests we were able to detect and identify targets of the size roughly equivalent to UAV at about 100 meters or 300 feet”  (Spendergast, 2014).  Researchers at the university are continuing to work on increasing the SAAs range.  In my opinion, a 100-meter SAA range on low power system weighing just over half a pound is impressive.  It should be noted that this technology could be up scaled to the effect that a larger sUAS with a SAA drawing more power can result in a longer detection range.     

Reference

Moses, Allistair A. (2013). RADAR Based Collision Avoidance for Unmanned Aircraft Systems. [ONLINE] Available at: http://digitaldu.coalliance.org/fedora/repository/codu%3A66898/Moses_denver_0061D_10839.pdf/Moses_denver_0061D_10839.pdf. [Last Accessed 28 February, 2015].

Pendergast, Stephen (2014). DU2SRI Miniature Radar May Give SUAS Sense and Avoid. [ONLINE] Available at: e.g. http://www.microsoft.com. [Last Accessed 28 February, 2015].

Zeitlin, Andrew D. (2010). Sense & Avoid Capability Development Challenges. [ONLINE] Available at: http://ieeexplore.ieee.org.ezproxy.libproxy.db.erau.edu/stamp/stamp.jsp?tp=&arnumber=5631723&tag=1. [Last Accessed 28 February, 2015].