Spectral Coexistence of Unmanned-Aircraft Control Links And L-Band Navaids: A 3d Whitespace Analysis

This paper describes a capability developed to analyze 3-dimensional (3D) whitespace opportunities for enabling spectral coexistence of a secondary radio frequency (RF) system in a frequency band with primary RF systems that must be protected against interference.The band analyzed in this study was the 960– 1164 Megahertz (MHz) segment of L-band. This band has been viewed for over a decade as a promising spectral resource for the command and control (C2) links of unmanned aircraft (UA). However, thus far there has been little if any UA system (UAS) C2 use of this band in the U.S. because of potential interference to incumbent safety-critical navigation and surveillance systems. Those systems most notably include two important classes of navigational aids (navaids): the civilian distance-measuring equipment (DME) and military tactical air navigation (TACAN) systems.In this paper we evaluate the feasibility of operating low-altitude UAS C2 links in L-band within portions of the U.S. national airspace while not causing interference to other aviation systems already using the band. Safety of the incumbent systems is assumed as the utmost priority. Preliminary results show whitespace spectrum is available in most of the U.S., with the amount of spectrum varying widely depending on location.While the 3D whitespace methodology described herein was developed for a particular band (L-band), new application (UAS C2), and set of incumbents (navaids), it could potentially be extended and generalized to other bands and use cases to identify additional opportunities for coexistence, thereby increasing overall spectral efficiency in those bands.