This white paper provides a broad overview of potential communication technology and spectrum usage options for unmanned aerial systems (UAS). This paper particularly focuses on the detect and avoid (DAA) or collision avoidance (CA) use case, in line with the vehicle-to-vehicle (V2V) unmanned aerial vehicles (UAV) use case white paper and examines the advantages and disadvantages of state-of-the-art technologies for DAA/CA use case. While specific frequency bands are discussed, along with communication requirements of the UAS, solutions for spectrum usage designs and experimentation have been reserved for white papers to emanate from future IEEE P1920 UAV standard groups.