  As new use cases are emerging for unmanned aerial systems (UAS), advanced
wireless communications technologies and systems need to be implemented and
widely tested. This requires a flexible platform for development, deployment,
testing and demonstration of wireless systems with ground and aerial nodes,
enabling effective 3D mobile communications and networking. In this paper, we
provide a comparative overview of software-defined radios (SDRs), with a
specific focus on SDR hardware and software that can be used for aerial
wireless experimentation and research. We discuss SDR hardware requirements,
features of available SDR hardware that can be suitable for small UAS, and
power measurements carried out with a subset of these SDR hardware. We also
present SDR software requirements, available open-source SDR software, and
calibration/benchmarking of SDR software. As a case study, we present AERPAW:
Aerial Experimentation and Research Platform for Advanced Wireless, and discuss
various different experiments that can be supported in that platform using
SDRs, for verification/testing of future wireless innovations, protocols, and
technologies.
