Wide band channel characterization for low altitude unmanned aerial system communication using software defined radios

In the near future, there will be a need for accommodating large populations of fast moving Unmanned Aerial Systems (UAS) operating in uncontrolled, very low level (VLL) (below 500 ft.) airspace. As is well-known, real-time knowledge of the wireless propagation channel is essential for the effective design and optimization of wireless communication systems. In this paper, we propose a software defined radio (SDR) based channel sounder employing a wideband linear frequency modulated continuous wave (FMCW) or chirp waveform technique for low altitude air-to-air (AA) links. This paper discusses both matched filter and heterodyne detector implementations in the receiver, and investigates advantages and disadvantages of both architectures for an SDR implementation in an AA scenario. We also discuss proper windowing techniques in the transmitter to improve sounding resolution. Some proof of concept measurement results using SDRs are presented for a simulated UAS scenario.