Orthogonal frequency division multiplexing and channel models for payload communications of unmanned aerial systems

Orthogonal Frequency Division Multiplexing (OFDM) can be a good candidate for wideband communications to transmit payload data from an Unmanned Aerial Vehicle (UAV) to the ground station in an Unmanned Aerial System (UAS). However, OFDM systems are prone to inter-channel interference caused by the Doppler spread. Furthermore, because of possible high speed of UAVs, the Doppler spread can be large. In order to design a proper OFDM system for a UAS, it is essential to have an appropriate air-to-ground channel model that accurately models the multipath and Doppler properties of the wideband channel from the UAV to the ground station. Six different channel models are proposed based on various scenarios of the altitude of the UAV (very low, low, and high) and the type of the environment that they are flying over (low-density suburban areas and high-density urban areas). Since no measurement data has been published for wideband signaling from UAVs to a ground station, these models are created by combining parameters of narrowband aeronautical channel models with downlink channel models of wideband terrestrial systems, including HiperLAN, LTE and IEEE 802.16 systems. These channel models were used to evaluate the performance of an OFDM for UAV-to-ground communications. Simulation results show that for high-speed UAVs, the number of sub-channels in an OFDM should be relatively small in order to have reliable communications.