Enabling Air-to-Air Wideband Channel Measurements between Small Unmanned Aerial Vehicles with Optical Fibers

In order to ensure safe and efficient operation and to prevent collisions, unmanned aerial vehicles (UAVs) need to communicate with each other with high reliability. To design respective communication systems, accurate air-to-air (A2A) channel models are needed, especially for urban environments, where the channel characteristics are hard to predict due to rich multipath propagation, diffractions and non line of sight (LOS) conditions. For these models, channel measurements in different scenarios are inevitable to model the real-world communication channel. However, small sized UAVs are very limited in carrying payload and in power supply, making it difficult or often impossible to use high performing channel-sounding hardware equipment. As a result, less resource demanding hardware with lower performance in the sense of clock synchronization, time resolution or dynamic range is usually applied leading to a limited propagation channel characterization. In this work, we describe a measurement setup that allows using arbitrary channel sounder hardware by exploiting analog optical links in order to enable A2A wideband channel measurements between small sized UAVs. We extend the operation of our MEDAV RUSKDLR channel sounder by guiding a 100 MHz bandwidth radio frequency (RF) signal at 5.2 GHz through two 600 m long optical fibers attached on two hexacopters after being converted with high bandwidth converters and show the feasibility of this setup with first flight trials in an urban scenario.