Uncrewed Systems Technology 046

10 Researchers at the ETH in Zurich have developed a combination of ultra-wideband (UWB) and wake-up radio (WUR) technologies for UAVs (writes Nick Flaherty). An open source hardware and software design supports high-precision landing of an off-the-shelf UAV and energy-efficient operation by improving the ranging and bandwidth of wireless links. The techniques improve the energy efficiency of the localisation and data acquisition cycle by up to 62% compared with previous approaches, and reduce power consumption from 190 µW to 2 µW. By modifying the flight control software, UWB radios on the ground can be used to improve localisation accuracy on both the UAV and the sensors to allow the UAV to land more accurately on a wireless charging pad and so boost the power efficiency. The researchers developed a new, multi-stage localisation technique by fusing data from GNSS satellites, UWB and asynchronous hardware to produce a WUR receiver that is enabled by a trigger from the UAV. The UAV, in this case a DJI M100, is the ‘master’ in the network, enabling and disabling the comms with the sensor node, which has the UWB wireless interface, a sensing application and wireless charging power modules. The UAV’s power module delivers power via appropriate power electronic circuitry such as a Class E/F rectifier and transmitting coil, directly connected to the UAV’s main battery. A specific module manages the UAV’s attitude during flight manoeuvres such as take-off, hovering, cruise and landing. The application layer was designed from scratch and includes an onboard computer, sensor data storage and flight sensors. The layer provides functionalities for the UAV to improve the localisation accuracy by fusing the GPS and UWB information, as well as an ultrasonic sensor. Standalone GNSS navigation has an accuracy of around 25 cm, which is not enough for landing on an inductive wireless power unit. Instead, the UWB distance sensor provides an accuracy to within 10 cm and works from a range of 20 cm out to 100 m. The first stage of the navigation needs only the GNSS system, which guides the UAV to within 10 m of the landing pad. During that stage, the altitude could be a fixed safe level, but at the end of the first stage a maximum altitude of a couple of metres is needed. The second stage starts at about 10 m away from the sensor node’s UWB antenna, receiving only the point- to-point scalar distance. To calculate a planar distance, a precise altitude value is required, which is taken from the ultrasonic sensor. The UWB distance estimation is used to compensate the GNSS error. A single UWB distance scalar measurement, however, cannot navigate the UAV to the actual sensor node’s location. A 2D gradient descendent algorithm is then used, with consecutive UWB measurements adjusting the flying direction. The ultrasonic sensor is then used for the height control. This is all implemented on a PCB that measures 70 × 70 mm, combined with the external UWB antenna of 30 x 40 mm. It is UWB-compliant to IEEE 802.15.4-2011 for two-way ranging and data transfer at rates of up to 6.8 Mbit/s in addition to Bluetooth 5.0. An onboard STM32WB55RGV from STMicroelectronics manages all the stacks and sensors. Combo boosts radio range Airborne vehicles Orolia has developed an atomic clock that is small enough to fit into a UAV (writes Nick Flaherty). The mRO-50 Ruggedized is a microwave optical double-resonance miniaturised rubidium oscillator. It provides a one-day holdover of less than 1 µs and a retrace of less than 1 -10 in a 50.8 x 50.8 x 20 mm form factor that takes up only 51 cm 3 of volume – about one-third the volume of standard rubidium oscillators – and consumes only 0.36 W of power, one-tenth of other timing systems. With an operating temperature of -40 º C to +80 º C, it can provide accurate frequency and precise time synchronisation for mobile applications such as military radio pack systems in GNSS-degraded or denied environments including underwater and in uncrewed systems. Atomic clock fits in UAVs Navigation October/November 2022 | Uncrewed Systems Technology