Unmanned Systems Technology 033 l SubSeaSail Gen6 USSV l Servo actuators focus l UAVs insight l Farnborough 2020 update l Transforma XDBOT l Strange Development REVolution l Radio telemetry focus

84 Focus | Radio telemetry The latest chip designs for WiFi6 add orthogonal frequency-division multiple (OFDM) access so that the bandwidth can be segmented, allowing multiple devices to receive data in the same time frame. That increases data transmission efficiency and reduces power consumption for network applications. New features such as Basic Service Set (BSS) Colouring in WiFi6 increases robustness in environments with lots of wireless, enabling better data throughput in areas where there are multiple access points and many clients, such as urban areas. With BSS Colouring, data from each access point is prescribed a ‘colour’, so that clients can identify which one is transmitting, resulting in improved network performance. Signal robustness is essential for telemetry, so the WiFi6 standard also has a dual-carrier mode. This allows the same information to be modulated on a pair of sub-carriers, which can ensure data gets through even in noisy environments. The advantage of course is that millions of WiFi6 chips will be used in networks in homes, offices and factories, driving down the costs. That gives UAV radio designers a single low-cost chip with the radio front end and all the processing to simplify the design process. Combining telemetry and payload data There is a clear trend to having a broadband radio system that is capable of IP traffic networking and which gives the flexibility to include payload data as well as command & control data. The more services that can be combined in a single radio the better, as it allows the platform – a UAV or UGV – to be used as a node in a mesh network. That means any spare bandwidth can be used to provide data to other vehicles on the ground or in the air, giving the system operator much more flexibility. This relies on sophisticated packetisation algorithms to ensure the Quality of Service (QoS) is maintained and that there is full control of the priority of the telemetry traffic for essential services. The sweet spot for long-distance, high- bandwidth comms that can combine telemetry and payload data is in the C band (from 4 to 8 GHz). This is the optimum frequency band from a physical perspective, where the frequencies are high enough to enable a compact unit, as the size of the antenna decreases. The radio signal attenuation from rain at frequencies above 8 GHz becomes a problem that limits the maximum operational range for the link. Using a phased array antenna with beam steering gives the best trade-off between range and bandwidth, but there are no suitable protocols. The proposed standards for 5G use beamforming/ MIMO technology but also use stationary base stations as a master to link to relatively simple handheld terminals. Complex algorithms for UAV designs need to support a moving base station with a narrow beam and with no August/September 2020 | Unmanned Systems Technology WiFi6 brings power efficiency advantages for UAV telemetry applications (Courtesy of Imagination Technologies) The sweet spot for long-distance, high-bandwidth comms that can combine telemetry and payload data is from 4 to 8 GHz This radio system can reach over 200 km for UAVs (Courtesy of Radionor)