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

86 master in an ad hoc network for long- range links of up to 250 km. To achieve this range needs a set of different waveforms, both short range and long haul. Waveforms known from the telecoms industry such as 5G or wi-fi are designed for short ranges of about 2 km, which can handle multiple reflections in a short time window. The long-range waveforms cope with reflections coming from distances of 1-100 km, so they are fundamentally different from a physical perspective. These need to be a robust waveform with a long delay spread, dealing with reflections from mountains, hills and man-made structures. That means the protocol has to handle a larger delay difference to eliminate the first, second, third and higher order reflections. In the air the delay can be huge, so designing an efficient protocol that operates effectively from a few kilometres to 200 km is challenging. Another design consideration with phased array is the need for a radio system with an array of radios and amplifiers. High power efficiency on the modulators is key to generating as little heat as possible. The optimum design gives 15 Mbit/s of user data throughput, with the protocol and encryption overhead on top with a range of more than 150 km. A 7 Mbit/s mode gives a range of more than 250 km. Both modes have a configurable latency via the QoS down to 5 ms. There is a key trade-off however between the latency, which is key for control & command signals, and the efficiency in such single-channel systems. A longer latency, perhaps 50- 100 ms, allows more data aggregation and higher transmission efficiency. Short latency breaks up the waveform and hence is less efficient. Users can configure the balance of latency, data rate and bandwidth for missions. The technology can also be adapted for different applications. One version of the radio is suitable for a typical 150 kg take-off-weight rotary UAV or a fixed-wing aircraft with a 5 m span. The phased array antenna measures 25 x 25 cm and weighs 2 kg; it has a peak transmission power of 250 W and consumes 150 W for a 200 km range. The smallest version weighs just 85 g with four phased array RF antennas and beamforming for smaller UAV platforms. Combined with a phased array antenna on the ground, the 85 g radio in a small, 2 kg take-off-weight quadcopter offers a range of 160 km with a data rate of 600 kbit/s. The system is a fully software-defined radio, with full flexibility for designing the waveforms and modifications, such as the ability to add algorithms for beam steering that keeps track of the position of the other antennas. A by-product of using a custom waveform and protocol is that it gives full control over the location of the other nodes in the mesh network. The incoming signal from other nodes gives the bearing and range of the other nodes. Locating one node accurately creates a positioning system that can replace GPS or a satellite service. The link is fully encrypted but doesn’t share location data. The relative position is calculated from the link, so applying one reference point provides the location of all the other nodes. Of course, adding amplifiers is a traditional way to boost the range of the radio link, but the challenge is making them small enough with low power consumption for UAV designs. For example, an S-band bidirectional power amplifier that operates from 2.2 to 2.5 GHz measures 2.3 x 2.3 x 0.45 in August/September 2020 | Unmanned Systems Technology This S-band amplifier weighs only 57 g (Courtesy of Triad RF) A by-product of using a custom waveform and protocol is that it gives full control over the location of other nodes in the mesh network