44 computational cost. The model could be adapted for other scenarios, including helping UAVs to conserve battery life. Handling interference Interference management is a key consideration of any wireless communications system, and with UAVs, it also plays a big role in determining system performance. A deep reinforcement approach has been developed to address interference, whereby each UAV in a swarm will act as a player and decide on its own path while minimising the latency and interference for the ground network. The UAVs are used to assist in the integrated access and backhaul (IAB) cellular in-band networks, and to reduce interference at various levels of networks. When it comes to interference management, power control is another feature that cannot be ignored. A machine-learning approach can manage overall network interference by controlling the UAV’s power and location. Ground vehicles For uncrewed ground vehicles used by the military, mmWave is gaining acceptance as the frequencies at 76 GHz are hard to locate and intercept. The latest systems use four radios and two modems for MIMO. Correcting for the Doppler effect in moving vehicles is vital and the digital signal processing in the modem needs to take this into account. This is even more complex when dealing with multiple signals through the MIMO system with slightly different phases. Initial rollouts for mmWave military systems use a mesh network with stationary receivers, but the next development will be a peer-to-peer mobile network where the ground vehicles connect to each other with AES256 encryption. This requires correction for the Doppler effect in all of the different vehicles, as well as a flat Level 2 self-organising network with beam steering to link them together, which is a higher computational load. Current systems can connect vehicles across distances of 5 km with data rates of 100 Mbps using a link budget of over 12 dB. While more power is available for ground vehicles than aerial systems, the four-radio mmWave system has a relatively low power consumption of 30 W. HAPS This is also attractive for HAPS systems that will adopt mmWave in the next two to three years, which will also require beam-steering and MANET technologies. The unlicensed 57-71 GHz band is available in North America and 59-63 GHz is available globally, with the upper bands above 64 GHz less susceptible to absorption by oxygen. Either band can be used to connect HAPS aircraft as the absorption issues are a lot lower at an altitude of 70,000 ft, enabling links of up to 100 Gbps. The 2019 World Administrative Radio Conference (WARC) agreed on the 38-39.5 GHz mmWave band, which can also be used for HAPS systems, providing a bandwidth of 1-2 Gbps. Rain attenuation is one of the key factors to consider. For a HAPS UAV at 20 km, the footprint can reach 70-80 km in diameter, and the link length will typically be about 40 km at an elevation of 30°. For most of North America and Europe (Zone K), where rainfall is around 42 mm/hour, attenuation February/March 2024 | Uncrewed Systems Technology Connecting a HAPS system to the ground (Image courtesy of Filtronic) A HAPS mmWave payload implementation (Image courtesy of Filtronic)
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