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6 Mission-critical info for UST professionals Platform one A UK developer of an autonomous flying base station has started testing key parts of its system (writes Nick Flaherty). Stratospheric Platforms is developing an electric high-altitude pseudo-satellite that can provide cellular coverage from 20 km (60,000 ft). The platform will use a hydrogen fuel cell to provide enough power for the base station as well as power for the electric engines to keep it in position. The company has successfully demonstrated high-speed 4G LTE connections to a live telecoms network. The demonstration used a remotely piloted H3Grob 520 aircraft at an altitude of 14 km with an LTE antenna delivering signals in the 2.1 GHz frequency band to user equipment on the ground.  The key to the system is a 9 m 2 digital steerable phased array antenna with 2048 dual polarisation phased array transceivers. That is equivalent to around 500 terrestrial antennas, and even with 4G it has a low latency, of about 1 ms. Beam steering allows for a configurable transmission cell of 100 km in diameter that can target areas of poor coverage, such as radio ‘shadow’ areas created by hills or valleys. A Voice over LTE call, a video call, a data call and video streaming were demonstrated on a standard smartphone and linked into a terrestrial live network with download speeds of 70 Mbit/s and upload speeds of 23 Mbit/s using a 10 MHz bandwidth. The fuel cell, which has already been tested on the ground, provides 290 kW of power, with 20 kW for the base station. This will provide a mission time of around nine days on its tank of hydrogen. The company is also working on a 5G antenna that will shortly be ready for flight testing in the stratosphere. It plans to deploy a commercial version of this system in 2024. Airborne vehicles Telecoms test for HAPS December/January 2021 | Unmanned Systems Technology Telecoms technology for the high altitude pseudo-satellite system powered by a fuel cell has been tested in a live network