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SoftBank verifies radio propagation characteristics of wireless networks

SoftBank Corp. announced today that it conducted a verification of radio propagation characteristics in the airspace environment above the ground, where the altitude and speed of movement are different from those on the ground, in cooperation with SkyFive AG, a company providing inflight connectivity services for civil aviation in Europe. The verification, which was conducted in Germany in February 2023, was done with the aim of understanding the above ground wireless environment and its communication performance characteristics.

With the recent increase in services that utilize small-sized drones, the use of wireless communications in the sky is increasing. This demand is expected to further increase for communications with drones and helicopters to assess damage following disasters, the provision of wireless backhaul to tethered balloons and other applications.

Since the surrounding environment affecting radio propagation differs greatly between the sky and the ground, it is necessary to correctly understand how the relationship between the location and altitude of base stations and terminals affects communication to provide a stable, high-quality wireless network.

For example, on the ground, radio waves are sometimes blocked by buildings and trees, but in the sky, there are virtually no obstacles and radio waves can reach farther. As a result, interference with radio waves emitted from neighboring base stations increases, causing a deterioration of reception quality and a reduction in communication speeds.

In addition, the movement speeds of communication terminals carried by drones and other aerial mobility devices is faster than those of smartphones and other devices used on the ground. This can cause a phenomenon in which the frequency is observed as a value differing from what it actually is (Doppler shift), or the reception level of radio waves fluctuates (fading), resulting in fluctuations in reception power and communication quality.

In cooperation with SkyFive, in February 2023 SoftBank conducted a verification of radio propagation characteristics between a radio base station on the ground and a terminal and antenna mounted on a crewed airplane, utilizing the 2 GHz frequency band used for mobile communications. The flights were conducted at varying altitudes and speeds in diverse combinations to simulate a range of potential use cases. Through this approach, SoftBank was able to gather data on radio wave propagation characteristics across a range of conditions.

The data obtained from this verification was evaluated by comparing it with the free-space propagation loss model and the propagation loss model for aerial vehicle published as a technical report (TR36.777) by 3GPP (a standards organization that formulates standards for mobile communication systems).

As a result, it was confirmed that even at distances beyond the base station radius and altitude ranges specified in TR36.777, the model can be referenced with some adjustments to estimate the propagation loss of radio waves. In predicting fading deviations, it was also found that when a wide area is covered as in this verification, it is necessary to take the elevation angle of the terminal from the base station into account in addition to the terminal altitude. This data will enable the prediction of communication quality in the airspace and will be useful for the optimal design and formation of networks. SoftBank expects that the data obtained from this verification will be useful in designing airspace communication networks that provide stable communication speeds and capacity.

SoftBank will continue its research and development of technologies to realize networks of even higher quality and convenience.

CT Bureau

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