SoftBank Advances Nullforming Towards Practical NTN Spectrum Sharing

As the industry looks beyond 5G and into 6G, one of the most interesting challenges is how terrestrial and non-terrestrial networks can coexist efficiently. Among the many techniques being explored, nullforming has emerged as a promising approach, and SoftBank has been steadily progressing this concept from theory to real-world validation.

Nullforming, sometimes referred to as null steering, is an adaptive antenna technique that allows a base station to suppress radio emissions in specific directions. In practical terms, while beamforming focuses energy towards a desired user or device, nullforming does the opposite by creating intentional “holes” in the radiation pattern to avoid causing interference. This is particularly useful in dense and heterogeneous environments where multiple systems operate in the same or adjacent spectrum.

The importance of this becomes clear when considering the growing role of non-terrestrial networks such as High Altitude Platform Stations. These aerial platforms can provide wide-area coverage from the stratosphere, but they also introduce a new interference dimension when sharing spectrum with terrestrial base stations. Efficient coexistence is therefore essential if spectrum is to be used effectively rather than fragmented into isolated allocations.

SoftBank first demonstrated the practical potential of nullforming in 2024. In that trial, the company used a high-altitude tethered aerostat equipped with a cylindrical antenna to show that it is possible to suppress interference towards terrestrial base stations while maintaining service to users connected to the aerial platform. The results confirmed that spectrum sharing between aerial and terrestrial systems could be achieved without significantly degrading performance, marking an important step towards integrating HAPS into mainstream mobile networks.

However, that early work was based on relatively static conditions. A tethered aerostat remains largely fixed in position, which simplifies the problem of directing nulls towards specific interference targets. The real challenge arises when dealing with moving platforms such as aircraft or future HAPS systems that continuously change position, orientation and relative geometry with respect to terrestrial networks.

This is where SoftBank’s latest announcement becomes particularly significant. In April 2026, the company revealed a new dynamic nullforming technology designed to address exactly this problem.

Unlike earlier implementations, this approach continuously adjusts the direction of the null in real time based on the position and attitude of the aerial platform. As the aircraft moves, the system tracks the relative location of terrestrial base stations and maintains suppression of interference in the required direction while still forming beams towards active users.

SoftBank validated this concept through a field trial conducted in late 2025. A base station equipped with the dynamic nullforming capability was mounted on a light aircraft flying at around 3,000 metres and speeds exceeding 200 km/h. During the trial, the aerial base station transmitted in the same frequency band as a terrestrial base station, while dynamically steering a null towards the terrestrial system to minimise interference.

The results demonstrated that even under highly dynamic conditions, it is possible to maintain communication performance while suppressing interference sufficiently to enable spectrum sharing. This is a notable step forward because it moves nullforming from controlled experimental setups into more realistic operational scenarios.

From a broader perspective, this work highlights a shift in how spectrum challenges are being addressed. Instead of relying solely on static allocation or exclusive licensing, techniques such as nullforming enable more intelligent and adaptive use of spectrum resources. This aligns well with the direction of 6G research, where concepts like dynamic spectrum sharing, integrated terrestrial and non-terrestrial networks, and AI-driven radio optimisation are expected to play a central role.

There are still challenges ahead. Accurate and low latency tracking of platform position and orientation is essential for dynamic nullforming to work reliably. The computational complexity of real time antenna control also increases significantly as systems become more adaptive. In addition, large scale deployment will require standardisation and interoperability across vendors and network domains.

Even so, SoftBank’s progression from static to dynamic nullforming provides a clear indication of how these challenges are being tackled incrementally. What began as a concept to suppress interference has evolved into a practical mechanism for enabling coexistence between fundamentally different network layers.

As non-terrestrial networks continue to gain momentum, particularly in the context of 6G, such techniques are likely to become increasingly important. The ability to share spectrum seamlessly between ground and aerial systems could unlock new coverage models and improve overall spectrum efficiency without requiring additional scarce frequency resources.

In that sense, nullforming is not just a niche antenna feature. It is becoming part of a broader toolkit that will help define how future wireless networks are designed, integrated and scaled.

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