Publication in ITU Journal: Research and Development of Local 5G Backhaul Systems

The article reports research results from the project “Research and Development of Satellite–Terrestrial Integrated Technologies for Beyond 5G” (Project ID: 21901), which was selected under NICT’s Advanced Communications and Broadcasting Research and Development Commissioned Program and conducted from fiscal year 2020 to fiscal year 2024.

Worldwide efforts toward the commercialization of networks integrating satellite communications with 5G and Beyond 5G technologies have been intensifying in recent years.

In 2019, NICT established the Study Group on the Integration of Satellite Communications and 5G/Beyond 5G, where effective use cases, technical challenges and solutions, evaluation and demonstration methods, and standardization activities were examined.
Furthermore, NICT signed a Letter of Intent with the European Space Agency (ESA) to strengthen Japan–Europe collaboration in this field, promoting global research and development of Non-Terrestrial Network (NTN) technologies and future communications infrastructure.

Based on these initiatives, NICT launched the commissioned R&D project “Research and Development of Satellite–Terrestrial Integrated Technologies for Beyond 5G” (Project ID: 21901).
Together with contractors Japan Radio Co., Ltd., SKY Perfect JSAT Corporation, and The University of Tokyo, the project was carried out from FY2020 to FY2024 under the Japan–Europe cooperation framework.

Phase 1 (FY2020–FY2021)

In Phase 1, Japan–Europe joint experiments on integrated satellite–5G control were conducted, including Japan’s first experiments involving geostationary satellite links in satellite–5G integration.

Phase 2 (FY2022–FY2024)

In Phase 2, GEO (Geostationary Earth Orbit) and LEO (Low Earth Orbit) satellite links were connected to local 5G networks, and demonstration experiments were conducted using disaster response scenarios as key use cases.

The experiments validated routing control, satellite QoS (Quality of Service) control, and network slicing technologies, successfully achieving dynamic backhaul path switching and QoS control.

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Results by Organization

SKY Perfect JSAT Corporation

SKY Perfect JSAT constructed a local 5G backhaul network environment utilizing multiple proprietary satellite communication links across different orbital layers, integrating QoS control and routing control.

The results demonstrated the effectiveness of dynamic network control in response to changing link conditions.
Specifically, the experiments confirmed that combining:

• high-capacity data transmission using LEO satellites (at altitudes of several hundred to several thousand kilometers), and
• stable bandwidth availability using GEO satellites (at approximately 36,000 km altitude)

enables both improved throughput and enhanced communication stability.

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The University of Tokyo

The University of Tokyo was responsible for Research Item 2: Research and Development of Local 5G Backhaul.

When satellite links are used as local 5G backhaul, it is essential to address challenges related to high latency and priority control to prevent traffic congestion under limited bandwidth, particularly during disaster situations.

To establish satellite–terrestrial integration technologies for Beyond 5G, the following three development objectives were defined.

Objective 1: SDN/NFV Technology Development

SDN/NFV technologies were developed to mitigate bandwidth and latency constraints of satellite links, including:

• emergency traffic detection,
• congestion control functions, and
• latency mitigation mechanisms.

Objective 2: Network Slicing Technology Development

Technologies were developed to enable static and dynamic placement of SDN/NFV-based functions for network slicing, along with associated network operation techniques.

Objective 3: Network Management Technology Development

Dynamic resource management technologies were developed to support the creation and deletion of network slices that include satellite components.

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Research Outcomes

Objective 1: SDN/NFV Technology Development

An increasing number of communication failures have been observed due to congestion in the 5G mobile core control plane, caused by control signals transmitted when many user equipment (UEs) attempt to connect simultaneously.

To address this issue, the study proposed control-plane slicing, which applies network slicing to the control plane of the 5G mobile core.
By applying control-plane slicing to frequently congested network functions (NFs) and implementing CPU-weighted resource allocation, congestion during UE–5GC initial connection processing was mitigated.

As a result, the average number of connectable UEs increased by 2.4 times, demonstrating improved congestion mitigation and priority control.

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Objective 2: Network Slicing Technology Development

In disaster monitoring systems, MQTT (Message Queuing Telemetry Transport) is commonly used for IoT sensor data transmission.
A network slicing scheme was proposed to improve MQTT communication performance.

Compared with conventional methods without slicing, the proposed approach increased the number of transmitted MQTT messages by more than 1,000.
Future work will focus on further stabilizing latency and jitter.

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Objective 3: Network Management Technology Development

A network slicing and management method for satellite–terrestrial integrated systems was established and implemented, applying QoS control based on GBR-class 5QI.

Different N‑NSSAI and 5QI values were preassigned per application and network slice.
When prioritization is required, the 5QI of non-priority applications is shifted to a GBR class and bandwidth parameters are adjusted, thereby restricting their bandwidth usage and securing available bandwidth for priority applications.

For future emergency use cases where human error must be minimized, the development of software that automatically applies network slicing based on predefined policies is considered essential.

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Conclusion

These results demonstrate the technical feasibility of practical local 5G operation using satellite communications and highlight the potential for deployment in disaster communications and non-terrestrial communication infrastructures in the Beyond 5G era.

Future efforts will require implementation into commercial systems and further functional enhancements considering social acceptance.
Ultimately, local 5G is expected to evolve into a next-generation cyber infrastructure that supports public safety and security across society.