Press Releases

Sep 16, 2026

Cross-Operator Joint Study on 5G Millimeter-Wave Infrastructure and Technical Architectures for Coverage Expansion

KDDI Corporation
NTT DOCOMO, INC.
SoftBank Corp.
Rakuten Mobile, Inc.

TOKYO, JAPAN, September 16, 2026 --- KDDI Corporation, NTT DOCOMO, INC., SoftBank Corp., and Rakuten Mobile, Inc. announced today that they signed a memorandum of understanding (MoU) on September 11, 2026, to launch a joint study on utilizing 5G millimeter-wave^*1 infrastructure and technical architectures to expand coverage.

While millimeter-wave spectrum enables ultra-high-speed, high-capacity data transmission, its propagation characteristics make signals susceptible to attenuation and obstruction by physical obstacles. Consequently, expanding millimeter-wave coverage requires the development of a large number of base stations and related equipment, making rapid coverage expansion an industry-wide challenge for telecommunication operators.
Based on the premise that each operator will continue its own millimeter-wave deployment, this initiative aims to deliver high-quality millimeter-wave experiences to more customers through cross-operator collaboration.

■ Overview of the Joint Study

Through this study, the companies will assess the technical feasibility of expanding the usage coverage of 5G millimeter-wave base stations among mobile network operators and evaluate efficient operational frameworks for its implementation. To achieve this expansion through collaboration among mobile network operators, this study will focus on technologies and approaches related to 5G millimeter-wave base stations, repeaters, and other related assets. While each operator actively deploys its own 5G millimeter-wave equipment, the companies will pursue concrete studies to effectively utilize deployed facilities.

Going forward, the companies will continue working to expand Japan's 5G millimeter-wave infrastructure and provide high-quality, seamless connectivity to a wider range of customers, thereby contributing to the advancement of Japan's digital infrastructure.

28GHz frequency band

About KDDI

KDDI is a leading Japanese telecommunications company with over 100 million customers. In recent years, KDDI has expanded beyond its core telecommunications business into areas such as AI, finance, energy, retail, and cybersecurity, contributing to structural reforms across various industries. Globally, KDDI provides mobile services, IoT services for connected cars, and data center connectivity, primarily in North America, Europe, and Asia. KDDI is driving social impact and transformation through its mid-term management strategy, "Power-to-Connect 2028." For more information, visit the KDDI website.
https://www.kddi.com/english/

About NTT DOCOMO

NTT DOCOMO, Japan's leading mobile operator with over 91 million subscribers, is one of the global leaders in 3G, 4G and 5G mobile network technologies. Under the slogan “Bridging Worlds for Wonder & Happiness,” DOCOMO is actively collaborating with global partners to expand its business scope from mobile services to comprehensive solutions, aiming to deliver unsurpassed value and drive innovation in technology and communications, ultimately to support positive change and advancement in global society.
https://www.docomo.ne.jp/english/

About SoftBank Corp.

Guided by the SoftBank Group's corporate philosophy, “Information Revolution - Happiness for everyone,” SoftBank Corp. (TOKYO: 9434) operates telecommunications and IT businesses in Japan and globally. Building on its strong business foundation, SoftBank Corp. is aiming to activate the potential of AI across its businesses and drive implementation in line with its “Activate AI for Society” growth strategy. While further growing its telecom business, SoftBank is expanding its AI computing infrastructure and AI and Cloud service businesses with the aim of becoming a provider of Next-generation Social Infrastructure. To learn more, please visit https://www.softbank.jp/en/corp/

About Rakuten Mobile

Rakuten Mobile, Inc. is a Rakuten Group company responsible for mobile communications, centered on its mobile network operator (MNO) business. Through continuous innovation and the deployment of advanced technology, Rakuten Mobile aims to redefine expectations in the mobile communications industry in order to provide appealing and convenient services for diverse customer needs.

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