Tokyo – October 12, 2026 -- KDDI, NTT DOCOMO, SoftBank and Rakuten Mobile signed a memorandum of understanding on September 11, 2026, to jointly study how 5G millimeter-wave base stations can serve customers across operator boundaries. The four carriers announced the agreement on September 16.
Four carriers will test technical feasibility of cross-operator mmWave use
The study will assess whether the usage coverage of 5G millimeter-wave base stations can be expanded among mobile network operators. The companies will also evaluate efficient operational frameworks for implementing such an arrangement.
The work will focus on technologies and approaches related to 5G millimeter-wave base stations, repeaters and other related assets. The operators plan concrete studies on how to make effective use of facilities that have already been deployed.
Signal attenuation makes dense base-station rollout the industry bottleneck
Millimeter-wave spectrum delivers ultra-high-speed, high-capacity data transmission. Its signals, however, are susceptible to attenuation and obstruction by physical obstacles. Expanding coverage therefore requires a large number of base stations and related equipment, which makes rapid coverage expansion an industry-wide challenge for operators.
Each operator keeps its own deployment plans in place
The initiative rests on the premise that each carrier will continue its own millimeter-wave deployment. Cross-operator collaboration is intended to bring high-quality millimeter-wave experiences to more customers, rather than replace individual rollouts. The release refers to the 28GHz frequency band in its notes on millimeter-wave technology.
The companies said they will continue working to expand Japan's 5G millimeter-wave infrastructure and provide seamless connectivity to a wider range of customers. The release did not disclose investment figures, timelines for study results or deployment targets.