• KDDI, NTT DOCOMO, SoftBank and Rakuten Mobile have agreed to study shared use of 5G millimetre-wave infrastructure
  • The work covers 28GHz base stations, repeaters and related assets, while each operator continues its own network deployment

The fact

KDDI, NTT DOCOMO, SoftBank and Rakuten Mobile have signed a memorandum of understanding to study shared use of 5G millimetre-wave infrastructure in Japan. The operators signed the agreement on 11 September and announced it on 16 September.

The study will examine the technical feasibility of expanding 28GHz coverage through shared base stations, repeaters and related infrastructure, as well as the operating arrangements needed to support that model. Millimetre-wave networks generally require denser infrastructure because high-frequency signals have shorter reach and are more easily blocked by buildings and other obstacles.

The memorandum does not commit the four companies to deploy a shared network. Each operator will continue its own millimetre-wave rollout while the study proceeds. No sharing ratio, commercial terms, operating structure or implementation timetable has been announced.

The assessment

The agreement opens the possibility of reducing some duplicated infrastructure where several operators want 28GHz coverage in the same place. A shared site or repeater could reduce the amount of separate equipment required, but the four companies first need rules for ownership, maintenance, access and fault handling.

Those decisions matter because sharing also creates common dependencies. If several operators rely on the same equipment at a venue or transport hub, a failure at that point could affect customers who otherwise appear to be using separate mobile networks. The study therefore needs to address resilience as well as deployment efficiency.

For BTW readers, the MoU changes the planning process, not Japan's current mmWave footprint. Enterprises that need 28GHz coverage should still judge each operator by the infrastructure available at their required locations until a shared system is actually agreed and deployed.

What to watch

Watch for a pilot deployment or a formal framework defining who owns shared equipment, how costs are divided and how faults are handled. Regulatory guidance will also matter if the four national operators begin coordinating coverage. A commercial agreement, rather than another study announcement, would show that infrastructure sharing is moving towards deployment.