Japan, Sept. 16 -- KDDI Corporation, NTT DOCOMO, INC., SoftBank Corp., and Rakuten Mobile, Inc. announced that they signed a memorandum of understanding (MoU) on September 11, 2026, to launch a joint study on utilizing 5G millimeter-wave 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 ...