This development was conducted as a part of the "R&D for Expansion of Radio Wave Resources" program sponsored by the Japanese Ministry of Internal Affairs and Communications (MIC).
The ever-increasing levels of wireless-communication traffic in recent years have consequently led to increasing demand for more communication frequencies. Utilization of the millimeter wave (mmWave) band represents a key technology for the development of the heterogeneous networks (HetNets)  that will be used for 5th generation wireless cellular networks (5G). However, the application of mmWaves to mobile communications is generally considered to be difficult because of the short communication range associated with these waves as a result of the high attenuation of radio power in the mmWave band. For outdoor applications of mmWaves in particular, one major difficulty is how to avoid the effects of rain, which can dramatically reduce the transmitted radio-wave power. For mobile applications of mmWaves, the significance of this problem is that network operators must strive to avoid the effects of low data throughput in commercial mobile devices with maximum data rates of several hundred Mbps, which are much lower than the multi-Gbps data rate of a typical mmWave-based wireless device, while also increasing frequency usage efficiency using multilevel modulation in these wireless devices.
To resolve the above problems, Tokyo Tech, Sony, JRC and KDDI Labs jointly developed a new wireless access network that combined 40 GHz operation for outdoor networks with 60 GHz operation for mobiles to enable large data size content delivery on the gigabyte scale as follows: