In a test conducted with Samsung Electronics earlier this month at Fuji Speedway, a motorsport racing circuit in Shizuoka Prefecture, Japan, NTT DOCOMO achieved a data speed of more than 2.5Gbps with a mobile device that was in a vehicle travelling 150km/h. The company said this trial verified the feasibility of stable connectivity for 5G mobile devices in fast-moving trains. Transmissions were conducted using the 28GHz high-frequency band, one of the candidate bands that the Ministry of Internal Affairs and Communications is considering to designate for commercial 5G networks in Japan.
DOCOMO said the problem of large path-loss of high-frequency radio signals was overcome with massive multiple-input multiple-output (MIMO) technologies that incorporate beamforming, which concentrates radio waves in a specific direction, and beam tracking, which adjusts the beam according to the fast-moving mobile device's location.
In a separate undertaking, DOCOMO conducted an outdoor data-transmission trial with Huawei from October 3 to 26. It was carried out in a field measuring 100,000 square meters, equivalent to 12 soccer pitches, in the Minato Mirai 21 waterfront of Yokohama. The trial involved 23 simultaneously connected mobile devices and achieved a cumulative 11.29Gbps of data throughput and latency below 0.5 milliseconds using the 4.5GHz frequency band.
The trial combined multi-user MIMO (MU-MIMO) technology for simultaneous multiple access and a precoding algorithm that optimizes signals for maximized performance and also limits inter-user interference. It achieved a MU-MIMO transmission of a maximum 79.82bps/Hz/cell, which was 1.8 times more efficient than an outdoor trial conducted in China in November 2015.
The successful outcomes of these trials will be exhibited at DOCOMO R&D Open House 2016 at the DOCOMO R&D Center in the Yokosuka Research Park near Yokohama, Japan on November 17 and 18.