5G in Japan

Similar to South Korea, Japan’s 5G mobile communication technology is also mainly pro- moted through industry‐academia partnerships. During 29–30 October 2013, supported by some international and regional organisations such as Japan’s Yokosuka Research Park (YRP) R&D Promotion Association, South Korea’s 5G Forum, Taiwan’s Wireless & Information Technology Communication Leaders United Board (WIT CLUB), China’s Future Forum, the EU’s METIS project team and China Mobile, the Summit on Future Information and Communication Technology (5G) (abbreviated as 5G Summit) was held in Beijing. The government representatives, experts, telecom operators and leading software and hardware manufacturers from Europe, China, Japan, South Korea and other countries and regions made keynote presentations with respect to the overall development strategy and R&D plan for 5G. Issues such as research on systematic 5G definition, research on 5G standardisation requirements, 5G spectrum planning and suggestions, 5G marketing analysis and visions, 5G innovative service applications and requirements, 5G‐oriented novel wireless transmission and network- ing technologies, strategies for future network evolution and convergence and international cooperation were discussed.

In February 2013, NTT DoCoMo, a Japanese telecom operator, announced, with the technical assistance of the Japanese Tokyo Institute of Technology, that it had successfully conducted an outdoor experiment on the transmission of 10 Gbps at the 11 GHz frequency band on Ishigaki Island, proving the technology to be far more powerful than LTE and LTE‐A. Three technologies were mainly used in the outdoor transmission of mobile sig- nals: MIMO, 64 QAM and turbo detection, which means a feedback is given upon the reception of the signals.

In October 2013, NTT DoCoMo displayed its 5G communication technology at the Combined Exhibition of Advanced Technologies (CEATEC) in Japan claiming to feature ‘ultra‐high speed and low delay’. The mobile device is installed with 24 antennas and can be seen as an action BS fully loaded with communication equipment. NTT DoCoMo hoped to keep the actual rate at over 5 Gbps at the final stage and make it the future standard. Furthermore, NTT DoCoMo intends to use 5G in wearable equipment for users to conveni- ently carry out various operations without using hands, including augmented reality, face identification, word identification, translation, and so on.

Japan’s major telecom operators include NTT DoCoMo, KDDI, SoftBank and E‐mobile in charge of mobile data operation and the Personal Access System company Willcom, to which NTT DoCoMo is the biggest contributor, in charge of the development of Japan’s 5G technology. NTT DoCoMo has been involved in international 5G research and promotion for a long time

and was in charge of one of the working groups of the METIS project. DoCoMo is devoted to the development of 5G technologies oriented to mobile communication services in 2020. To increase the communication capacity and improve users’ throughput capacity, it actively advocates small cells – the output power of the traditional macro‐cell BSs is 10–40 W. By allocating multiple cells with even lower output power (tens to hundreds of mW), this technol- ogy covers certain areas with higher communication demand within the macro‐cells. In a nutshell, the macro‐cell BSs – responsible for the ‘surface’ coverage of vast areas – use the low‐frequency bands, while the small cells in the ‘point’ areas demanding higher data rates use the high‐frequency bands. For example, the small cells will use the 3.5 GHz frequency band in the near future and high‐frequency bands at 10 GHz or above in the future. At this time, the control signals that judge which cell the terminal is to connect are all transmitted by macro cells. This concept is called ‘Phantom‐cell’ [38]. DoCoMo planned to propose the Phantom‐cell to 3GPP. As other communication equipment manufacturers have proposed the same concept, DoCoMo will focus on the use of small cells to promote technical development.

At the comprehensive IT exhibition CEATEC Japan 2013, held on 1 October 2013 at Makuhari Messe (in Mihama Ward, Chiba), NTT DoCoMo simulated the new‐generation mobile communication ‘5G’ it conceived. In an interview with Engadget, a representative of NTT DoCoMo said that the biggest challenge in constructing the 5G network was how to deal with the limitation of high‐frequency communication bands. To address this problem, they have planned to realise the signal transmission at high‐frequency bands using a large number of antenna components. For the simulation, DoCoMo considered Shinjuku, Tokyo, as the model and set seven macro‐cells using 26 MHz bandwidth in the 2 GHz frequency band and 12 small cells using 1 GHz bandwidth at the 20 GHz frequency band to construct the HetNet system. As the frequency band used for small cells is the 20 GHz band featuring strong recti- linear propagation, the small cells become the LAN covering a few to tens of meters. The antennas used for the macro cells are 2×4 MIMO and those used for the small cells are 128×4 MIMO (i.e. Massive MIMO). According to DoCoMo, ‘the aim of using Massive MIMO is to bar jamming through the beamforming technology’.

At the Broadband World Forum (BBWF) 2013, NTT DoCoMo studied the possibility of launching 5G services at the 2020 Tokyo Olympics. ‘Although it seems to be far‐fetched, we still need to consider it carefully’, said Takehiro Nakamura, Director of the Wireless System Design Team of NTT DoCoMo, in his speech. He added that, at the conception stage, what 5G entails depends on who the lecturer is. According to NTT DoCoMo, 5G represents the increase in the capacity of the access network by 1000x. Takehiro predicted that this would require the support of the ‘wireless connection to multiple personal terminals’ in the next few years. DoCoMo proposed the use of more spectrum from high‐frequency bands and the large‐scale MIMO technology to realise such a huge increase in capacity. MIMO technology has remark- ably increased the number of convergence antennas in the access network. Takehiro said that, based on the simulation test of this operator, the increase in the capacity by 30x can be realised using 100 MHz bandwidth at 3.5 GHz in 12 small cells, and the use of 400 MHz spectrum at 10 GHz in the same number of small cells can accommodate the increase by 125x. To realise the incredible capacity increase of 1000x, Takehiro said, the use of 1–20 GHz spectrum in 12 small cells with the use of large‐scale MIMO technology can help the operators attain such a goal. However, he admitted the use of such high‐frequency spectrums could only benefit the outdoor network environment. ‘We should consider new RATs to create the great gains we

Drivers for 5G: The ‘Pervasive Connected World’ 23 need’, said Takehiro. But he insisted that 5G should be a technology that industry should care-

fully take into consideration.

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