Seizo Onoe, chief technical officer at NTT Docomo, points to five aspects of 5G that he believes will result in success for the new communications standard:
- Global standardization
- Implementation of key technologies
- A deployment scenario that integrates existing assets and emphasizes a strong combination of 4G and 5G
- Collaboration and consensus within the telecom mobile industry
- Collaboration across industries to create new business models and ecosystems
Perhaps most pertinent to the NTT 5G philosophy is the importance of an evolutionary approach from 4G to 5G, emphasizing the efficient integration of lower frequency and higher frequency bands to meet the network challenges 5G will introduce. The company also believes the entire network architecture should support this evolution toward 5G radio access. Following are two of the areas in which NTT Docomo is innovating.
NTT 5G: Phantom Cell
In line with its views about integration, NTT Docomo is advocating for a unique concept, deemed Phantom Cell architecture, which combines a small cell using a higher frequency band and broader bandwidth, and a macro-cell using a conventional lower frequency band. NTT sees a lack of capacity solutions for high-traffic outdoor environments that can also support good mobility and connectivity.
The company’s Phantom Cell solution envisions a massive deployment of small cells that leverages high-frequency reuse at high-frequency bands in conjunction with a macrocell. The macro-cell dynamically controls the discovery and usage of small cells in a master-slave configuration. To realize this concept, NTT 5G introduces a new method of managing connections between mobile terminals and small cell nodes, splitting the radio link’s control plane and user plane.
NTT 5G: Speed and Performance
NTT Docomo has been working on speed trials with a number of operators, including Huawei and Nokia. In 2015, NTT Docomo partnered with Nokia to attain download speeds of 2 Gb/s across the 70 GHz millimeter wave (mmWave) spectrum.
“Utilizing higher-frequency bands, including mmWave, is key to delivering extremely high performance in 5G,” said Onoe. “We believe that high-frequency spectrum shall be used, not just for small cells as a means to complement the existing network, but also for building solid area coverage through coordination with existing lower frequency bands.”
Later, in 2016 and 2017, NTT Docomo conducted large-scale field trials with Huawei, making use of a new numerology and frame structure, aligning with the 3GPP 5G New Radio (5GNR) standard. Testing attained 11.29 Gb/s total user throughput, and latency was about a tenth of that experienced on 4G networks. NTT Docomo and Huawei plan to continue to expand their trials, including mobility and large coverage, which they jointly see as the most important aspects of launching the 5G network.
NTT 5G Is All About Partners
NTT Docomo has successfully conducted many 5G trials for years, involving a bevy of other industry partners, such as Ericsson, Fujitsu, and Samsung. The trial with Ericsson studied the feasibility of massive multiple-input multiple-output (MIMO) technology. With Fujitsu, NTT 5G tests focused on a multi-base station cooperative transmission system. In tests with Samsung, NTT 5G testing involved data-receiving speed in fast-traveling vehicles, using beamforming and beam tracking.