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NEC and NTT DOCOMO conduct verification trials of Massive MIMO technology to realize 5G

March 29, 2017

The use of next-generation 5G wireless communication network technology is expected to lead to the creation of a variety of new services in a wide range of areas that had not been included in the realm of wireless networks up to now. These services include automated driving, logistics optimization, infrastructure monitoring, energy distribution optimization, remote medicine, etc.

NEC's research and development has focused on element technology, aiming to realize 5G. To that end, verification trials were recently conducted with NTT DOCOMO on "Massive MIMO (multiple-input multiple-output)" technology. The goal is to achieve a service with increased capacity and higher quality by adopting 5G.

The trial utilizing Massive MIMO is one of the 5G element technologies that allows multiple users to simultaneously use the same frequency resource through a method called beam forming by using large number of antenna elements. The beams are transmitted separately in multiple directions using the high frequency band (microwave) that is able to assign wide frequency bandwidth. For example, even though in a crowded large-scale stadium, the Massive MIMO system can deliver a wireless beam to each individual, so everyone can enjoy appropriate video streaming without interference.

The trials were conducted in the city of Yokosuka in Kanagawa Prefecture from November to December 2016 and in Tokyo's Shibuya Ward in January 2017. These trials were organized mainly in an outdoor environment densely packed with buildings, utility poles, vehicles and people, and in an indoor environment with many obstacles such as columns and walls. In the trial, NEC's low-SHF band-compatible massive-element Active Antenna System (AAS) were used to verify Massive MIMO technologies.

Characteristics of NEC's massive-element AAS

The massive-element AAS is a transmitter/receiver that has large number of antenna elements and utilizes "beam forming" technology.

NEC's massive-element AAS consists of 128 antenna elements that link two units, where the 64 antenna elements for the low-SHF band has been installed, in a matrix form. Basically, beam forming performance is enhanced by the number of antenna elements. Moreover NEC's high-integration and heat radiation technologies have also enabled a compact A4 size per unit.

Trial in Yokosuka
The low-SHF band-compatible massive-element AAS
Base Station (upper right) and mobile terminal (lower right)

The "low-SHF band" is the 3 to 6GHz frequency band in the Super High Frequency band (3 to30GHz) and it is expected to exploit high frequencies for wideband signal communication for 5G high data rate and large capacity. Furthermore, it is estimated to be adopted for commercial use around 2020, NEC has been working actively to leverage the low-SHF band for early Massive MIMO technology commercialization.

Trials conducted in the environments with many obstacles

If the massive-element AAS transmits beams to each mobile handset that is adjacent to another in an environment with many obstacles, the beams interfere with each other and communication quality will be degraded. It is also difficult to utilize the multi-path of its own signals because they come from different direction due to a reflection or a wrap-around caused by buildings, columns, etc.

Prior to commercialization, these issues need to be resolved. NEC verified that the low-SHF band-compatible massive-element AAS would be able to provide the communication quality required for 5G in such environments.

The low-SHF band-compatible massive-element AAS
Trial in Shibuya Ward

NEC's low-SHF band-compatible massive-element AAS adapts fully-digitized antenna beam control technology, which improves the precision of beam forming. While transmitting beams to the target mobile handsets, it is capable of forming beams that counteract interfering signals using the multi-path. It can also form beams that improve communication quality by efficiently combining the multi-path of its own signals with the direct waves.

Improving spectral efficiency and making it large capacity / improving communication quality

The trials demonstrated that by applying the characteristics of NEC's low-SHF band-compatible massive-element AAS, an appropriate beam could be formed for each mobile handset even though they are close together. This enabled concurrent communication with several handsets while maintaining high communication quality. The trials also verified that spectral efficiency was reliably maintained at a level roughly eight times(Note 1) higher than that achieved by LTE in indoor environments.

In these trials, NEC was able to verify that Massive MIMO technology improved spectral efficiency, achieved high-capacity, and enhanced communication quality.

NEC will continue with its technology development and verification trials for the commercialization of 5G.

Check here to see a video of the verification trials.

Low SHF band-compatible massive-element Active Antenna System (AAS) 5G field trial

Note 1:Comparing with 2 spatial multiplexing in LTE, as of February 20, 2017, based on NEC research.

*ACKNOWLEDGEMENT
This technical article includes a part of results of "The research and development project for realization of the fifth-generation mobile communications system" commissioned by The Ministry of Internal Affairs and Communications, Japan.

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