Fujitsu Doubles Same-Cell Wireless Communication Capacity for 5G

Beijing, China and Kawasaki, Japan, September 04, 2015

Fujitsu R&D Center Co., Ltd. and Fujitsu Laboratories Ltd. today announced the development of a new wireless technology that doubles the capacity of a single cell, using the same wireless frequency simultaneously, as a step toward 5G.

Full-duplex is a technology that simultaneously transmits and receives wireless signals on the same frequency, which is a way to increase wireless communication capacity, but reducing interference from the sending signal to the receiving signal is problematic. Fujitsu has developed a new scheduling technology that reduces the inter-device and inter-base-station interference, using a transceiver separation type where separate base stations are responsible for the tasks of sending and receiving to multiple devices within the same cell. This results in a communication capacity of up to double the current existing half-duplex communication technology within a single small cell. In wireless environments with a high concentration of users, such as shopping malls or stadiums, it is anticipated that this will result in a smoother communication environment that reduces capacity loss.

Details of this technology are being presented by the Fujitsu R&D Center at the Vehicular Technology Conference 2015 (VTC2015-Fall), opening Sunday, September 6 in Boston, United States.

Development Background

Targeting the commercial launch around 2020, 5G, the next-generation wireless communication system, is currently being researched and developed to fulfil the explosion in communication volumes caused by the popularity of smartphones, and to support the expected future proliferation of services.

It is estimated that wireless communication capacity will need to be 1,000 times greater in 2020 than in 2010. To satisfy this, the 5G system uses small cell technology for which research and development are already under way. In small cell technology, the area covered by a given base station is narrower and a given frequency is used in different areas, both of which lead to increased capacity (Figure 1).

Figure 1: Small-cell technology

Issues

Only using small cell technology by itself to continuously deal with increasing communication capacity is problematic. Full-duplex – a technology where wireless signals are simultaneously sent and received on the same frequency – is used to increase capacity. However, as a principle, because sent signals leak into received signals, there is a need for solutions that mitigate this problem (Figure 2).

Figure 2: Transmitted-signal leakage with full-duplex transmissions

About the Technology

Fujitsu has developed a transceiver separation type full-duplex communication technology that reduces inter-base-station and inter-device interference by using a base-station transceiver separation architecture. This allocates sending and receiving to devices within a cell to macro-cell and small-cell base stations, respectively (Figure 3). Fujitsu also developed a scheduling technology to enable this approach to full-duplex.

Figure 3: Transceiver separation type full-duplex transmissions

Following is a processing overview of the technology.

1. Types of processing

1. Optimized device pairing
   Selects the two devices within a single small cell that have the least mutual interference when using the same frequency.
2. Optimized device transmission power control
   Controls transmission power so as to ensure wireless quality and minimize interference with other devices using the same frequency at the same time.

2. Characteristics of scheduling operations

Optimized scheduling for a device takes into account combinations of three factors: the device receiving the downlink signal, the device sending the uplink signal, and the device’s transmission power. Assuming there are ten candidates for each factor, signal processing here needs to check a total of some 1,000 combinations. Fujitsu developed an algorithm that puts the candidates into the best ordering, which reduces the signal-processing workload for device scheduling to a few tenths of what it would be otherwise for these three types of candidates. They also developed an algorithm that accurately picks transmission-power candidates based on the grouping of devices, which reduces the processing workload to about 1/40th overall.

Results

In system-level simulations using this technology, a single small cell was found to achieve up to twice the communication capacity of existing half-duplex communication.

In wireless environments with a high concentration of users, such as shopping malls or stadiums, installing this technology will provide smoother communication environments that limit capacity degradation.

Future Plans

Fujitsu R&D Center plans to continue its work to further reduce the communication capacity degradation caused by interference between small-cell base stations and macro-cell base stations within this transceiver separation type full-duplex communication technology. Fujitsu Laboratories, meanwhile, will continue its investigation of the architecture and its efforts at developing deployment technology as part of its proposal for inclusion in the 5G standard, aiming for implementation of this technology around 2023.