SoftBank Corp. successfully demonstrates terahertz communication coverage beyond 5G/6G using its proprietary antenna technology | Company Profile

Reasons for using terahertz communication

In recent years, amid growing demand for faster and larger capacity wireless communications, research and development into Beyond 5G/6G technology, which aims for throughput exceeding 100 Gbps, is underway around the world. Among these, terahertz (THz) wireless technology, which has a wider frequency band than the millimeter wave band used in 5G, is expected to be a solution for realizing ultra-high speed wireless systems.

Terahertz waves have a large propagation loss, so research is being conducted to extend the communication distance by using narrow beams from high-gain antennas and put terahertz wireless communication into practical use. By extending the communication distance, it is expected that terahertz waves will be used as an alternative to optical fiber, such as for high-speed communication in areas where it is difficult or impossible to lay optical fiber.

SoftBank is actively conducting research and development to utilize terahertz (THz) wireless technology for mobile communications, and has successfully verified communication coverage in outdoor environments, confirming that THz communication is possible even outside the line of sight.^*1However, to put communication with terminals into practical use, it is necessary to develop a system that can continuously track the beam, which poses challenges in terms of the complexity of the equipment and the tracking accuracy of the terminal. Furthermore, expanding the communication area like the base stations of conventional mobile systems causes power dispersion, significantly reducing the THz wireless communication area.

SoftBank therefore conducted a demonstration experiment of vehicle-specific THz coverage, which prevents power dispersion by limiting the communication area to roads only, thereby expanding the communication area even when vehicles are traveling outdoors.

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In general base stations, high-gain sector antennas are installed to create a wide communication area. These antennas transmit radio waves in a wide pattern in the horizontal plane and in a narrow beam in the vertical plane. However, a phenomenon occurs in which the received signal is weaker at points close to the macro base station compared to points a little further away. Therefore, in order to ensure stability along the direction of road traffic in terahertz wireless communication for vehicles, a communication area is created that covers a narrow area in the horizontal plane and a wide area in the vertical plane.

SoftBank applied the characteristics of the cosecant squared beam pattern (hereinafter, cosecant squared characteristics) to construct the in-vehicle communication area. This is a technology used in aviation radar, etc., and the received power level of the base station and the terminal is constant regardless of the horizontal distance between the antennas, which may be at different heights. To realize the cosecant squared characteristics in communication, a special antenna configuration is required. SoftBank developed a unique cosecant pattern antenna (hereinafter, cosecant antenna) that realizes the cosecant squared characteristics in both the base station and the terminal. This realizes a system that ensures constant received power while maintaining high antenna gain. Antennas with such special characteristics tend to be large in size for current mobile communication frequency bands. However, because the wavelength of terahertz waves is short, SoftBank was able to realize a size of 1.5cm x 1.3cm x 1.0cm (for base station) and 1.5cm x 1.3cm x 1.5cm (for terminal).

Field Test Description

For this outdoor demonstration experiment, SoftBank conducted the experiment on a road near its headquarters in Minato Ward, Tokyo. On the transmitting side, they installed a radio device equivalent to a base station equipped with a cosecant antenna on the pedestrian deck about 10 meters above ground, and transmitted a 5G modulated signal converted to a frequency of 300 GHz. On the receiving side, they used a measurement vehicle equipped with a cosecant antenna and equipment to convert the 300 GHz frequency back to 5G, and measured the 5G signal while driving along the straight road below the pedestrian deck.

In the experiment, measurements were taken while changing the vehicle’s speed from a low speed to the speed limit of 30km/h. In both cases, it was confirmed that the test signal could be stably received and demodulated even while the vehicle was moving in a section of approximately 140m from near the base station to the edge of the road. Although the measurement distance was limited to 140m due to the length of the road, there was sufficient power available at the cell edge, so it is believed that it is possible to cover longer distances.

SoftBank will continue to verify various use cases and accelerate research and development toward the practical application of terahertz wireless technology. This initiative aims to realize ultra-high speed wireless communications in the Beyond 5G/6G era and contribute to the growth of the communications industry.

For more information, please visit the SoftBank Corp. Advanced Technology Laboratories website.
URL: https://www.softbank.jp/en/corp/technology/research/story-event/051/?adid=press