World's first seamless switching experiment between 60 GHz band wireless LAN and 5G/LTE based on distance measurement using radio waves

Demonstrated avoidance of communication interruption in an ultra-high-speed mobile environment through demonstration experiments using formula cars

News Highlights:

Tokyo - April 26, 2024 - NTT Corporation (NTT) has devised a technology to seamlessly switch between 60 GHz band wireless LAN (WiGig¹), a non-mobile wireless communication system, and 5G/LTE, a mobile wireless communication system, by distance estimation using radio waves, and has successfully demonstrated this technology in an ultra-high-speed mobile environment using a formula car.
　This technology combines a high-frequency band non-mobile wireless communication system, which was previously available only for mobile terminals with a limited range of movement, such as indoors, with a mobile wireless communication system seamlessly, enabling the technology to be used even for mobile terminals that move over a wide area, such as high-speed mobile trains and drones. This technology enables mobile terminals to use high-frequency band non-mobile wireless communication systems as off-road destinations for mobile wireless systems, and is expected to increase the capacity of wireless communications.
　This technology will be introduced at the Tsukuba Forum 2024² to be held from, May 16 to 17, 2024.

1. Background

In the IOWN³/6G era, in addition to higher frequency bands such as the millimeter wave band and the sub-terahertz band, it is expected that non-mobile wireless communication systems, such as wireless LANs, that can achieve high-capacity communication will be used to increase the capacity of wireless communications.
　WiGig is one of the non-mobile wireless communication systems using high-frequency bands that can meet these expectations. WiGig is a 60 GHz version of a wireless LAN and is a non-mobile wireless communication system capable of wireless transmission of up to 4.62Gbit/s⁴ in a single frequency channel. However, the zone where a single base station can provide service is narrower than that of a mobile wireless communication system, and it is difficult to use a non-mobile wireless communication system for mobile terminals that move at high speed over a wide range of areas, such as drones, cars, and high-speed trains, due to the problem that it is not possible to switch the connection destination base station or communication method until communication is completely interrupted.
　In response to this problem, NTT developed the Base Station Switching Control Technology⁵, which instructs and controls the appropriate base station switching timing and switching destination based on the positioning of the terminal using WiGig communication radio waves, and the Terminal-Driven Dynamic Site Diversity Control Technology⁶, which avoids the interruption of communication during base station switching by controlling the coordination of multiple radio units, with the aim of adapting the non-mobile wireless communication system itself to the mobile terminal, that is, switching the base station of the non-mobile wireless communication system without interruption, and demonstrated its effectiveness in an ultra-high-speed mobile environment using a formula car.
　However, the above problem also manifests itself when the mobile terminal leaves the area of the non-mobile wireless communication system. In other words, due to the nature of the non-mobile wireless communication system that attempts to maintain a connection with the currently connected base station, the switch to the mobile wireless communication system is not performed until the connection is disconnected and communication is completely interrupted, resulting in a problem in which communication with the network is temporarily disconnected (communication interruption: Figure 1). Thus, to increase the capacity of wireless communications by utilizing a non-mobile wireless communication system in a mobile terminal, it was necessary to have a control technology that not only made the non-mobile wireless communication system itself compatible with the mobile, but also realized seamless linkage with the mobile wireless communication system.

Figure 1 Challenges in Merging Mobile and Non-mobile Radios

2. Results of the research

To solve the above problem, NTT has focused on the fact that WiGig communication radio waves themselves are capable of highly accurate communication distance estimation based on the wideband nature of high-frequency band radios. NTT has devised a technique (Seamless switching technology) to seamlessly switch communication to a mobile wireless communication system by avoiding communication interruption by detecting that the terminal reaches the area edge of the non-mobile wireless communication system based on the estimated distance and switching to mobile wireless communication before the connection with the non-mobile wireless communication system is disconnected.
　In this method, by acquiring information on the round-trip transfer time of the beam control information required for wireless communication in the high-frequency band, the communication distance with the base station of the non-mobile wireless communication system is estimated at the terminal side without relying on other positioning systems such as GPS. When the communication distance approaches the expected communication limit of the non-mobile wireless communication system, the terminal switches communication to the mobile wireless communication system side even when the connection with the non-mobile wireless communication system is maintained.
　This makes it possible to seamlessly switch communication to the mobile communication system side and maintain communication without being affected by the deterioration of transmission characteristics at the area edge of the non-mobile wireless communication system. This makes it possible to further increase the capacity of wireless communication by utilizing the non-mobile wireless communication system in mobile terminals.

Figure 2 Proposed Seamless Switching Technology

3. Overview of the experiment

A demonstration test of this technology was conducted at the 2024 All Japan Super Formula Championship Official Joint Test (February 21 to 22, 2024) under the technical cooperation of the racing team "DOCOMO TEAM DANDELION RACING" for the provision and operation of a formula car that reproduces an ultra-high-speed travel environment, and NTT DOCOMO, INC. and DOCOMO Technology, Inc. for the construction of an area for the ultra-high-speed travel test and the installation of a terminal on a vehicle.
　As shown in Figure 3, two WiGig radio units are installed in the rear of the vehicle, a 5G/LTE smartphone is installed in the cockpit, and a function control unit for controlling these functions is installed in the side pontoon on the left side of the vehicle. The radio function section generates dummy data for throughput measurement at a rate of 5 [Mbit/s] and switches the communication system based on the control of the proposed seamless switching technology.
　On the ground side, six WiGig base stations were installed on the left and right sides of the main straight of the Suzuka Circuit. WiGig was used for communication on the main straight, and 5G/LTE was used for other locations in the course (Figure 4). The base station switching control technology described above is applied to the six WiGig base stations, and the terminal-driven dynamic site diversity control technology using two WiGig radio units is applied to the terminals, so that no communication interruption occurs in the WiGig zone. In addition, dummy data sent from the vehicle side was configured to reach the throughput measurement server installed on the ground side via the WiGig base station in the WiGig zone and via the 5G/LTE base station in other locations, and the throughput measured by the server was evaluated.
　Figure 5 shows the throughput without seamless switching technology and Figure 6 shows the throughput with seamless switching technology. In Figure 5, you can see that there are several tens of meters (hundreds of milliseconds in time) where the throughput is 0 [bit/s] when switching from WiGig to 5G/LTE. Due to the nature of non-mobile wireless communication systems, it is not possible to switch communications to 5G/LTE until after WiGig is completely disconnected. On the other hand, in Figure 6, it can be seen that there is no communication interruption in switching from WiGig to 5G/LTE by applying the proposed seamless switching technology. In other words, by applying the seamless switching technology, we confirmed that we could avoid communication interruption by switching the communication to the mobile communication system side in advance using the ranging function based on communication radio waves at the area edge of the non-mobile wireless communication system.
　At the time of this technology demonstration, the vehicle speed was up to 278 km/h at around 550 m, and 254 km/h or more at the point of switching from WiGig to 5G/LTE (measured by GPS installed for the experiment), demonstrating the effectiveness of the proposed seamless switching technology in an ultra-high-speed mobile environment.

Figure 3 Formula Car and In-vehicle System Configuration Used in the Experiment

Figure 4 Experimental Structure

Figure 5 Throughput Characteristics Without Application of the Proposed Technology

Figure 6 Throughput Characteristics When the Proposed Technology is Applied

4. Outlook

Through this experiment, we applied WiGig, one of the high-frequency band non-mobile wireless communication systems, to a high-speed mobile terminal. We confirmed that we could stably achieve large-capacity transmission by avoiding degradation of characteristics by switching the communication to the mobile wireless communication system before the connection is disconnected by detecting the approach to the area edge of the non-mobile wireless communication system by using the ranging function of communication radio waves.
　This result is expected to be used not only in WiGig but also in various high-frequency band wireless transmission systems, and as a technology to select other wireless systems appropriately without relying on external positioning systems such as GPS in a mobile environment where terminals move, even if the mobile environment is not a very high-speed mobile environment such as this experiment. Specifically, in the following use cases, it is possible to utilize non-mobile wireless communication systems such as high-frequency band wireless LANs in addition to the conventional mobile wireless communications such as 5G.

In the future, we will use the results of this demonstration experiment to study the technology to apply this technology in various usage environments and realize more stable and large-capacity wireless transmission. Although this experiment targets non-mobile wireless communication systems, the underlying technology is a range-finding function that focuses on the nature of high-frequency bands. This technology is expected to be used not only for non-mobile wireless communication but also for wireless communication systems in all high-frequency bands. Through this technology, we will continue to study its application to high-frequency band wireless communication systems that are being considered in the IOWN/6G era.

¹WiGig
Short for Wireless Gigabit. Wireless LAN standard using 60 GHz band based on IEEE 802.11ad standard

²Tsukuba Forum 2024
https://www.tsukuba-forum.jp/e/

³Innovative Optical and Wireless Network (IOWN) The IOWN is comprised of three components: the "All Photonics Network (APN)," which makes it possible not only for networks but also for terminal processing; the "Digital Twin Computing," which enables advanced and real-time interaction between objects and humans in cyberspace; and the "Cognitive Foundation," which efficiently deploys various ICT resources

⁴Single Carrier Basic Mode Maximum Transmission Rate IEEE Std-802.11TM-2016 (Revision of IEEE Std 802.11-2012)

⁵https://group.ntt/en/newsrelease/2021/02/03/210203a.html

⁶https://group.ntt/en/newsrelease/2022/02/25/220225a.html

⁷LiDAR (Light Detection and Ranging)
Sensing method for grasping the surrounding environment by observing reflection from objects existing in the surroundings by irradiating light such as laser

About NTT

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