[Highlights]
[Summary]
The National Institute of Information and Communications Technology (NICT, President: Hideyuki Tokuda, Ph.D.) Network System Research Institute performed a proof-of-concept demonstration of an uninterrupted communication system for high-speed trains by adopting a combination of a linear cell network configuration, a high-speed seamless fiber-wireless system in the millimeter-wave (mmWave) band, and an ultra-fast optical-path switching technique. We successfully transmitted data at a rate of 20 Gbit/s from each remote radio station using a wavelength-division-multiplexing fiber-wireless network for the transmission of mmWave signals in the 90-GHz band. Ultra-fast switching of the optical paths to the remote radio stations in less than 10 μs was also successfully demonstrated using ultra-fast wavelength-tunable lasers, indicating that a smooth and uninterrupted communication (handover-free) network can be realized for high-speed railways. Handover-free communication has been considered a big challenge for avoiding significant degradation of the throughput of high-mobility users, which includes users on high-speed trains, due to the frequently interrupted connections with radio stations. The use of seamless convergence of fiber-optic and wireless networks in high-frequency mmWave bands shows that such a challenge can be overcome, even when the trains are moving at high speeds of 500 km/h or faster. The results of this demonstration were published as a post-deadline paper at the 41st Optical Fiber Communication Conference and Exhibition (OFC2018).
[Background]
The demands for high-speed and smooth communications are rapidly increasing, even from users who are on highly moving vehicles, such as high-speed trains, because of the explosive popularization of smartphones and other personal multimedia devices. In current cellular networks, however, connections to internet networks during high-speed movement are frequently interrupted because of radio station switching (handover). To overcome this limitation, we developed a high-speed and handover-free communication network for high-speed trains using a seamless wavelength-division-multiplexing (WDM) radio-over-fiber (RoF) and wireless network in the high-frequency bands. This work was conducted as a part of a project titled "Research and development of millimeter-wave backhaul technology for high-speed vehicles", funded by the Ministry of Internal Affairs and Communications (MIC), Japan (Research representative: Hitachi Kokusai Electric Inc.).
[Achievements]
The system consists of the following principal technologies:
In high-speed railways, the remote radio station that should be activated to communicate with a train can be determined precisely using information about the location of the train from a train operation direction center. By distributing signals to radio stations appropriately, a smooth and uninterrupted (handover-free) communication system can be realized. In addition, owing to the use of a centralized network, remote radio stations can be greatly simplified and, thus, the cost and power consumption of the system can be significantly reduced.
[Future Prospects]
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