Towards uninterrupted communication for users moving at 500 km per hour
- High-capacity transmissions of 20 Gbit/s over a converged fiber-wireless network in the 90-GHz band.
- Ultra-fast remote radio station switching in less than 10 μs to realize a handover-free communication network.
- Possibility for developing smooth communications for high-speed trains, even while they move at high speeds of 500 km/h or more.
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).
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.).
In this work, NICT developed a technology to transmit 20-Gbit/s radio signals in the 90-GHz band from a central station to 50 remote radio stations using a switchable WDM-RoF and mmWave wireless network. The switching of the remote radio stations in accordance with the movement of trains can be controlled from the central station, and a switching time of less than 10 μs was achieved using high-speed wavelength-tunable lasers.
The system consists of the following principal technologies:
- High-speed wavelength tunable laser sources.
- 16-QAM multilevel modulation/demodulation technology with a sampling speed of 5GHz.
- High-speed optical-to-electrical converter for mmWave signal generation.
- Linear cell configuration for signal distribution to railway tracks.
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.
In the future, in collaboration with Hitachi Kokusai Electric Inc., the Railway Technical Research Institute, the Electronic Navigation Research Institute (part of the National Institute of Maritime, Port and Aviation Technology), and other related parties in the aforementioned MIC-funded project, we will implement field test demonstrations on actual railway lines.