HTML5 Webook

50/64

48Research Highlightsthe Ministry of Internal Affairs and Communications (MIC), Japan (Re-search representative: Hitachi Kokusai Electric Inc.).In this work, the NICT researchers developed a technology to transmit approximately 20-Gbit/s radio signals (16-QAM, carrier frequency of 7 GHz and sampling rate of 6 GHz) in the 90-GHz band from a central station to 50 remote radio stations using a switch-able wavelength-division-multiplexing radio-over-fiber 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 switch-ing time of less than 10 µs was achieved using high-speed wave-length-tunable lasers. “We demonstrat-ed that the signal distribution to ra-dio stations can be switched in less than 10 µs.”In high-speed railways, the radio stations that the trains are approaching can be precisely predicted using train information such as train location and velocity, which is available at the train operation center. Thus, appropriate sig-nal distribution to the corresponding radio stations can be performed by means of high-speed optical switching technologies, such as high-speed wavelength-tunable lasers. Naokatsu Yamamoto, Director of the NSRI Net-work Science and Convergence De-vice Technology Laboratory, stated, “We demonstrated that the signal dis-tribution to radio stations can be switched in less than 10 µs. This indi-cates that an uninterrupted communi-cation system for high-speed railways can be constructed, even for trains moving at 500 km/h or faster.” Handover-free communication has faced a significant challenge in terms of 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. With this network configuration, the devel-opment of an uninterrupted network for high-mobility users can be imple-mented in an easier way than in stan-dard cellular networks because the necessary control signals are available at central stations.Dr. Yamamoto further said, “In the future, in collaboration with Hitachi Kokusai Electric Inc., the Railway Tech-nology Research Institute, the Elec-tronic Navigation Research Institute (part of the National Institute of Mari-time, Port and Aviation Technology In-stitute), and other related parties in the aforementioned MIC-funded project, we will implement field test demon-strations on actual railway lines.”ReferencePham Tien Dat, Atsushi Kanno, Keizo Inagaki, Toshimasa Umezawa, Fançoir Rottenberg, Jérome Louveaux, Naokatsu Yamamoto, and Tetsuya Kawanishi, “High-Speed and Hando-ver-Free Communications for High-Speed Trains Using Switched WDM Fiber–Wireless System,” in Proc. 41st Optical Fiber Com-munication Conference and Exhibition (OFC), March 2018, paper Th4D. 2.Conceptual diagram of the proposed communication system for high-speed railways (left) and radio station switching and performance of 16-QAM signals (right).