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術及び光・電波融合システムについて概説した。ユーザが使う通信手段が無線アクセスへと収れんする中、その無線アクセスシステムを支えるための光アクセス技術は、ユーザの目に直接触れにくいインフラ設備化が加速すると考えられる。しかしながら、光アクセスシステムの高度化により無線アクセスシステムが実現されていることも紛れもない事実である。有線・無線の伝送メディアを意識しないで利用可能な融合型アクセスシステムの実現に向け、光と電波を更に高度に融合した通信システムの研究開発を加速させていく予定である。謝辞本研究は、総務省「電波資源拡大のための研究開発」の一部として実施された。本研究成果の一部は、光産業創成大学院大学　北山教授、朱助教との共同研究により実施された。空港滑走路面異物検知レーダシステムの共同実験に際し、日立国際電気株式会社 佐藤洋介博士、柴垣信彦氏、加島謙一氏、国立研究開発法人海上・港湾・航空技術研究所電子航法研究所 米本成人博士及び成田国際空港株式会社の関係者皆様に感謝する。【参考文献【1V. Chandrasekhar, J. G. Andrews, and A. Gatherer, “Femtocell networks: a survey,” IEEE Commun. Mag., vol.46, no.9, pp.59–67, Sept. 2008.2J. G. Andrews et al., "What will 5G be?" IEEE J. Sel. Areas Commun., vol.32, no.6, pp.1065–1082, June 2014.33GPP TR38.913: “Study on scenarios and requirements for next gen-eration access technologies,” July 2018.4“C-RAN: The Road towards Green RAN,” China Mobile White Paper, v2, 2011. 5Y. Yoshida, “Mobile xHaul evolution: Enabling tools for a flexible 5G xHaul network (tutorial),” in proc. OFC2018, paper Tu2K.1, 2018.6A. Checko et al., "Cloud RAN for mobile networks—A technology overview," IEEE Commun. Surveys Tuts., vol.17, no.1, pp.405–426, Sept. 2014.7T. Kawanishi et al.,“Wired and Wireless Links to Bridge Networks: Seamlessly Connecting Radio and Optical Technologies for 5G Networks,” IEEE Microw. Mag., vol.19, no.3, pp.102–111 (2018).8CPRI Specification v7.0, Technical Report, 2015.93GPP TR 38.816 V1.0.0: “Study on CU-DU lower layer split for NR,” Dec. 2017.10S. Park et al., "Fronthaul compression for cloud radio access networks: Signal processing advances inspired by network information theory," IEEE Signal Process. Mag., vol.31, no.6, pp.69–79, Nov. 2014.11ETSI standard, GS Open Radio Interface (ORI) 002-1 V4.1.1, Oct. 2014.12M. Xu et al., "Key technologies for next-generation digital RoF mobile fronthaul with statistical data compression and multiband modulation," J. Lightw. Technol., vol.35, no.17, pp.3671–3679, Sept. 2017.13S. H. Kim et al., “Experimental demonstration of CPRI data compression based on partial bit sampling for mobile front-haul link in C-RAN,” in proc. OFC 2016, paper W1H.5, March 2016.14L. Zhang et al., "Digital mobile fronthaul employing differential pulse code modulation with suppressed quantization noise," Opt. Express vol.25, no.25, p. 31936, Dec. 2017.15eCPRI Specification v1.2, Technical Report, June 2018.16P. Zhu et al., “MIMO fronthaul compression inspired by parametric stereo audio coding,” 信学技報, vol.117, no.422, CS2017-83, pp.25–30, 2018年1月.17P. Zhu et al., “256-antenna massive MIMO fronthaul uplink with 10GBd PAM4 optical interface enabled by adaptive space-time compression,” in proc. the 44th European Conference on Optical Communication (ECOC), paper Tu3B.6, Sept. 2018. 18R. Badeau et al., “Fast approximated power iteration subspace track-ing,” IEEE Trans. Signal Proc., vol.53, no.8, pp.2931–2941, Aug. 2005.19ITU-T Recommendation G.726, 1990.20P. T. Dat et al., “Radio-on-radio-over-fiber: efficient fronthauling for small cells and moving cells,” IEEE Wireless Communications, vol.22, no.5, pp.67–75, Oct. 2015.21P. T. Dat et al., “Full-Duplex Transmission of LTE-A Carrier Aggregation Signal over a Bidirectional Seamless Fiber-Millimeter-Wave System,” IEEE/OSA Journal of Lightwave Technology, vol.34, no.2, pp.691–700, Jan. 2016. 22T. Kawanishi et al., “High-speed control of lightwave amplitude, phase, and frequency by use of electrooptic effect,” IEEE J. Sel. Topics Quantum Electron.,vol.13, no.1, pp.79–91, Jan./Feb. 2007. 23A. Kanno et al., “Millimeter-Wave Radio-Over-Fiber Network for Linear Cell Systems,” Journal of Lightwave Technology, vol.36, no.2, pp.533–540. Jan. 2018. 24P. T. Dat et al., “Radio-over-Fiber-based Seamless Fiber-Wireless Convergence for Small Cell and Linear Cell Networks,” Proc. OFC 2018, M4J.5. 25P. T. Dat et al., “Simultaneous transmission of multi-RATs and mobile fronthaul in the MMW bands over an IFoF system,” proc. OFC 2017, W1C. 4. 26P T. Dat et al., “Energy and deployment efficiency of a millimeter-wave Radio-on-Radio-over-fiber system for railways,” OFC 2013, JTh2A.61. 27P. T. Dat et al., “High-Speed and Handover-Free Communications for High-Speed Trains Using Switched WDM Fiber-Wireless System,” Proc. OFC 2018, Th4D.2. 28P. T. Dat et al., “Cell-less Network for Handover-Free Communications to High-Speed Trains Using a Switched WDM Fiber–Wireless Backhaul,” to be presented at ECOC 2018. 29川西哲也,木内等, “光で電波を見る,” NICT News, no.430, pp.3–4（2013）30N. Shibagaki, “Experimental Study of Photonic Based Radar for FOD Detection Systems Using 90 GHz-Band,” Air Traffic Manag. System, vol.420, pp.239–248 (2017).31Y. Sato et al., “90GHz-band FOD detection Radar System for Runway Surveillance,” ENRI International Workshop on ATM/CNS, Tokyo, Japan, EN-I-80, Nov. 2017.菅野敦史 （かんの　あつし）ネットワークシステム研究所ネットワーク基盤研究室主任研究員博士（理学）光ファイバ無線、高速光変調Pham Tien Dat　（ふぁん　てぃえん　だと）ネットワークシステム研究所ネットワーク基盤研究室研究員Ph.D.光ファイバ無線、光無線通信654-3　光ファイバ無線技術　～光・電波ネットワークのシームレスな融合に向けた波形伝送技術の研究開発～