family name 'at' c.titech.ac.jp


Main Research Interests

  • Distributed systems
  • Distributed algorithms
  • Distributed agreement
  • Blockchain protocols
  • Network failure detection
  • Robot coordination algorithms
  • Robot network protocols
  • Multi-robot fault-tolerant middleware


Xavier Défago is a professor in the School of Computing, Tokyo Institute of Technology (Tokyo Tech) since 2016. He obtained his master's degree in Computer Science (spec. Computer Engineering) in 1995 at the Swiss Federal Institute of Technology in Lausanne (EPF Lausanne, Switzerland). After graduation, he worked for one year as a research intern at the NEC C&C Central Research Labs in Kawasaki, Japan. He then returned to the EPFL as an assistant and obtained his Ph.D. in Computer Science in 2000, under the guidance of Prof. André Schiper.

The same year, he joined the Graduate School of Knowledge Science at the Japan Advanced Institute of Science and Technology (JAIST) as a research associate, and then moved to the Graduate School of Information Science as a research associate professor (2003) and later as an associate professor (2006).

In parallel, Xavier was a PRESTO researcher for the Japan Science and Technology Agency (JST) from 2002 to 2006. Recently, he was also invited as a CNRS researcher in France, to work both at LIP6, UPMC, Paris, and at I3S, UNS, Inria Sophia Antipolis in 2013.

Xavier has published more than 80 research papers in prestigious journals and conferences which have been cited numerous times. He has served as PC chair for SRDS 2014, ICDCS 2012, and SSS 2011. He is a member of ACM, IEEE, IEEE-CS, EATCS, IPSJ, and a regular member of the IFIP working group 10.4 on dependable computing and fault-tolerance. His research interests include distributed algorithms, fault-tolerance, group communication, and cooperative autonomous mobile robot networks.

Selected Papers

  • Using model checking to formally verify rendezvous algorithms for robots with lights in Euclidean space. X. Défago, A. Heriban, S. Tixeuil, K. Wada. Robotics Auton. Syst., 2023. doi: 10.1016/j.robot.2023.104378
  • Solving simultaneous target assignment and path planning efficiently with time-independent execution. K. Okumura, X. Défago. Artif. Intell., 2023. doi: 10.1016/j.artint.2023.103946
  • Offline Time-Independent Multiagent Path Planning. K. Okumura, F. Bonnet, Y. Tamura, X. Défago. IEEE Trans. Robotics 39(4):2720-2737 (2023). doi: 10.1109/TRO.2023.3258690
  • Resilient real-valued consensus in spite of mobile malicious agents on directed graphs. Y. Wang, H. Ishii, F. Bonnet, X. Défago. IEEE Trans. Parallel Distributed Syst. 33(3):586-603 (2022). doi: 10.1109/TPDS.2021.3096074
  • Resilient Consensus for Multi-Agent Systems Under Adversarial Spreading Processes. Y. Wang, H. Ishii, F. Bonnet, X. Défago. IEEE Trans. Netw. Sci. Eng. 9(5):3316-3331 (2022). doi: 10.1109/TNSE.2022.3176214
  • Priority inheritance with backtracking for iterative multi-agent path finding. K. Okumura, M. Machida, X. Défago, Y. Tamura. Artif. Intell., 2022. doi: 10.1016/j.artint.2022.103752
  • Time-Independent Planning for Multiple Moving Agents. K. Okumura, Y. Tamura, X. Défago. In Proc. AAAI Conf. on Artificial Intelligence (AAAI), 35(13):11299-11307, Feb. 2021. link
  • Active Modular Environment for Robot Navigation. S. Kameyama, K. Okumura, Y. Tamura, X. Défago. In Proc. IEEE Intl. Conf. on Robotics and Automation (ICRA), June 2021. [PDF]
  • Iterative Refinement for Real-Time Multi-Robot Path Planning. K. Okumura, Y. Tamura, X. Défago.. In Proc. IEEE/RSJ Intl. Conf. on Intelligent Robots and Systems (IROS), Sep. 2021.
  • Roadside-Assisted Cooperative Planning using Future Path Sharing for Autonomous Driving. M. Hirata, M. Tsukada, K. Okumura, Y. Tamura, H. Ochiai, X. Défago. In Proc. IEEE Vehicular Technology Conference (VTC Fall), pp. 1-7, Sep. 2021. doi: 10.1109/VTC2021-Fall52928.2021.9625324
  • Using Model Checking to Formally Verify Rendezvous Algorithms for Robots with Lights in Euclidean Space. X. Défago, A. Heriban, S. Tixeuil, K. Wada. In Proc. 39th IEEE Symp. on Reliable Distributed Systems (SRDS), pp. 113-122, Sep. 2020. doi: 10.1109/SRDS51746.2020.00019
  • Communication Efficient Self-Stabilizing Leader Election. X. Défago, Y. Emek, S. Kutten, T. Masuzawa, Y. Tamura. In Proc. 33rd Intl. Symp. on Distributed Computing (DISC), LIPIcs, Volume 179, pp. 11:1-11:19, Oct. 2020. doi: 10.4230/LIPIcs.DISC.2020.11
  • Self-stabilizing gathering of mobile robots under crash or Byzantine faults. X. Défago, M. Potop-Butucaru, P. Raipin-Parvédy. Distrib. Comput., pp. 393-421, 2020. doi: 10.1007/s00446-019-00359-x online
  • Tight bound on mobile Byzantine Agreement. F. Bonnet, X. Défago, T.-D. Nguyen, M. Potop-Butucaru. Theor. Comput. Sci. 609:361-373 (2016). doi: 10.1016/j.tcs.2015.10.019
  • The Gathering Problem for Two Oblivious Robots with Unreliable Compasses. T. Izumi, S. Souissi, Y. Katayama, N. Inuzuka, X. Défago, K. Wada, M. Yamashita. SIAM Journal on Computing 41(1):26-46 (2012). doi: 10.1137/100797916
  • Definition and specification of accrual failure detectors. X. Défago, P. Urbán, N. Hayashibara, T. Katayama. In Proc. IEEE/IFIP Intl. Conf. on Dependable Systems and Networks (DSN), pp. 206-215, 2005. doi: 10.1109/DSN.2005.37
  • The φ accrual failure detector. N. Hayashibara, X. Défago, R. Yared, T. Katayama. In Proc. 23rd IEEE Intl. Symp. on Reliable Distributed Systems (SRDS), pp. 66-78, 2004. doi: 10.1109/RELDIS.2004.1353004
  • Total order broadcast and multicast algorithms: Taxonomy and survey. X. Défago, A. Schiper, and P. Urbán. ACM Computing Surveys 36(4):372-421 (2004). doi: 10.1145/1041680.1041682
  • ...see more

Projects and Repositories

  • stats-ci: A Rust crate to compute confidence intervals for sample data.
  • spin-light: A generic model for model-checking rendezvous algorithms of robots with lights in SPIN/Promela.
  • ScalaNeko: A development framework for prototyping distributed algorithms in Scala


Xavier Défago
Department of Computer Science, School of Computing
Tokyo Institute of Technology
(office: West Bldg. 8, Room E803)
W8-84, 2-12-1 Ookayama, Meguro-ku Tokyo, 152-8550 JAPAN
E-mail:'family name' @ c.titech.ac.jp