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

  • 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
  • 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.
  • 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
  • Priority Inheritance with Backtracking for Iterative Multi-agent Path Finding. K. Okumura, M. Machida, X. Défago, Y. Tamura. In Proc. 28th Intl. Joint Conf. on Artificial Intelligence (IJCAI), pp. 535-542, Aug. 2019. doi: 10.24963/ijcai.2019/76
  • Killing Nodes as a Countermeasure to Virus Expansion. F. Bonnet, Q. Bramas, X. Défago, Thanh Dang Nguyen. In Proc. 24th Intl. Coll. Structural Information and Communication Complexity (SIROCCO), LNCS 10641, pp. 227-243, Jun. 2017. doi: 10.1007/978-3-319-72050-0_14
  • 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
  • Using eventually consistent compasses to gather memory-less mobile robots with limited visibility. S. Souissi, X. Défago, M. Yamashita. ACM Trans. on Autonomous and Adaptive Systems, 2009. doi: 10.1145/1462187.1462196
  • Non-uniform circle formation algorithm for oblivious mobile robots with convergence toward uniformity. X. Défago, S. Souissi. Theor. Comput. Sci. 396(1-3):97-112 (2008). doi: 10.1016/j.tcs.2008.01.050
  • Collision Prevention Platform for a Dynamic Group of Asynchronous Cooperative Mobile Robots. R. Yared, X. Défago, J. Iguchi-Cartigny, M. Wiesmann. Journal of Networks 2(4):28-39 (2007). doi: 10.4304/jnw.2.4.28-39 [PDF]
  • 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
  • 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
  • Semi-passive replication and Lazy Consensus. X. Défago and A. Schiper. Journal of Parallel and Distributed Computing 64(12):1380-1398 (2004). doi: 10.1016/j.jpdc.2004.08.006
  • 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
  • ...see more


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