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Documents authored by Kamei, Sayaka

Document
DOI: 10.4230/LIPIcs.OPODIS.2024.12
Crash-Tolerant Perpetual Exploration with Myopic Luminous Robots on Rings

Authors: Fukuhito Ooshita, Naoki Kitamura, Ryota Eguchi, Michiko Inoue, Hirotsugu Kakugawa, Sayaka Kamei, Masahiro Shibata, and Yuichi Sudo

Published in: LIPIcs, Volume 324, 28th International Conference on Principles of Distributed Systems (OPODIS 2024)

Abstract
We investigate crash-tolerant perpetual exploration algorithms by myopic luminous robots on ring networks. Myopic robots mean that they can observe nodes only within a certain fixed distance ϕ, and luminous robots mean that they have light devices that can emit a color from a set of colors. The goal of perpetual exploration is to ensure that robots, starting from specific initial positions and colors, move in such a way that every node is visited by at least one robot infinitely often. As a main contribution, we clarify the tight necessary and sufficient number of robots to realize perpetual exploration when at most f robots crash. In the fully synchronous model, we prove that f+2 robots are necessary and sufficient for any ϕ ≥ 1. In the semi-synchronous and asynchronous models, we prove that 3f+3 (resp., 2f+2) robots are necessary and sufficient if ϕ = 1 (resp., ϕ ≥ 2).
Cite as

Fukuhito Ooshita, Naoki Kitamura, Ryota Eguchi, Michiko Inoue, Hirotsugu Kakugawa, Sayaka Kamei, Masahiro Shibata, and Yuichi Sudo. Crash-Tolerant Perpetual Exploration with Myopic Luminous Robots on Rings. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 12:1-12:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{ooshita_et_al:LIPIcs.OPODIS.2024.12,
  author =	{Ooshita, Fukuhito and Kitamura, Naoki and Eguchi, Ryota and Inoue, Michiko and Kakugawa, Hirotsugu and Kamei, Sayaka and Shibata, Masahiro and Sudo, Yuichi},
  title =	{{Crash-Tolerant Perpetual Exploration with Myopic Luminous Robots on Rings}},
  booktitle =	{28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
  pages =	{12:1--12:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-360-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{324},
  editor =	{Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.12},
  URN =		{urn:nbn:de:0030-drops-225486},
  doi =		{10.4230/LIPIcs.OPODIS.2024.12},
  annote =	{Keywords: mobile robots, crash faults, LCM model, exploration}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2024.55
Brief Announcement: Self-Stabilizing Graph Exploration by a Single Agent

Authors: Yuichi Sudo, Fukuhito Ooshita, and Sayaka Kamei

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
In this paper, we present two self-stabilizing algorithms that enable a single (mobile) agent to explore graphs. The agent visits all nodes starting from any configuration, i.e., regardless of the initial state of the agent, the initial states of all nodes, and the initial location of the agent. We evaluate the algorithms using two metrics: cover time, which is the number of moves required to visit all nodes, and memory usage, which includes the storage needed for the state of the agent and the state of each node. The first algorithm is randomized. Given an integer c = Ω(n), the cover time of this algorithm is optimal, i.e., O(m) in expectation, and the memory requirements for the agent and each node v are O(log c) and O(log (c+δ_v)) bits, respectively, where n and m are the numbers of nodes and edges, respectively, and δ_v is the degree of v. The second algorithm is deterministic. It requires an input integer k ≥ max(D,δ_max), where D and δ_max are the diameter and the maximum degree of the graph, respectively. The cover time of this algorithm is O(m + nD), and it uses O(log k) bits both for agent memory and each node.
Cite as

Yuichi Sudo, Fukuhito Ooshita, and Sayaka Kamei. Brief Announcement: Self-Stabilizing Graph Exploration by a Single Agent. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 55:1-55:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{sudo_et_al:LIPIcs.DISC.2024.55,
  author =	{Sudo, Yuichi and Ooshita, Fukuhito and Kamei, Sayaka},
  title =	{{Brief Announcement: Self-Stabilizing Graph Exploration by a Single Agent}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{55:1--55:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.55},
  URN =		{urn:nbn:de:0030-drops-212832},
  doi =		{10.4230/LIPIcs.DISC.2024.55},
  annote =	{Keywords: mobile agents, self-stabilization, graph exploration}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2021.9
Asynchronous Gathering in a Torus

Authors: Sayaka Kamei, Anissa Lamani, Fukuhito Ooshita, Sébastien Tixeuil, and Koichi Wada

Published in: LIPIcs, Volume 217, 25th International Conference on Principles of Distributed Systems (OPODIS 2021)

Abstract
We consider the gathering problem for asynchronous and oblivious robots that cannot communicate explicitly with each other but are endowed with visibility sensors that allow them to see the positions of the other robots. Most investigations on the gathering problem on the discrete universe are done on ring shaped networks due to the number of symmetric configurations. We extend in this paper the study of the gathering problem on torus shaped networks assuming robots endowed with local weak multiplicity detection. That is, robots cannot make the difference between nodes occupied by only one robot from those occupied by more than one robot unless it is their current node. Consequently, solutions based on creating a single multiplicity node as a landmark for the gathering cannot be used. We present in this paper a deterministic algorithm that solves the gathering problem starting from any rigid configuration on an asymmetric unoriented torus shaped network.
Cite as

Sayaka Kamei, Anissa Lamani, Fukuhito Ooshita, Sébastien Tixeuil, and Koichi Wada. Asynchronous Gathering in a Torus. In 25th International Conference on Principles of Distributed Systems (OPODIS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 217, pp. 9:1-9:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{kamei_et_al:LIPIcs.OPODIS.2021.9,
  author =	{Kamei, Sayaka and Lamani, Anissa and Ooshita, Fukuhito and Tixeuil, S\'{e}bastien and Wada, Koichi},
  title =	{{Asynchronous Gathering in a Torus}},
  booktitle =	{25th International Conference on Principles of Distributed Systems (OPODIS 2021)},
  pages =	{9:1--9:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-219-8},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{217},
  editor =	{Bramas, Quentin and Gramoli, Vincent and Milani, Alessia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2021.9},
  URN =		{urn:nbn:de:0030-drops-157845},
  doi =		{10.4230/LIPIcs.OPODIS.2021.9},
  annote =	{Keywords: Autonomous distributed systems, Robots gathering, Torus}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2019.27
Gathering on Rings for Myopic Asynchronous Robots With Lights

Authors: Sayaka Kamei, Anissa Lamani, Fukuhito Ooshita, Sébastien Tixeuil, and Koichi Wada

Published in: LIPIcs, Volume 153, 23rd International Conference on Principles of Distributed Systems (OPODIS 2019)

Abstract
We investigate gathering algorithms for asynchronous autonomous mobile robots moving in uniform ring-shaped networks. Different from most work using the Look-Compute-Move (LCM) model, we assume that robots have limited visibility and lights. That is, robots can observe nodes only within a certain fixed distance, and emit a color from a set of constant number of colors. We consider gathering algorithms depending on two parameters related to the initial configuration: M_{init}, which denotes the number of nodes between two border nodes, and O_{init}, which denotes the number of nodes hosting robots between two border nodes. In both cases, a border node is a node hosting one or more robots that cannot see other robots on at least one side. Our main contribution is to prove that, if M_{init} or O_{init} is odd, gathering is always feasible with three or four colors. The proposed algorithms do not require additional assumptions, such as knowledge of the number of robots, multiplicity detection capabilities, or the assumption of towerless initial configurations. These results demonstrate the power of lights to achieve gathering of robots with limited visibility.
Cite as

Sayaka Kamei, Anissa Lamani, Fukuhito Ooshita, Sébastien Tixeuil, and Koichi Wada. Gathering on Rings for Myopic Asynchronous Robots With Lights. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 27:1-27:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{kamei_et_al:LIPIcs.OPODIS.2019.27,
  author =	{Kamei, Sayaka and Lamani, Anissa and Ooshita, Fukuhito and Tixeuil, S\'{e}bastien and Wada, Koichi},
  title =	{{Gathering on Rings for Myopic Asynchronous Robots With Lights}},
  booktitle =	{23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
  pages =	{27:1--27:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-133-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{153},
  editor =	{Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.27},
  URN =		{urn:nbn:de:0030-drops-118139},
  doi =		{10.4230/LIPIcs.OPODIS.2019.27},
  annote =	{Keywords: LCM robot system, ASYNC schedulers, myopic, luminous, ring networks}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2019.43
Brief Announcement: Neighborhood Mutual Remainder and Its Self-Stabilizing Implementation of Look-Compute-Move Robots

Authors: Shlomi Dolev, Sayaka Kamei, Yoshiaki Katayama, Fukuhito Ooshita, and Koichi Wada

Published in: LIPIcs, Volume 146, 33rd International Symposium on Distributed Computing (DISC 2019)

Abstract
In this paper, we define a new concept neighborhood mutual remainder (NMR). An NMR distributed algorithms should satisfy global fairness, l-exclusion and repeated local rendezvous requirements. We give a simple self-stabilizing algorithm to demonstrate the design paradigm to achieve NMR, and also present applications of NMR to a Look-Compute-Move robot system.
Cite as

Shlomi Dolev, Sayaka Kamei, Yoshiaki Katayama, Fukuhito Ooshita, and Koichi Wada. Brief Announcement: Neighborhood Mutual Remainder and Its Self-Stabilizing Implementation of Look-Compute-Move Robots. In 33rd International Symposium on Distributed Computing (DISC 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 146, pp. 43:1-43:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{dolev_et_al:LIPIcs.DISC.2019.43,
  author =	{Dolev, Shlomi and Kamei, Sayaka and Katayama, Yoshiaki and Ooshita, Fukuhito and Wada, Koichi},
  title =	{{Brief Announcement: Neighborhood Mutual Remainder and Its Self-Stabilizing Implementation of Look-Compute-Move Robots}},
  booktitle =	{33rd International Symposium on Distributed Computing (DISC 2019)},
  pages =	{43:1--43:3},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-126-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{146},
  editor =	{Suomela, Jukka},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2019.43},
  URN =		{urn:nbn:de:0030-drops-113504},
  doi =		{10.4230/LIPIcs.DISC.2019.43},
  annote =	{Keywords: neighborhood mutual remainder, self-stabilization, LCM robot}
}
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