# Hirotsugu Kakugawa's research while affiliated with Ryukoku University and other places

## Publications (144)

Chapter
This paper considers perpetual exploration of anonymous cactus graphs with distinguishable cycles by a single mobile agent under the restriction that nodes have no storage (e.g., whiteboards or token places). A cactus with distinguishable cycles allows the agent to distinguish at each node the two incident edges contained in each cycle from other i...
Article
A self-stabilizing distributed algorithm is guaranteed eventually to reach and stay at a legitimate configuration regardless of the initial configuration of a distributed system. In this paper, we propose the generalized dominating set problem, which is a generalization of the dominating set and $k$-redundant dominating set problems. In the general...
Article
In self-organizing distributed systems in which there is no centralized controller, cooperation of processes and fault-tolerance are crucial. The former can be formalized by process synchronization, which is one of the fundamental problems in concurrent, parallel and distributed computing. The latter can be formalized by self-stabilization. A self-...
Article
Mobile agents (agents) are objects which can migrate autonomously in a distributed system and execute actions at visited nodes. One of the most fundamental problems of agents is exploration, which requires that each node should be visited by at least one agent. For a long time, researchers focus on exploration of static networks while exploration o...
Article
We consider the 1-maximal independent set (1-MIS) problem: given a graph G = (V, E), our goal is to find a 1-maximal independent set (1-MIS) of a given network G, that is, a maximal independent set (MIS) S ⊂ V of G such that S ∪ {v, w} ∖ {u} is not an independent set for any nodes u ∈ S, and v, w ∉ S (v ≠ w). We give a silent, self-stabilizing, and...
Chapter
We consider the dispersion problem for mobile agents. Initially, k agents are located at arbitrary nodes in an undirected graph. Agents can migrate from node to node via an edge in the graph synchronously. Our goal is to let the k agents be located at different k nodes while minimizing the number of steps before dispersion is completed and the work...
Preprint
We consider the dispersion problem for mobile agents. Initially, k agents are located at arbitrary nodes in an undirected graph. Agents can migrate from node to node via an edge in the graph synchronously. Our goal is to let the k agents be located at different k nodes with minimizing the number of steps before dispersion is completed and the worki...
Article
Full-text available
In this paper, we present the first leader election protocol in the population protocol model that stabilizes within O(log n) parallel time in expectation with O(log n) states per agent, where n is the number of agents. Given a rough knowledge m of lg n such that m ≥ lg n and m = O(log n), the proposed protocol guarantees that exactly one leader is...
Article
In this paper, we consider the partial gathering problem of mobile agents in asynchronous unidirectional ring networks. The partial gathering problem is a generalization of the (well-investigated) total gathering problem, which requires that all the k agents distributed in the network terminate at a single node. The partial gathering problem requir...
Article
We consider the leader election problem in the population protocol model, which Angluin et al. proposed in 2004. A self-stabilizing leader election is impossible for complete graphs, arbitrary graphs, trees, lines, degree-bounded graphs, and so on unless the protocol knows the exact number of nodes. In 2009, to circumvent the impossibility, we intr...
Article
In this paper, we consider the uniform deployment problem of mobile agents in asynchronous unidirectional ring networks. This problem requires agents to spread uniformly in the network. In this paper, we focus on the memory space per agent required to solve the problem. We consider two problem settings. The first setting assumes that agents have no...
Article
We consider the local (1,|Ni|)‐critical section (CS) problem where Ni is the set of neighboring processes for each process Pi. It dynamically maintains two disjoint dominating sets and is one of the generalizations of the mutual exclusion problem. The problem is one of controlling the system in such a way that, for each process, among its neighbors...
Chapter
In this paper, we present the first leader election protocol in the population protocol model that stabilizes within $$O(\log n)$$ parallel time in expectation with $$O(\log n)$$ states per agent, where n is the number of agents. Given a rough knowledge m of the population size n such that $$m \ge \log _2 n$$ and $$m=O(\log n)$$, the proposed proto...
Chapter
An effective atomic cross-chain swap protocol is introduced by Herlihy [Herlihy, 2018] as a distributed coordination protocol in order to exchange assets across multiple blockchains among multiple parties. An atomic cross-chain swap protocol guarantees; (1) if all parties conform to the protocol, then all assets are exchanged among parties, (2)even...
Chapter
We consider the 1-maximal independent set (1-MIS) problem: given a graph $$G=(V,E)$$, our goal is to find an 1-maximal independent set (1-MIS) of a given network G, that is, a maximal independent set (MIS) $$S \subset V$$ of G such that $$S \cup \{v,w\} \setminus \{u\}$$ is not an independent set for any nodes $$u \in S$$, and $$v,w \notin S$$ ($$v... Article A loosely-stabilizing leader election protocol with polylogarithmic convergence time in the population protocol model is presented in this paper. In the population protocol model, which is a common abstract model of mobile sensor networks, it is known to be impossible to design a self-stabilizing leader election protocol unless the exact number of... Article This paper considers the global (l,k)-critical section problem which is the problem of controlling a system in such a way that at least l and at most k processes must be in the critical section at any time in the network, while each process alternates between in the critical section and out of the critical section. In this paper, first, a distribut... Article Wireless energy transfer is a technology to transmit electricity without wire, and it is a promising technology for charging battery of mobile devices. In battery powered sensor networks, it is important to balance electric energy of batteries of nodes in order to maximize the life time of networks. In this paper, we propose three distributed proto... Conference Paper In this paper, we present a leader election protocol in the population protocol model that stabilizes within O(log n) parallel time in expectation with O(log n) states per agent, where n is the number of agents. Given a rough knowledge m of the population size n such that m ≥ = log2 n and m=O(log n), this protocol guarantees that exactly one leader... Chapter In this paper, we consider the partial gathering problem of mobile agents in asynchronous unidirectional rings. This problem requires that, for a given positive integer g, all the agents terminate in a configuration such that at least g agents or no agent exist at each node. While the previous work achieves move-optimal partial gathering using dist... Chapter Self-stabilization [2] is a promising paradigm for designing distributed systems that are highly-tolerant of transient faults and adaptive to topology changes, since it guarantees that a system can recover its intended behavior even when its configuration (or global state) is arbitrarily changed by transient faults or topology changes. However, the... Preprint An effective atomic cross-chain swap protocol is introduced by Herlihy [Herlihy, 2018] as a distributed coordination protocol in order to exchange assets across multiple blockchains among multiple parties. An atomic cross-chain swap protocol guarantees; (1) if all parties conform to the protocol, then all assets are exchanged among parties, (2)even... Article In this paper, we consider the partial gathering problem of mobile agents in arbitrary networks. The partial gathering problem is a generalization of the (well-investigated) total gathering problem, which requires that all the agents meet at the same node. The partial gathering problem requires, for a given positive integer g, that each agent shoul... Preprint In this paper, the leader election problem in the population protocol model is considered. A leader election protocol with logarithmic stabilization time is given. Given a rough knowledge m of the population size n such that m >= \log_2 n and m=O(log n), the proposed protocol guarantees that exactly one leader is elected from n agents within O(log... Article In the population protocol model [Angluin et al. 2006], it is impossible to design a self-stabilizing leader election protocol without any knowledge of the exact number of nodes in the system. The notion of loose-stabilization, which relaxes the closure requirement of self -stabilization, was introduced in 2009 to circumvent this impossibility. The... Preprint This paper considers the global (l,k)-CS problem which is the problem of controlling the system in such a way that, at least l and at most k processes must be in the CS at a time in the network. In this paper, a distributed solution is proposed in the asynchronous message-passing model. Our solution is a versatile composition method of algori... Conference Paper Chapter In this paper, we consider the uniform deployment problem of mobile agents in asynchronous unidirectional ring networks. This problem requires agents to spread uniformly in the network. In this paper, we focus on the memory space per agent required to solve the problem. We consider two problem settings. The first setting assumes that agents have no... Article In this paper, we consider the uniform deployment problem of mobile agents in asynchronous unidirectional rings, which requires the agents to uniformly spread in the ring. The uniform deployment problem is in striking contrast to the rendezvous problem which requires the agents to meet at the same node. While rendezvous aims to break the symmetry,... Conference Paper A dominating set in a distributed system is a set of nodes such that each node is contained in the set or has at least one neighbor in the set. Conference Paper In this paper, we consider the uniform deployment problem or the uniform scattering problem) of mobile agents in ring networks, which requires agents initially deployed at arbitrary nodes to spread uniformly in the ring. Conference Paper We propose a fault-tolerant algorithm to simulate message-passing algorithms in mobile agent systems. We consider a mobile agent system with k agents where f of them may crash for a given f (\(\le k-1$$). The algorithm simulates a message-passing algorithm, say Z, with $$O((m+M)f)$$ total agent moves where m is the number of links in the network an...
Article
Full-text available
In this paper, we consider the partial gathering problem of mobile agents in asynchronous tree networks. The partial gathering problem is a generalization of the classical gathering problem, which requires that all the agents meet at the same node. The partial gathering problem requires, for a given positive integer g, that each agent should move t...
Article
This paper discusses the generalized local version of critical section problems including mutual exclusion, mutual inclusion, k-mutual exclusion and l-mutual inclusion. When a pair of numbers (li, ki) is given for each process Pi, it is the problem of controlling the system in such a way that the number of processes that can execute their critical...
Conference Paper
This paper discusses the generalized local version of critical section problems including mutual exclusion, mutual inclusion, k-mutual exclusion and l-mutual inclusion. When a pair of numbers (li, ki) is given for each process Pi, it is the problem of controlling the system in such a way that the number of processes which can be execute their criti...
Conference Paper
In this paper, we consider the uniform deployment problem of mobile agents in asynchronous unidirectional rings, which requires the agents to uniformly spread in the ring. The uniform deployment problem is striking contrast to the rendezvous problem which requires the agents to meet at the same node. While the rendezvous aims to break the symmetry,...
Article
Full-text available
In this paper, we consider the partial gathering problem of mobile agents in asynchronous unidirectional rings equipped with whiteboards on nodes. The partial gathering problem is a new generalization of the total gathering problem. The partial gathering problem requires, for a given integer $g$, that each agent should move to a node and terminate...
Article
Local mutual inclusion is a process synchronization problem where, for each process, at least one of its processes and neighbors must be in the critical section. We propose a self-stabilizing distributed solution to the local mutual inclusion problem. Convergence time of the proposed algorithm is one round under the weakly fair distributed daemon.
Article
Full-text available
Mutual exclusion is a fundamental process synchronization problem in concurrent systems. In this paper, we propose a unified framework for mutual exclusion, k-mutual exclusion, mutual inclusion, ℓ-mutual inclusion and such, what we call critical section problem. Then, we show that critical section problem is characterized by a pair of integers.
Article
In the mutual inclusion problem, at least one process is in the critical section. However, only a solution for two processes with semaphores has been reported previously. In this study, a generalized problem setting is formalized and two distributed solutions are proposed based on an asynchronous message-passing model. In the local problem setting...
Conference Paper
In the population protocol model Angluin et al. proposed in 2004, there exists no self-stabilizing protocol that solves leader election on complete graphs without knowing the exact number of nodes. To circumvent the impossibility, we previously introduced the concept of loose-stabilization, which relaxes the closure requirement of self-stabilizatio...
Conference Paper
In this paper, we consider the partial gathering problem of mobile agents in asynchronous tree networks. The partial gathering problem is a new generalization of the total gathering problem, which requires that all the agents meet at the same node. The partial gathering problem requires, for given input g, that each agent should move to a node and...
Article
We consider the gathering problem of multiple (mobile) agents in anonymous unidirectional ring networks under the constraint that each agent knows neither the number of nodes nor the number of agents. For this problem, we fully characterize the relation between probabilistic solvability and termination detection. First, we prove for any (small) con...
Article
Randomization is a technique to improve efficiency and computability of distributed computing. In this paper, we investigate fault tolerance of distributed computing against faults of random number generators. We introduce an RNG (Random Number Generator)-fault as a new class of faults; a random number generator on an RNG-faulty process outputs the...
Conference Paper
In this paper, we present a local-information-based self-optimizing routing protocol Zigzag in virtual grid networks. A virtual grid network is obtained by virtually dividing a wireless network into a grid of geographical square regions called cells, and is used in MANETs and sensor networks to reduce energy consumption. A single node is selected a...
Article
We investigate the relation between the (ideal) time and space complexities for the gathering problem with kk anonymous agents in asynchronous anonymous tree networks. The gathering problem requires that all the agents in the network have to meet at a single node within a finite time. Although an asymptotically space-optimal algorithm is known, its...
Conference Paper
A self-stabilizing protocol is guaranteed to eventually reach a safe (or legitimate) configuration even when started from an arbitrary configuration. Most of self-stabilizing protocols require each process to keep communicating with all of its neighbors forever even after reaching a safe configuration. Such permanent communication impairs efficienc...
Conference Paper
We consider the rendezvous problem of multiple (mobile) agents in anonymous unidirectional ring networks under the constraint that each agent knows neither the number of nodes nor the number of agents. First, we prove for any (small) constant p(0<p≤1) that there exists no randomized algorithm that solves, with probability p, the rendezvous problem...
Article
A key problem in designing self-stabilising algorithm is to minimise the stabilisation time (also called convergence time), that is, the maximum time necessary to bring a system into a legitimate configuration after an arbitrary initialisation or after a fault; this process is called stabilisation. Except for Masuzawa and Kakugawa (2005); Nakaminam...
Article
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This paper introduces a smart office chair, Owens Luis, whose pronunciation has a meaning of “an encouraging chair (****)” in Japanese. For most of the people, office environments are the place where they spend the longest time while awake. To improve the quality of life (QoL) in the office, Owens Luis monitors an office worker's mental and physiol...
Article
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We propose a smart office system that recognizes office workers' mental and physiological states to improve their quality of life at office. We integrated our systems into a single smart office environment. In this article we show the implementation of the smart office system and the details of each of its components such as I/O devices.
Conference Paper
A self-stabilizing protocol can achieve its intended behavior regardless of the initial configuration (i.e., global state). Thus, a self-stabilizing protocol has autonomous adaptability to any change of network environments: after the last change occurs, the protocol starts to converge to its intended behavior. This advantage makes self-stabilizing...
Article
A wireless sensor network is a set of nodes, each is equipped with a sensing device and a wireless communication device. Because centralized control is hard to achieve in a large scale sensor network, self-∗ is a key concept in the design of a wireless sensor network. Self-stabilization is one of the self-∗ properties, and it is one of the most pro...
Conference Paper
The resource allocation problem is one of the fundamental problems for conflict resolution in distributed systems. In this paper, we consider the (n,m,k,d)-resource allocation problem, proposed by Joung [Joung, Distributed Computing (2010)], which is a generalization of the k-mutual exclusion problem and the group mutual exclusion problem. We propo...
Article
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We consider the exploration problem with a single agent in undirected graphs. Starting from an arbitrary node, the agent has to explore all the nodes and edges in the graph and return to the starting node. Our goal is to minimize both the number of agent moves and the memory space of the agent, which dominate the amount of communication during the...
Conference Paper
In this paper, we present a learning support system DASE-E to help students understand fundamental concepts of distributed algorithms in computer science. DASE-E is a collaborative learning system, in which the task of students is to devise a distributed algorithm. DASE-E offers a set of small wireless terminals with accelerometers. Each student pl...
Conference Paper
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The maximum leaf spanning tree (MLST) is a good candidate for constructing a virtual backbone in self-organized multihop wireless networks, but is practically intractable (NP-complete). Self-stabilization is a general technique that permits to recover from catastrophic transient failures in self-organized networks without human intervention. We pro...
Conference Paper
We investigate the relation between the time complexity and the space complexity for the rendezvous problem with k agents in asynchronous tree networks. The rendezvous problem requires that all the agents in the system have to meet at a single node within finite time. First, we consider asymptotically time-optimal algorithms and investigate the min...
Article
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Self-stabilization is a theoretical framework of non-masking fault-tolerant distributed algorithms. A self-stabilizing system tolerates any kind and any finite number of transient faults, such as message loss, memory corruption, and topology change. Because such transient faults occur so frequently in mobile ad hoc networks, distributed algorithms...
Article
One of the desired properties of distributed systems is self-adaptability against faults. Self-stabilizing protocols provide autonomous recovery from any finite number of transient faults. However, in practice, catastrophic faults rarely occur, while small-scale faults are more likely to occur. Fault-containing self-stabilizing protocols promise no...
Article
Ant colony optimization (ACO) routing algorithm is one of adaptive and efficient routing algorithms for mobile ad hoc networks (MANETs). In ACO routing algorithms, ant-like agents traverse the network to search a path from a source to a destination, and lay down pheromone on the path. A data packet is transferred along a path selected with probabil...
Article
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Self-stabilizing protocols provide autonomous recovery from finite number of transient faults. Fault-containing self-stabilizing protocols promise not only self-stabilization but also quick recovery and small effect from small scale of faults. In this paper, we introduce a timer-based composition of fault-containing self-stabilizing protocols that...
Conference Paper
Full-text available
The maximum leaf spanning tree (MLST) is a good candidate for constructing a virtual backbone in self-organized multihop wireless networks, but is practically intractable (NP-complete). Self-stabilization is a general technique that permits to recover from catastrophic transient failures in self-organized networks without human intervention. We pro...
Conference Paper
A wireless sensor network is a set of nodes, each is equipped with sensors and a wireless communication device. Cached Sensornet Transform (CST for short) is a methodology for design and implementation of self-stabilizing algorithms for sensor networks. It transforms a self-stabilizing algorithm in the abstract computational model to a program for...
Article
Wireless LANs, which consist of access points and wireless stations, have widely spread in recent years. Routing in wireless LANs suffers the problem that each wireless station selects an access point and a wired path to its destination station. It is desired to design an adaptive routing protocol for wireless LANs since throughputs of communicatio...
Conference Paper
A self-stabilizing protocol guarantees that starting from an arbitrary initial configuration, a system eventually comes to satisfy its specification and keeps the specification forever. Although self-stabilizing protocols show excellent fault-tolerance against any transient faults (e.g. memory crash), designing self-stabilizing protocols is difficu...
Article
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Biologically-inspired approaches are one of the most promising approaches to realize highly-adaptive distributed systems. Biological systems inherently have self-* properties, such as self-stabilization, self-adaptation, self-configuration, self-optimization and self-healing. Thus, the application of biological systems into distributed systems has...
Article
Unstructured overlay networks are widely adopted in large-scale and heterogeneous peer-to-peer (P2P) systems for their scalability and flexibility. A distinct feature of such systems is that they randomly route messages e.g., by flooding or random walk. In such systems, the number of messages and tasks carrying by those messages each peer receives...
Article
A desired property of large distributed systems is self adaptability against the faults that occur more frequently as the size of the distributed system grows. Self-stabilizing protocols provide autonomous recovery from finite number of transient faults. Fault-containing self-stabilizing protocols promise not only self-stabilization but also contai...
Article
Full-text available
Resource search is a fundamental problem in large-scale and highly dynamic Peer-to-Peer (P2P) systems. Unstructured search approaches are widely used because of their flexibility and robustness. However, such approaches incur high communication cost. The index-dissemination-based search is a kind of efficient unstructured search approach. We invest...
Conference Paper
In wireless ad hoc or sensor networks, a connected dominating set is useful as the virtual backbone because there is no fixed infrastructure or centralized management. Additionally, in such networks, transient faults and topology changes occur frequently. A self-stabilizing system tolerates any kind and any finite number of transient faults, and do...
Conference Paper
With the spread of wireless technology, mobile ad hoc networks is getting increased attention in recent years. In mobile ad hoc networks, network topologies dynamically change because of node mobility. Thus, it is important to design an algorithm that has strong stability against frequent topology changes. Attractor selection is one of the biologic...