Publishing type：Research paper (scientific journal)   Publisher：SAGE Publications  

When nodes and/or links are down in a network, the network may not function normally. Most of the existing work focuses on the reachability between two nodes along a path, that is, path reliability, and that through arbitrary paths, that is, network reliability. However, in case of wireless multi-hop networks and road networks, it may be inefficient or difficult to recalculate a path from the source to the destination when a failure occurs at an intermediate link in the path. In such cases, we can expect that the reachability between two nodes will improve by taking a detour from the entry of the failure link (i.e. failure point) to the destination without traversing the failure link. Since the detour may also increase the communication/travel delay, in this paper, we propose a new path metric (i.e. path reachability including distance-constrained detours), which consists of the conventional path reachability and the reachability along distance-constrained detours under arbitrary link failures in the original path. We first prove the two important characteristics: (1) the proposed metric is exactly the same as the network reliability in case of no distance constraint and (2) it is upper bounded by the diameter constrained network reliability. Through numerical results using a grid network and more realistic networks (i.e. wireless networks and a road network), we show the fundamental characteristics of the proposed metric and analyze the goodness of several representative paths in terms of the proposed metric as well as the conventional metrics (i.e. path length and path reachability).

DOI： 10.1177/1748006x221133600

researchmap

Other Link： http://journals.sagepub.com/doi/full-xml/10.1177/1748006X221133600

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.23919/cnsm55787.2022.9965166

researchmap

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/noms54207.2022.9789758

researchmap

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/globecom46510.2021.9685205

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

DOI： 10.1007/s12083-021-01182-7

researchmap

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/icbc51069.2021.9461125

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/nem.2190

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tnsm.2020.3044329

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

In current Proof-of-Work (PoW) blockchain systems, miners usually form mining pools to compete with other pools/miners in the mining competition. Forming pools can give miners steady revenues but will introduce two critical issues. One is mining pool selection, where miners select the pools to join in order to maximize their revenues. The other is a Block WithHolding (BWH) attack, where pools can inject part of their hash/mining power into other pools to obtain additional revenues without contributing to the mining process of the attacked pools. Reasoning that the BWH attack will have significant impacts on the pool selection, we therefore investigate the mining pool selection issue in the presence of a BWH attack in this paper. In particular, we model the pool selection process of miners as an evolutionary game and find the Evolutionarily Stable States (ESSs) of the game (i.e., stable pool population states) as the solutions. Previous studies investigated this problem from the perspective of pool managers and neglected the revenues from attacked pools (attacking revenues), leading to less accurate and insightful findings. This paper, however, focuses on the payoffs of miners and carefully takes the attacking revenues into consideration. To demonstrate how the problem is solved, we consider the scenario with two mining pools and further investigate the case where one pool attacks the other and the case where the two pools attack each other. The results in this paper show that pools can attract more miners to join by launching a BWH attack and the attack power significantly affects the stable pool populations.

DOI： 10.3390/app11041617

Web of Science

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1109/JIOT.2020.3033434

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communications Engineers (IEICE)  

DOI： 10.1587/transcom.2021cep0004

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communications Engineers (IEICE)  

DOI： 10.1587/transcom.2021cet0001

researchmap

Publishing type：Research paper (scientific journal)  

researchmap

Other Link： https://dblp.uni-trier.de/db/journals/corr/corr2103.html#abs-2103-04016

Publishing type：Research paper (scientific journal)  

DOI： 10.1504/IJHT.2020.10034657

researchmap

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/brains49436.2020.9223293

researchmap

Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

When a large-scale disaster occurs, each evacuee should move to an appropriate refuge in a speedy and safe manner. Most of the existing studies on the refuge assignment consider the speediness of evacuation and refuge capacity while the safety of evacuation is not taken into account. In this paper, we propose a refuge assignment scheme that considers both the speediness and safety of evacuation under the refuge capacity constraint. We first formulate the refuge assignment problem as a two-step integer linear program (ILP). Since the two-step ILP requires route candidates between evacuees and their possible refuges, we further propose a speedy and reliable route selection scheme as an extension of the existing route selection scheme. Through numerical results using the actual data of Arako district of Nagoya city in Japan, we show that the proposed scheme can improve the average route reliability among evacuees by 13.6% while suppressing the increase of the average route length among evacuees by 7.3%, compared with the distance-based route selection and refuge assignment. In addition, we also reveal that the current refuge capacity is not enough to support speedy and reliable evacuation for the residents.

DOI： 10.3390/ijgi9070442

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s12083-020-00925-2

researchmap

Other Link： http://link.springer.com/article/10.1007/s12083-020-00925-2/fulltext.html

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Network functions virtualization (NFV) is a new paradigm to achieve flexible and agile network services by decoupling network functions from proprietary hardware and running them on generic hardware as virtual network functions (VNFs). In the NFV network, a certain network service can be modeled as a sequence of VNFs, called a service chain. Given a connection request (origin node, destination node, and service chain requirement, which is a sequence of functions), the service chaining problem aims to find an appropriate service path, which starts from the origin and ends with the destination while executing the VNFs at the intermediate nodes in the required order. Some existing work noticed that the service chaining problem was similar to the shortest path tour problem (SPTP). To the best of our knowledge, this is the first work that exactly formulates the service chaining problem as an SPTP-based integer linear program (ILP). Through numerical results, we show the SPTP-based ILP can support 1.30-1.77 times larger scale systems than the existing ILP.

DOI： 10.1109/NetSoft48620.2020.9165364

Scopus

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.comnet.2020.107383

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Due to the rapid penetration of the Internet of Things (IoT) into human life, illegal access to IoT resources (e.g., data and actuators) has greatly threatened our safety. Access control, which specifies who (i.e., subjects) can access what resources (i.e., objects) under what conditions, has been recognized as an effective solution to address this issue. To cope with the distributed and trust-less nature of IoT systems, we propose a decentralized and trustworthy Capability-Based Access Control (CapBAC) scheme by using the Ethereum smart contract technology. In this scheme, a smart contract is created for each object to store and manage the capability tokens (i.e., data structures recording granted access rights) assigned to the related subjects, and also to verify the ownership and validity of the tokens for access control. Different from previous schemes which manage the tokens in units of subjects, i.e., one token per subject, our scheme manages the tokens in units of access rights or actions, i.e., one token per action. Such novel management achieves more fine-grained and flexible capability delegation and also ensures the consistency between the delegation information and the information stored in the tokens. We implemented the proposed CapBAC scheme in a locally constructed Ethereum blockchain network to demonstrate its feasibility. In addition, we measured the monetary cost of our scheme in terms of gas consumption to compare our scheme with the existing Blockchain-Enabled Decentralized Capability-Based Access Control (BlendCAC) scheme proposed by other researchers. The experimental results show that the proposed scheme outperforms the BlendCAC scheme in terms of the flexibility, granularity, and consistency of capability delegation at almost the same monetary cost.

DOI： 10.3390/s20061793

researchmap

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/ccnc46108.2020.9045338

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s12083-019-00763-x

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Inderscience Publishers  

DOI： 10.1504/ijor.2020.10034355

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/ojits.2020.3019935

researchmap

Publishing type：Research paper (scientific journal)  

researchmap

Other Link： https://dblp.uni-trier.de/db/journals/corr/corr2009.html#abs-2009-02933

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/Blockchain50366.2020.00047

researchmap

Other Link： https://dblp.uni-trier.de/db/conf/blockchain2/blockchain2020.html#FujitaZSK20

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Inderscience Enterprises Ltd.  

Marine shrimp farming operations in Southeast Asia are still traditional and need to be improved in efficiency. In this paper, we first model a marine shrimp supply chain network, which consists of suppliers, farms, distribution centres, traders, and consumers. We also develop a mixed-integer linear programming under the push strategy framework in order to maximise the farmer's profit. Through a sensitivity analysis, we examine how the increase in costs affects the profits. The computational results are presented to demonstrate the feasibility of a real case of smart marine shrimp farming.

DOI： 10.1504/IJOR.2020.109757

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/globecom38437.2019.9013321

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/globecom38437.2019.9014155

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.comcom.2019.08.012

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

? 2018 Springer-Verlag GmbH Germany, part of Springer Nature It has been highly expected to achieve speedy and reliable evacuation guiding under large scale disasters. As for the speedy evacuation, an automatic evacuation guiding scheme has been proposed, which is a reactive approach based on implicit interactions among evacuees, their mobile devices, and networks. In this scheme, an evacuation route is given by the shortest path, which may not be safe. In this paper, we propose a speedy and reliable path selection based on the geographical risk map for the existing automatic evacuation guiding, which is a proactive approach that allows evacuees to evacuate speedily while avoiding encounters with blocked road segments as much as possible. First, the proposed scheme enumerates candidates of short paths from the evacuee’s current location to the refuge. Then, it selects the most reliable one from the candidates by taking into account road blockage probabilities, each of which is an estimated probability that the corresponding road is blocked under a certain disaster. Through simulation experiments, we show that the proposed scheme can improve the safety of evacuation in terms of the number of encounters with blocked road segments while keeping both the average and maximum evacuation times unchanged, compared with the shortest path selection. We further demonstrate how the proactive function, i.e., geographical risk analysis, and the reactive function, i.e., information sharing, contribute to the system performance.

DOI： 10.1007/s12652-018-0826-z

researchmap

Other Link： http://link.springer.com/article/10.1007/s12652-018-0826-z/fulltext.html

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

researchmap

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

BitTorrent, which is one of the successful Peer-to-Peer (P2P) file distribution systems, adopts the tit-for-tat (TFT) strategy in game theory to encourage cooperation among peers, i.e., each peer has to provide fragments of the original file, called pieces, to others so as to retrieve its demanding pieces from them. Because the TFT strategy can restrict free riding behavior of peers, there are also several TFT-based P2P streaming systems and the performance of such existing systems has been analyzed. However, optimal piece flow in TFT-based P2P streaming has not been revealed yet. In this paper, a discrete-time model of TFT-based P2P streaming is first developed and integer linear programming (ILP) is formulated to determine the optimal piece flow where the average play-out delay is minimized. By solving the ILP using existing solver, i.e., CPLEX, we can obtain numerical examples of optimal piece flow. The analysis of obtained optimal piece flow reveals that (1) optimal piece selection is based on the balance between in-order piece retrieving and the rarest-first piece retrieving, (2) optimal peer selection depends on the upload capacities of peers and the stage of streaming, (3) the number of pieces does not affect the system performance, (4) the maximum play-out delay can be bounded by the ratio of the number of peers to the server's upload capacity, and (5) how the relaxation of TFT constraint can improve the system performance.

DOI： 10.1016/j.comnet.2018.04.004

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer New York LLC  

When large-scale disasters occur, evacuees have to evacuate to safe places quickly. They, however, may not be able to afford to obtain sufficient information for their evacuations under such emergent situations. In this paper, we propose an automatic evacuation guiding scheme using evacuees’ mobile nodes, e.g., smart phones. The key idea to achieve automatic evacuation guiding is implicit interactions between evacuees and their mobile nodes. Each mobile node tries to navigate its evacuee by presenting an evacuation route. At the same time, it can also trace the actual evacuation route of the evacuee as the trajectory by measuring his/her positions periodically. The proposed scheme automatically estimates blocked road segments from the difference between the presented evacuation route and the actual evacuation route, and then recalculates the alternative evacuation route. In addition, evacuees also share such information among them through direct wireless communication with other mobile nodes and that with a server via remaining communication infrastructures. Through simulation experiments, we show that 1) the proposed scheme works well when the degree of damage is high and/or road segments are continuously blocked, 2) the average evacuation time can be improved even in small penetration ratio of the proposed system, and 3) the direct wireless communication can support many evacuations at almost the same level as the communication infrastructure when the number of evacuees becomes large.

DOI： 10.1007/s10707-016-0270-1

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Inderscience Publishers  

DOI： 10.1504/ijor.2020.10022448

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SAGE Publications  

Both pre-disaster approaches, e.g., mitigation and preparedness, and post-disaster approaches, e.g., response and recovery, play important roles to mitigate the damage from large-scale disasters. From the viewpoint of disaster response, there have been studies on evacuation guiding schemes and applications using evacuees’ mobile devices, e.g., smart phones. On the other hand, disaster preparedness has also been studied mainly on geographical information analysis, e.g., road blockage probability and people flow data. The road blockage probability is the probability that the corresponding road is blocked due to collapse of roadside buildings when an earthquake occurs. The people flow data express the people flow in usual time. In this paper, with the help of evacuation guiding schemes, road blockage probability, and people flow data, we propose a road network risk analysis approach that considers people flow in both ordinary and evacuation situations, which can be used to as a tool to strengthen the urban fabric for fostering better evacuees’ responses in disaster situations. First, the proposed approach derives ordinary road demand, which is the degree of road usage at a certain interval in an ordinary situation, from the people flow data. Then, it calculates evacuation road demand, i.e., the degree of road usage at a certain interval in an evacuation situation, by extending the edge betweenness centrality under the assumption that people located according to the ordinary road demand move to refuges along their evacuation paths. Finally, it detects roads with high risk of encountering blocked road segments by combining the road blockage probability and evacuation road demand. Through numerical experiments under a case study of Arako area of Nagoya city in Japan, we show the proposed approach can detect such high-risk roads. Furthermore, we show the detected roads spatially change according to the people flow in ordinary situations, evacuation behavior, and disaster occurrence time.

DOI： 10.1177/2399808318802940

researchmap

Other Link： http://journals.sagepub.com/doi/full-xml/10.1177/2399808318802940

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

In cognitive radio networks, secondary users (SUs) must accurately sense the spectrum of primary user (PU) to acquire their own communication opportunities without interfering PU's communication. Collaborative spectrum sensing (CSS) among SUs can improve the probability to detect PU's communication, compared to non-collaborative spectrum sensing, where each SU senses signal independently. In this paper, we propose a communication opportunity maximization scheme for CSS in multiple PUs cognitive radio networks. First, we define an objective function that represents SU's communication opportunity and a constraint on miss detection probability. In the proposed scheme, each SU forms a group with other SUs to meet the constraint and maximize its own communication opportunity according to the objective function and the constraint. Through simulation experiments with a two-PU scenario, we show that the proposed scheme can improve the ratio of winning SUs, that can use PU's channel, to the whole SUs, in comparison with the non-collaborative spectrum sensing. We also show that it can quickly increase the overall throughput of winning SUs up to the theoretical upper bound.

DOI： 10.1109/ATNAC.2017.8215373

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer International Publishing  

When a large-scale disaster occurs, evacuees have to evacuate to safe places quickly. For this purpose, an automatic evacuation guiding scheme based on cooperation between evacuees and their mobile nodes has been proposed. The previous work adopts shortest-distance based route selection and does not consider the impact of traffic congestion caused by evacuation guiding. In this paper, we propose congestion-aware route selection in the automatic evacuation guiding. We first adopt a traffic congestion model where each evacuee’s moving speed on a road is determined by the population density of the road and his/her order among evacuees traveling in the same direction. Based on this congestion model, each evacuee’s mobile node estimates the cost, i.e., traveling time, of each road in the area. Each mobile node collects information about blocked road segments and positions of other evacuees through communication infrastructures or other mobile nodes. Based on the obtained information, it calculates and selects the smallest-cost route. Through simulation experiments, we show that the congestion-aware route selection can reduce both average and maximum evacuation times compared to the shortest-distance-based route selection, especially under highly congested situations. Furthermore, we show that the congestion-aware route selection can work well even under highly damaged situations where only direct wireless communication among mobile nodes is available.

DOI： 10.1186/s13638-017-0948-6

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s41070-017-0013-1

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Springer Verlag  

When large-scale disasters occur, evacuees have to evacuate to a refuge quickly. For this purpose, there has been proposed an automatic evacuation guiding scheme based on implicit interactions among evacuees, their mobile devices, and networks. In this scheme, an evacuation route is obtained as the shortest path, which may not be safe. In this paper, we propose a short and reliable path selection for existing automatic evacuation guiding, which allows evacuees to evacuate quickly while avoiding encounters with blocked road segments as much as possible. First, the proposed scheme calculates k-shortest (k≥ 1) paths from the current location to the destination, with the help of the existing algorithm. Then, it selects the most reliable one from the candidates by taking into account road blockage probabilities, each of which is an estimated probability that the corresponding road is blocked under a certain disaster. Through simulation experiments, we show that the proposed scheme can reduce the number of encounters with blocked road segments with an appropriate value of k, while keeping the average/maximum evacuation time compared with the shortest path selection.

DOI： 10.1007/978-3-319-65515-4_3

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In this paper, we consider a data-flow management mechanism for data center networks, in which a centralized controller called arbiter manages data flows. We propose a simple algorithm for the arbiter to distribute flows over different time points and paths, in a preemptive scheduling and traffic load-balancing manner. The proposed algorithm is based on table-driven resource reservation, in which states of all the links in a data-center network are registered in a single table, and its information is updated whenever a new flow-request arrives at the arbiter. We evaluate the performance of the proposed algorithm through simulation experiments, investigating bit allocation rate and flow allocation rate, under different flow-size distributions. Numerical results show that the proposed algorithm can achieve high bit allocation rate without collisions. It is also shown that the proposed algorithm can allocate many flows within a small time interval even when the variance of flow-size is large.

DOI： 10.1109/APCC.2016.7581436

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER INT PUBLISHING AG  

We have proposed an automatic evacuation guiding scheme based on cooperation between evacuees and their mobile nodes. In the previous work, we assume that information about blocked road segments is shared among mobile nodes through Epidemic routing, which is a Delay Tolerant Network (DTN) routing protocol. In this paper, we propose an information sharing scheme called On-Demand Direct Delivery, which can reduce the network load compared to Epidemic routing. Since each evacuee moves to a safe place, he/she will require the information about blocked road segments in the region from the current position to the safe place. The proposed scheme selectively retrieves the information about blocked road segments in that region, through Direct Delivery. Through simulation experiments, we show the proposed scheme can keep the effectiveness of evacuation guiding with reduction of network load to about 1/36, compared to Epidemic routing.

DOI： 10.1007/978-3-319-44215-0_17

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

One of the most important technical problems in store-carry-forward routing is to reduce the number of message copies in networks without increasing the message delivery delay. In order to solve this problem, we focus on utility-based routing schemes, where for a message, utility of a node indicates its proximity to the destination node of the message. Utility-based routing schemes are promising when relay nodes, i.e., nodes with the message (copy), have sufficient opportunities to encounter other nodes. On the other hand, when relay nodes are in extremely sparse areas of nodes and they have few opportunities to encounter other nodes, the routing schemes do not work effectively. This observation naturally leads us to propose a location-aware utility-based routing scheme. The proposed scheme combines a utility-based routing scheme with location-aware probabilistic forwarding, where the forwarding probability is determined based on both node utility and node density at the contact location. With several simulation scenarios, we evaluate the performance of the proposed scheme in terms of the mean number of copies in the network and the mean message delivery delay.

DOI： 10.1109/ICOIN.2015.7057881

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

When large-scale disasters occur, evacuees have to evacuate to safe places quickly. In this paper, we propose an automatic evacuation guiding scheme using mobile nodes of evacuees. Each node tries to navigate its evacuee by presenting an evacuation route. It can also trace the actual evacuation route of the evacuee as the trajectory by measuring his/her positions periodically. The proposed scheme automatically estimates blocked road segments from the difference between the presented evacuation route and the actual evacuation route, and then recalculates the alternative evacuation route. In addition, evacuees also share such information among them through direct wireless communication with other mobile nodes and that with a server via remaining communication infrastructures. Through simulation experiments, we show that 1) the effectiveness of the proposed scheme becomes high with the increase of degree of damage and 2) the effect of information sharing through communication infrastructures is higher than that through direct wireless communication.

DOI： 10.1007/978-3-319-23144-0_1

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Peer-to-Peer (P2P) file distribution systems can efficiently disseminate massive contents, such as disk images of operating systems, from a server to many users in a piece-by-piece manner. In particular, the BitTorrent protocol optimizes each peer's download speed by applying the tit-for-tat (TFT) strategy, where each peer preferentially uploads piece(s) to peer(s) from which it can download missing pieces faster. To the best of our knowledge, however, the optimality of TFT-based P2P file distribution has not been studied sufficiently. In this paper, we aim to understand the optimal scheduling in TFT-based P2P file distribution. First, we develop a discrete-time model of TFT-based P2P file distribution and formulate its optimal scheduling as a two-step integer linear programming problem. The first step is to minimize the average file retrieval time among peers, and the second step is to improve fairness among peers. We analyze the optimal solution obtained by the existing solver and reveal the characteristics of the optimal scheduling. Specifically, we show that it is crucial to distribute pieces from the server indirectly to peers with large upload capacity via those with small upload capacity.

DOI： 10.1587/transcom.E97.B.2650

Web of Science

researchmap

Language：Japanese   Publishing type：Research paper (other academic)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Hindawi Publishing Corporation  

We propose a method for tracking multiple pedestrians using a binary sensor network. In our proposed method, sensor nodes are composed of pairs of binary sensors and placed at specific points, referred to as gates, where pedestrians temporarily change their movement characteristics, such as doors, stairs, and elevators, to detect pedestrian arrival and departure events. Tracking pedestrians in each subregion divided by gates, referred to as microcells, is conducted by matching the pedestrian gate arrival and gate departure events using a Bayesian estimation-based method. To improve accuracy of pedestrian tracking, estimated pedestrian velocity and its reliability in a microcell are used for trajectory estimation in the succeeding microcell. Through simulation experiments, we show that the accuracy of pedestrian tracking using our proposed method is improved by up to 35% compared to the conventional method.

DOI： 10.1155/2014/719029

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：HINDAWI PUBLISHING CORPORATION  

We propose a method for tracking multiple pedestrians using a binary sensor network. In our proposed method, sensor nodes are composed of pairs of binary sensors and placed at specific points, referred to as gates, where pedestrians temporarily change their movement characteristics, such as doors, stairs, and elevators, to detect pedestrian arrival and departure events. Tracking pedestrians in each subregion divided by gates, referred to as microcells, is conducted by matching the pedestrian gate arrival and gate departure events using a Bayesian estimation-based method. To improve accuracy of pedestrian tracking, estimated pedestrian velocity and its reliability in a microcell are used for trajectory estimation in the succeeding microcell. Through simulation experiments, we show that the accuracy of pedestrian tracking using our proposed method is improved by up to 35% compared to the conventional method.

DOI： 10.1155/2014/719029

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In sparsely populated mobile ad hoc networks (MANETs), mobile nodes are chronically isolated each other and they meet very occasionally. Global clock synchronization among nodes in such networks is a challenging problem because reference clock information cannot be disseminated promptly over nodes due to the lack of stable connections among nodes. In recent years, averaging-based algorithms for distributed global clock synchronization have been studied. In this paper, we conduct the continuous-time analysis of the simplest one, called the simple averaging scheme, where two mobile nodes exchange their local clock times when they meet and adjust their own clocks to the average of them. Through the analysis and simulation experiments, we reveal how the clock accuracy of nodes and meeting rates among them affect the rate of convergence to the steady state and the accuracy of clock synchronization in steady state.

DOI： 10.1109/JSAC.2013.130414

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：HINDAWI PUBLISHING CORP  

We consider a pedestrian tracking system where sensor nodes are placed only at specific points so that the monitoring region is divided into multiple smaller regions referred to as microcells. In the proposed pedestrian tracking system, sensor nodes composed of pairs of binary sensors can detect pedestrian arrival and departure events. In this paper, we focus on pedestrian tracking in microcells. First, we investigate actual pedestrian trajectories in a microcell on the basis of observations using video sequences, after which we prepare a pedestrian mobility model. Next, we propose a method for pedestrian tracking in microcells based on the developed pedestrian mobility model. In the proposed method, we extend the Bayesian estimation to account for time-series information to estimate the correspondence between pedestrian arrival and departure events. Through simulations, we show that the tracking success ratio of the proposed method is increased by 35.8% compared to a combinatorial optimization-based tracking method.

DOI： 10.1155/2013/187479

Web of Science

PubMed

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electronics, Information and Communication, Engineers, IEICE  

Communication among isolated networks (clusters) in delay tolerant networks (DTNs) can be supported by a message ferry, which collects bundles from clusters and delivers them to a sink node. When there are lots of distant static clusters, multiple message ferries and sink nodes will be required. In this paper, we aim to make groups, each of which consists of physically close clusters, a sink node, and a message ferry. Our objective is minimizing the overall mean delivery delay of bundles in consideration of both the offered load of clusters and distances between clusters and their sink nodes. Based on existing work, we first model this problem as a nonlinear integer programming. Using a commercial nonlinear solver, we obtain a quasi-optimal grouping. Through numerical evaluations, we show the fundamental characteristics of grouping, the impact of location limitation of base clusters, and the relationship between delivery delay and the number of base clusters. © 2013 The Institute of Electronics, Information and Communication Engineers.

DOI： 10.1587/transcom.E96.B.2076

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

A perfect cell partitioning (PCP) scheme is described for controlling the transmission power of base stations in a cellular communication system to prevent radio frequency interference among adjacent base stations. A base station using this scheme can use its entire frequency range, while one using the conventional scheme can use only a quarter of it. Simulation and analytic results showed that the PCP scheme is more effective than the conventional one when the node density is lower than 6. However, the probability of successful communication is relatively low. A modified version of this scheme in which the base station sacrifices the nodes near its border has a significantly higher probability. Simulation and analytic results showed that the success probability of the modified scheme is as much as 0.67 higher than that of the original one when the occupation ratio is 1.2 and that a base station using the modified scheme can use its frequency range more effectively than one using the original or conventional scheme. © 2012 ACADEMY PUBLISHER.

DOI： 10.4304/jcm.7.10.749-757

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

Communication among isolated networks (clusters) in delay tolerant networks (DTNs) can be supported by a message ferry, which collects bundles from clusters and delivers them to a sink node. When there are lots of distant static clusters, multiple message ferries and sink nodes will be required. In this paper, we aim to make groups each of which consists of physically close clusters, a sink node, and a message ferry. Our main objective is minimizing the overall mean delivery delay of bundles in consideration of both offered load of clusters and distance between clusters and their sink nodes. We first model this problem as a nonlinear integer programming, based on the knowledge obtained in our previous work. Because it might be hard to solve this problem directly, we take two-step optimization approach based on linear integer programming, which yields an approximate solution of the problem. Through numerical results, we show the two-step optimization approach works well. © 2012 IEEE.

DOI： 10.1109/WAINA.2012.160

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

This paper considers a delay tolerant network, where a message ferry travels multiple isolated clusters, collects data from nodes in the clusters, and finally delivers the data to a sink node. In our previous work, we proposed a self-organized data aggregation technique for collecting data from nodes efficiently, which can automatically accumulate data from cluster members to a limited number of cluster members called aggregators. The proposed scheme was developed based on the evolutionary game theoretic approach, in order to take account of the inherent selfishness of the nodes for saving their own battery life. The number of aggregators can be controlled to a desired value by adjusting the energy that the message ferry supplies to the aggregators. In this paper, we further examine the proposed system in terms of success of data transmission and system survivability. We first introduce a new type of game model with retransmissions. Through both theoretic and simulation approaches, we then reveal feasible parameter settings which can achieve a system with desirable characteristics: Stability, survival, and successful data transfer. © 2012 ICST Institute for Computer Science, Social Informatics and Telecommunications Engineering.

DOI： 10.1007/978-3-642-32615-8_27

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

In delay tolerant networks (DTNs), the opportunity of communication among isolated networks (clusters) can be provided by a message ferry which moves around the network to proactively collect bundles and deliver them to a sink node. When there are lots of distant static clusters, the message ferry should visit them efficiently to minimize the mean delivery delay of bundles. In this paper, we propose an algorithm for determining the optimal visiting order of isolated static clusters in DTNs. We show that the minimization problem of the overall mean delivery delay in our system is reduced to that of the weighted mean waiting time in the conventional polling model. We then solve the problem with the help of an existing approach to the polling model and obtain a quasi-optimal balanced sequence representing the visiting order. Through numerical examples, we show that the proposed visiting order is effective when arrival rates at clusters and/or distances between clusters and the sink are heterogeneous.

DOI： 10.3934/naco.2011.1.563

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.5402/2011/970943

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

In a Peer-to-Peer (P2P) file-sharing system, a node finds and retrieves its desired file. If multiple nodes cache the same file to provide others, we can achieve a dependable file-sharing system with low latency and high file availability. However, a node has to spend costs, e. g., processing load or storage capacity, on caching a file. Consequently, a node may selfishly behave and hesitate to cache a file. In such a case, unpopular files are likely to disappear from the system. In this paper, we aim to reveal whether effective caching in the whole system emerges from autonomous and selfish node behavior. We discuss relationship between selfish node behavior and system dynamics by using evolutionary game theory. Through theoretic analysis, we show that a file-sharing system can be robust to file disappearance depending on a cost and demand model for caching even if nodes behave selfishly. Furthermore, we also conduct several simulation-based analysis in terms of network structures, evolving network, load balancing, and system stability. As a result, we demonstrate that a file-sharing system with good properties, i.e., robustness to file disappearance, low search latency, well load-balancing, and high stability, can be achieved independent of network structures and dynamics.

DOI： 10.1007/s12083-009-0045-7

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Custody transfer in delay tolerant networks (DTNs) provides reliable end-to-end data delivery by delegating the responsibility of data transfer among special nodes (custodians) in a hop-by-hop manner However. storage congestion occurs when data increases and/or the network is partitioned into multiple sub-networks for a long time The storage congestion can be alleviated by message ferries which move around the network and proactively collect data from the custodians In such a scenario. data should be aggregated to some custodians so that message ferries can collect them effectively In this paper. we propose a scheme to aggregate data into selected custodians. called aggregators. in a fully distributed and autonomous manner with the help of evolutionary game theoretic approach Through theoretical analysis and several simulation experiments. taking account of the uncooperative behavior of nodes, we show that aggregators can be selected in a self-organized manner and the number of aggregators can he controlled to a desired value

DOI： 10.1587/transcom.E93.B.490

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Wireless mesh networks have been attracting many users in recent years. By connecting base stations (mesh nodes) with wireless connections, these network can achieve a wide-area wireless environment with flexible configuration and low cost at the risk of radio interference between wireless links. When we utilize wireless mesh networks as infrastructures for Internet access, all network traffic from mobile nodes goes through a gateway node that is directly connected to the wired network. Therefore, it is necessary to distribute the traffic load by deploying multiple gateway nodes. In this paper, we propose a spanning tree construction algorithm for TDMA-based wireless mesh networks with multiple gateway nodes so as to maximize the traffic volume transferred between the mesh network and the Internet (system throughput) by taking account of the traffic load on the gateway nodes, the access link capacity and radio interference. Through a performance evaluation, we show that the proposed algorithm increases the system throughput regardless of the bottleneck position and achieves up to 3.1 times higher system throughput than a conventional algorithm.

DOI： 10.1587/transcom.E93.B.99

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Peer-to-Peer (P2P) file sharing is one of key technologies for achieving attractive P2P multimedia social networking. In P2P file-sharing systems, file availability is improved by cooperative users who cache and share files. Note that file caching carries costs such as storage consumption and processing load. In addition, users have different degrees of cooperativity in file caching and they are in different surrounding environments arising from the topological structure of P2P networks. With evolutionary game theory, this paper evaluates the performance of P2P file sharing systems in such heterogeneous environments. Using micro-macro dynamics, we analyze the impact of the heterogeneity of user selfishness on the file availability and system stability. Further, through simulation experiments with agent-based dynamics, we reveal how other aspects, for example, synchronization among nodes and topological structure, affect the system performance. Both analytical and simulation results show that the environmental heterogeneity contributes to the file availability and system stability. © 2010 Yusuke Matsuda et al.

DOI： 10.1155/2010/369814

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Since files are directly exchanged between nodes in P2P file-sharing systems such as Winny and Bittorrent, it is difficult to comprehensively grasp the system conditions and control the system dynamics. In this paper, we design and implement a system that can achieve real-time measurement of files which are highly interested and frequently distributed over the Winny network. We introduce a node for the measurement into the Winny network and passively measure queries passing through the node with low measurement overhead and high adaptability to the changes of network conditions. To achieve the real-time measurement, we combine the sliding window method and frequent pattern mining. The experimental results show that we can clearly reveal the transition of frequently distributed files in real-time.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Wireless mesh networks have been attracting many users in recent years. By connecting base stations (mesh nodes) with each other via wireless connections, they can achieve a wide-area wireless environment with flexible-configuration and low-cost properties at the risk of radio interference between wireless links. When we utilize the wireless mesh networks as an infrastructure for Internet access, all network traffic from mobile nodes goes through a gateway node which is directly connected to the wired network. Therefore, we need to distribute the traffic load by deploying multiple gateway nodes. In this paper, we propose a spanning tree construction algorithm for TDMA-based wireless mesh networks with multiple gateway nodes, which aims to maximize the traffic going to wired network (system throughput) by taking account of the traffic load on the gateway nodes, the access link capacity and the radio interference. Through simulation experiments, we show that the proposed algorithm increases the system throughput regardless of the bottleneck position and achieves up to 3.1 times higher system throughput than the conventional algorithm.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Wireless Mesh Networks (WMNs) have attracted significant interest as a cost-effective wireless network infrastructure. However, the efficiency of wireless resource utilization decreases by radio interference when multiple transmissions in an interference region occur simultaneously. One of possible solutions for this problem is to control the transmission power of mesh nodes. In this report, we propose a power control method of wireless mesh nodes for increasing spatial reuse in WMNs with TDMA MAC protocol. The proposed method decreases radio interference, considering the ill-effect of the increase in path length by cutting too many wireless links. Numerical evaluation results reveal that the proposed method decreases the frame length by up to 27% with non-sensitive parameter setting.

CiNii Books

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In mobile ad hoc networks (MANETs), time synchronization can be achieved by distributing time information among nodes. This type of time synchronization, however, does not work well under considerable long delay caused by sparse population. In this paper, we propose a simple yet effective scheme for relative time synchronization. When two mobile nodes meet, they exchange their clock information and adjust their own clocks to the average. Through simulation experiments, we show that the variance of the difference between the local and reference times remains within a certain finite range that depends on the frequency of nodes' meetings.

DOI： 10.1109/INCOS.2009.20

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Wireless Mesh Networks (WMNs) have attracted significant interest as a cost-effective wireless network infrastructure. However, the efficiency of wireless resource utilization decreases by radio interference when multiple transmissions in an interference region. occur simultaneously. So decreasing radio interference is one of the major problems in wireless network. In the present paper, we propose a degree-based power control method of wireless mesh, nodes to enhance spatial reuse in WMNs with TDMA MAC protocol. The proposed method is an attempt to reduce the radio interference and improve the spatial reuse of the WMN by decreasing the transmission power of mesh. nodes, while maintaining the network connectivity at a certain level. Numerical evaluation results reveal that the proposed method decreases the frame length by up to 22%.

DOI： 10.1109/ICN.2009.22

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Wireless mesh networks have been attracting many users in recent years to achieve a wide-area wireless environment with flexible-configuration and low-cost properties by connecting base stations (mesh nodes) with. each other via wireless connections. When the wireless mesh networks are aired as an infrastructure for Internet access, all network traffic from. mobile nodes go through a gateway node which is directly connected to the wired network. Therefore, we need to distribute the entire traffic load by deploying multiple gateway nodes and each mesh node should select a gateway node to access the Internet according to its traffic load, processing power, and access link capacity. In this paper, we propose a routing method that distributes the traffic load on the gateway nodes. Through several simulations, we show that the proposed method can. uniformly distribute the traffic load on gateway nodes, keeping the tune complexity and suppressing an increase in the path length at most 15 % compared to the conventional shortest path routing.

DOI： 10.1109/ICN.2009.21

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In delay tolerant networks (DTNs), custody transfer mechanism provides reliable end-to-end data transfer in which special nodes (custodians) transfer data with custody in a hop-by-hop manner As a result, storage congestion occurs when data with custody increases and/or the network, is partitioned into multiple sub-networks for a long time. The storage congestion can be alleviated with the help of message ferries. In such a scenario, data should be aggregated to some custodians so that message ferries can effectively collect them. In this paper, we propose a scheme to aggregate data into selected custodians, called aggregators, in a fully distributed and autonomous manner by, using evolutionary game theoretical approach where we can also control the number of aggregators to a desired value.

DOI： 10.1109/WOWMOM.2009.5282459

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Mobile Ad Hoc Networks (MANETs) are temporal and infrastructure-independent wireless networks that consist of mobile nodes. For instance, a MANET can be used as an emergent network for communication among people when a disaster occurred. Since there is no central server in the network, each node has to find out its desired information (objects) by itself. Constructing a mobile Peer-to-Peer (P2P) network over the MANET can support the object search, Some researchers proposed construction schemes of mobile P2P networks, such as Ekta and MADPastry. They integrated DHT-based application- layer routing and network-layer routing to increase search efficiency. Furthermore, MADPastry proposed a clustering method which groups the overlay nodes according to their physical distance. However, it has also been pointed out that the search efficiency deteriorates in highly dynamic environments where nodes quickly move around. In this paper. we focus on route disappearances in the network layer which cause the deterioration of scar h efficiency. We describe the detail of this problem and evaluate quantitatively it through simulation experiments. We extend MADPastry by introducing a method sharing objects among nodes in a cluster. Through simulation experiments, we show that the proposed method can achieve tip to 2.5 times larger success rate of object search than MADPastry.

DOI： 10.1093/ietcom/e91-b.12.3851

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In Peer-to-Peer (P2P) file sharing systems, file availability is improved by users cooperatively caching and sharing files. However, many users may hesitate to cache files cooperatively due to the cost for caching, such as storage consumption, processing load, and bandwidth consumption. In such a case, unpopular files are likely to disappear from the system. In this paper, we reveal how the selfish user behavior affects the system performance using evolutionary game theoretic approach. Specifically, we focus on situations where users are heterogeneous in terms of aggressiveness in cooperative caching. Analytical results show that the user heterogeneity contributes to the stability of file availability.

CiNii Books

researchmap

Language：Japanese   Publishing type：Research paper (other academic)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In Peer-to-Peer (P2P) file sharing systems, file availability is improved by users cooperatively caching and sharing files. However, many users may hesitate to cache files cooperatively due to the cost for caching, such as storage consumption, processing load, and bandwidth consumption. In such a case, unpopular files are likely to disappear from the system. In this paper, we reveal how the selfish user behavior affects the system performance using evolutionary game theoretic approach. Specifically, we focus on situations where users are heterogeneous in terms of aggressiveness in cooperative caching. Analytical results show that the user heterogeneity contributes to the stability of file availability.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we focus on tracking moving objects in a building using a binary-sensor network. In buildings, there are multiple points where objects temporarily change their velocities, such as doors and stairs. We call these points as gates. We assume that the velocity of an object does not almost change before and after passing a gate. We first divide the entire area in a building into multiple sub-regions each of which has gates as their entrances. To track objects in a sub-region, we apply the conventional method based on a Bayesian estimation. The conventional method conducts object tracking using statistically obtained information on object velocities. We expect that we can improve accuracy of object tracking by proposing a method to share the velocity information among sub-regions. Through simulation experiments, we demonstrate that the accuracy of object tracking has a maximum of 35% improvements compared with the conventional method.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

With the wide spread of mobile devices, information discovery methods over mobile ad hoc networks (MANETs) are required. Recent studies have revealed that integrating a distributed hash table (DHT) substrate and network-layer routing can increase search efficiency. Furthermore, some researchers have additionally proposed a clustering method which groups the overlay nodes according to their physical distance. However, it has also been pointed out that the search efficiency deteriorates in highly dynamic environments. In this paper, we propose a method sharing pointers among nodes in a cluster. Through simulation experiments, we show that the proposed method improves the success ratio of object search up to 40% compared with existing method.

CiNii Books

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

With the wide spread of mobile devices, information discovery methods over mobile ad hoc networks (MANETs) are required. Recent studies have revealed that integrating a distributed hash table (DHT) substrate and network-layer routing can increase search efficiency. Furthermore, some researchers have proposed a clustering method which groups the overlay nodes according to their physical distance. However, it has also been pointed out that the search efficiency deteriorates in highly dynamic environments. In this paper, we propose a method sharing pointers among nodes in a cluster. Through simulation experiments, we show that the proposed method improves the success ratio of object search up to 40% compared with existing method.

DOI： 10.1109/PERCOM.2008.38

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

When more than two electronic tags respond to a reader request, the request fails. This is referred to as the collision problem. To overcome this problem, a novel electronic tag readout method, termed the response probability control method (RPCM), is proposed in this paper. In the RPCM, the reader indicates the response probability of a request, ensuring rapid and simultaneous readout of multiple electronic tags. We have already reported the basic RPCM characteristics for a large number of nonmoving electronic tags. In this paper, the extended characteristics of electronic tags located on a conveyor belt are simulated and a portion of them is analyzed. The RPCM and the existing dynamic framed slotted ALOHA (DFSA) method are compared. The simulation demonstrated that, in the case of nonmoving electronic tags, the readout of the RPCM is 1.6 times faster than that of DFSA, while in the case of moving electronic tags, it is more than 2.5 times faster.

DOI： 10.1109/JSYST.2007.907681

Web of Science

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Books

researchmap

本稿では,BluetoothやZigBeeなどセル範囲の小さな通信方式を対象としたサービス領域において,領域の境界におけるノードの動きから領域内のノード分布を推定するモデルを提案する.提案モデルでは,領域に対するノードの出入りを観測し,領域内のノードの移動を再現する.まず,ノードとして人に着目し,実際に人が通行する場所を観測した.観測結果から,領域内におけるノードの移動軌跡が直線で近似できること,移動速度が正規分布に従うことが分かった.さらに,ノードの侵入位置と離脱位置の対応付けを推測する方法として,組み合わせ最適化及びベイズ推定を利用した推定法を提案した.評価の結果,対応付けの再現率は,組み合わせ最適化による推定法では0.736,ベイズ推定法では1となった.

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

As the number of nodes increases, the capacity of ad-hoc wireless networks is constrained by radio interference. Especially, when a source node cannot directly communicate with its destination node, every packet has to travel through one or more relay nodes. The throughput decreases as the number of relayed hop count increases. To effectively use the limited radio resources, we propose a scheme that a node avoids radio interference among its adjacent nodes by appropriately controlling its transmission power. In this case, the capacity is expected to quite improve when each node sets distance to physical distance to the next hop. However, this may be difficult to realize in practical environments. In this paper, through analysis and simulation experiments, we examine the optimal communication distance to maximize the network capacity when all nodes take the same communication distance. Results showed that the communication distance to maximize the network capacity depends on the node density. We further showed that the network capacity is independent of the node density. In addition, the proposed scheme could improve the network capacity up to 2.1 times higher than the traditional scheme.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In a P2P file-sharing system, a node finds and retrieves its desired file. If multiple nodes cache the same file to provide others, we can achieve a file-sharing system with low latency and high file availability. However, a node has to spend costs, e.g., processing load or storage capacity, on caching of a file. Consequently, a node may selfishly behave and hesitate to cache a file. In such a case, there is a possibility that unpopular files disappear from the system. In this paper, we aim to accomplish effective caching in the whole system that emerges from autonomous and selfish node behaviors. We first discuss relationship between selfish node behaviors and system dynamics according to evolutionary game theory. As a result, we show that a file-sharing system can be robust to file disappearance depending on a model of cost and demand for caching even if nodes behave selfishly.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In a P2P file-sharing system, a node finds and retrieves its desired file. If multiple nodes cache the same file to provide others, we can achieve a file-sharing system with low latency and high file availability. However, a node has to spend costs, e.g., processing load or storage capacity, on caching of a file. Consequently, a node may selfishly behave and hesitate to cache a file. In such a case, there is a possibility that unpopular files disappear from the system. In this paper, we aim to accomplish effective caching in the whole system that emerges from autonomous and selfish node behaviors. We first discuss relationship between selfish node behaviors and system dynamics according to evolutionary game theory. As a result, we show that a file-sharing system can be robust to file disappearance depending on a model of cost and demand for caching even if nodes behave selfishly.

CiNii Books

researchmap

? 2007 International Society for Photogrammetry and Remote Sensing. All rights reserved. In this paper, we propose a mobility model which estimates a node distribution in a service area from node flows on the boundary of the area. Our model targets new wireless communication techniques, such as Bluetooth and ZigBee, whose transmission ranges, called cells, are relatively small. The proposed model reproduces the mobility of nodes in an area by the observation of the incoming and outgoing nodes to the area. At first, we focus on a person as a node and observe an area where people actually pass through. From the observation results, we show that a node moves along with an approximately straight line with a velocity following a normal distribution. Furthermore, we propose two methods that estimate correspondences between incoming and outgoing events to the area; combinatorial optimization based method (COM) and Bayesian estimation based method (BEM). As a result, the reproduction ratio of COM is 0.736, and that of BEM is 1.

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In a P2P file-sharing system, a node finds and retrieves its desired file. If multiple nodes cache the same file to provide others, we can achieve a file-sharing system with low latency; and high file availability However, a node has to spend costs, e.g., processing load or storage capacity, on caching of a file. Consequently, a node may selfishly behave and hesitate to cache a file. In such a case, there is a possibility that unpopular files disappear from the system. In this paper, we aim to accomplish effective caching in the whole system that emerges from autonomous and selfish node behavior We first discuss relationship between selfish node behavior and system dynamics according to evolutionary game theory As a result, we show that a file-sharing system can be robust to file disappearance depending on a cost and demand model for caching even if nodes behave selfishly.

DOI： 10.1109/ISCC.2007.4381627

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

As the number of nodes increases, the capacity of ad-hoc wireless networks is constrained by radio interference. Especially when a source node cannot directly communicate with its destination node, every packet has to travel through one or more intermediate nodes. The throughput decreases as the number of relayed hop count increases. To effectively use the limited radio resources, we propose a scheme that a node avoids radio interference among its adjacent nodes by appropriately controlling its transmission power. In this case, the network capacity is expected to quite improve when each node sets its communication distance to physical distance to the next intermediate node. However, this may be difficult to realize in practical environments. In this paper, we examine the optimal communication distance to maximize the network capacity when all nodes take the same communication distance. Results showed that the communication distance to maximize the network capacity depended on the node density. We further showed that the network capacity was independent of the node density. In addition, the proposed scheme could improve the network capacity up to 2.1 times higher than the traditional scheme.

DOI： 10.1109/ICMWCN.2007.4668171

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：INSTICC-INST SYST TECHNOLOGIES INFORMATION CONTROL & COMMUNICATION  

In a cellular system, a base station can smoothly communicate with nodes in its cell by avoiding overlap of frequency range with its adjacent cells. From the viewpoint of graph theory, that needs to divide the original frequency range into at least four sub-ranges. This leads to deteriorate the transmission rate. To tackle this problem, we propose Complete Cell Partitioning (CCP) that enables a base station to use the whole of the original frequency range by avoiding overlap of its own cell with the adjacent cells. CCP is achieved by appropriately controlling the transmission power on base stations. We first analytically derive success probability of CCP when nodes are randomly located in the whole region. Then, we verify the analysis by comparing with simulation results. The analytical and simulation results show that CCP enables to use the original frequency range more effectively than the traditional cellular system regardless of the number of nodes in a cell.

Web of Science

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Since a peer searches for its desired file in a P2P file sharing system, the structure of an overlay network determines the effectiveness of search in terms of network load and search latency. In this paper, based on the Barabasi-Albert (BA) model, we propose a novel method to construct a low-diameter and location-aware overlay network where peers can find physically-close providers without introducing much load on underlying physical networks. We also propose a rewiring method to improve the structure of the overlay network and a recovery method to cope with random peer departures and malicious attacks. Through several simulation experiments using real physical topologies, we found that the proposed methods could construct a resilient overlay network that improved reachability up to 60% compared with BA model while shortening physical distance from neighboring peers.

CiNii Books

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Since a peer searches for its desired file in a P2P file sharing system, the structure of an overlay network determines the effectiveness of search. In this paper, based on the Barabasi-Albert (BA) model, we propose a novel scheme (LLR) to construct a low-diameter and location-aware overlay network where peers can easily find physically-close file holders. LLR has a rewiring method to improve the structure of an overlay network and a recovery method to cope with disappearance of peers. Through several simulation experiments using real physical topologies, we found that LLR could construct an overlay network that had the higher reachability than BA and the higher correlation between physical and logical distances.

DOI： 10.1109/COLCOM.2006.361863

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

An electronic tag such as RFID is expected to create new services that cannot be achieved by the traditional bar code. Specifically, in a distribution system, simultaneous readout method of a large amount of electronic tags embedded in products is required to reduce costs and time. In this paper, we propose novel methods, called Response Probability Control (RPC), to accomplish this requirement. In RPC, a reader firstly sends an ID request to electronic tags in its access area. It succeeds reading information on a tag only if other tags do not respond. To improve the readout efficiency, the reader appropriately controls the response probability in accordance with the number of tags. However, this approach cannot entirely avoid a collision of multiple responses. When a collision occurs, ID information is lost. To reduce the amount of lost data, we divide the ID registration process into two steps. The reader first gathers the former part of the original ID, called temporal ID, according to the above method. After obtaining the temporal ID, it sequentially collects the latter part of ID, called remaining ID, based on the temporal ID. Note that we determine the number of bits of a temporal ID in accordance with the number of tags in the access area so that each tag can be distinguishable. Through simulation experiments, we evaluate RPC in terms of the readout efficiency. Simulation results show that RPC can accomplish the readout efficiency 1.17 times higher than the traditional method where there are a thousand of electronic tags whose IDs are 128 bits.

DOI： 10.1117/12.685791

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

In this paper, we focus on an information gathering system where a reader continuously collects information from mobile nodes in its access area, such as environmental information cameras and sensors. We assume that a mobile node is relatively tiny and does not have a high-precision antenna to sense carriers emitted by other nodes. Although a random access method like ALOHA can be easily used, it has disadvantages of transmission efficiency and energy consumption. To tackle these problems, we propose a novel method that is a combination of random and selective accesses. At first, a reader sends an ID request to all nodes. Then, each node replies its ID to the reader at a response probability involved in the request. Finally, the reader selectively gathers information from nodes according to the obtained ID lists. In our method, non-registered nodes and non-deleted nodes affect the system performance. The non-registered node is a node that is in the access area but its ID is not registered to the reader. The non-deleted node is a node that leaves the area but its ID is still registered to the reader. In this paper, we first derive their numbers by an analysis using the Inversion Formula of Palm Calculus. Then, we conduct simulation experiments to verify the analysis. Simulation results show that the proposed method performs well in a wide range of mobility by appropriately controlling the response probability.

DOI： 10.1117/12.685666

Web of Science

researchmap

Publishing type：Research paper (scientific journal)  

With the growth of computing power and the proliferation of broadband Internet access, the use of media streaming has become widely diffused. In this paper, based on our previous work, we propose a Peer-to-Peer (P2P) media streaming system that can provide a large number of users with continuous media streaming services while dynamically adapting to peer departures and changes in network conditions. For this purpose, we propose a new media retrieval method that dynamically switches provider peers. Through several simulation experiments, we show that the proposed media retrieval method improves the completeness of media playout compared with previous methods. Furthermore, we also show that our search method is more robust to peer departures than flooding methods.

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

With the growth of computing power and the proliferation of broadband access to the internet, the use of media streaming has become widely diffused. By using the peer-to-peer (P2P) communication architecture, media streaming can be expected to smoothly react to changes in network conditions and user demands for media streams. In this paper, to achieve continuous and scalable media streaming, we introduce our scalable media search and in-time retrieval methods. Through several simulation experiments, we show that our methods can accomplish continuous media play-out for popular media streams without introducing extra load on the system. However, we also show that an LRU cache replacement algorithm cannot provide users with continuous media play-out for unpopular media streams. To tackle this problem, we take inspiration from biological systems to propose a new cache replacement algorithm that considers the balance between supply and demand for media streams. We demonstrate that our proposed algorithm can improve the continuity of media play-out compared with LRU. Furthermore, we find that the proposed algorithm can adapt to changes in the popularity of various media. Copyright (C) 2004 AEI.

DOI： 10.1002/ett.1014

Web of Science

researchmap

Language：Japanese   Publisher：Institute of Systems, Control and Information Engineers  

CiNii Books

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER-VERLAG BERLIN  

With the growth of computing power and the proliferation of broadband access to the Internet, the use of media streaming has become widely diffused. By using the P2P communication architecture, media streaming can be expected to smoothly react to changes in network conditions and user demands for media streams. To achieve continuous and scalable media streaming, we proposed scalable media search and retrieval methods in our previous work. However, through several simulation experiments, we have shown that an LRU (Least Recently Used) cache replacement algorithm cannot provide users with continuous media play-out for unpopular media streams. In this paper, inspired by biological systems, we propose a new algorithm that considers the balance between supply and demand for media streams. Through several simulation experiments, it has been shown that our proposed algorithm could improve the completeness of media play-out compared with LRU.

Web of Science

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

With the growth of computing power and the proliferation of broadband access to the Internet, media streaming has widely diffused. By using the P2P communication architecture, media streaming can be expected to smoothly react to network conditions and changes in user demands for media-streams. In this paper, we propose efficient methods to achieve continuous and scalable media streaming system. In our mechanisms, a media stream is divided into blocks for efficient use of network bandwidth and storage space. We propose scalable search methods, algorithms to determine an optimum provider peer from search results, and a caching algorithm considering on the balance between supply and demand for media streams. Through several simulation experiments, it was shown that proposed mechanisms could accomplish continuous media streaming without deteriorating the system scalability.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

With the growth of computing power and the proliferation of broadband access to the Internet, media streaming has widely diffused. By using the P2P communication architecture, media streaming can be expected to smoothly react to network conditions and changes in user demands for media-streams. In this paper, we propose efficient methods to achieve continuous and scalable media streaming system. In our mechanisms, a media stream is divided into blocks for efficient use of network bandwidth and storage space. We propose scalable search methods, algorithms to determine an optimum provider peer from search results, and a caching algorithm considering on the balance between supply and demand for media streams. Through several simulation experiments, it was shown that proposed mechanisms could accomplish continuous media streaming without deteriorating the system scalability.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

With the growth of computing power and the proliferation of broadband access to the Internet, media streaming has widely diffused. By using the P2P communication architecture, media streaming can be expected to smoothly react to network conditions and changes in user demands for media-streams. In this paper, we propose efficient methods to achieve continuous and scalable media streaming system. In our mechanisms, a media stream is divided into blocks for efficient use of network bandwidth and storage space. We propose scalable search methods, algorithms to determine an optimum provider peer from search results, and a caching algorithm considering on the balance between supply and demand for media streams. Through several simulation experiments, it was shown that proposed mechanisms could accomplish continuous media streaming without deteriorating the system scalability.

CiNii Books

researchmap

The proxy mechanism widely used in WWW systems offers low-delay data delivery by means of "proxy server." By applying proxy mechanisms to video streaming system, we expect that high-quality and low-delay video distribution can be accomplished without introducing extra load on the system. In addition, it is effective to adapt the quality of cached video data appropriately in the proxy if user requests are diverse due to heterogeneity in terms of the available bandwidth, end-system performance, and user's preferences on the perceived video quality. In this paper, we propose proxy caching mechanisms to accomplish high-quality and low-delay video streaming services, In our proposed system, a video stream is divided into blocks for efficient use of cache buffer. A proxy cache server is assumed to be able to adjust the quality of cached or retrieved video blocks to requests through video filters. We evaluate our proposed mechanisms in terms of the required buffer size, the play-out delay and the video quality through simulation experiments. Furthermore, to verify the practicality of our mechanisms, we implement our proposed mechanisms on a real system and conducted experiments. Through evaluations from several performance aspects, it is shown that our proposed mechanisms can provide users with a low-latency and high-quality video streaming service in a heterogeneous environment.

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE COMPUTER SOC  

With the growth of computing power and the proliferation of broadband access to the Internet, media streaming has widely diffused. Although the proxy caching technique is one method to accomplish effective media streaming, it cannot adapt to the variations of user locations and diverse user demands. By using the P2P communication architecture, media streaming can be expected to smoothly react to network conditions and changes in user demands for media-streams. In this paper, we propose efficient methods to achieve continuous and scalable media streaming system. In our mechanisms, a media stream is divided into blocks for efficient use of network bandwidth and storage space. We propose two scalable search methods and two algorithms to determine an optimum provider peer from search results. Through several simulation experiments, we show that the FLS method can perform continuous media play-out while reducing the amount of search traffic to 1/6 compared with full flooding.

DOI： 10.1109/PTP.2003.1231508

Web of Science

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The proxy mechanism widely used in WWW systems offers low-delay data delivery by means of "proxy server". By applying proxy mechanisms to the video streaming system, we expect that high-quality and low-delay video distribution can be accomplished without introducing extra load on a system. In addition, it is effective for proxy to adapt the quality of cached video data to users requests if requests are diverse due to heterogeneity in terms of the available bandwidth, end-system performance, and user's preferences on the perceived video quality. We have proposed proxy caching mechanisms to accomplish the high-quality and highly-interactive video streaming services. In our proposed system, a video stream is divided into blocks for efficient use of a cache buffer. A proxy server is assumed to be able to adjust the quality of a cached or retrieved video block to a request through video filters. In this paper, to verify the practicality of our mechanisms, we implemented them on a real system and conducted experiments. Through evaluations from several performance aspects, it was shown that our proposed mechanisms can provide users with a video streaming service in a heterogeneous environment.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Image Information and Television Engineers  

The proxy mechanism widely used in WWW systems offers low-delay data delivery by means of "proxy server". By applying proxy mechanisms to the video streaming system, we expect that high-quality and low-delay video distribution can be accomplished without introducing extra load on a system. In addition, it is effective for proxy to adapt the quality of cached video data to users requests if requests are diverse due to heterogeneity in terms of the available bandwidth, end-system performance, and user's preferences on the perceived video quality. We have proposed proxy caching mechanisms to accomplish the high-quality and highly-interactive video streaming services. In our proposed system, a video stream is divided into blocks for efficient use of a cache buffer. A proxy server is assumed to be able to adjust the quality of a cached or retrieved video block to a request through video filters. In this paper, to verify the practicality of our mechanisms, we implemented them on a real system and conducted experiments. Through evaluations from several performance aspects, it was shown that our proposed mechanisms can provide users with a video streaming service in a heterogeneous environment.

DOI： 10.11485/itetr.26.48.0_41

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The proxy mechanism is now widely used in WWW system in order to offer low-delay data delivery with an assistance of the "proxy server". By applying the proxy mechanism to video transfer, we can expect a low-delay and interactive video streaming service provided without intoroducing extra load on the stream. In addition, if the proxy appropriately adapts the quality of cached video data to the requested quality, video streams can be delivered to users by considering their heterogeneous QoS requirements. In this paper, we consider mechanisms of data retrieval, prefetching and replacement for the proxy cache. Through simulation experiments, we show that our proposed proxy caching mechanism achieves a high-quality and low-delay video distribution which meeting user's demand.

CiNii Books

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The proxy mechanisms widely used in WWW systems offer low-delay data delivery by a means of "proxy server". By applying the proxy mechanism to the video transfer, we expect a real-time and interactive video streaming without introducing extra load on the system. In addition, if the proxy appropriately adjusts the quality of cached video data to the user's demand, video streams can be delivered to users considering their heterogeneous QoS requirements. In this paper, we propose proxy caching mechanisms that can achieve a high-quality video transfer considering the user's demand and the available bandwidth. In our system, a video stream is divided into pieces. The proxy caches them in local buffer, adjusts their quality if necessary, transmits them to users, replaces them with cached data, and retrieves them from the video server, considering user's requirement. We evaluate the proposed video caching mechanisms and compare their performance in terms of the required buffer size, the play-out delay and the video quality. Consequently, the validity of the video quality adjustment in the proxy is confirmed.

DOI： 10.1117/12.434278

Web of Science

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Books

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Large distributed systems, such as peer-to-peer networks and wireless sensor networks, provide users with multiple services by using lots of computational resources. Because such resources are limited, it is important to allocate them dynamically in response to users' demands. Centralized resource allocation schemes, however, have a potential drawback of scalability. In this paper, we propose a decentralized resource allocation scheme, where agents, which are running on the computational resources, autonomously determine services to provide. Specifically, we apply evolutionary game theory to achieve self-organizing resource allocation. Through analysis and simulation experiments, we show the effectiveness of the proposed scheme in terms of convergence accuracy, spatial distribution of service share, and stability.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Recently, service providers have been using data centers (DCs) to provide cloud services. When they use multiple DCs, which are geographically distributed, they require communication for maintenance operations among them, e.g., synchronization and update. Because such maintenance operations need to send identical data from one source to multiple destinations, we apply overlay multicast. Note that main traffic yielded by cloud services temporally changes and the charge for access links is determined by their peak traffic. In this paper, we aim to maximize the amount of overlay multicast traffic under the constraint of the peak traffic. We first formulate our problem as a linear programming. We further propose a scheme for estimating the peak traffic. Through simulation experiments, we show the effectiveness of the proposed method in terms of the amount of overlay multicast traffic and peak traffic.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Recently, it is required to construct inexpensive communication infrastructures in rural areas and emergency networks in disaster areas. In such environments, there are multiple isolated clusters, such as villages in rural areas or emergency shelters in disaster areas. In this paper, we focus on ferry-assisted DTNs in which a special mobile node called a message ferry visits clusters to support communication with external networks through a special cluster, called a base cluster, which has access links. In the ferry assisted DTNs, visiting order of the message ferry determines the mean delivery delay of data (bundles), which is the average time interval from the generation of a bundle in a cluster to the completion of its delivery to the base cluster. In this paper, we propose a hybrid visiting order method that combines the two types of existing visiting order in consideration of the proximity between clusters. Through simulation experiments, we evaluate the effectiveness of the proposed method in terms of the average delivery delay.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In recent years, there have been many studies on monitoring in mobile sensor networks, e.g., disaster prevention, crime prevention, environmental monitoring, and ecosystem monitoring. Because mobile sensors are usually powered by batteries, it is important to achieve monitoring with low power consumption. In this paper, we propose a monitoring scheme composed of two phases: search phase and observation phase. In the search phase, mobile sensors aim to discover important places speedily. After that, they continue to observe the important places in the observation phase. Under the assumption that importance values of places in a monitoring area are inde- pendent and identically distributed according to a uniform distribution, we formulate the optimal phase transition to be an optimal stopping problem and derive the optimal phase transition rule. Through both the numerical and simulation experiments, we show the effectiveness of the proposed scheme.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

When large-scale disasters occur, evacuees have to evacuate to safe places quickly. In this paper, we propose an evacuation guiding scheme using mobile terminals of evacuees. Each terminal tries to navigate its evacuee by presenting an evacuation route. It can also trace the actual evacuation route of the evacuee as the trajectory by measuring his/her positions periodically. The proposed scheme automatically estimates blocked road segments from the difference between the presented evacuation route and actual evacuation route, then recalculates the alternative evacuation route. In addition, evacuees also share such information among them through communication with other mobile terminals and that with a server via communication infrastructures. Through simulation experiments, we evaluate fundamental characteristics of the proposed scheme, impact of degree of disaster, and effect of information sharing.

CiNii Books

researchmap

Language：Japanese   Publisher：一般社団法人電子情報通信学会  

In recent years, mobile sensor networks have been expected to realize environmental monitoring and ecosystem monitoring. It is desirable that mobile sensors autonomously cooperate with each other in a distributed manner such that they can cover important locations in the target area. Game theoretical approaches have been attracting many researchers to achieve such distributed cooperative control. In the game theoretical approaches, we need to design a game model and a learning algorithm. The game model should be designed to enhance the accuracy of coverage in steady state. The learning algorithm should be designed to lead the system to appropriate steady states, independent of initial states. In this paper, we propose a learning algorithm where mobile sensors efficiently explore the area by sharing their search histories and speedily move to their appropriate locations. Through simulation experiments, we demonstrate that the proposed algorithm can achieve high accuracy of coverage even when each mobile sensor explores a limited range of the entire area.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Peer-to-Peer (P2P) file distribution systems can efficiently disseminate massive contents, such as disk images of operating systems, to many users in a piece-by-piece manner. In particular, BitTorrent protocol optimizes each peer's download speed by applying tit-for-tat (TFT) strategy, where each peer preferentially uploads piece(s) to peer(s) from which it can download missing pieces faster. To the best of our knowledge, however, it has not been sufficiently studied on the optimality of such TFT-based P2P file distribution. In this paper, we aim to figure out the optimal scheduling in the TFT-based P2P file distribution. First, we formulate the scheduling in TFT-based P2P file distribution as a integer linear programming, where the variables are piece transfers between peers at each time and the objective function is the minimization of the average file retrieving time among peers. Through the analysis of the optimal solution obtained by the existing solver, we reveal the characteristics of the optimal scheduling.

CiNii Books

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Books

J-GLOBAL

researchmap

Language：Japanese   Publisher：一般社団法人電子情報通信学会  

Because overlay networks for inter-data center communication are composed of reliable nodes, high-speed overlay multicast is expected to be realized using the information about the underlying IP networks. In this paper, we aim to achieve the high-speed multicast based on multiple trees by taking account of the IP-level interference between them. We first formulate the tree-set selection problem for high-speed multicast in overlay networks with linear capacity constraints. We further propose a space-efficient heuristic algorithm to solve this problem. Through numerical results, we show that the heuristic algorithm can obtain quasi-optimal tree set.

CiNii Books

researchmap

Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

Communication among isolated networks (clusters) in delay tolerant networks (DTNs) can be supported by a message ferry, which collects bundles from clusters and delivers them to a sink node. When there are lots of distant static clusters, multiple message ferries and sink nodes will be required. In this paper, we aim to make groups each of which consists of physically close clusters, a sink node, and a message ferry. Our main objective is minimizing the overall mean delivery delay of bundles in consideration of both offered load of clusters and distance between clusters and their sink nodes. We first model this problem as a nonlinear integer programming, based on the knowledge obtained in our previous work. Because it might be hard to solve this problem directly, we take two-step optimization approach based on linear integer programming, which yields an approximate solution of the problem. Through numerical results, we show the two-step optimization approach works well.

CiNii Books

researchmap

Language：Japanese   Publisher：一般社団法人電子情報通信学会  

Each user in the Peer-to-Peer (P2P) file-sharing systems potentially tends to maximize its own benefit rather than the overall system efficiency and performance. On the other hand, there are lots of indistinct points left in the users' selfish behavior and its influence on the system performance. In this paper, we measure the BitTorrent system, which is one of the most famous P2P file-sharing systems, and evaluate users' behavior and system availability. The measurement is conducted through communications with a tracker which manages information about peers sharing the files and with each of those peers. The measurement result shows that about half of users stop opening the file to the public within several hours after completing the file retrieval. In addition, we show that the system is supported not only by a few peers that remain to be providers of the file for a long term, but also by most peers that are temporal suppliers during their own file retrieval.

CiNii Books

researchmap

Language：Japanese  

researchmap

Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Books

researchmap