掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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その他リンク： http://journals.sagepub.com/doi/full-xml/10.1177/1748006X221133600

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

DOI： 10.23919/cnsm55787.2022.9965166

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

DOI： 10.1109/noms54207.2022.9789758

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

DOI： 10.1109/globecom46510.2021.9685205

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

DOI： 10.1109/icbc51069.2021.9461125

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/nem.2190

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tnsm.2020.3044329

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/JIOT.2020.3033434

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Electronics, Information and Communications Engineers (IEICE)  

DOI： 10.1587/transcom.2021cep0004

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Electronics, Information and Communications Engineers (IEICE)  

DOI： 10.1587/transcom.2021cet0001

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掲載種別：研究論文（学術雑誌）  

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その他リンク： https://dblp.uni-trier.de/db/journals/corr/corr2103.html#abs-2103-04016

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

DOI： 10.1109/brains49436.2020.9223293

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掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

DOI： 10.1007/s12083-020-00925-2

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その他リンク： http://link.springer.com/article/10.1007/s12083-020-00925-2/fulltext.html

掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.comnet.2020.107383

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

DOI： 10.1109/ccnc46108.2020.9045338

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Inderscience Publishers  

DOI： 10.1504/ijor.2020.10034355

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/ojits.2020.3019935

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掲載種別：研究論文（学術雑誌）  

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その他リンク： https://dblp.uni-trier.de/db/journals/corr/corr2009.html#abs-2009-02933

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

DOI： 10.1109/Blockchain50366.2020.00047

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その他リンク： https://dblp.uni-trier.de/db/conf/blockchain2/blockchain2020.html#FujitaZSK20

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

DOI： 10.1109/globecom38437.2019.9013321

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

DOI： 10.1109/globecom38437.2019.9014155

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.comcom.2019.08.012

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掲載種別：研究論文（学術雑誌）  

? 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

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その他リンク： http://link.springer.com/article/10.1007/s12652-018-0826-z/fulltext.html

記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）  

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記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1177/2399808318802940

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その他リンク： http://journals.sagepub.com/doi/full-xml/10.1177/2399808318802940

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1504/ijor.2020.10022448

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s41070-017-0013-1

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

? Springer International Publishing Switzerland 2016. 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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：日本語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

P2Pファイル共有システムでは,ファイルのやりとりが個々のノード間で行われることから,システム内の状況やシステムの挙動を把握・制御することが非常に困難である.本稿では,P2Pファイル共有システムの一つであるWinnyにおいて,ユーザの関心の高い高頻度に流通するファイルを実時間で計測可能なシステムの設計と実装を行う.計測用のノードを実際のWinnyネットワークに導入し計測を行うが,他のノードから受信した検索要求のみを解析の対象とするパッシブ計測を用いることで,計測負荷の軽減と状況変化への高い追従性を実現する.さらに,情報の解析にはスライディングウィンドウ方式と頻出パターンマイニング手法を複合的に用いることで,実時間計測を達成する.実証実験の結果を通じて,高頻度流通ファイルの時間変化を実時間で詳細に把握できることを示す.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

無線メッシュネットワークでは,複数の無線基地局(メッシュノード)を無線リンクにより相互接続することで,無線リンク間の電波干渉の問題はあるものの,広範囲な無線アクセス環境を低コストかつ容易に構築できる.無線メッシュネットワークをインターネットアクセスのためのインフラとして用いる場合,有線ネットワークとの接続拠点であるゲートウェイノードにトラヒック負荷が集中するため,複数のゲートウェイノードを設置しトラヒック負荷を分散させる必要がある.本稿では,複数のゲートウェイノードを持つTDMA型無線メッシュネットワークにおいて,ゲートウェイノードの負荷,有線ネットワークへのアクセス回線容量及び無線リンク間の電波干渉を総合的に考慮し,有線ネットワークへ流れるトラヒック量(システムスループット)を最大化するスパニングツリーの構築法を提案する.シミュレーション評価の結果,提案手法はボトルネックの位置によらずシステムスループットを向上でき,従来の最短経路ツリー構築法に比べ,最大で3.1倍の性能を実現できることを示した.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

無線メッシュネットワークはマルチホップの無線リンクによって構成され,低コストで容易に導入できることから近年関心が高まっている.しかし,隣接メッシュノード間の送信における電波の干渉は,無線資源の利用効率の低下を引き起こす.無線メッシュネットワークの性能向上のためには電波干渉を低減することが大きな課題の1つであり,干渉の低減の方法としてメッシュノードの通信電力の制御が挙げられる.本稿では,TDMA方式を用いた無線メッシュネットワークにおいて,メッシュノードの通信電力を制御することで無線資源の利用効率を向上する電力制御手法を提案する.提案手法では,電力制御による干渉の減少だけではなく,同時に生じる経路長の増大に着目し制御を行う.シミュレーション評価の結果,無線メッシュネットワークの規模に応じたパラメータ設定を行うことで,無線資源の利用効率を最大27%向上できることを示す.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

Peer-to-Peer (P2P)型ファイル共有システムでは,ノードが協力的にファイルをキャッシュし,他のノードへ提供することでファイル可用性が向上する.しかしながら,ファイルのキャッシングにはストレージの消費,処理負荷,帯域の消費などのコストがともなうため,ユーザが自身の利益のみを優先しキャッシングに対して非協力的な行動をとると,需要の低いファイルがシステムから消失するなどの問題が発生する.そこで本稿では,ユーザの利己的な振る舞いがシステム全体の性能に与える影響を進化ゲーム理論を用いて明らかにする.特に,キャッシングに対する積極性がユーザごとに異なる状況に着目し検討した結果,ユーザの多様性はファイル可用性の観点で有利に働くことがわかった.

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記述言語：日本語   掲載種別：研究論文（その他学術会議資料等）   出版者・発行元：一般社団法人電子情報通信学会  

Peer-to-Peer (P2P)型ファイル共有システムでは,ノードが協力的にファイルをキャッシュし,他のノードへ提供することでファイル可用性が向上する.しかしながら,ファイルのキャッシングにはストレージの消費,処理負荷,帯域の消費などのコストがともなうため,ユーザが自身の利益のみを優先しキャッシングに対して非協力的な行動をとると,需要の低いファイルがシステムから消失するなどの問題が発生する.そこで本稿では,ユーザの利己的な振る舞いがシステム全体の性能に与える影響を進化ゲーム理論を用いて明らかにする.特に,キャッシングに対する積極性がユーザごとに異なる状況に着目し検討した結果,ユーザの多様性はファイル可用性の観点で有利に働くことがわかった.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本稿では,2値センサを利用した建物内におけるオブジェクトの追跡手法について検討する.建物内には,扉や階段といったオブジェクトの移動速度が一時的に変化する地点(ゲート)が存在する.ただし,ゲートの通過前後ではオブジェクトの移動速度は大きく変化しないと考えられる.そこでまず,領域全体をゲートを出入り口に持つ小規模な領域(サブ領域)に分割する.サブ領域内でのオブジェクト追跡にはベイズ推定に基づく従来方式を用いる.従来方式では,統計的な移動速度情報を用いてオブジェクトの追跡を行うため,サブ領域間で移動速度情報を共有するための方式を導入することで追跡精度の向上が期待できる.シミュレーション評価により,提案方式を用いることで追跡の成功率が最大で約35%向上することを示す.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

近年のモバイル端末の普及に伴い,MANET上での情報発見技術の確立が求められている.これまでに,DHTとネットワーク層のルーチングプロトコルを統合することで,情報発見の効率を高められることがわかっている.さらに,ノードの物理的な位置に基づいてDHT上でクラスタリングを行う手法が検討されているが,ノードの移動速度が速い環境下では効率の低下が指摘されている.そこで本稿では,クラスタ内でオブジェクト情報を共有することで,従来手法に比べて検索成功率を最大で40%近く改善できることを示す.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

大量電子タグの高速一括読出しを実現する新しい応答確率制御法について報告する.リーダによる複数の電子タグの同時読出しは,読出し要求に対して,1個の電子タグのみが応答を返す場合に成功する.本論文で提案する応答確率制御法は,読出し要求に対して電子タグが応答する確率をリーダから指定して,読出し成功確率の向上を図る.基本的な特性を明らかにするとともに,読出し状況からリーダにおいて最適な応答確率を推定する方法を示し,これが十分利用できることを示した.この結果,大量の電子タグを高速に読み出せる見通しを得た.既存の複数電子タグ一括読出し法としてFSA(Flamed Slotted ALOHA)とそれを改良したDFSA(Dynamic FSA)がある.属性情報を含むような可変長の読出しに高い効率が期待できること,無応答の検出時間が短い場合,これを利用して読出し速度の高速化が可能なこと等において本方法が優れ,試算した条件のもとでは約1.6倍の高速化が可能であった.なお,本論文はシミュレーション確認による方法の提案であり,実装確認は今後の課題である.

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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.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

無線アドホックネットワークでは,領域内におけるノード数の増加にともない,電波の衝突による通信容量の低下が問題となる.特に,送受信ノードが互いの送信電力範囲内に存在しない場合には,他のノードを中継するマルチホップ通信により情報を交換する必要があり,その場合にはホップ数の増加に伴いスループットが低下してしまう.限られた電波資源を有効に活用するための方法として,ノードが送信電力を調整することにより,領域をノード間で空間的に分割することが考えられる.各ノードが次ホップのノードまでの距離を通信距離とすることができれば,通信容量の大幅な改善が期待できるが,他ノードとの距離を得ることは困難であると考えられる.そこで本稿では,すべてのノードが均一な通信距離を用いた場合に,領域全体の通信容量を最大化するような最適な通信距離を解析とシミュレーション評価により明らかにした.その結果,通信容量を最大にする通信距離はノード密度に依存し,通信容量の最大値はノード密度に依らない値をとることが明らかになった.さらに,従来方式と比べて2.1倍の通信容量を実現できることを示した.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

P2Pファイル共有システムでは,ノードは自分の必要とするファイルを検索,取得する.複数のノードが同一ファイルをキャッシュし,他のノードに提供することによって,低遅延でファイル可用性の高いファイル共有が期待できる.しかしながら,ファイルのキャッシングには処理負荷,ストレージ資源などのコストがかかるため,ノードが利己的に振る舞うと,十分にファイルがキャッシュされず,特に人気の低いファイルがシステムから消失するなどの問題が発生する可能性がある.そこで本稿では,ノードの自律的,利己的な振る舞いによってシステム全体で適切なキャッシングが行われる機構の実現を目指し,進化ゲーム理論により,ノードの振る舞いがシステム全体のダイナミクスに与える影響について検証した.その結果,キャッシングに対するコストと需要のモデルによっては,ノードが利己的に振る舞ったとしてもファイルがシステムから消失することのない,ファイル共有が実現可能であることを示した.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

P2Pファイル共有システムでは,ノードは自分の必要とするファイルを検索,取得する.複数のノードが同一ファイルをキャッシュし,他のノードに提供することによって,低遅延でファイル可用性の高いファイル共有が期待できる.しかしながら,ファイルのキャッシングには処理負荷,ストレージ資源などのコストがかかるため,ノードが利己的に振る舞うと,十分にファイルがキャッシュされず,特に人気の低いファイルがシステムから消失するなどの問題が発生する可能性がある.そこで本稿では,ノードの自律的,利己的な振る舞いによってシステム全体で適切なキャッシングが行われる機構の実現を目指し,進化ゲーム理論により,ノードの振る舞いがシステム全体のダイナミクスに与える影響について検証した.その結果,キャッシングに対するコストと需要のモデルによっては,ノードが利己的に振る舞ったとしてもファイルがシステムから消失することのない,ファイル共有が実現可能であることを示した.

CiNii Books

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? 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.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

P2Pファイル共有システムではピアは論理網を利用して所望するファイルの検索を行うため,論理網の構造が下位の物理網の負荷及び検索効率に影響を及ぼす.そこで本稿では,Barabasi-Albert(BA)モデルに基づく高速なファイル検索,取得のための論理網構築手法を提案する.提案手法では,物理網特性を考慮した論理網を構築することにより,下位の物理網の負荷を抑えるとともに,ピアはより物理的に近い取得先ピアをより早く発見することができる.さらに,動的に論理リンクを切り替えることにより,論理網の構造を改善し,ピア消失などの障害から回復することができる.現実的な物理網トポロジを用いたシミュレーションにより,BAモデルに比べて最大で約60%程度到達率を向上させるとともに,隣接ピアが物理的にも近く,また,障害回復力を有する論理網を構築できることを示した.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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掲載種別：研究論文（学術雑誌）  

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.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：日本語   出版者・発行元：システム制御情報学会  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

コンピュータの高性能化,アクセス回線容量の増加を背景に,マルチメディアのストリーミング配信の利用が広まっている.本稿では,P2P型通信技術を用いることにより,ネットワークの負荷変動やメディアに対するユーザ要求の変化に柔軟に対応しつつ,途切れなくスケーラブルなストリーミング配信を実現するための効果的な手法を提案する.具体的には,帯域やキャッシュバッファの有効利用のためブロックと呼ばれる単位に分割されたメディアを効率よく検索,取得するためのスケーラブルなブロック検索手法とブロック取得先決定アルゴリズム,およびメディアに対する需要と供給のバランスを考慮したキャッシングアルゴリズムを提案している.シミュレーションによる評価を通して,スケーラビリティを低下させることなく途切れの少ないストリーミング配信が実現可能であることを示した.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

コンピュータの高性能化,アクセス回線容量の増加を背景に,マルチメディアのストリーミング配信の利用が広まっている.本稿では,P2P型通信技術を用いることにより,ネットワークの負荷変動やメディアに対するユーザ要求の変化に柔軟に対応しつつ,途切れなくスケーラブルなストリーミング配信を実現するための効果的な手法を提案する.具体的には,帯域やキャッシュバッファの有効利用のためブロックと呼ばれる単位に分割されたメディアを効率よく検索,取得するためのスケーラブルなブロック検索手法とブロック取得先決定アルゴリズム,およびメディアに対する需要と供給のバランスを考慮したキャッシングアルゴリズムを提案している.シミュレーションによる評価を通して,スケーラビリティを低下させることなく途切れの少ないストリーミング配信が実現可能であることを示した.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

コンピュータの高性能化,アクセス回線容量の増加を背景に,マルチメディアのストリーミング配信の利用が広まっている.本稿では,P2P型通信技術を用いることにより,ネットワークの負荷変動やメディアに対するユーザ要求の変化に柔軟に対応しつつ,途切れなくスケーラブルなストリーミング配信を実現するための効果的な手法を提案する.具体的には,帯域やキャッシュバッファの有効利用のためブロックと呼ばれる単位に分割されたメディアを効率よく検索,取得するためのスケーラブルなブロック検索手法とブロック取得先決定アルゴリズム,およびメディアに対する需要と供給のバランスを考慮したキャッシングアルゴリズムを提案している.シミュレーションによる評価を通して,スケーラビリティを低下させることなく途切れの少ないストリーミング配信が実現可能であることを示した.

CiNii Books

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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.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

WWWシステムで広く用いられているプロキシ技術を適用することにより,システムに大きな負荷を与えることなく,実時間で応答性の高い動画像ストリーミングサービスが実現できると考えられる.さらに,プロキシで蓄積データを適切に品質調整することにより,ネットワークへの接続形態,システム性能,再生動画像に対するユーザの好みなどによりさまざまに異なる要求品質に合わせた動画像配信が実現可能である.我々の研究グループでは,動画像品質調整機能を有するプロキシが通信状態やユーザの要求品質を考慮して,適切に動画像データを取得,蓄積,品質調整,転送するシステムのための効果的なプロキシキャッシング機構を検討している.本稿では,提案手法を実システムへ実装し,処理遅延,再生動画像品質,トラヒック量などの観点から評価を行った.その結果,提案手法を用いることで,利用可能な帯域にあわせて,実時間で動画像品質調整を行う動画像配信が提供可能であることを示した.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人 映像情報メディア学会  

WWWシステムで広く用いられているプロキシ技術を適用することにより,システムに大きな負荷を与えることなく,実時間で応答性の高い動画像ストリーミングサービスが実現できると考えられる.さらに,プロキシで蓄積データを適切に品質調整することにより,ネットワークヘの接続形態,システム性能,再生動画像に対するユーザの好みなどによりさまざまに異なる要求品質に合わせた動画像配信が実現可能である.我々の研究グループでは,動画像品質調整機能を有するプロキシが通信状態やユーザの要求品質を考慮して,適切に動画像データを取得,蓄積,品質調整,転送するシステムのための効果的なプロキシキャッシング機構を検討している.本稿では,提案手法を実システムヘ実装し,処理遅延,再生動画像品質,トラヒック量などの観点から評価を行った.その結果,提案手法を用いることで,利用可能な帯域にあわせて,実時間で動画像品質調整を行う動画像配信が提供可能であることを示した.

DOI： 10.11485/itetr.26.48.0_41

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

WWWシステムで広く用いられているプロキシ技術を適用することにより, システムに大きな負荷を与えることなく, 実時間で応答性の高い動画像ストリーミングサービスが実現できると考えられる. さらに, プロキシで蓄積データを適切に品質調整することにより, クライアントごとのQoS要求にもとづいた動画像配信が実現可能である. 本稿では, クライアントの要求品質を考慮した高品質で高速な動画像配信を提供するプロキシキャッシュシステムを実現するため, プロキシにおける動画像データ取得, 先読み, 置き換え手法について検討した. シミュレーションによる評価の結果, 提案手法を用いることにより, より少ないキャッシュバッファで, ネットワークに与える負荷が小さく低遅延な動画像配信が提供可能であることを示した.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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記述言語：日本語   出版者・発行元：電子情報通信学会  

CiNii Books

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記述言語：日本語   出版者・発行元：電子情報通信学会  

CiNii Books

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記述言語：日本語   出版者・発行元：電子情報通信学会  

CiNii Books

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記述言語：日本語   出版者・発行元：電子情報通信学会  

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

CiNii Books

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記述言語：日本語   出版者・発行元：電子情報通信学会  

CiNii Books

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記述言語：日本語   出版者・発行元：電子情報通信学会  

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

Peer-to-Peer(P2P)ネットワークや無線センサネットワークといった大規模分散システムでは,多数の計算機資源を用いて複数のサービスを提供している.システムを構成する計算機資源は有限であることから,ユーザに高品質なサービスを提供するためには,需要に応じた計算機資源の割当が重要となる.ただし,システム規模の増大に伴い,集中型制御による資源割当は困難となる.そこで本稿では,計算機上で動作するエージェントと呼ばれるソフトウェアが自律分散的にサービスを選択することで計算機資源の割当を実現する方式を提案する.特に,このサービス選択に進化ゲーム理論を応用することで,自己組織型資源割当の実現を目指す.解析とシミュレーション評価により,収束精度,サービスシェアの空間的分布,安定性の観点から提案手法の有効性を示す.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

近年,サービス事業者がデータセンタを利用してクラウドサービスを提供する動きが広まっている.地理的に分散した複数のデータセンタを使用する場合には,それらの間で同期や更新といったメンテナンス操作のための通信が必要となる.これらは同一のデークを複数地点に配信する特徴を持つことから,オーバレイマルチキャストの利用が考えられる.ここで,サービス提供のために生じるメイントラヒックが時間的に変動することと,サービス事業者はアクセス回線のピークトラヒック量により回線使用料を支払うことに注意が必要である.そこで本稿では,ピークトラヒックの制約の下でマルチキャストのトラヒック量を最大化することを目指す.まず,想定する問題を線形計画問題として定式化する.さらに,ピークトラヒックの推定手法を提案する.シミュレーション評価により,マルチキャストトラヒック量とピークトラヒック量の観点で提案手法の有効性を示す.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

近年,過疎地における安価な通信インフラや被災地における緊急用ネットワークの構築が求められている.このような環境では,過疎地における村,被災地における避難所といった孤立した拠点(クラスタ)が複数存在する.そこで本研究では,メッセージフェリーと呼ばれる特別な移動ノードがクラスタを巡回し,アクセス回線を有した特別なクラスタ(ベースクラスタ)を介して外部ネットワークとの通信を実現するフェリー支援型DTNに着目する.フェリー支援型DTNでは,フェリーのクラスタに対する訪問順序が,平均配送遅延(各クラスタで発生したデータがフェリーによってベースクラスタに届けられるまでの平均時間)を決める.本研究では,既存の訪問順序をクラスタ間の近傍性を考慮して組み合わせたハイブリッド型訪問順序決定方式を提案する.シミュレーションにより平均配送遅延の観点から提案方式の有効性を評価する.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

近年,防災・防犯,環境や生態系の観測などの様々な場面においてモバイルセンサネットワークによるモニタリングの研究が盛んに行われている.多くのモバイルセンサはバッテリで駆動されるため,低消費電力でのモニタリングが重要となる.そこで本稿では,各モバイルセンサが担当領域内の重要な箇所を迅速に発見するための探索フェーズと,探索フェーズによって発見された重要箇所を継続的に監視するための監視フェーズの2フェーズからなるモニタリング方式を提案する.各モバイルセンサが担当する領域内の各所の重要度が独立同一な一様分布に従うという仮定の下で,フェーズの切り替え規則を求める問題を最適停止問題としてとらえ,理論的に最適なフェーズの切り替え規則を導く.さらに数値実験とシミュレーション実験により,提案手法の有効性を示す.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

大規模災害発生後,被災者は迅速に安全な避難先へと移動する必要がある.本稿では,避難者が所有するモバイル端末を用いた避難誘導方式を提案する.モバイル端末は避難経路を避難者に提示することで避難誘導を試みる.一方,モバイル端末は定期的に位置情報を計測することで,避難者の実際の避難行動を軌跡情報として把握できる.この推薦経路と軌跡情報とのずれから,通行不能箇所を自動的に推定し,避難経路を再計算する.さらに,他の避難者端末と通信可能となった際や通信インフラを介してサーバと通信可能となった際は,避難者間で通行不能箇所の情報を共有する.シミュレーション評価により,提案方式の基本的特性,被災の程度による影響,情報共有の効果を示す.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

近年,環境や生態系の観測にモバイルセンサネットワークの利用が期待されている.このとき,モバイルセンサ端末同士が自律分散的に協調動作することで,領域内の重要箇所を被覆できることが望ましい.このような分散協調制御の実現にゲーム理論を応用する動きが広まっている.これは,システムの定常状態における被覆の精度が高くなるようなゲームの設計と,任意の状態から適切な定常状態へと到達するための学習アルゴリズムの設計からなる.本研究では,モバイルセンサ端末同士が領域に対する探索履歴情報を共有することで効率的に探索を行い,適切な箇所へと迅速に移動する学習アルゴリズムを提案する.シミュレーション評価により,提案手法を用いることで各モバイルセンサ端末が領域中の限られた範囲のみを探索したとしても,高い被覆精度を実現できることを示す.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

OSのディスクイメージなど大容量のファイルを多数の端末に配信する際にPeer-to-Peer (P2P)ファイル配信システムが有効である.特に,BitTorrentではファイルをピースと呼ばれる単位に分割し,各ピアが高速にピースを取得可能なピアに対して積極的にピースを提供するというしっぺ返し戦略を導入することで,ファイル配信の効率化を図っている.一方で,このようなしっぺ返し戦略を用いたファイル配信の最適性については十分に検討されていない.そこで本研究では,しっぺ返し戦略を用いたP2Pファイル配信における最適なピース配信スケジューリングを,時点毎のピア間でのピースの授受を変数とし,平均ファイル取得完了時間を最小化する整数線形計画問題として定式化する.この問題を既存の線形ソルバで解き,得られた解を分析することで,最適なピース配信スケジュールの特徴を明らかにする.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

CiNii Books

J-GLOBAL

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

データセンタ間通信など高信頼ノードから構成されたオーバレイネットワークにおいては,下位のIPネットワークの情報を用いることで高速なオーバレイマルチキャストの実現が可能となる.本研究では,木と木の間のIPリンクの相互干渉を考慮に入れた上で複数の木を用いることで高速なマルチキャストの実現を目指す.まず想定する問題を線形容量制約付きマルチキャスト木集合問題として定式化する.さらに,この問題を解くための空間計算量を抑えたヒューリスティックアルゴリズムを提案し,数値評価を通して,ヒューリスティックアルゴリズムにより準最適解を得られることを示す.

CiNii Books

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

耐遅延ネットワーク(DTN)における孤立したネットワーク(クラスタ)間の通信はメッセージフェリーがクラスタからバンドルを集め,シンクノードに配送することで実現される.このとき,距離の離れたクラスタが多数存在する場合は複数のメッセージフェリーとシンクノードが必要となる.本稿では,距離の近いクラスタ群,シンクノードとメッセージフェリーがそれぞれ1台ずつ配置されたグループの構成手法を検討する.このとき,システム全体でのバンドルの平均配送遅延を最小化するようなグループ化を目指す.まず,我々の問題を先行研究の知見を踏まえて,配送遅延が最小となるようなグループ構成問題を非線形整数計画問題として定式化する。しかし,この問題を直接解くことは困難である.加えて,最小の配送遅延を達成するグループ構成は,負荷が軽く,かつ,シンクノードとの距離が大きいクラスタの性能を犠牲にする傾向がある.そこで,各クラスタで生じるバンドルの処理要求に対する負荷とクラスターシンクノード間の距離を考慮した上で,フェリーの移動距離とクラスタからの総負荷をグループ間でできる限り均一化することを目的とする二段階の整数計画問題を用いる.数値結果を通して,提案する二段階の最適化手法を用いれば,適切なグループ化が実現できることを示す.

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

Peer-to-Peer (P2P)ファイル共有システムに参加する各ユーザは,システム全体としての効率・性能の向上よりも各自にとっての利益を優先して行動する傾向がある.一方で,こうしたユーザの利己的な振る舞い及びそれらがシステム性能に与える影響に関しては不明瞭な部分が多く残されている.そこで本稿では,利用ユーザ数の多いBitTorrentシステムを実測し,ユーザの振る舞いとシステムの可用性を評価する.実測は,ファイル共有に参加中のピアの情報を管理するトラッカ及び個々のピアとの通信を介して実現する.実測結果から,約半数のユーザがファイル取得完了後,数時間以内にファイルの公開を停止することを示す.さらに,長期間,ファイルの提供者となるピアが少数存在する一方で,ほとんどのピアがファイル取得中に他のピアに対する一時的な供給源となることでシステムが機能していることを示す.

CiNii Books

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

CiNii Books

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