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DOI： 10.1587/essfr.10.4_282

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society for Simulation Technology  

<p>Information floating (IF) is an invisible infrastructure in which mobile nodes can receive information that seems to be floating in a designated area. IF is realized by successively transferring information from a mobile node to other nodes in an epidemic manner with wireless direct communication in designated areas. IF has many potential applications, such as advertisements for local communities, specific communication for disasters, alert systems for pedestrians and vehicles, and so on. To design alert systems on a road, some articles theoretically analyze the mean lifetime of the floating in a one-dimensional street. In past researches, however, identical traffic volume and velocity were assumed in all the lanes. The difference in traffic volume between lanes and the correlation between traffic volume and velocity were omitted for simplicity. In this paper, we recognize the importance of these two factors and reveal their effects on the mean lifetime of IF with a new theoretical method. In it, we consider not only the effects of the above two factors but also the complicated features of IF that were ignored in previous methods.</p>

DOI： 10.15748/jasse.3.97

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<p>During large-scale disasters, some regions can become isolated from critical information exchanges due to problems with communication infrastructures. In this paper, we consider information exchange among isolated shelters in such cases using epidemic transmission, which distributes information without infrastructure by direct communication between nodes and their movements. As mobile nodes for epidemic transmission, we consider transport vehicles that are leaving a distribution center to deliver relief goods to shelters. These transport vehicles receive information from the shelters and distribute it to other shelters together with the relief goods. As a result, information is shared by the shelter. Suppose that transport vehicles move along different traveling paths and exchange information at the distribution center. Transport vehicles can also get new information from other transport vehicles while they wait for new relief goods to arrive at the distribution center. Transport vehicles might be able to receive more new information by waiting for a longer time, although such additional waiting time causes a greater delay of the delivery of relief goods. In this paper, we consider the relation between relief goods delivery and information sharing by transport vehicles with epidemic transmission and analyze how the additional waiting time affects the delay of relief goods and the time needed for information sharing by computer simulation.</p>

DOI： 10.15748/jasse.3.114

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

Information floating delivers information to mobile nodes in specific areas without meaningless spreading of information by permitting mobile nodes to directly transfer information to other nodes by wireless links in designated areas called transmittable areas. In this paper, we assume that mobile nodes change direction at intersections after receiving such information as warnings and local advertisements and that an information source remains in some place away from the transmittable area and continuously broadcasts information. We analyze performance of information floating under these assumptions to explore effects of the behavior changes of mobile nodes, decision deadline of the behavior change, and existence of a fixed source on information floating. We theoretically analyze the probability that a node cannot receive information and also derive the size of each transmittable area so that this probability is close to desired values.

DOI： 10.1587/transfun.E99.A.1529

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Language：Japanese   Publisher：Japan Society for Simmulation Technology  

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/11083627

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

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

Delay Tolerant Network (DTN) has been emerged to support the network connectivity of the disruptive networks. A variety of routing methods have been proposed to reduce the latency for message delivery. PROPHET was proposed as a probabilistic routing that utilizes history of encounters and transitivity of nodes, which is computed as contact probability. While PROPHET improves the performance of DTN due to contact probability, contact probability is just one parameter reflecting the mobility pattern of nodes, and further study on utilizing contacting information of mobility pattern is still an important problem. Hence, in this paper, we try to improve routing for DIN by using a novel metric other than contact probability as mobility information. We propose the routing protocol to use mean residual contact time that describes the contact period for a given pair of nodes. The simulation results show that using the mean residual contact time can improve the performance of routing protocols for DTN. In addition, we also show in what situations the proposed method provides more efficient data delivery service. We characterize these situations using a parameter called Variation Metric.

DOI： 10.1587/transinf.E95.D.451

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

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This paper considers a network problem in charging infrastructure for electric vehicles (EVs). It generally takes a longer time to charge the empty battery of an EV than refueling of gasoline vehicles. It is not easy to actually reduce the waiting time for charging. However, if charging is done during shopping or eating, the charging time is no longer the waiting time. Of course, we may sometimes have to wait a longer time to charge batteries than shopping time to prevent running out of the batteries during the next drive. This means that we have a trade off between the extra waiting time and possibility to run out of battery. In this paper, we theoretically consider properties of this trade off and theoretically analyze characteristics of the extra waiting time needed to guarantee that an EV does not run out of battery in a drive. We discuss effects of some factors such as density of charging stations, the number of outlets in each station, the number of waiting cars, and so on. © 2011 IEEE.

DOI： 10.1109/SGMS.2011.6089020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

In ad hoc networks, the analysis of connectivity performance is crucial. The waiting time to deliver message M from source S to destination D is a measure of connectivity that reflects the effects of mobility, and some approximate methods have been proposed to theoretically analyze the mean waiting time in one-dimensional ad hoc networks that consist of mobile nodes moving along a street. In this paper, we extend these approximate methods to analyze the mean waiting time in two-dimensional networks with a lattice structure with various flows of mobile nodes. We discuss how the mean waiting times behave in such complicated street networks and how to approximate two kinds of mean waiting times. We show that our approximate methods can successfully compute the mean waiting times for even traffic patterns and roughly estimate them for uneven traffic patterns in two-dimensional lattice networks. In these analyses, we consider two shadowing models to investigate how shadowing affects the waiting time. We also discuss the effect of different positions of S on the mean waiting time.

DOI： 10.1142/S0218126610007006

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

Analysis of waiting time to deliver a message M from a source S to a destination D is deeply related to connectivity analysis, which is an important issue in fundamental studies of mobile multi-hop networks. In [1], we compared the mean waiting times of two methods to deliver M with the mean value of the minimum waiting time. The mean minimum waiting time was obtained by computer simulation because theoretical analysis of this mean is not easy, although another two methods were analyzed theoretically. In this paper, we propose an approximate method to theoretically analyze the mean minimum waiting time in a one-dimensional street network, and show that this method gives a good approximation of the mean minimum waiting time. Also, we consider shadowing and change of directions of mobile nodes at intersections as negative factors arising in two-dimensional street networks. We extend the above method to compute the mean minimum waiting time considering these factors, and discuss how the mean minimum waiting time is affected by these factors.

DOI： 10.1587/transfun.E92.A.2236

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

In multi-hop wireless networks, since source and destination nodes usually have some candidate paths between them, communication quality depends on the selection of a path from these candidates. For network design, characterizing the best path is important. To do this, in [1], [2], we used expected transmission count (ETX) as a metric of communication quality and showed that the best path for ETX is modeled by a path that consists of links whose lengths are close to each other in static one-dimensional multi-hop networks with a condition that the ETX function of a link is a convex monotonically increasing function. By using the results of this characterization, a minimum route ETX can be approximately computed in a one-dimensional random network. However, other metrics fail to satisfy the above condition, like medium time metric (MTM). In this paper, we use MTM as a metric of communication quality and show that we cannot directly apply the results of [1], [2] to the characterization of the best path for MTM and the computation of minimum route MTM. In this paper, we characterize the path that minimizes route MTM in a different manner from [1], [2] and propose a new approximate method suitable for the computation of minimum route MTM.

DOI： 10.1587/transfun.E92.A.2227

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

In multi-hop Wireless networks. communication quality depends oil the selection of it path between Source and destination nodes from several candidate paths. Exploring low path selection affects communication quality is important to characterize the best path. To do this. in [1]. We used expected transmission count (ETX) as it metric of communication quality and theoretically characterized minimum route ETX, which is the ETX of the best path, in it static one-dimensional random multi-hop network. In this paper. we characterize minimum route ETX in static two-dimensional multi-hop networks. We give the exact formula of minimum route ETX in it two-dimensional network. assuming that nodes are located with lattice structure and that the ETX function satisfies three conditions for simplifying analysis. This formula can be Used as all upper bound of minimum route ETX Without two of the three conditions. We show that this upper bound is Close to minimum route ETX by comparing it with simulation results. Before deriving the formula, We also give the formula for a one-dimensional network where nodes are located at constant intervals. We also Show that minimum route ETX in the lattice network is close to that in it two-dimensional random network if the node density is large. based on a comparison between the numerical and simulation results.

DOI： 10.1587/transcom.E92.B.745

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

In multi-hop wireless networks, communication quality depends on the route from a source to a destination. In this paper, we consider a one-dimensional multi-hop wireless network where nodes are distributed randomly and theoretically analyze the relation between communication quality and routing policy using a measure called the Expected Transmission Count (ETX), which is the predicted number of data transmissions required to send a packet over that link, including retransmissions. First, we theoretically analyze the mean length of links, the mean number of hops, and the mean route ETX, which is the sum of the ETXs of all links in a route, of Longest Path Routing (LPR), and Shortest Path Routing (SPR). Second, we propose Adjustable Routing (AR), an approximation to Optimum Routing (OR), which minimizes route ETX. We theoretically compute the above characteristic values of AR. We also theoretically compute a lower bound of the mean route ETX of OR. We compare LPR, SPR, and OR using the results of analyses and show differences between these algorithms in the route ETX.

DOI： 10.1093/ietcom/e91-b.8.2533

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

In mobile multi-hop networks, a source node S and a destination node D sometimes encounter a situation where there is no multi-hop path between them when a message M, destined for D, arrives at S. In this situation, we cannot send M from S to D immediately; however, we can deliver M to D after waiting some time with the help of two capabilities of mobility. One of the capabilities is to construct a connected multi-hop path by changing the topology of the network during the waiting time (Capability 1), and the other is to move M closer to D during the waiting time (Capability 2). In this paper, we consider three methods to deliver M from S to D by using these capabilities in different ways. Method 1 uses Capability I and sends M from S to D after waiting until a connected multi-hop path appears between S and D. Method 2 uses Capability 2 and delivers M to D by allowing a mobile node to carry M from S to D. Method 3 is a combination of Methods 1 and 2 and minimizes the waiting time. We evaluate and compare these three methods in terms of the mean waiting time, from the time when M arrives at S to the time when D starts receiving M, as a new approach to connectivity evaluation. We consider a one-dimensional mobile multi-hop network consisting of mobile nodes flowing in opposite directions along a street. First, we derive some approximate equations and propose an estimation method to compute the mean waiting time of Method 1. Second, we theoretically analyze the mean waiting time of Method 2, and compute a lower bound of that of Method 3. By comparing the three methods under the same assumptions using results of the analyses and some simulation results, we show relations between the mean waiting times of these methods and show how Capabilities 1 and 2 differently affect the mean waiting time.

DOI： 10.1093/ietcom/e91-b.6.1874

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

We investigated performance improvement in a cellular system by introducing direct communication between terminals. Previous research has indicated that direct communication efficiently uses channels; however, this is not always so. We studied two factors that affect how much efficiency improves. One is the distribution of terminals. We defined some typical distributions with localization of terminals and analyzed how the difference between the distributions affected the performance improvement by direct communication. Another factor is the mobility of terminals, because mobility shortens the length of time during which terminals are directly connected. We analyzed how mobility affected performance improvement by direct communication. For the analyses, we used some theoretical techniques.

DOI： 10.1093/ietfec/e89-a.7.1940

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

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Other Link： http://hdl.handle.net/10191/18486

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

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Other Link： http://hdl.handle.net/10191/18487

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

Wireless network systems introducing both of the cellular concept and the ad-hoc concept have been proposed. Communication between two nodes in a cell is guaranteed by relaying capability of the base station in these systems. Additionally, two nodes can directly communicate with each other while they are close to each other. We call this type of network a two-hop wireless network. The teletraffic performance of this network depends on various parameters such as the size of a cell, location of nodes, the communication range of nodes; channel assignment schemes, teletraffic behavior and so on. The purpose of this paper is to theoretically analyze the teletraffic performance of the network, which has been evaluated by computer simulation; by introducing a simple model. This paper shows a technique to analyze the performance in this model. Also, this paper considers the range in which the two-hop wireless network works well for the efficient use of channels.

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

This paper discusses the teletraffic characteristics of cellular systems using Dynamic Channel Assignment. In general. it is difficult to exactly and theoretically analyze the teletraffic characteristics of Dynamic Channel Assignment. Also, it is not easy to theoretically evaluate influence of mobility on the traffic characteristics. This paper proposes approximate techniques to analyze teletraffic characteristics of Dynamic Channel Assignment considering mobility. The proposed techniques are based on Clique Packing approximation.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BALTZER SCI PUBL BV  

This paper discusses stochastic characteristics of hierarchical multi-hop wireless networks. It is assumed that terminals and base stations are distributed according to specific distributions, respectively. It is also assumed that a multi-hop wireless network is logically divided into clusters by a clustering algorithm. In this paper, the Lowest ID Cluster algorithm and another simple clustering algorithm are considered. Using theoretical techniques based on the stochastic geometry, this paper analyzes fundamental characteristics of the multi-hop wireless networks with the clustering algorithms.

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This paper describes communication traffic characteristics in cellular systems employing the concept of reuse partitioning and Dynamic Channel Assignment. Such systems have a problem of the spatial unbalance of blocking probability. The objective of this paper is overcoming this problem. To accomplish this objective, we use a method for analyzing communication traffic characteristics. We also show results on traffic characteristics in the systems.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society for Simulation Technology  

If mobile nodes such as vehicles and pedestrians deliver information by direct wireless communication between mobile nodes and movement of mobile nodes carrying information, disordered and unnecessary spread of information arises. To overcome this problem, a method to permit mobile nodes to transmit information only in transmittable areas has been considered. This method is called Information Floating. Theoretical analysis of Information Floating is important because it is necessary for some purposes such as control of the size of a transmittable area, and has been studied in various situations. In this paper, we consider Information Floating by pedestrians walking toward opposite directions along a street, and theoretically analyze performance of Information Floating under the assumption that the communication range changes due to the positional relationship between mobile nodes because the mobile nodes themselves become obstacles. From the numerical results, we show that degree of effects of the assumption that mobile nodes themselves become obstacles on performance of Information Floating depends on the densities of mobile nodes and the difference between the densities of mobile nodes moving toward the opposite directions, and show effectiveness of the proposed theoretical method. Based on these results, we show a method to decide the size of a transmittable area suitable to the situation where mobile nodes themselves become obstacles.

DOI： 10.11308/tjsst.14.9

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：日本シミュレーション学会  

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&nbsp;&nbsp;Epidemic routing can deliver messages in the case where there is never a connected path from source to destination. By using Epidemic routing repeatedly, the technique called Information Floating can maintain information in specific area. Information Floating is more effective when there are many mobile nodes. We consider effect of public space on information floating. A public space is a social space and mobile nodes are easy to gather in the space. If we can identify a place that is not a public space but where information tends to stay, it will maintain more information. We introduce to use a covering problem to identify this place. A covering problem is one of location problems that find the best place on road networks, communication networks, etc. In this paper, we identify where to put the fixed stations with information by applying a covering problem, and we show its effectiveness in computer simulation.<br>

DOI： 10.11308/tjsst.9.73

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society for Simulation Technology  

&nbsp;&nbsp;An ad-hoc cellular system, which is a combination of a cellular system and direct communication, has been proposed to utilize limited frequency resources. In this system, a mobile terminal is directly connected to another terminal if these terminals are close to each other. Otherwise, the terminals communicate with each other via a base station of the cellular system. Performance analysis of the ad-hoc cellular system has been done in various situations. In this paper, we consider a mobility model where terminals go back and forth between a central point and their home points in the cell. This model assumes mobility of people between a shelter and their homes in a disaster situation. In this paper, we analyze teletraffic characteristics of an ad-hoc cellular system considering this mobility model. We analyze teletraffic characteristics of this system consisting of one cell assuming that terminals tend to gather a certain point with high probability by theoretical methods and computer simulation. Throughout analysis, we showed that direct communication works efficiently in this model, where terminals tend to gather a certain point. Furthermore, we showed how teletraffic characteristics are affected by the positon of the certain point and distribution of terminals.<br>

DOI： 10.11308/tjsst.8.109

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DOI： 10.14923/transcomj.2016IAP0009

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DOI： 10.1587/essfr.9.4_370

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Epidemic transmission can distribute information over the service area by direct wireless communication between mobile nodes and mobility of the mobile nodes. By using epidemic transmission repeatedly, we can send information to mobile nodes entering a specific area. This is called Information Floating (IF). In this paper, we consider IF to distribute an advertisement to guide customers to a target place (shopping place). The purpose of advertisement delivery is to deliver an advertisement to mobile nodes before they arrive at the target place and to guide mobile nodes to the target place. We divide a service area into some small areas, and consider how to decide the areas where the advertisement is virtually floated. To do this, we use probe data such as traffic volume entering each small area. We consider three methods to decide the areas for IF, and evaluate these methods by computer simulation. Two of the three methods use probe data. In computer simulation, we consider uniform and non-uniform traffic distributions, and small and large traffic volumes to assume various situations. We show effective methods in the various situations.<br>

DOI： 10.11308/tjsst.7.85

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

Recently, Electric Vehicle (EV) is considered as one of important technologies of smart grid; however, there are some problems for spreading EVs. One of these problems is that charging the battery of an EV needs a longer time than refueling of gasoline vehicles. To overcome these problems, for example, some local governments in Japan started projects in which restaurants and shops rent outlets for charging EV of their customers while doing something such as eating or shopping. Under such projects, if an EV driver knows information on chargers such as the locations of chargers and the mean waiting times for using chargers, the driver may be able to reduce the time spent only for charging (pure waiting time). In this paper, we theoretically analyze the mean of the pure waiting time in cases where drivers know and do not know the above information. From the numerical results, we discuss what information is important to reduce the pure waiting time.

DOI： 10.1109/ISADS.2015.50

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DOI： 10.1587/essfr.6.73

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Other Link： http://hdl.handle.net/10623/33634

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE/IEEK  

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Delay Tolerant Networks have been emerged to support intermittent connectivity of frequently partitioned networks. A routing issue of Delay Tolerant Networks is concerned about the extremely long delay of opportunistic intermittent connections. For considering routing protocols of Delay Tolerant Networks, a forwarding decision and the buffer management scheme are important to improve the successful message delivery opportunity. In this paper, we propose the composite methods to improve Spray and Wait routing protocol. The proposed method consists of the use of an ACK message and message forwarding based on the delivery probability. The proposed composite methods can resolve the disadvantages of Spray and Wait routing protocol. In according to the simulation, the proposed method shows better delivery rate and lower communication overhead compared to other routing protocols. ©2010 IEEE.

DOI： 10.1109/ISCIT.2010.5665178

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In multi-hop wireless networks, if we know the packet reception rates of all links in the network, we can find the path with the minimum energy consumption. However, to obtain the packet reception rates with high accuracy, we need a number of exchanges of probe packets. Also, the energy consumption along a path depends on a routing method. In this paper, we consider three routing methods and evaluate the relation between the number of broadcasts of probe packets and the total energy consumption along the paths selected by these methods. © 2010 IEEE.

DOI： 10.1109/ICTC.2010.5674826

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Estimation of link travel times from measured values is a critical service of floating car information systems (probe car information systems), and the results of estimation are utilized to improve quality of vehicle navigation. Because actual link travel times are affected by various factors, such as time period, traffic volume, and weather, these factors should be considered to estimate the link travel time. Also, they should be considered to estimate the minimum amount of data needed to estimate link travel time while maintaining accuracy to optimize the floating car systems. In the systems currently being implemented, however, effects of the weather are not utilized to estimate the link travel time, and the minimum amount of necessary data has not been studied in detail. This paper reveals the effect of weather differences on estimated link travel time using data actually obtained by floating car systems. In particular, this paper pays attention to effects of snowfall. This paper also evaluates the amount of data required to obtain estimated link travel times considering effects of various factors. © Springer Science+Business Media, LLC 2010.

DOI： 10.1007/s13177-010-0015-8

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In multi-hop wireless networks, we often encounter a situation where there are some candidate paths between source node S and destination node D, and have to choose a path from the candidates. Although ordinary routing protocols select paths with minimum hops, QoS (Quality of Service) routing protocols evaluate paths using measures of QoS, such as expected transmission count (ETX). In multi-hop wireless networks with QoS routing, it is an important issue to identify and characterize the best path from the viewpoint of network design. To do this, in [1], we proposed an approximate method to theoretically compute minimum route ETX in static one-dimensional random multihop wireless networks, and in [2], we theoretically identified the best path and gave an exact formula to compute minimum route ETX in static lattice multi-hop wireless networks. In this paper, we propose a new approximate method to theoretically analyze minimum route ETX in a two-dimensional random network. In this method, we extend the approximate method proposed in [1] to be used for two-dimensional random networks. We show this approximate method well describes minimum route ETX by comparing the numerical results of the theoretical methods and simulation results. ©2009 IEEE.

DOI： 10.1109/ISCIT.2009.5341111

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We propose a novel interference canceller with an automatic phase control (APC) circuit that compensates for the phase error of interference signals. The proposed APC circuit estimates and compensates for the phase rotation of interference signals, enabling the proposed interference canceller with APC to achieve high BER performance. We use a maximum likelihood sequence estimation (MLSE) interference canceller for fixed wireless access (FWA) co-channel interferences. Degradations of signal replica accuracy incur a BER performance penalty. The novel APC circuit, which uses a simple estimation algorithm, can effectively compensate for frequency offset and phase rotation. Computer simulations show that our proposed interference canceller improves BER performance. ©2008 IEEE.

DOI： 10.1109/ICCSC.2008.141

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In this paper, we analyze reliability of a street mobile multi-hop network which connects two fixed nodes considering effects of change of topology with time. As a measure of reliability, we use the mean waiting time from the moment when a source node fails to transmit data to a destination due to absence of the multi-hop path to the moment when a multi-hop path appears between them. We theoretically compute the mean waiting time in a case where the fixed nodes can be connected by a two hop path and in another case where they need at least a three hop path to be connected, and show that there is a big difference in the mean waiting time between these two cases.

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In an ad-hoc network, some nodes relay more communications than others. Since relaying is resource consuming, unfairness in terms of the number of communications relayed by different nodes is not desirable. This paper discusses a simple Charging/Rewarding scheme as a method to reduce the unfairness in the network. We explain the reason why such scheme works well in a mobile network but does not work well in a static network and discuss some methods to improve performance in the static network.

DOI： 10.1109/ISCAS.2005.1465249

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

In an ad-hoc network, some nodes relay more communications than others. Since relaying is resource consuming, unfairness in terms of the number of communications relayed by different nodes is not desirable. This paper discusses a simple Charging/Rewarding scheme as a method to reduce the unfairness in the network. We explain the reason why such scheme works well in a mobile network but does not work well in a static network and discuss some methods to improve performance in the static network. © 2005 IEEE.

DOI： 10.1109/ISCAS.2005.1465249

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

In a cellular system with multi-hop networking, a mobile node is connected to a base station by relaying capability of other mobile nodes even though this node has no direct link to the base station. In order to guarantee reliability in cell design, we need to estimate the degree of cell extension considering some factors such as mobility characteristics and relaying capacity of relay nodes. This paper investigates how to estimate the degree of cell extension considering both mobility and capacity.

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

A multi-hop wireless network connects a pair of terminals by a path consisting of other terminals and wireless links; however, if terminals are randomly distributed, every pair of terminals is not always connected. Then, introducing special facilities called relay facilities to a multi-hop network has been proposed to improve connectivity. The relay facilities are used only for relaying terminals. This paper assumes that we have n relay facilities, and each of the relay facilities must be allocated at one of designated points given in advance. Under this assumption, this paper considers how to select n from the given designated points to improve connectivity between terminals.

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

In this paper, teletraffic characteristics of a cellular system using direct communication considering mobility are analyzed. In these systems, communication between two terminals in a cell is guaranteed by relaying capability of the base station. Additionally, two terminals can directly communicate with each other. The purpose of this paper is to theoretically analyze teletraffic performance of these systems considering effect of mobility. We evaluate the mean holding time in the cell for various velocities of nodes. To confirm the validity of the analysis, the results of simulation are also shown. This paper shows relation between the teletraffic performance and the mean holding time for various velocities of nodes.

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

In a cellular system with multi-hop networking, when a mobile node enters an area where mobile nodes cannot hear the base station, this node is connected to the base station by relaying capability of other mobile nodes. As a result, a cell is extended by multi-hop networking. This paper theoretically analyzes the extent of such cell extension, and discusses relation between cell extension and some mobility patterns.

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

This paper presents novel flooding schemes for wireless mobile ad hoc networks. Clustering of nodes is assumed as a basic ad hoc network structure. GWF (Gateway Forwarding) and SGF (Selected Gateway Forwarding) are presented based on clustering. A new protocol, termed FGS (Flooding Gateway Selection) protocol, between a cluster head and its gateways to realize SGF is presented. It is shown that SGF significantly improves the packet delivery performance in ad hoc networks by reducing flooding traffic.

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

This paper considers a new cellular mobile communication system, where a terminal can directly communicate with another terminal. Though there is a theoretical technique to analyze teletraffic characteristics of the system, this technique assumes that nodes never move. So, to analyze the teletraffic characteristics of this system considering mobility, computer simulation is usually used. This paper proposes a technique to theoretically analyze the call arrival rate, the mean holding time and the offered traffic in the new cellular system considering mobility. This paper assumes that the system consists of a single cell, terminals move along a single route and some channels are reserved for terminal-to-terminal communications.

DOI： 10.1109/KMN.2002.1115165

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：INTERNATIONAL ACADEMIC PUBLISHERS LTD  

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

This paper considers the call dropping probability in cellular systems with multi-hop wireless networking, and evaluates relation between the call dropping probability and mobility patterns of nodes. Also, this paper considers difference between a cellular network with multi-hop networking and a multi-hop network without base stations. To compare these networks, the call dropping probability and the mean life time of a path are considered.

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

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Other Link： http://hdl.handle.net/10191/8286

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

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Language：Japanese   Publisher：The Japan Society for Simulation Technology  

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Other Link： http://hdl.handle.net/10191/22472

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

The concept of an open community network is presented as a vision for general-purpose ad hoc networks. An open community network is a novel information infrastructure for local communities based on wireless multihopping technologies. A method for calculating number of PHS (Personal Handy Phone System) devices per CP to meet traffic demands is presented and numerical examples are given. An experimental system for an open community network using PHS is described and some research issues for developing an open community network are identified. © 2001 IEEE.

DOI： 10.1109/ISCAS.2001.922383

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

In a multihop network, radio packets are often relayed through inter-mediate nodes (repeaters) in order to transfer a message. We consider a scheduling problem in a multihop network using two graph theoretical models. In this report, we prove that this problem is NP-hard, and we propose approximation algorithms for it. © 2001 IEEE.

DOI： 10.1109/ISCAS.2001.922382

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

When a mobile station with a call in progress moves across cell boundary in a cellular mobile communications system, the system must switch the circuit to the base station in the destination cell to enable uninterrupted communications in a process sailed "handoff." However, if a circuit to the destination base station cannot he secured when a handoff is attempted. the call is forcibly terminated. Studies have therefore been performed on methods of decreasing the percentage of forcibly terminated calls by giving handoff calls priority. With the aim of simplifying system design, we propose a system for automatically setting the number of circuits reserved for handoff based on the handoff block rate. In this paper, we describe this system and Evaluate static traffic characteristics taking into account reattempt calls, the occurrence of which can have a major effect on system performance. We also consider the effects of the proposed system on service quality since giving priority to handoff calls and decreasing the rate of forced terminations results in a tradeoff with the blocking rate of new call attempts. Finally, we evaluate the traffic characteristics associated with the number of control requests, an important element in estimating the processing capacity required by control equipment at the time of system design.

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

To implement soft handoff in cellular communication systems that employ code division multiple access (CDMA), it is necessary to establish communication lines between the switch and multiple base stations and distribute the communication data via these multi-connections to the base stations simultaneously. This means that, when soft handoff is performed with the same amount of communication line resources as hard handoff, the blocking probability is higher than for hard handoff, and service quality is thus worse. Furthermore, handoffs occur more frequently as the size of cells becomes smaller, and tills increases the probability of forced terminations. Switches must be endowed with greater processing capacity to accommodate the more frequent handoffs. The use of the queuing handoff method can be expected, in general, to mitigate forced termination probability compared with the immediate handoff method. In this regard, we propose a prioritized queuing handoff method that gives priority to fast-moving mobile stations (MSs) as a way to mitigate forced terminations even more than the non-priority queuing method without appreciably increasing the processing load. We then compare the traffic characteristics of our proposed method with these of three other methods in micro cell systems-immediate method, non-priority queuing method, and conventional hard handoff method without multi-connections-by computer simulation. Here, considering that the proposed method gives priority to fast-moving calls, traffic characteristics for these methods were evaluated separately for slow- and fast-moving MSs. The results reveal that proposed method can reduce the forced termination probability and total call failure probability more than non-priority queuing method without having an appreciable impact on slow-moving calls.

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

In a multihop network, radio packets are of ten relayed through inter-mediate stations (repenters) in order to transfer a radio packet from a source to its destination. We consider a scheduling problem in a multihop network using a graphtheoretical model. Let D = (V, A) be the digraph with a vertex set V and an are set A. Let f be a labeling of positive integers on the arcs of A. The value of f(u, v) means a frequency band assigned on the link from u to v. We call f antitransitive if S(u, v) not equal f(v, w) for any adjacent arcs (u, v) and (v, w) of D. The minimum antitransitive-labeling problem is the problem of finding a minimum antitransitive-labeling such that the number of integers assigned in an antitransitive labeling is minimum. In this paper, we prove that this problem is NP-hard, and we propose a simple distributed approximation algorithm for it.

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

This paper considers multi-hop radio communication systems where terminals and base stations coexist. In these systems, a terminal is connected to a base station via a multi-hop connection if this terminal cannot directly communicate with this base station. This paper evaluates the ability of one-dimensional multi-hop radio communication systems to cover the service area by multi-hop connections. To evaluate this ability, this paper analyzes the probability that every terminal in a region between adjacent two base stations can communicate with at least a base station and the ratio of the mean number of terminals which are in the region and can communicate with at least a base station to the mean number of terminals in the region.

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

This paper considers multi-hop wireless networks consisting of wireless terminals and fixed wireless stations. It is assumed that terminals are randomly distributed and fixed stations are regularly distributed. A terminal can directly communicate with another terminal, and a terminal can relay information from a terminal to another terminal. Fixed wireless stations can communicate with terminals, collect information from terminals, distribute information to terminals and play the role of relay stations. This paper analyzes covering performance of some of the multi-hop radio networks which are different in network structure.

DOI： 10.1109/IECON.2000.972286

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

This paper considers PHS based wireless ad hoc networks. In the ad hoc networks, a terminal uses a communication channel based on PHS, and communicates with another terminal by using the direct communication mode of PHS. It is assumed that if a terminal fails to send the information, the terminal retries to send the information after an appropriate time interval. This paper considers some schemes for link scheduling and setting the time interval in retrial. To evaluate the schemes, we actually develop the ad hoc networks. From the evaluation, this paper discusses characteristics of the schemes.

DOI： 10.1109/IECON.2000.972283

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：PUBLISHING HOUSE ELECTRONICS INDUSTRY  

This paper considers a multi-cluster wireless multi-hop network where terminals and base stations coexist. This paper considers three kinds of clustering schemes, which generate clusters. This paper assumes that a cluster consists of a base station and terminals. This paper evaluates the probability that the clusters include every terminal and members in each cluster are connected.

DOI： 10.1109/ICCT.2000.890904

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

This paper presents a vision of the universal as hoc network and shows novel flooding schemes for wireless mobile ad hoc networks. Clustering of nodes is used to enhance flooding performance. GWF (Gateway Forwarding) and SGF (Selected Gateway Forwarding) are presented based on clustering. A new protocol, termed FGS (Flooding Gateway Selection) protocol, between a cluster head and its gateways to realize SGF is presented. It is shown that SGF significantly improves the packet delivery performance in ad hoc networks by reducing flooding traffic.

DOI： 10.1109/IECON.2000.972281

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

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

Multimedia mobile communication systems with high-speed radio transmission supported by asynchronous transfer mode (ATM) technologies have been intensively studied over the last few years. Smaller radio zones termed microcells and picocells will be used in this kind of mobile communication systems for the purpose of high-speed radio transmission. When the coverage of a radio zone is smaller, the amount of traffic per radio zone is relatively low. It is not possible to use the cable circuits connecting the switch and base stations in an efficient manner because of the lack of the scale effect of traffic. With smaller radio zones, moreover, handoff occurs frequently as a mobile station moves. The switch is required a large capacity to handle the processing of frequent handoffs. This paper proposes a mobile network architecture controlled by the concentrated grouping of base stations. A special feature of this configuration is the ability of the network's switches to efficiently accommodate numerous base stations that control small radio zones. It can also lighten the handoff control load of switches; the effect of handoff frequency reduction is evaluated with computer simulation.

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

The demand for communication services is rapidly increasing, because the mobile communication service is synonymy of an ideal communication style realizing communication in anytime, anywhere and with anl one. There exist various problems to which computational geometry and graph & network theory is applicable in mobile communication services. For example, it is well known that coloring algorithms of graphs are applicable in channel assignment algorithms in cellular systems. In this paper, we show new results in graph theoretic or computational geometric research of cellular mobile communications.

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

This paper describes an approximate theoretical method to analyze communication traffic characteristics of a cellular mobile communication system on the two-dimensional plane assuming that calls are generated by subscribers on vehicles moving along a road network. Our problems are to analyze the teletraffic characteristics of the cellular system by using the parameters indicating the vehicles&apos; how characteristics on the road network.

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

This paper describes the design of a cellular mobile communication system on the two-dimensional plane using spatial data. This paper considers spatial data indicating vehicles' flow characteristics on the road network. This paper discusses how to determine the number of channels in each cell considering the spatial data.

DOI： 10.1109/TENCON.1999.818641

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

To implement soft-handoff in mobile communication systems that employ code division multiple access (CDMA), it is necessary to distribute the communication data to the multiple base stations simultaneously. For that reason, when soft handoff is performed with the same amount of communication line resources as hard handoff, the call blocking probability is higher than for hard handoff. We therefore evaluate the traffic characteristics for the various multi-connection line set-up methods, which include immediate call processing, a simple queuing processing, and a modified queuing processing to give a priority to fast-moving calls, by means of a computer simulation. The evaluation results show that the probability of forced termination at handoff can be reduced by employing a queuing scheme at the time of multi-connection line setup and that the probability of call termination can be further reduced by giving fast-moving calls priority in the allocation of multi-connection lines. © 1999 IEEE.

DOI： 10.1109/VETECF.1999.798635

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

Dynamic Channel Assignment (DCA), which improves the efficiency of channel use in cellular mobile communication systems, requires finding an available channel for a new call after the call origination. This causes the delay which is defined as the time elapsing between call origination and completion of the channel search. For system planning, it is important to evaluate the delay characteristic of DCA because the delay corresponds to the waiting time of a call and influences service quality. It is, however, difficult to theoretically analyze the delay characteristics except its worst case behavior. The time delay of DCA has not been theoretically analyzed. The objective of this paper is analyzing the distribution and the mean value of the delay theoretically. The theoretical techniques in this paper are based on the techniques for analyzing the blocking rate performance of DCA.

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

In this paper we extend the p-collection problem to a flow network with lower bounds, and call the extended problem the lower-bounded p-collection problem. First we discuss the complexity of this problem to show NP-hardness for a network with path structure. Next we present a linear time algorithm for the lower-bounded 1-collection problem in a network with tree structure, and a pseudo-polynomial time algorithm with dynamic programming type for the lower-bounded p-collection problem in a network with tree structure. Using the pseudo-polynomial time algorithm, we show an exponential algorithm, which is efficient in a connected network with few cycles, for the lower-bounded p-collection problem.

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

This paper describes communication traffic characteristics in cellular systems where Dynamic Channel Assignment is used and the traffic intensity in each cell is not equal. Clique Packing is used as a model of Dynamic Channel Assignment, and communication traffic characteristics of Clique Packing under the unequal load are discussed. Communication traffic characteristics of practical Dynamic Channel Assignment methods, such as First-Available method, are also discussed by using the Clique Packing model. The results of this paper contribute to estimation of the blocking performance of Dynamic Channel Assignment under the unequal traffic load.

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

This paper discusses teletraffic modelling in CDMA cellular systems. We consider some different conditions for call acceptance, and discuss methods for evaluating the teletraffic behavior in the CDMA system where each of the conditions is used. We characterize communication traffic in the CDMA cellular system which employs each of the conditions by using some packing algorithms for modelling Dynamic Channel Assignment in FDMA/TDMA systems. It is shown that the methods for analyzing the FDMA/TDMA cellular systems are also applicable to the CDMA cellular systems.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SCRIPTA TECHNICA PUBL  

This paper discusses the communication traffic characteristics of Dynamic Channel Assignment (DCA) in cellular mobile communication systems. In general, it is difficult theoretically to analyze the communication traffic characteristics of DCA. This paper proposes an approximate method called clique packing, for analyzing the blocking probability performance of an idealized DCA. For calculating the blocking probability of clique packing, an approximate formula is derived which is based on the Erlang B formula and is in a simple form. it is shown that the numerical results of the approximate method agree with computer simulation results.
An approximate analytical method for calculation of the blocking rate of practical DCA methods such as the first-available method also is proposed. To calculate the blocking rate of the practical DCA methods, the simple formula for clique packing is used after modeling the practical DCA methods as clique packing. It is shown that the modeling is appropriate. This modeling enables the blocking rate of the practical DCA methods to be calculated by using the approximate formula for clique packing.

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

Dynamic Channel Assignment (DCA), which improves the efficiency of channel use in cellular mobile communication systems, requires finding an available channel for a new call after the call origination. This causes the delay which is defined as the time elapsing between call origination and completion of the channel search. For system planning, it is important to evaluate the delay characteristic of DCA because the delay corresponds to the waiting time of a call and influences service quality. It is, however, difficult to theoretically analyze the delay characteristics except its worst case behavior. The objective of this paper is analyzing the distribution and the mean value of the delay theoretically. This analysis is based on the Clique Packing model for analyzing the blocking rate performance of DCA.

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

In cellular mobile systems, an alternative approach for a Dynamic Channel Assignment problem is presented. It adaptively assigns the channels considering the cochannel interference level. The Dynamic Channel Assignment problem is modeled on the different cellular system from the conventional one. In this paper, we formulate the rearrangement problem in the Dynamic Channel Assignment and propose a novel strategy for the problem. The proposed algorithm is based on an artificial neural network as a specific dynamical system, and is successfully applied to the cellular system models. The computer simulation results show that the algorithm utilized for the rearrangement is an effective strategy to improve the traffic characteristics.

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

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

In mobile communication systems using Dynamic Channel Assignment, channels are possible to be rearranged so that blocking probability can be made low. The smaller the number of cells where channels are rearranged, the smaller the load on the base stations in the cells. Also, we can reduce the deterioration of communication quality caused by reassingning a new channel to a call instead of the channel already assigned. In this paper, we consider not only how to rearrange channels but also which channel should be rearranged and assigned to a new call in rearrangement, and propose very simple but effective methods for rearrangement. The ways to select a candidate channel to be rearranged and assigned to a new call in the new methods make the number of cells where a channel is rearranged smaller. We also examine the relations between characteristics and the number of cells where a channel is rearranged. Using computer simulation results, the properties of the new rearrangement methods are compared with those of the traditional methods.

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

In general, dynamic channel assignment has a better performance than fixed channel assignment in a cellular mobile communication system. However, it is complex to control the system and a lot of equipments are required in each cell when dynamic channel assignment is applied to a large service area. Therefore, it is effective to limit the size of the service area in order to correct the defects of dynamic channel assignment. So, we propose an application of dynamic channel assignment to a part of a service area when fixed channel assignment is applied to the remaining part of the area. In the system, the efficiency of channel usage in some cells sometimes becomes terribly low. The system has such a problem to be improved. We show that the rearrangement of the channel allocation is effective on the problem.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE PUBL B V  

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Event date： 2013.9

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Event date： 2013.5

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When a large-scale disaster occurs such as an earthquake or tsunami, a disaster monitoring system which transmits camera images captured in the disaster area to a disaster management office using a capacity-limited network like an ad-hoc network can be useful. Since the transmitting rate of video data is comparatively large, wireless channel congestion may easily occur as the monitoring becomes large-scale. In this paper, we propose a video rate control scheme which is realized by appropriately set the video compression ratio of the source node when packet loss due to the congestion occurs and evaluate our scheme through a simple experimental network. We confirm significant adjustment in received video data ratio and improvement in video quality at the receiver node through our experiments.

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Event date： 2013.5

Language：Japanese  

This paper deals with a wireless periodical sensor data collection system, which accommodates a number of sensor nodes directly to the base station. The system uses media access using the reserved slots with CSMA/CA. When the number of sensor nodes increases, congestion occurs because the number of free slots decreases, we propose to apply source rate control to avoid congestion. In this report, parameters such as the control interval detecting congestion and the amount of change in the data acquisition interval are studied by simulation. It is found that throughput and fairness of received throughput increase by appropriately adjusting these parameters.

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Other Link： http://id.nii.ac.jp/1001/00092069/

Event date： 2013.3

Language：Japanese  

Delay Tolerant Networks (DTNs)are networks that enable us to exchange information by tolerating a long delay time. DTNs can be applied to various purposes such as disaster communication, regional information dissemination and so on. In this report, we consider to apply DTNs to regional spreading and automatic collection of electronic free papers. As a related work, a model of barter exchange generating the currency, which is called Yasutomi's model, is proposed. In this report, we try to apply this model to the above spreading and collection of electronic free papers. We propose an information-exchange method that utilizes the view vector, which is introduced in Yasutomi's model, and show that the view vector accelerate the spreading of new electronic paper and the collection of 01d electronic paper. In addition, we propose another method to make the above method more effective and evaluate this method.

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Event date： 2013.3

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Delay Tolerant Networks (DTNs) are networks that enable us to exchange information by tolerating a long delay time. In this report, we consider DTNs realized by epidemic transmissions, in which information is spread by wireless transmission between nodes and mobility of the nodes. While a DTN is generally used for communica- tion between a pair of specific nodes, it is sometimes used to transmit information to unspecified nodes in a specific area. For example, such situations can be seen in information delivery in a local area and that in disaster situations. In such cases, the destination of information is not a specific node but a specific space; therefore, information has to be stayed in the destination space so that people entering the space later get the information as well as people being there. In this report, we consider to make information stay in a specified space during a specific time period suppressing useless information spreading. To do this, we consider to restrict wireless transmissions between nodes in a designated time and space in epidemic transmission. We evaluate this method to show basic properties of the relation between limit on information exchanges and stay of information.

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Event date： 2013.3

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Abstract Delay Tolerant Networks (DTNs)are networks that enable us to exchange information by tolerating a long delay time. DTNs can be applied to various purposes such as disaster communication, regional information dissemination and so on. In wireless DTNs, we have to diffuse copies of information among mobile nodes to deliver information to destination. Information tends to reach destination more easily if more copies are spread over the network. At the same time, however, many unnecessary exchanges of copies of information cause waste of battery of mobile nodes and unnecessary traffic among the network. Hence, it is necessary to control diffusion of copies of information by reducing exchanges of copies between mobile nodes. In this report, we virtually define small regions in the service area, and assume that a database stores location information of mobile nodes and a log of communi- cation of each node. The database system gives statistical information on exchange of flows of copies in each small region and that between a pair of small regions. Based on the information, we restrict information exchange in small regions that are not so necessary to diffuse information. We show the effectiveness of the proposed method by computer simulation in lattice road networks.

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Event date： 2012.11

Language：Japanese  

Recently, Electric Vehicle (EV) is considered as an important technology; however, there are some problems for spreading EVs. One of these problems is that charging the battery of an EV needs a longer time than refueling of gasoline vehicles. Deployment of charging stations is also a problem. To overcome these problems, for example, some local governments in Japan started projects in which restaurants and shops rent outlets for charging EV of their customers during eating or shopping. Under such projects, if an EV driver utilizes information on locations of chargers, the driver may be able to reduce the time spent only for charging. In this report, we theoretically analyze the time spent only for charging in a case where drivers utilize the above information. Through the analysis, we discuss how the above information reduces the time spent only for charging. We also consider how chargers should be deployed to commercial facilities considering the difference of popularity of the facilities.

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Event date： 2012.9

Language：Japanese  

Recently, Electric Vehicle (EV) is considered as an important technology;however, there are some problems for spreading EVs. One of these problems is that charging the battery of an EV needs a longer time than refueling of gasoline vehicles. To overcome these problems, for example, some local governments in Japan started projects in which restaurants and shops rent outlets for charging EV of their customers during eating or shopping. On the other hand, other local government in Japan has developed a system to efficiently reserve chargers by sharing information on usage of chargers. In this paper, we consider the above service to rent outlets during eating or shopping, and discuss how methods to reserve chargers affect the waiting time for charging EVs.

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Event date： 2012.8

Language：Japanese  

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Event date： 2012.8

Language：Japanese  

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Event date： 2012.8

Language：Japanese  

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Event date： 2012.6

Language：Japanese  

Recently, Electric Vehicle (EV) is considered as an important technology; however, there are some problems for spreading EVs. One of these problems is that charging the battery of an EV needs a longer time than refueling of gasoline vehicles. Deployment of charging stations is also a problem. To overcome these problems, for example, some local governments in Japan started projects in which restaurants and shops rent outlets for charging EV of their customers during eating or shopping. Under such projects, if an EV driver knows information on chargers such as the locations of chargers and the mean waiting time for using chargers, the driver may be able to reduce the time spent only for charging. In this report, we theoretically analyze the mean of the time spent only for charging in cases where drivers know and do not know the above information. From the numerical results, we discuss what information is important to reduce the time spent only for charging.

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Event date： 2012.1

Language：Japanese  

If a large-scale disaster occurs, communication infrastructures may be unavailable, and some regions or villages may become informationally isolated. In this case, it is important to ensure a way to exchange information between these isolated regions. To do this, it is known that an epidemic transmission with delay tolerant routing, in which mobile nodes deliver information by itself, is effective. By using an epidemic transmission, we can confirm the safety of the family in other regions with some delay time. In this report, we consider a situation where some shelters are informationally isolated, and consider to introduce an information shuttle, which exchanges information on evacuees by using an epidemic transmission. We discuss how information shuttles reduce the time until an evacuee confirms the safety of the family and the time until an evacuee meets the family. We also discuss effects of the behaver of an evacuee and the scheduling of information shuttles.

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Presentation type：Public lecture, seminar, tutorial, course, or other speech  

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Language：Japanese  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学 災害科学国際研究所  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学 災害科学国際研究所  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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