Throughout the world, people can post information about their local area in their own languages using social networking services. Multilingual short text clustering is an important task to organize such information, and it can be applied to various applications, such as event detection and summarization. However, measuring the relatedness between short texts written in various languages is a challenging problem. In addition to handling multiple languages, the semantic gaps among all languages must be considered. In this article, we propose two Wikipedia-based semantic relatedness measurement methods for multilingual short text clustering. The proposed methods solve the semantic gap problem by incorporating the inter-language links of Wikipedia into Extended Naive Bayes (ENB), a probabilistic method that can be applied to measure semantic relatedness among monolingual short texts. The proposed methods represent a multilingual short text as a vector of the English version of Wikipedia articles (entities). By transferring texts to a unified vector space, the relatedness between texts in different languages with similar meanings can be increased. We also propose an approach that can improve clustering performance and reduce the processing time by eliminating language-specific entities in the unified vector space. Experimental results on multilingual Twitter message clustering revealed that the proposed methods outperformed cross-lingual explicit semantic analysis, a previously proposed method to measure relatedness between texts in different languages. Moreover, the proposed methods were comparable to ENB applied to texts translated into English using a proprietary translation service. The proposed methods enabled relatedness measurements for multilingual short text clustering without requiring machine translation processes.

Due to the spread of smartphones and tablet devices, many photographs are uploaded and shared on the Internet. Cameras often have sensors such as GPS and digital compass. These sensor data are attached to photograph data as metadata. Metadata is helpful to retrieve photographs that show the designated points. For this request, existing systems search the photographs taken in constant distance from the designated points and show them to the users. However, some of them do not cover the designated point when their photographing orientations are largely different from the direction for the point or obstacles hide the point. So, the users often check many photographs to find their desirable photographs showing the designated points. In this paper, we propose a method to calculate the probability that photographs show the designated points. By showing the photographs that have high scores with priority, the users can find their desirable photographs with less checking. Also, we develop a system to retrieve photographs using our proposed scoring method.

Inverse Document Frequency (IDF) is widely accepted term weighting scheme whose robustness is supported by many theoretical justifications. However, applying IDF to word N-grams (or simply N-grams) of any length without relying on heuristics has remained a challenging issue. This article describes a theoretical extension of IDF to handle N-grams. First, we elucidate the theoretical relationship between IDF and information distance, a universal metric defined by the Kolmogorov complexity. Based on our understanding of this relationship, we propose N-gram IDF, a new IDF family that gives fair weights to words and phrases of any length. Based only on the magnitude relation of N-gram IDF weights, dominant N-grams among overlapping N-grams can be determined. We also propose an efficient method to compute the N-gram IDF weights of all N-grams by leveraging the enhanced suffix array and wavelet tree. Because the exact computation of N-gram IDF provably requires significant computational cost, we modify it to a fast approximation method that can estimate weight errors analytically and maintain application-level performance. Empirical evaluations with unsupervised/supervised key term extraction and web search query segmentation with various experimental settings demonstrate the robustness and language-independent nature of the proposed N-gram IDF.

This paper describes non-diffusion-based molecular communication and its application to an inbody mobile bionanosensor network. In the inbody mobile bionanosensor network, bio-nanomachines migrate in the environment while they release adhesive molecules that bind to a surface in the environment. The concentration gradient of adhesive molecules is thus formed over the surface, and bio-nanomachines migrate based on the gradient to coordinate their behavior. In the non-diffusion-based molecular communication, the formation of concentration gradient of adhesive molecules relies on the mobility of bio-nanomachines and thus the effective communication range may be limited. However, the non-diffusion-based molecular communication can maintain a high and stable concentration of molecules in the environment, allowing bio-nanomachines to detect the concentration to coordinate their behavior. Through mathematical modeling and performance evaluation, this paper demonstrates that the non-diffusion-based molecular communication may apply to induce coordinated behavior among mobile bio-nanomachines in the inbody environment considered in this paper.

Location-based service (LBS) is a typical application for mobile ad hoc networks (MANETs). In an LBS, it is effective for nodes to acquire data using convex hull queries, which retrieve the information necessary for calculating the convex hull of all nodes composing a given network. In a naive approach, the query-issuing node can determine the convex hull of the network by flooding a query throughout the entire network and receiving location information on all the nodes, but this involves excessive traffic. In addition, since the network topology changes dynamically, due to the movement of nodes, the set of vertices of the convex hull changes. Therefore, the query-issuing node must determine the convex hull in a short period of time. In this paper, we propose convex hull query processing methods for reducing traffic and response time while maintaining high accuracy of the query result in MANETs. In these methods, nodes reply with information on nodes which are convex hull vertices. In the Local Convex Hull (LCH) method, nodes reply with information on nodes which are vertices of the local convex hull, which is the convex hull composed of nodes whose information has already been received. In the Local Wrapping (LW) method, the query is transmitted only to nodes on the outer boundary. Experimental results show that our proposed methods reduce traffic and achieve short response time and high accuracy of the query result, in comparison with a naive method.

In this paper, we consider a problem of range-based continuous query processing in mobile ad hoc networks (MANETs). Due to the advantage that no infrastructure is needed, MANETs are useful in various situations such as disaster sites. In such applications, information monitoring techniques are required, for example, to obtain the information on victims. In MANETs, the bandwidth and batteries of nodes are limited and nodes move freely, thus conventional techniques for fixed and wired networks are hard to apply to MANETs. Moreover, periodic data retrieval approach is inefficient because it incurs large traffic to obtain data items continuously. We therefore propose a communication-efficient method for continuously monitoring data existing around a query originating node. Our proposed method does not rely on periodic approach, but rather extends query transmission ranges dynamically and continuously to deal with nodes' movement. Query receiving nodes estimate the current position of the query originating node and forward data items toward the position. This approach also enables efficient data forwarding when data updates occur. Simulation experiments demonstrate the efficiency and scalability of our method.

In this paper, we propose a signature-based top-k query processing method against data replacement attacks in mobile ad hoc networks (MANETs). In order to rapidly identify a greater number of malicious nodes, nodes share information about identified malicious nodes with other nodes. If nodes share only this information, however, malicious nodes may successfully transmit false information identifying normal nodes as malicious. Therefore, in the proposed method, when nodes send reply messages during query processing, they attach encrypted information about the sent data items (i.e., digital signatures), providing the query-issuing node with critical information about the data items sent by nodes in the network, and thereby enabling it to identify malicious nodes, using the received signatures. After identifying the malicious nodes, it floods the network with a notification message including the signatures in which the identified malicious nodes have replaced higher-score data items to their own lower-score items.

As we are in the big data era, techniques for retrieving only user-desirable data objects from massive and diverse datasets is being required. Ranking queries, e.g., top-k queries, which rank data objects based on a user-specified scoring function, enable to find such interesting data for users, and have received significant attention due to its wide range of applications. While many techniques for both centralized and distributed top-k query processing have been developed, they do not consider query keywords, i.e., simply retrieving k data with the best score. Utilizing keywords, on the other hand, is a common approach in data (and information) retrieval. Despite of this fact, there is no study on retrieving top-k data containing all query keywords. We define, in this paper, a new query which enriches the conventional top-k queries, and propose some algorithms to solve the novel problem of how to efficiently retrieve k data objects with the best score and all query from distributed databases. Extensive experiments on both real and synthetic data have demonstrated the efficiency and scalability of our algorithms in terms of communication cost and running time.

This paper first reveals the relationship between Inverse Document Frequency (IDF), a global term weighting scheme, and information distance, a universal metric defined by Kolmogorov complexity. We concretely give a theoretical explanation that the IDF of a term is equal to the distance between the term and the empty string in the space of information distance in which the Kolmogorov complexity is approximated using Web documents and the Shannon-Fano coding. Based on our findings, we propose N-gram IDF, a theoretical extension of IDF for handling words and phrases of any length. By comparing weights among N-grams of any N, N-gram IDF enables us to determine dominant N-grams among overlapping ones and extract key terms of any length from texts without using any NLP techniques. To efficiently compute the weight for all possible N-grams, we adopt two string processing techniques, i.e., maximal substring extraction using enhanced suffix array and document listing using wavelet tree. We conducted experiments on key term extraction and Web search query segmentation, and found that N-gram IDF was competitive with state-of-the-art methods that were designed for each application using additional resources and efforts. The results exemplified the potential of N-gram IDF.

In this paper, we propose a data forwarding method for efficient data gathering in wireless sensor networks with multiple mobile sinks which freely move in the target region. In our proposed method, each sensor node forwards data packets based on information on connectivity (the status of connection with mobile sinks). As the way to share information on connectivity among neighboring nodes, we integrate push-based and pull-based mechanisms we have proposed in [5]. The integrated mechanism utilizes advertisement from the nodes with good connectivity together with request from the nodes which hold data to transmit. By the complementary use of these mechanisms, our proposed method reduces the traffic for sharing information while realizing an efficient data forwarding.

This paper considers mobile bionanosensor networks designed for target tracking in molecular environments. The mobile bionanosensor network considered in this paper consists of nano-to-microscale bio-nanomachines that coordinate their activity by propagating the two types of signaling molecules: attractants for a group of bio-nanomachines to move toward targets, and repellents to spread over the environment. A mathematical model for target tracking is developed and the performance of mobile bionanosensor networks is defined based on distributions of targets and bio-nanomachines. Numerical results are then shown to facilitate discussion of the impact of attractants and repellents on target tracking performance.

In dense mobile wireless sensor networks, it is desirable to gather sensor data with as low traffic as possible. When an application requires geographical boundaries of sensor readings, it is able to satisfy the requirement while reducing traffic by gathering sensor data only from nodes located close to the boundaries. In order to do so, it is necessary to detect nodes located close to the boundaries (boundary detection). Until now, many boundary detection methods have been proposed, assuming networks constructed by fixed nodes. In these methods, each node preliminarily recognizes locations of itself and all its neighboring nodes. When applying this approach to a dense and mobile environment, it takes a large amount of traffic for exchanging information on locations of nodes. In this paper, we propose an efficient boundary detection method in dense mobile wireless sensor networks, which makes use of overhearing sensor data. In our proposed method, each node determines whether it exists close to a boundary or not based on sensor data overheard from its neighboring nodes. When a node determines that it dose not exist close to the boundary, it stops transmitting its own sensor data. By doing so, traffic for boundary detection can be reduced. We confirmed the effectiveness of our proposed method through simulation experiments.

Location-based services (LBSs) are important applications for mobile users. We consider an application in which the source node periodically disseminates location-based information in mobile ad hoc networks (MANETs). We define beneficial information as that which may be of benefit to mobile users planning to pass near the location related to the information. However, typically, mobile users change their route or travel direction when the mobile node receives beneficial information such as traffic jam and accident information (we call these information the negative location-based information). Thus, a significant problem lies in determining the proper target area for the dissemination of such information in dynamic networks because the source node is difficult to effectively know where to disseminate it. In this paper, we propose a novel location-based information dissemination method in MANETs by use of some fixed nodes. Our proposed method requires neither a positioning system, nor previous knowledge, to efficiently disseminate the information. However, the fixed nodes autonomously expand the relevant dissemination area. Through simulation experiments, we confirm that the proposed method suppresses ineffectual overhead, and that mobile users can efficiently and early receive the beneficial information.

In mobile ad hoc networks (MANETs), it is effective for mobile nodes to retrieve data items using top-k queries, in which data items are ordered according to a particular attribute score, and the query-issuing node acquires the data items with the k highest scores. However, accurate results may not be acquired in environments where malicious nodes are present. In top-k queries, it is important to neutralize attacks in which malicious nodes attempt to replace necessary data items with unnecessary ones (we call these, data replacement attacks). In this paper, we propose methods for top-k query processing and malicious node identification against data replacement attack in MANETs. In the top-k query processing method, in order to maintain accuracy of the query result, nodes reply with data items with the k highest scores, along multiple routes. Moreover, to enable detection of data replacement attacks, reply messages include information on the route along which reply messages are forwarded, and thus the query-issuing node can know the data items that properly belong to the message. In the malicious node identification method, the query-issuing node first narrows down the malicious node candidates, using the received message information, and then requests information on the data items sent by these candidates. In this way, the query-issuing node can identify the malicious node. Finally, we verify, through simulation experiments, that the proposed top-k query processing method achieves high accuracy of the query result, and that the malicious node identification method effectively identifies a malicious node.

Top-k queries, which retrieve the k data items with the highest scores, have been receiving considerable attention because of their utility for many real life applications. In this paper, we propose an efficient query routing scheme enabling top-k data retrieval by only necessary nodes, named CTR. CTR employs a new clustering framework for top-k query processing, and in this framework, nodes holding high rank data items become ClusterHeads (CHs), and top-k queries are transmitted between CHs via gateway nodes which belong to multiple clusters. Each CH maintains a record of hop counts between itself and high rank data items, enabling it to judge whether or not to transmit a query on the fly. As a result, CTR reduces overhead while keeping high accuracy of the query result. Extensive experiments have demonstrated that CTR functions well in terms of accuracy of the query result, overhead, and delay.

In recent years, video-on-demand services such as YouTube or Hulu have become popular. These VoD services often adopt P2P (Peer-to-Peer) streaming techniques to manage many users' requests. Some services provide different quality services for the users. For example, the users who pay money for the service provider can watch high-quality videos, and others can only watch low-quality videos. In such a multiple bit rate video delivery, since high-quality videos have high bit rate, their interruption time is very long compared with that for low-quality videos when many peers watch high-quality videos. In this paper, we propose a method to reduce interruption time for users watching high-quality videos in multiple bit rate video delivery. Our evaluation results show that our proposed method can reduce their interruption times.

In mobile ad hoc networks (MANETs), locationbased service (LBS) is a typical application. In a LBS, it is valuable for each node to grasp the convex hull of nodes which compose a network by using a convex hull query. However, if the query-issuing node acquires the information on all the nodes, the information on nodes which are not the vertexes of the convex hull is replied, which is unnecessary for a convex hull detection. In this paper, we propose a convex hull query processing method, which reduces traffic and also maintains high accuracy of the query result in MANETs. An experimental result shows that our proposed method reduces traffic and achieves high accuracy of the query result compared with a naive method.

In dense mobile wireless sensor networks, it is desirable to reduce traffic for data gathering as much as possible while satisfying an application requirement. In this paper, focusing on an application which monitors the time-variant shape of events, we discuss an approach to achieve an efficient monitoring with small traffic in dense mobile wireless sensor networks.

With the increase of data generation in distributed fashions such as peer-to-peer systems and sensor networks, top-k query processing which returns only a small set of data that satisfies many users' preferences, becomes a substantial issue. When data are periodically updated in each epoch e.g., weather information, without any techniques, a naive solution is to aggregate all data and their updates to ensure the correctness of final answers, however, it is too costly in terms of data transfer especially for data aggregator nodes. In this paper, we propose a top-k monitoring query processing method in 2-tier distributed systems based on a publish-subscribe scheme. A set of top-k subscriptions specifying summary scope of users' interests is informed to aggregators to limit the number of transferred data records for each epoch. In addition, instead of issuing subscriptions of all queries, our method identifies a small set of minimal subscriptions resulting in lower communication overhead. Our experiments show that our technique is efficient and outperforms other comparative reactive methods.

In this demonstration, we introduce MLJ (MultiLingual Journalism, http://mljournalism.com), a first Web-based system that enables users to search any topic of latest tweets posted by media outlets and journalists beyond languages. Handling multilingual tweets in real time involves many technical challenges: language barrier, sparsity of words, and real-time data stream. To overcome the language barrier and the sparsity of words, MLJ harnesses CL-ESA, a Wikipedia-based language-independent method to generate a vector of Wikipedia pages (entities) from an input text. To continuously deal with tweet stream, we propose one-pass DP-means, an online clustering method based on DP-means. Given a new tweet as an input, MLJ generates a vector using CL-ESA and classifies it into one of clusters using one-pass DP-means. By interpreting a search query as a vector, users can instantly search clusters containing latest related tweets from the query without being aware of language differences. MLJ as of March 2014 supports nine languages including English, Japanese, Korean, Spanish, Portuguese, German, French, Italian, and Arabic covering 24 countries.

In this paper, we propose two beacon-less kNN query processing methods for reducing traffic and maintaining high accuracy of the query result in mobile ad hoc networks (MANETs). In these methods, the query-issuing node first forwards a kNN query using geo-routing to the nearest node from the point specified by the query (query point). Then, the nearest node from the query point forwards the query to other nodes close to the query point, and each node receiving the query replies with the information on itself. In this process, we adopt two different approaches: the Explosion (EXP) method and the Spiral (SPI) method. In the EXP method, the nearest node from the query point floods the query to nodes within a specific circular region, and each node receiving the query replies with information on itself. In the SPI method, the nearest node from the query point forwards the query to other nodes in a spiral manner, and the node that collects a satisfactory kNN result transmits the result to the query-issuing node. Experimental results show that our proposed methods reduce traffic and achieve high accuracy of the query result, in comparison with existing methods.

ABSTRACT Wireless sensor networks (WSNs) which is proposed in the late 1990s have received unprecedented attention, because of their exciting potential applications in military, industrial, and civilian areas (e.g., environmental and habitat monitoring). Although WSNs have become more and more prospective in human life with the development of hardware and communication technologies, there are some natural limitations of WSNs (e.g., network connectivity, network lifetime) due to the static network style in WSNs. Moreover, more and more application scenarios require the sensors in WSNs to be mobile rather than static so as to make traditional applications in WSNs become smarter and enable some new applications. All this induce the mobile wireless sensor networks (MWSNs) which can greatly promote the development and application of WSNs. However, to the best of our knowledge, there is not a comprehensive survey about the communication and data management issues in MWSNs. In this paper,focusing on researching the communication issues and data management issues in MWSNs, we discuss different research methods regarding communication and data management in MWSNs and propose some further open research areas in MWSNs.Copyright © 2011 John Wiley & Sons, Ltd.

In mobile ad hoc networks (MANETs), to acquire only necessary data items, it is effective that each mobile node retrieves data items using a top-k query, in which data items are ordered by the score of a particular attribute and the query-issuing mobile node acquires data items with k highest scores. In our previous works, we proposed top-k query processing methods for reducing traffic and also keeping high accuracy of query result. Those methods focus on the traffic reduction by not sending back unnecessary data items. However, queries are forwarded to all of nodes in the entire area by flooding, and thus, many nodes which do not contribute to the query result have to send redundant top-k queries and replies, which increases unnecessary traffic. In this paper, we propose a routing method for top-k query processing in MANETs. In this method, when each mobile node sends a top-k query, it refers to its own routing table consisting of the ranking of scores of data items in the network and identifiers of nodes to which queries are forwarded to obtain the necessary data items. Moreover, each node updates its own routing table when the link disconnection occurs and scores of data items are updated.

In dense mobile sensor networks, to reduce traffic for gathering sensor data, it is desirable to efficiently gather sensor data from the minimum number of mobile sensor nodes necessary to guarantee the sensing granularity, which the application requires. For this aim, in our previous work, we have proposed a data gathering method using mobile agents (DGUMA). However, DGUMA does not consider geographical distribution of data values, and all agents have to send their own readings to the sink. Thus, multiple readings with the same value are sent to the sink. In this paper, we extend DGUMA in order to further reduce the traffic considering geographical distribution of data values. In the extended method, mobile agents aggregate multiple readings with the same value into one reading and forward the aggregated data to reduce the traffic. Moreover, our extended method dynamically controls communication routes from each agent to the sink so that the agents can effectively aggregate the readings. We confirmed the effectiveness of our proposed method through some simulation experiments.

This paper describes a novel probabilistic method of measuring semantic similarity for real-world noisy short texts like microblog posts. Our method adds related Wikipedia entities to a short text as its semantic representation and uses the vector of entities for computing semantic similarity. Adding related entities to texts is generally a compound problem that involves the extraction of key terms, finding related entities for each key term, and the aggregation of related entities. Explicit Semantic Analysis (ESA), a popular Wikipedia-based method, solves these problems by summing the weighted vectors of related entities. However, this heuristic weighting highly depends on the rule of majority decision and is not suited to short texts that contain few key terms but many noisy terms. The proposed probabilistic method synthesizes these procedures by extending naive Bayes and achieves robust estimates of related Wikipedia entities for short texts. Experimental results on short text clustering using Twitter data indicated that our method outperformed ESA for short texts containing noisy terms.

In dense mobile wireless sensor networks, it is desirable to gather sensor data from the minimum number of nodes necessary to guarantee the sensing granularity. For this aim, in our previous work, we have proposed a data gathering method using mobile agents. However, this method cannot gather all the sensor data in the situation where some mobile agents cannot be deployed due to low node density. In this paper, we extend our previous method in order to gather all the sensor data even when some mobile agents disappear. First, when a mobile agent disappears, the extended method redeploys the disappeared agent. In addition, when the redeployment is failed, the extended method regathers sensor data which is missed by the disappearance of the agent. We confirmed the effectiveness of the extended method through some simulation experiments.

In mobile ad hoc networks (MANETs), to acquire only necessary data items, it is effective for each mobile node to retrieve data items using a top-k query. In our previous work, we proposed a routing method for top-k query processing to reduce traffic while keeping highly accurate query result by using a routing table. This method performs query transmission by unicast to each node which contributes to collect the data items with k-highest scores. However, in highly dynamic networks, the accuracy of query result decreases because its query transmission approach makes only single route to each data item. To solve this problem, we extend the previous method in order to achieve robust routing. In our proposed method of this paper, each node does not unicast a query message, but multicasts the query message to the nodes in its routing table. This method makes multipath transmission of query messages, so that prevents from decreasing of the accuracy of the query result in highly dynamic networks. The simulation results show that our proposed method outperforms our previous method as to accuracy of the query result.

Vehicular ad hoc networks (VANETs) have been attracting increasing research interests for the past decade. To address the routing problem, many protocols have been proposed in the past several years. Routing protocols for VANETs, mostly based on the ideas of “Geographical Routing” (or geo-routing for short), typically have nodes periodically broadcast one-hop beacon messages to reveal their positions to neighbors. Nevertheless, packet loss and thus deterioration of routing performance in these protocols are anticipated in urban areas due to high density of vehicles in the network. In this paper, we propose two new VANET routing protocols, namely, Routing Protocol with Beacon Control (RPBC) and Routing Protocol with BeaconLess (RPBL), to alleviate packet losses. In RPBC, each vehicle determines whether to transmit a beacon message based on a new beacon control scheme proposed in this paper, which by minimizing redundant beacon messages reduces transmission overhead significantly. On the other hand, RPBL is a beaconless protocol where a node broadcasts a packet to its neighboring nodes and transmits packet via multiple paths to achieve high delivery ratio. Moreover, as packets in geo-routing protocols include the location of the sender, it can be used for routing without heavily relying on beacons. Accordingly, we propose the idea of virtual beacons and use it to further improve our proposed protocols. We conduct comprehensive experiments by simulation to validate our ideas and evaluate the proposed protocols. The simulation results show that our proposals can achieve high delivery ratios, short delays, and small overhead.

Context aware systems on smart-phones aim to provide useful information by analysing and recognizing users' situations from built-in sensors logs. Especially, predicting user actions is one of the important functions for the context aware systems on smart-phones because this function enables context aware systems to provide proactive and responsive services. Therefore the next location prediction is also an important function for context aware systems. This paper introduces a next location prediction method based on context recognition. In this method, we define a context as combinations of features which are extracted from a set of relational data generated from a phone's sensor logs. We applied Mixed Membership Stochastic Blockmodels (MMSB) to context extraction. We then collected sensor logs of a single user over a period of three months and conducted an evaluation using this collected dataset. An an evaluation using the dataset was conducted and the result shows that 60% of the test dataset ranked in the top 30% of all candidates of the next locations.

Accurately locating unknown nodes is a critical issue in the study of wireless sensor networks (WSNs). Many localization approaches have been proposed based on anchor nodes, which are assumed to know their locations by manual placement or additional equipments such as global positioning system. However, none of these approaches can work properly under the adversarial scenario. In this paper, we propose a novel scheme called two-step secure localization (TSSL) stand against many typical malicious attacks, e.g. wormhole attack and location spoofing attack. TSSL detects malicious nodes step by step. First, anchor nodes collaborate with each other to identify suspicious nodes by checking their coordinates, identities and time of sending information. Then, by using a modified mesh generation scheme, malicious nodes are isolated and the WSN is divided into areas with different trust grades. Finally, a novel localization algorithm based on the arrival time difference of localization information is adopted to calculate locations of unknown nodes. Simulation results show that the TSSL detects malicious nodes effectively and the localization algorithm accomplishes localization with high localization accuracy.

ABSTRACT In wireless sensor networks (WSNs), many applications require sensor nodes to obtain their locations. Now, the main idea in most existing localization algorithms has been that a mobile anchor node (e.g., global positioning system‐equipped nodes) broadcasts its coordinates to help other unknown nodes to localize themselves while moving according to a specified trajectory. This method not only reduces the cost of WSNs but also gets high localization accuracy. In this case, a basic problem is that the path planning of the mobile anchor node should move along the trajectory to minimize the localization error and to localize the unknown nodes. In this paper, we propose a Localization algorithm with a Mobile Anchor node based on Trilateration (LMAT) in WSNs. LMAT algorithm uses a mobile anchor node to move according to trilateration trajectory in deployment area and broadcasts its current position periodically. Simulation results show that the performance of our LMAT algorithm is better than that of other similar algorithms. Copyright © 2011 John Wiley & Sons, Ltd.

Mobile devices have become popular to access the information on-the-move. However, the physical restrictions of mobile devices such as display size and input capabilities and the changes of users' contexts may affect the users' information needs and search behaviors. In order to design a new search service which takes mobile users' situation into consideration, it is essential to understand search behaviors of mobile users in detail. In this work, we conducted a diary study using 26 participants in Japan, focusing on how mobile context affects users' information needs and search behaviors. In particular, we focus on detailed behaviors when users failed to find the information they needed. Our main findings include that user's search behaviors were affected not only by the information needs but also the place where the searches were conducted, which might be an important cue to design future mobile search services and applications.

A variety of services utilizing users' positions have become available because of rapid advances in Global Positioning System (GPS) technologies. Since location information may reveal private information, preserving location privacy has become a significant issue. We proposed a dummy-based method of anonymizing location to protect this privacy in our previous work that generated dummies based on various restrictions in a real environment. However, the previous work assumed a simplified mobility model in which users kept moving and did not stop. If we assume a more realistic mobility model in which users often pause to visit various attractions, it becomes increasingly more difficult to generate dummies that will move naturally. In this paper, we assumed that the users' movements are known in advance and propose a dummy-based anonymization method based on user movements, where dummies move naturally while stopping at several locations. We simulated user movements on real map information and verified the method we propose was more effective than the previous one.

Sleep scheduling algorithms for duty-cycled sensor networks have received great attention, since sensors should dynamically be awake and asleep to save energy consumption. Among all current sleep scheduling algorithms, only the recently proposed energy consumed uniformly-connected k-neighborhood (EC-CKN) algorithm focuses on not only the coverage of the resultant network, but also the network lifetime after sleep scheduling. However, all sleep scheduling processes ignore the fact that potential insider attacks actually can seriously affect or destroy proper sleep scheduling operations and properties. In this paper, we discuss these vulnerabilities and propose corresponding countermeasures for EC-CKN, i.e., secure neighborhood authentication.

In a kNN query processing method, it is important to appropriately estimate the range that includes kNNs. While the range could be estimated based on the node density in the entire network, it is not always appropriate because the density of nodes in the network is not uniform. In this paper, we propose two kNN query processing methods in MANETs where the density of nodes is ununiform; the One-Hop (OH) method and the Query Log (QL) method. In the OH method, the nearest node from the point specified by the query acquires its neighbors' location and then determines the size of a circle region (the estimated kNN circle) which includes kNNs with high probability. In the QL method, a node which relays a reply of a kNN query stores the information on the query result for future queries.

A diversified search result for an underspecified query generally contains web pages in which there are answers that are relevant to different aspects of the query. In order to help the user locate such relevant answers, we propose a simple extension to the standard Search Engine Result Page (SERP) interface, called AspecTiles. In addition to presenting a ranked list of URLs with their titles and snippets, AspecTiles visualizes the relevance degree of a document to each aspect by means of colored squares ("tiles"). To compare AspecTiles with the standard SERP interface in terms of usefulness, we conducted a user study involving 30 search tasks designed based on the TREC web diversity task topics as well as 32 participants. Our results show that AspecTiles has some advantages in terms of search performance, user behavior, and user satisfaction. First, AspecTiles enables the user to gather relevant information significantly more efficiently than the standard SERP interface for tasks where the user considers several different aspects of the query to be important at the same time (multi-aspect tasks). Second, AspecTiles affects the user's information seeking behavior: with this interface, we observed significantly fewer query reformulations, shorter queries and deeper examinations of ranked lists in multi-aspect tasks. Third, participants of our user study found AspecTiles significantly more useful for finding relevant information and easy to use than the standard SERP interface. These results suggest that simple interfaces like AspecTiles can enhance the search performance and search experience of the user when their queries are underspecified.

People carry around mobile devices all the time in their daily life and get various information from the Internet in various situations. When searching for information (content) by using mobile devices, users' activities (e.g., walking and standing) and their situations (e.g., commuting in the morning and going out downtown in the evening) often change and this change may affect their degree of concentration on the display of mobile devices and their information needs. Therefore, search systems should provide users with an amount of information suitable for their activities and with a type of information suitable for their situations. In this paper, we present the design and implementation of a content search system considering mobile users' activities and situations, which aims to reduce users' load of operations in content searching. Our system recognizes user's activities and switches between two kinds of content search systems according to the user's activity: the location-based content search system runs when the user is standing, while the menu-based content search system runs when the user is walking. Both systems present information based on the user's situation. We also introduce a user's activity recognition method for mobile devices. This method classifies user's activity into standing, walking, and running using the sensors equipped in mobile devices.

Smart-phone users can search for information about surrounding facilities or a route to their destination. However, it is difficult to get or search for information while walking because of low legibility. To address this problem, users have to stop walking or enlarge the screen. Our previously proposed system for smart-phone switches the information presentation policies in response to the user's context. In this paper we describe our context recognition mechanism for this system. This mechanism estimates user context from sensors embedded in a smart-phone. We use a Support Vector Machine for the context classification and compare four types of feature values consisting of FFT and 3 types of Wavelet Transforms. Experimental results show that recognition rates are 87.2 % with FFT, 90.9 % with Gabor Wavelet, 91.8 % with Haar Wavelet, and 92.1 % with MexicanHat Wavelet.

In this paper, we propose a dynamic route construction method based on measured characteristics of radio propagation in a real environment. Our method first measures characteristics of radio propagation for each link, and determines a communication route from every node to the sink node and its transmission power based on the measured characteristics. While operating the system, our method dynamically reconstructs communication routes according to the change in the characteristics of radio propagation. We conduct an experiment to verify that our method can construct efficient communication routes in terms of energy-efficiency and quality of communication even when the characteristics of radio propagation dynamically change.

Map-based application is one of the most popular applications using a built-in GPS receiver. Users often use applications based on geographic information in situations where they share the same information needs with friends or families and conduct some tasks together. However, it is difficult to communicate geographic information with each other because existing map-based applications are basically designed for solitary work. In this paper, to support collaborative work using map-based applications, we explore important factors for collaborative use of map interface. We conducted a user experiment using a map-based application implemented with some functions for supporting collaborative work. The result shows that it is important to i) enable users to share information among multiple devices and view it individually on their own displays when they use a map together, and ii) synchronize users' displays and map operations when they communicate geographic information with each other.

To solve the secure localization problems, a number of secure localization schemes have been developed at present. However, most of these techniques cannot survive collusion attacks where a majority of malicious nodes launch colluding attacks. In this paper, we introduce a new collusion attack model called Collaborative Collusion Attack Model (CCAM) and propose a novel scheme called Two-Step Format Detection (TSFD) that is well suited to WSN which is a resource constrained environment. The TSFD has reasonable and acceptable communication cost and algorithm complexity. Through simulations, we compare the performance of TSFD with other secure localization schemes and show that TSFD has more efficient and resilient performance.

Top-k query is a very useful and important query in wireless sensor networks (WSNs), aiming to find the k nodes with highest readings among the sensor nodes. In WSNs, there are generally two kinds of networks: always-on WSNs (AO-WSNs) in which sensors always keep awake and duty-cycled WSNs (DC-WSNs) where sensors dynamically sleep and wake. To the best of our knowledge, there are a lot of work about top-k query in AO-WSNs but little research has been done regarding top-k query in DC-WSNs. However, DC-WSN is a very practical network model in which energy consumption can be greatly saved. In this paper, we analyze the research issues when implementing top-k query in DC-WSNs and propose the DCDC-WSNs (DC-WSNs with data replication (DR) and connected k-neighborhood (CKN)) to implement top-k query. Further theoretical analysis and simulation results show that implementing top-k query in DCDC-WSNs can achieve the best tradeoff with respect to query data accessibility and query cost (total energy consumption, query response time), compared with AO-WSNs and DCC-WSNs (DC-WSNs with only CKN).

In mobile ad hoc networks (MANETs), location based service (LBS) is a typical application. In a LBS, it is effective for each node to acquire data using a k Nearest Neighbor (kNN) query, which retrieves the information on the nearest k nodes from the location specified by the query. However, existing methods for kNN query processing in wired networks and wireless sensor networks cannot be applied in MANETs dueto the movement of mobile nodes. In this paper, we propose the Explosion (EXP) method, which is a kNN query processing method for reducing traffic and also keeping high accuracy of the query result in MANETs. An experimental result shows that our proposed method reduces traffic and achieves high accuracy of the query result compared with a naive method.

Recently, there has been increasing interest in Mobile Wireless Sensor Networks (MWSNs) that are constructed by mobile sensor nodes held by ordinary people, which has led to a new concept called urban sensing. In such MWSNs, mobile sensor nodes densely exist, and thus, there are basically many sensor nodes for each geographical point that can sense the point in the entire sensing area. To reduce the communication cost for sensing operations, it is desirable to gather the sensor data from the minimum number of the mobile sensor nodes which are necessary to guarantee the sensing coverage or the quality of services. In this paper, to achieve this, we propose a data gathering method using mobile agents in dense MWSNs. The proposed method guarantees the sensing coverage of the entire area using mobile agents that autonomously perform sensing operations, transmit sensor readings, and move between sensor nodes. By gathering only sensor readings generated by sensor nodes where agents are running, our proposed method can achieve efficient gathering of sensor readings.

Most of the recent set-top boxes for digital video broadcasting can connect to the Internet. They can receive data from broadcast systems and from communication systems. Since such hybrid video broadcasting environments are suitable for large-scale streaming delivery, several schemes to reduce interruption time which occurs while playing video in hybrid broadcasting environments have been proposed. However, these schemes do not create sophisticated broadcast schedules. By dividing video data into several segments and broadcasting them according to an effective broadcast schedule, we can further reduce interruption time. In this paper, we propose an interruption time reduction scheme for hybrid video broadcasting environments. Our proposed scheme exploits the division-based broadcasting technique. In the division-based broadcasting technique, segments are broadcast so that clients can receive them until the time to play each of them. Also, we consider the prefetch of video data. By these techniques, we reduce interruption time effectively. Our simulation experiments revealed that our proposed scheme could reduce interruption time further than conventional schemes.

In this paper, we propose a method which acquires related words (entities) from multiple words by naturally disambiguating their meaning and considering their contexts. In addition, we introduce a bootstrapping method for improving the coverage of association relations. Experimental result shows that our method can acquire related words depending on the contexts of multiple words compared to the ESA-based method.

In a mobile ad hoc network (MANET), since mobility of mobile hosts causes frequent network partitioning, consistency management of data operations on replicas becomes a crucial issue. In our previous work, we have defined several consistency levels for MANET applications and designed protocols to achieve these consistency levels. These protocols are mainly based on a dynamic quorum system to cope with network partitioning and node and network failures. In this paper, we further investigate the impact of quorum construction on the system performance through simulation studies. Specifically, we change the number of mobile hosts that replicate data items and which hosts replicate each data item in the simulations and examine the impact on the system performance in terms of data availability and traffic.

Recent mobile devices are mostly equipped with a GPS receiver. This trend has arisen a variety of location based services (LBSs) which enable users to search local information of their current locations. To use LBSs, a user needs to send his/her location information to a service provider. Users' location information is inherently private, since it can reveal the critical information. In this paper, we propose a method to protect the user's location privacy by sending the user's location with dummy locations, which are determined based on the user's current location. We conduct an experiment to evaluate the effectiveness of our proposed method using real users' trajectories on a real map.

In the Skip Graph, which is a structured overlay network that supports range retrievals, a key is supposed to consist of a single value. Therefore, the Skip Graph cannot perform range-to-range retrievals. In the present research, we extend the Skip Graph, enabling it to retain a range as a key, and propose the Range-Key Skip Graph, which can perform range-to-range retrievals. We also implement the proposed scheme and evaluate it on the PlanetLab.

Two Phase geographic Greedy Forwarding (TPGF) is a pure on-demand geographic greedy forwarding protocol for wireless multimedia sensor networks (WMSNs). Unlike position-based routing protocols, TPGF has explicit route discovery, i.e., a node greedily forwards a routing packet to the neighbor that is the closest one to the destination to build a route. Thus, TPGF is vulnerable to some greedy forwarding attacks, e.g., spoofing or modifying control packets. In this paper, we identify such vulnerabilities and propose corresponding countermeasures for TPGF, e.g., secure neighbor discovery, route discovery.

Geographical contour lines are often used for the analysis of the sensor data distribution on wide area. In this paper, we propose a method to reconstruct contour lines by collecting sensor data from widely distributed sensors. In this case, it is redundant to collect all sensors from wide area since geographically closed sensors sense similar data. We propose a sensor data collection method for peer-to-peer sensor network to realize spatial interpolation of sensor data. In our proposal, we assume hierarchical Delaunay overlay network (HDOV) to collect sensor data uniformly. In addition, using structure of HDOV, more local sensor data is collected that affect on the spatial interpolation. By this mechanism, redundant sensor data to reconstruct geographical contour lines is reduced. The simulation result shows that our proposal can reconstruct accurate geographical contour lines, reducing target node and message numbers for data collection.

Photo sharing is one of the most popular Web services. Photo sharing sites provide functions to add tags and geo-tags to photos to make photo organization easy. Considering that people take photos to record something that attracts them, geo-tagged photos are a rich data source that reflects people's memorable events associated with locations. In this paper, we focus on geo-tagged photos and propose a method to detect people's frequent trip patterns, i.e., typical sequences of visited cities and durations of stay as well as descriptive tags that characterize the trip patterns. Our method first segments photo collections into trips and categorizes them based on their trip themes, such as visiting landmarks or communing with nature. Our method mines frequent trip patterns for each trip theme category. We crawled 5.7 million geo-tagged photos and performed photo trip pattern mining. The experimental result shows that our method outperforms other baseline methods and can correctly segment photo collections into photo trips with an accuracy of 78%. For trip categorization, our method can categorize about 80% of trips using tags and titles of photos and visited cities as features. Finally, we illustrate interesting examples of trip patterns detected from our dataset and show an application with which users can search frequent trip patterns by querying a destination, visit duration, and trip theme on the trip.

There are many constraints on electrical power and communication in wireless sensor networks since sensor nodes can only be equipped with poor devices. Therefore, it is important to construct an effective communication route in terms of energy-efficiency and quality of communication. Many studies have been conducted to address this issue. In particular, controlling the transmission power of each individual node has been one of the hottest issues in recent years. Most conventional studies have assumed an environment in which radio signals transmitted by nodes propagate equally in all directions. However, this model cannot be applied to real environments due to several effects such as the presence of obstacles and antenna characteristics. In this paper, we propose a routing method based on the measured characteristics of radio propagation in a real environment. Our method first involves measuring the characteristics of radio propagation for all radio links. Second, the transmission power of each individual node and a communication route from the node to the sink node are determined based on the measured characteristics.

In this paper, we propose a novel energy-efficient data transmission reduction method for periodical data gathering in wireless sensor networks (WSNs). Our method exploits overhearing, which is a typical characteristic of wireless communications. In our method, each node in a WSN autonomously determines whether its own reading is redundant or not by using the overheard packets transmitted by its neighbors. The redundancy of a reading is evaluated by a simple spatial interpolation using the readings of its neighbors. If the reading is determined as redundant, the node stops transmitting it. Furthermore, we present an evaluation based on simulation experiments with various parameters and show that our method suppresses data transmissions and reduces total energy consumption.

Recent spread of various data broadcasting services leads to provide enormous and various data. Since, data that a client needs are a part of them, there has been an increasing interest in information filtering techniques where a client automatically chooses and stores the necessary data. Generally, when a client performs filtering, it applies some filters sequentially and the time required for filtering changes according to the order of filters. On the other hand,in recent years, there have been many studies about attractor selection which is an autonomous parameter control technique based on the knowledge from living organisms.In this paper, in order to reduce the load for filtering, we propose a novel method which adaptively changes the order of filters according to the change in broadcast contents.This method adaptively decides the control parameters for filtering by using attractor selection.

In recent years, there has been an increasing interest in a broadcast database system where the server periodically broadcasts contents of a database to mobile clients such as PDAs and smart phones. There are three query processing methods in the broadcast database system. Generally, mobile clients have limits in energy consumption, i.e., battery,and each of the three methods consumes different amount of energy for query processing. In this paper, we propose a new method which dynamically chooses one of the three query processing methods considering energy consumption.

There is increasing demand for tangible user interfaces(TUIs), for easy and intuitive control of applications. In order to allow use of TUI devices for controlling applications,a system needs to associate functions with the TUI devices. Although several TUI applications and toolkit shave been proposed, it is difficult to use them for various applications since they require the user to perform several inconvenient operations. Therefore, we propose a preference learning algorithm for an automatic matching between TUI devices and application functions. A user can freely place and easily operate the TUI devices, and our system creates and learns user's preference data. Our system does this by determining three concrete types of user preferences specialized for each application and six abstract types of those common to all applications. Our proposed system has achieved over 80% accuracy in automatic matching.

Cellular phones are widely used to access the Web. However, because of their small screens and poor interfaces, it is inconvenient to browse Web pages designed for desktop PCs. In this paper, we propose two novel functions that virtually extend a cellular phone's screen so that users can acquire more information from the small screens than the traditional Web browsing using cellular phones. The first function presents previews of adjacent areas of the currently displayed area of a Web page so that users can understand what information is in the neighboring areas. The other presents previews of Web pages linked from the current page to help users to select an appropriate link connecting to a page containing the information of interest. As a platform for the implementation of these functions, we use cellular phones equipped with sensors to provide a user-friendly interface.

Advances in wireless communication technology have led to an increasing interest in mobile sensor networks.In our previous work, we proposed a method that controls the movement of sensor nodes by using push-based broadcast and communication among nodes.In this method, nodes autonomously move based on the broadcast information on where they can communicate with the sink,and they construct a temporal network to deliver their sensor readings to the sink.However, this method has two problems.First, it cannot sufficiently reduce the moving distances of nodes.Seconds, this method assumes an ideal environment in which node failures do not occur, whereas node failures do occur in real environments.In this paper, we extend our previous method to solve these problems. We also show the results of simulation experiments regarding a performance evaluation of the extended method.

In this paper, we propose an efficient node deployment strategy in sparse sensor networks. Our strategy, named DATFM/DF (Data Acquisition and Transmission with Fixed and Mobile node with deliberate Deployment of Fixed nodes), deploys sensor nodes based on the analysis of our previous mobile sensor control method, DATFM. As a result, DATFM/DF improves the efficiencies of sensing and data gathering. Furthermore, we conduct simulation experiments to evaluate the performance of our strategy.

Cellular phones are widely used to access the Web, however, it is inconvenient to browse large-sized pages designed for desktop PCs. Since cellular phones display only small part of a Web page, users easily get lost within the page while scrolling around. Even though pages are well structured by nature, users cannot recognize it because visible portion is strictly limited. To smartly browse pages using cellular phones, navigation is essential. In this paper, we propose a novel Web browser that models browsing as motoring cities, by setting routes on Web pages and presenting traffic signs to navigate users. Users can follow routes by auto-scrolling without burdensome operations.

In ad hoc networks, to acquire only necessary data items, it is effective that each mobile node retrieves data items using a top-k query, in which data items are ordered by the score of a particular attribute, and the query-issuing mobile node acquires data items with the k highest scores. In this paper, we propose a message processing method for a top-k query for reducing traffic and keeping the accuracy of the query result, i.e., guaranteeing that data items with the k highest scores in the entire network are acquired. When a mobile node transmits query and reply messages, our method can be used to reduce candidates of data items included in the top-k result to prevent unnecessary data transmissions. Moreover, if a mobile node detects a disconnection of a radio link, it searches for an alternative path to transmit the reply message to the query-issuing node. We present simulation results to evaluate the performance of our proposed method.

In this paper, we present the results of performance evaluation of our energy-efficient data transmission reduction method in wireless sensor networks (WSNs). In our method, each node in a WSN autonomously determines whether its own reading is redundant or not by using the overheard packets transmitted by its neighbors. The redundancy of a reading is evaluated by a simple spatial interpolation using the readings of its neighbors. If the reading is determined as redundant, the node stops transmitting it. Since our method may be affected by packet losses, we conduct simulation experiments with a practical model of lossy links. The results show that our method suppresses data transmissions and reduces total energy consumption even in a lossy environment.

In recent years, there has been an increasing interest in sensor networks, in which sensor nodes such as temperature or humidity sensors communicate with each other for environmental monitoring and so on. In sensor networks, it is important to reduce the energy consumption, since sensor nodes have limits in battery. Most researches achieve this by reducing sensor amount of transmitted data. However, there is a problem that the amount of transmitted data become large and their energy consumption becomes high when there are a lot of nodes in the sensing area. To solve the problem, we previously proposed a data gathering method. In this method, the data sink estimates the data value of nodes, broadcasts the estimated values, and then, sensor nodes whose observed values are largely different from the estimated values send the data. However, this method has a problem that it cannot sufficiently reduce the energy consumption. In this paper, we propose a new broadcast-based data gathering method. In this method, the data sink reduces the nodes which send their observed values when the reliability of gathered values by the data sink is high.

In mobile ad hoc networks, when a mobile host receives a data request from another host, the host usually transmits the requested data item by unicast. However, if mobile hosts hold data items that are frequently requested by others, they have to transmit the data items many times and consume a large amount of power. In this paper, we propose a data transmission method for not only maintaining data availability but also reducing traffic for data access. In our proposed method, each mobile host sends a data request attached with the deadline to receive the requested data item by the determined time. Moreover, each mobile host collects multiple requests for data items and transmits the requested data items by multicast, and thus, reduces data traffic. We also show the results of simulation experiments regarding the performance of our proposed method.

Geographical context is very important for images. Millions of images on the Web have been already assigned latitude and longitude information. Due to the rapid proliferation of such images with geographical context, it is still difficult to effectively search and browse them, since we do not have ways to decide their relevance. In this paper, we focus on the geographical relevance of images, which is defined as to what extent the main objects in an image match landmarks at the location where the image was taken. Recently, researchers have proposed to use game based approaches to label large scale data such as Web images. However, previous works have not shown the quality of collected game logs in detail and how the logs can improve existing applications. To answer these questions, we design and implement a Web-based and multi-player game to collect human knowledge while people are enjoying the game. Then we thoroughly analyze the game logs obtained during a three week study with 147 participants and propose methods to determine the image geographical relevance. In addition, we conduct an experiment to compare our methods with a commercial search engine. Experimental results show that our methods dramatically improve image search relevance. Furthermore, we show that we can derive geographically relevant objects and their salient portion in images, which is valuable for a number of applications such as image location recognition.

Research on the automatic construction of bilingual dictionaries has achieved impressive results. Bilingual dictionaries are usually constructed from parallel corpora, but since these corpora are available only for selected text domains and language pairs, the potential of other resources is being explored as well. In this article, we want to further pursue the idea of using Wikipedia as a corpus for bilingual terminology extraction. We propose a method that extracts term-translation pairs from different types of Wikipedia link information. After that, an SVM classifier trained on the features of manually labeled training data determines the correctness of unseen term-translation pairs.

Wikipedia, a huge scale Web based encyclopedia, attracts great attention as an invaluable corpus for knowledge extraction because it has various impressive characteristics such as a huge number of articles, live updates, a dense link structure, brief anchor texts and URL identification for concepts. We have already proved that we can use Wikipedia to construct a huge scale accurate association thesaurus. The association thesaurus we constructed covers almost 1.3 million concepts and its accuracy is proved in detailed experiments. However, we still need scalable methods to analyze the huge number of Web pages and hyperlinks among articles in the Web based encyclopedia.

Accessing information when we are on the move is a key feature if mobile computing environments, and using an optical see-through head mounted display (HMD) is one of the most suitable ways to do this. Although the HMD can display information without interfering with the user’s view, when the sight behind the display is too complex or too bright, the information displayed can bee very difficult to see. To solve this problem, we have created a way of laying out information for the optical see-through HMD. The ideal area for displaying information is determined by evaluating the sight image behind the HMD captured by a pantoscopic camera mounted on it. Moreover, if there is no suitable area for displaying information, our method select involves using the sight image around users use to the ideal direction and instructing them to face the direction. Our method displays information to ideal areas.

There are many kinds of events where participants converge and move around freely looking at points of interest. Since in these event spaces, the participants go where they want, some problems may arise for the event manager such as people staying in one area too long or congestion that occurs at specific attractions. Therefore, we propose here a new navigation system that has a route planning algorithm to satisfy the objectives of the event manager. In an actual test of our system, we found that the participants' actions were in line with the objectives of the event manager. Moreover, we also found that our system performs better by using wearable computing technologies because detailed information on participants is acquired.

We recently have seen illumination using Light Emitting Diodes (LEDs) on the street. The current illumination is difficult to control of flexibly and dynamically. In response to this problem, we propose a method controlling numerous LEDs collectively, dynamically, and flexibly by using a projector and small devices with optical sensors. We designed and implemented a small device to achieve our mechanism, which has an LED, an optical sensor, and a microcomputer to react to the light illuminated from a projector. Moreover, it has functions to self adjust the threshold and recognize optical commands, which are required for collective control. We discuss how effective our proposed device was in a study to evaluate it and in field tests done at actual events.

Web-based dictionaries, such as Wikipedia, have become dramatically popular among the Internet users in past several years. The important characteristic of Web-based dictionary is not only the huge amount of articles, but also hyperlinks. Hyperlinks have various information more than just providing transfer function between pages. In this paper, we propose an efficient method to analyze the link structure of Web-based dictionaries to construct an association thesaurus. We have already applied it to Wikipedia, a huge scale Web-based dictionary which has a dense link structure, as a corpus. We developed a search engine for evaluation, then conducted a number of experiments to compare our method with other traditional methods such as cooccurrence analysis.

Recently, gadgets and clothes using luminous equipments, which consist of wearable fashion, have attracted attention in many events such as fashion shows and exhibitions. Flicker patterns of these electronic equipments are sometimes controlled by microcomputers. By using a microcomputer, it is possible to use a complex pattern controlled by a program. However, it is difficult for a user to program his/her desired flicker pattern with a microcomputer. In this paper, we present a control system of flicker patterns focusing on LEDs. Our proposing system introduces the notion of the incremental programming for designing flicker patterns. Then, a long time pattern can be stored in a microcomputer by compressing a flicker pattern data. Moreover, we discuss the validity of this system through experiences in several events.

In this paper, we investigate adaptive control for broadcast scheduling and base station caching in the hybrid wireless broadcast (HWB) environment. The proposed adaptive method can adapt well to different access conditions and bandwidth capabilities and adequately exploit the three data delivery modes: push-based broadcast, pull- based broadcast, and pull-based point-to-point communication. Simulation studies demonstrated that our proposed method achieves significant performance improvement in average waiting time and success rate.

In mobile ad hoc networks, a mobile host holding data items frequently accessed by other hosts needs to transmit them many times and consumes more power than other hosts. In this paper, we propose replica allocation methods for not only improving data availability but also balancing the power consumption among mobile hosts. In these methods, each mobile host replicates data items taking into account their access frequencies, the numbers of their replicas, and the host's remaining battery power. We present simulation results to evaluate the performance of our proposed methods.

Cellular phones are widely used to access the WWW. However, most available Web pages are designed for desktop PCs. Cellular phones only have small screens and poor interfaces, and thus, it is inconvenient to browse such large sized pages. In addition, cellular phone users browse Web pages in various situations, so that appropriate presentation styles for Web pages depend on users' situations. In this paper, we propose a novel Web browsing system for cellular phones that allocates various functions for Web browsing on each numerical key of a cellular phone. Users can browse Web pages comfortably, selecting appropriate functions according to their situations by pushing a single button.

In this paper, based on the Hybrid Wireless Broadcast (HWB) model, we investigate a cooperative data management strategy to provide more efficient data delivery to the mobile clients. This strategy integrates broadcast scheduling with cache management of the base station by making effective use of the HWB data dissemination, namely push- and pull- based broadcast and pull-based point-topoint wireless communication. Simulation study demonstrates that the proposed cooperation strategy can improve the system performance.

In mobile ad hoc networks where data items are updated, each mobile host cannot verify whether its own replica is the same version as the original when it does not connect to the mobile host holding the original (original holder). In this paper, we propose two update log dissemination methods that efficiently verify the validity of tentative accesses to replicas. In the first method, the original holder efficiently disseminates the update logs to other hosts. In the other method, mobile hosts which are not the original holder also manage the update logs and two newly connected mobile hosts re-disseminate the logs. We also present simulation results to evaluate the performance of our methods.

In this paper, we propose a TDMA slot assignment protocol to realize the high channel utilization in an ad hoc sensor network where nodes have different communication ranges. Our protocol prevents inconsistency of the slot assignment information by considering the directions of wireless links with the neighbors when each node assigns a slot to itself. Furthermore, we verify the effectiveness of our protocol by simulation experiments. The results show that our protocol utilizes the channel bandwidth effectively even when nodes have different communication ranges.

In the near future, small ubiquitous devices will be embedded into most of artifacts to support human dailylife. In such environments, we need multiple types of human-computer interfaces for enjoying ubiquitous services. This paper describes several ubiquitous gadgets; ubiquitous chip, Pin&Play, and VCC, to provide flexible ubiquitous services and user interfaces. The integrative use of these devices achieves the physical and intuitive interaction between users and ubiquitous services.

In recent years, there has been an increasing interest in broadcast database systems, where the server periodically broadcasts contents of a database to mobile clients such as PDAs. There are three query processing methods in the broadcast database system: (i) the server processes a query and then broadcasts the query result to the client; (ii) the client stores all data that are necessary in processing the query and then processes it locally; and (iii) the server and the client collaborate in processing the query. Since the performance of each method changes according to the system situation, such as query frequency, it is difficult to decide the optimal method among them statically. In this paper, we propose a new query processing method which dynamically changes the query processing method based on query frequency. This method improves not only the response time but also the success rate of query processing compared with the traditional methods.

In this paper, we introduce two our approaches to browse large Web pages designed for desktop PCs using mobile devices with small screens and poor input interfaces. In the first approach, multiple mobile users collaboratively browse large Web pages. We call this approach collaborative browsing. In the second approach, automatic scrolling in a large Web page is performed, where contents in the page are traversed. This enables users to rapidly view the page with the users’ minimum operations.

GeoNote.net is a social network system which allows users to share geographic information among their friends network. The system has various notable features and uses several key technologies such as social network construction methods, security for personal information, geographic information management on mobile devices including cellular phones, retrieval of geographic information according to the friends network, and so on. In this paper, we describe the system under design aspects and implementation aspects.

Data replication is effective for improving data availability in ad hoc networks. In an environment where data updates occur, replicas of a data item may be inconsistent. To solve this problem, quorum based consistency management is a promising approach. To reduce communication overhead, it is better to make the number of mobile hosts in each quorum small. In this paper, we propose a consistency management method that constructs quorums with fewer mobile hosts.

Because of advances in information technologies, car navigation systems have come into widespread use as useful tools to guide drivers where they want to go. Conventional car navigation systems present the most suitable route according to a destination input into the system. However, since the required operation to input the destination costs so much, users do not usually use car navigation systems for daily driving. In this paper, to exploit the effective functions of car navigation systems, we propose a new system that automatically predicts user purpose and destination. The proposed car navigation system presents various information based on predicted purpose without interaction from users.

Recently, there has been an increasing interest in a social network. In a social network, nodes and links represent participants and their friendships, respectively. We have designed and implemented a query propagation mechanism and its applications to realize a social network composed by cellular phone users. In these applications, users can retrieve information from their friends or their friends’ friends by propagating the query in the network. To propagate a query in a wide range and improve the query success ratio, most users who receive the query must relay it to all their friends. However, this increases communication packets. In this paper, we propose a query routing method to decrease the number of communication packets by using user profiles.

In mobile computing environments, handheld devices with low functionality restrict the services provided for mobile users. We propose a new concept of collaborative browsing, where mobile users collaboratively browse Web pages designed for desktop PC. In collaborative browsing, a Web page is divided into multiple components, and each is distributed to a different device. In mobile computing environments, the number of handheld devices, their capabilities, and other conditions can vary widely amongst mobile users who want to browse content. Therefore, we developed a page partitioning method for collaborative browsing, which divides a Web page into multiple components. Moreover, we designed and implemented a collaborative Web browsing system in which users can search and browse their target information by discussing and watching partial pages displayed on multiple devices

It is difficult for users of mobile devices such as cellular phones equipped with a small screen and a poor input interface to browse Web pages designed for desktop PCs with large displays. Many studies and commercial products have tried to solve this problem. Web pages include images that have various roles such as site menus, line headers for itemization, and page titles. However, most studies of mobile Web browsing haven't paid much attention to the roles of Web images. In this paper, we define eleven Web image categories according to their roles and use these categories for proper Web image handling. We manually categorized 3,901 Web images collected from forty Web sites and extracted image features of each category according to the classification. By making use of the extracted features, we devised an automatic Web image classification method. Furthermore, we evaluated the automatic classification of real Web pages and achieved up to 83.1% classification accuracy. We also implemented an automatic Web page scrolling system as an application of our automatic image classification method.

Summary form only given. Recently, there has been increasing interest in research of data sharing in peer-to-peer networks. In this paper, we propose a new update propagation strategy that achieves not only load balancing but also delay reduction, where the update information is immediately notified to all peers holding the replicas when the update occurs. The proposed strategy creates an n-ary tree whose root is the owner of the original data and the other nodes are peers holding its replicas, and propagates the update information according to the trees. Moreover, we verify the effectiveness of the proposed strategy by simulation experiments.

This article presents a Web content adaptation and delivery mechanism based on application-level quality of service (QoS) policies. To realize effective Web content delivery for users, two kinds of application-level QoS policies, transmission time and transmission order of inline objects, are introduced. Next, we define a language to specify these policies. We show that transmission order control can be implemented using HTTP/1.1 pipelined requests in which a client recognizes the transmission order description in a Web page and simulates parallel transmission of inline objects by HTTP/1.1 range requests. Experimental results show that our proposed mechanism realizes effective content delivery to a diverse group of Internet users. Finally, we introduce two methods to specify application-level QoS policies, one by content authors, and the other by end users.

Virtual space, which models the real world, brings lots of benefits when it covers a considerably wide area and can be used in a mobile computing environment. However, there are some difficulties in implementing virtual space on the mobile computing environment, mainly due to hardware limitations such as computation power, communication capability, and memory size. In this paper, we ease the difficulties of using large-scale virtual space based on the real world (LVBR) in the mobile environment. We have established a scalable and efficient method of constructing and managing LVBR on cellular phones, and have implemented a system named KEITAI-Space. KEITAI-Space is designed to provide the scalable photo-based virtual space to cellular phones that takes into account the hardware limitations. The virtual space is made of a collection of photos and can be edited and expanded by people with cellular phones on hand.

Due to the recent popularization of digital broadcasting systems, broadcasting continuous media data such as music or movies has attracted much attention. In general continuous media data broadcasting, since clients have to wait to receive data before playing it, various methods to reduce waiting time have been studied. Some reduce the waiting time by dividing the data into several segments and broadcasting precedent segments frequently with a single channel. However, by dividing the data into finer segments and producing an effective broadcast schedule, the waiting time can be further reduced. In this paper, we propose an effective scheduling method to reduce waiting time with finer data division

Due to the recent prevalence of digital broadcasting, various schemes for broadcasting continuous media data, such as music or movies, have been studied. However, most of these studies cannot enable fast-forward operations. That is, when a user fast-forwards data, the client cannot play the data continuously. We propose a scheme to enable fast-forward operations. Our proposed scheme, which is based on the CHB (cautious harmonic broadcasting) scheme, reduces the waiting time of clients under the condition that clients can play the data without interruptions until its end, even when a user fast-forwards it.

In wearable computing environments, a user brings and uses his/her own computer to acquire various services wherever he/she goes. This type of computer, which acts as a service platform for wearable computing, needs autonomy and simplicity of services, flexibility of services/devices configuration, and power saving functions. Since most conventional wearable computing systems do not fulfil all of these requirements, we propose A-WEAR, which is a rule-based wearable computing system. We employ an event-driven rule as a behavior description language of A-WEAR to achieve autonomy and simplicity. Furthermore, we employ a plug-in mechanism to achieve flexibility and power saving. Using our system, we can easily provide and use various services for wearable computing environments.

In this paper we propose a TDMA slot assignment protocol to improve the channel utilization, which controls the excessive increase of unassigned slots by changing the frame length dynamically. Our proposed protocol assigns one of the unassigned slots to a node which joins the network. If there are no unassigned slots available, our proposed protocol generates unassigned slots by depriving one of the multiple slots assigned to a node, or enlarging frame length of nodes which can cause collision with each other. Moreover, by setting frame length as a power of 2 slots, our proposed protocol provides the collision-free packet transmission among nodes with different frame length. The simulation results show that our proposed protocol improves the channel utilization dramatically as compared with the conventional protocols.

In recent years, due to the increasing popularization of various broadcast services, there has been an increasing demand for information filtering techniques. Although filtering methods that have been proposed filter data in their own ways, mathematical representation of these methods does not exist. Consequently, it is not possible to qualitatively evaluate various filtering methods, to optimize processing methods in filtering, or to design a declarative language for filtering processes. In our previous work we have defined a filtering function that represents filtering as a function, and clarified the properties of different filtering methods. In practice, current filtering methods actually consist of multiple methods. In this paper, we make it possible to qualitatively represent those filtering methods by introducing the concept of composition into the framework of filtering function. Moreover, we reveal the characteristics of those combined filtering methods by clarifying the properties of composite filtering functions.

Recently, there has been an increasing interest in the research of push-based information systems that deliver data using broadcast in both wired and wireless environments. In push-based systems, since a server can meet all requests for broadcast data pending in a system with one broadcast, a larger throughput can be expected when there exists a large number of clients. In this paper to reduce the response time of data access, we propose a new scheduling strategy of broadcast program considering an environment where clients issue requests for multiple data items consecutively with think-time. The proposed strategy reduces the average response time by broadcasting the optimal data item at present according to clients' access characteristics such as access frequencies, correlations among data items, and think-time.

As of now, it is not uncommon for one to use multiple computers in separate places such as at home, office or school. A number of applications currently exist to allow a user to easily access and control these computers remotely via a notebook computer or web page. Unfortunately, even with such solutions, it is rather inconvenient, for example, to try accessing your computer while walking downtown or riding a train. On the other hand, considering that cellular phones have been accepted as multi-function devices capable of karaoke, digital photography and web browsing in countries like Japan, it may prove beneficial to support remote PC access on a cellular phone. With this in mind, we created Rajicon, a system to provide an easy to use interface to remotely operate a PC's GUI operating system via a cellular phone. Rajicon supports image based navigation of a remote PC's desktop and mouse/key operations. In addition, Rajicon provides functions for keyboard shortcuts, specialized window adjustment operations and text extraction. We have performed extensive evaluations with five subjects and discuss the results in this paper. We also discuss the lead author's latest adaption of Rajicon to a PDA.

Cellular phones have become popular and have been recognized as light-weight portable computers because of their various advanced functions such as E-mail, WWW browsing, and schedule management. However, since they are too small to display a large amount of information, users cannot make use of them as conveniently as normal computers. To solve this problem, we propose a remote display environment. In a remote display environment, there are large displays every- where in the real world, which we call remote displays. A user makes use of a cellular phone as a remote controller to display information on a remote display. We also describe our implementation of a WWW browsing system as an application in a remote display environment. Moreover, we describe our design and implementation of an access control mechanism by assuming applications in which multiple users simultaneously access one remote display.

Methods for efficient mining of frequent patterns have been studied extensively by many researchers. However, the previously proposed methods still encounter some performance bottlenecks when mining databases with different data characteristics, such as dense vs. sparse, long vs. short patterns, memory-based vs. disk-based, etc. In this study, we propose a simple and novel hyper-linked data structure, H-struct and a new mining algorithm, H-mine, which takes advantage of this data structure and dynamically adjusts links in the mining process. A distinct feature of this method is that it has very limited and precisely predictable space overhead and runs really fast in memory-based setting. Moreover it can be scaled up to very large databases by database partitioning, and when the data set becomes dense, (conditional) FP-trees can be constructed dynamically as part of the mining process. Our study shows that H-mine has high performance in various kinds of data, outperforms the previously developed algorithms in different settings, and is highly scalable in mining large databases. This study also proposes a new data mining methodology, space-preserving mining, which may have strong impact in the future development of efficient and scalable data mining methods.

Dynamic relocation of databases through networks, or database migration, will soon become a powerful standard database operation effectively using recent advances in broadband networks. In our previous work, a transaction processing method has been proposed in distributed database environments, based on database migration operations. Generally, database replication is an effective technique to improve transaction processing throughput in conventional systems. We propose a replica management method for use with database migration. Database migration is used at the beginning of a transaction to dynamically relocate database replicas. The performance of the proposed method is evaluated using simulation results.

This paper describes an e-mail system for wearable computing environments. In this system, we extend the conventional mail format and the server/client(browser) architecture by considering the specific features of wearable computing environments, i.e., full time operation, hands-free use of computer, and close relationship to our daily life. A mail author can specify the behavior of his/her mail by embedding several useful commands in the mail. A user can specify in the mail various conditions as commands such as time, location of the recipient, and status of various sensors to allow an adaptive behavior in the mail. We also describe other features of the system to support user's wearable computing life.

Because of the recent development of network technologies such as ATM (Asynchronous Transfer Mode), broader channel bandwidth is becoming available everywhere in the world wide networks. As one of the new technologies to make good use of such broadband channel, dynamic relocation of databases through networks, which we call database migration, will soon become a powerful and basic database operation of practical use. We discuss our proposal of a distributed database system, DB-MAN (distributed database system based on DataBase Migration in ATM Networks), which takes advantage of database migration in virtual LANs (local area networks) of ATM networks. DB-MAN has two notable mechanisms: a mechanism for selecting the transaction processing method and a mechanism for concurrency control with database migration. The former, is a mechanism which chooses the more efficient method between two transaction processing methods: the conventional method based on the two phase commit protocol and our method employing database migration. The latter is a mechanism to prevent the transaction processing throughput from deteriorating in environments where data contention is a significant factor. Then we show simulation results regarding performance comparison between our proposed system and the conventional distributed database system based on the two phase commit protocol. The obtained results demonstrate that effective use of database migration gives higher performance than that of the conventional system.

Due to recent developments in network technologies, broader channel bandwidth is becoming prevalent in worldwide networks. As one of the new technologies making good use of such broadband channels, dynamic relocation of databases through networks, database migration, will soon be used in practice as a powerful and basic database operation. We propose two transaction processing methods to take advantage of database migration in broadband networks. These methods choose the most efficient transaction processing method between the conventional method, based on the two-phase commit protocol, and our method, using database migration. We also propose a concurrency control mechanism and a recovery mechanism for our proposed methods. Simulation results are presented comparing the performance of our proposed methods and the conventional transaction processing method based on the two-phase commit protocol. The results demonstrate that the effective use of database migration produces better performance than the conventional method.

Deductive databases have the ability to deduce new facts from a set of existing facts by using a set of rules. They are also useful in the integration of artificial intelligence and databases. However, when recursive rules are involved, the number of deduced facts can become too large to be practically stored, viewed or analyzed. This seriously hinders the usefulness of deductive databases. In order to overcome this problem, we propose four methods to discover characteristic rules from a large number of deduction results without actually having to store all the deduction results. This paper presents the first step in the application of knowledge discovery techniques to deductive databases with large numbers of deduction results.

The authors present an extension to the work of I. Suzuki and T. Kasami (see Proc. 3rd Int. Conf. Distributed Compact Syst., p.365-70 (1982)), where a mutual exclusion algorithm uses a message called a token to transfer the privilege of entering a critical region among the participating sites. The proposed algorithm checks whether the token is lost during network failure, and regenerates it if necessary. The mutual exclusion requirement is satisfied by guaranteeing regeneration of only one token in the network. Failures in a computer network are classified into three types: processor failure, communication controller failure, and communication link failure. To detect failures, a time-out mechanism based on message delay is used. The execution of the algorithm is described for each type of failure; each site follows a rather simple execution procedure. Each site is not required to observe the failure of other sites or communication links.>

Two algorithms, control token transfer algorithm (CTTA) and regenerate, are proposed to realize mutual exclusion in a computer network environment using a resilient circulating token. The algorithm CTTA uses a message called token to transfer the privilege of entering a critical region among the participating sites. The algorithm regenerate checks whether the token is lost during system failures, and regenerates it if necessary. Failures in a computer network are classified into three types. The execution of these two algorithms is described for each type of system failure. To detect system failures, a time-out mechanism based on message delay is used.>

The semijoin provides a means of reducing the amount of data transmission among sites in a distributed database system. Previously the semijoin has been studied mainly for reducing communication cost in an environment with global public communication networks. In a local area system, however, wide bandwidth is usually available and the communication cost is virtually negligible. In view of this, we adopt a simplified model of a local area network, imposing no constraint on the transmission line capacity and the communication processing capability at each site. For this model, an efficient algorithm for obtaining the shortest semijoin schedule, in the sense of minimizing the total number of semijoin transmissions, is developed. It is based on a schedule diagram newly introduced to represent the semijoin schedule.

This paper treats the file redundancy issue in distributed database systems, asking what is the optimal number of file copies, given the ratio r of the frequency of update requests to the frequency of all file access requests (i.e., queries and updates). Formulations of this type of problem, including optimal file allocation, have been attempted by a number of authors, and some algorithms have been proposed. Although such algorithms can be used to solve particular problems, it seems difficult to draw general conclusions applicable to a wide variety of practical distributed database systems. To probe into this hard to formulate but interesting problem, our paper constructs simplified network models of distributed database systems, and computes the optimal number of file copies, as well as their locations, to minimize the communication cost. For several network types, we plot the optimal number of file copies as a function of the ratio r.