Showing papers by "Shojiro Nishio published in 2003"

Dynamic TDMA slot assignment in ad hoc networks

Abstract: 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.

Data replication methods based on the stability of radio links in ad hoc networks

Abstract: To improve data accessibility in ad hoc networks, we have proposed a few methods of replicating data items on mobile hosts by considering the data access frequencies from mobile hosts to each data item and the network topology. In this paper, we consider the stability of radio links among mobile hosts to enhance our previously proposed methods. We show that the newly proposed methods are more efficient by simulation results.

Cache Invalidation for Updated Data in Ad Hoc Networks

Abstract: Recent advances in computer and wireless communication technologies have led to an increasing interest in ad hoc networks which are constructed of only mobile hosts. In this paper, we propose two cache invalidation methods in ad hoc networks where each data item is updated at inconstant intervals. In the first method, when a mobile host holding an original data item updates the data item, it broadcasts an invalidation report to all connected mobile hosts. In the other method, when two mobile hosts are connected, they rebroadcast invalidation reports received before to newly connected mobile hosts. Our proposed methods reduce the number of accesses to invalid cached data items which have been updated and the number of roll backs caused by such invalid accesses. We also show the results of simulation experiments regarding the performance evaluation of our proposed methods.

Realizing a visual marker using LEDs for wearable computing environment

Abstract: In order to utilize the real world via computers by means of camera images in augmented reality systems, the concise coordinate information of the systems must be identified. Image-based approaches are promising for this purpose since they provide direct mapping from the camera images to the coordinate system for virtual objects, and therefore, no camera calibration is necessary. However, the conventional image-based markers are typically stickers, and the information they deliver is limited and susceptible to change dynamically. In this paper, we propose a location marking method, called VCC (visual computer communication), which uses more intelligent markers. In our method, a marker, consisting of 16 LEDs (light-emitting diodes), keeps blinking to provide both coordinate information and attached information such as an address or a URL.

On functional properties of information filtering

Abstract: With the widespread use of satellite broadcasting and data broadcasting, the kind and amount of broadcast content are increasing rapidly. In an environment in which large amounts of data are received, it is very difficult for the user to locate the necessary data, and it is desirable to develop a filtering method that can automatically extract only the necessary data. A large number of filtering methods for such a purpose have been proposed. However, the mathematical basis for the qualitative representation of these methods has not been established, and there is as yet no method for qualitative evaluation and optimization of the method and no design of a declarative language for filtering. In this paper, filtering is defined as a function. By representing the properties of various filtering methods as conditions to be satisfied by the function, a mathematical basis for information filtering is established. The relations among the properties of the filtering methods are analyzed by identifying the inclusive relations among the constraints representing various properties. On the basis of the mathematical basis discussed in this paper, real filtering methods are classified. By selecting processing matched to the required properties, more efficient filtering will be realized. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(11): 37–49, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10199

Scheduling methods based on data division for continuous media data broadcast

Abstract: Recently, various schemes have arisen to broadcast continuous media data such as audio and video. Some of them have focused on reducing clients' waiting time under the continuity condition, i.e., to play data completely without any interruptions. These schemes usually employ multiple channels to broadcast continuous media data. However, receivers of many existing broadcast systems such as those equipped with wireless LAN or Bluetooth cannot receive data from multiple channels concurrently. In this paper, we propose and evaluate a scheduling scheme to reduce the waiting time of clients with a single channel.

Composition of filtering functions

Abstract: 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.

A portable electric bass using two pdas

Abstract: The DoublePad/Bass is a musical instrument that consists of two PDAs with touch panel displays. A user holds a PDA in each hand as if playing an electric bass. The left hand specifies a note on one PDA and the right hand touches the touch panel of the other PDA to generate a sound. Musicians who can play an electric bass should be easily able to play the DoublePad/Bass.

Realization of personalized presentation for digital contents based on browsing history

Abstract: Recently, the tremendous amount of information is digitalized and becoming available on the World Wide Web. These digital contents are nowadays easily accessible to a lot of Internet users. However, most web sites today are comprised of a large number of web pages and hyperlinks, often making it difficult for visitors to browse through and to find their desired information quickly. To address the problem, this paper proposes a newly web site personalization method by utilizing content browsing history. Web sites based on our model consist of a set of small components, and browsing history considered as visitor's preference is used to identify components to be presented on a web page.

Telecontrol of ultra-high voltage electron microscope over global IPv6 network

Abstract: Osaka University has an ultra-high voltage electron microscope (UHVEM) which can provide high quality specimen images for worldwide researchers. For usability improvements, we have worked on telecontrol of the UHVEM. We introduce a part of our activities on the telecontrol of the UHVEM. In order to remotely control the microscope, we must provide high quality dynamic images of the specimen with low latency to the remote site. We have used DVTS for image transfer. In iGrid2002, we transported DV streams over global IPv6 networks from the UHVEM in Osaka, Japan, to the National Center for Microscopy and Imaging Research in San Diego and iGrid2002 conference venue in Amsterdam, Holland. This experiment shows the availability of current IPv6 networks and the new possibility of future IPv6 networks. We also describe our current telecontrol system and future work.

Scheduling correlated broadcast data considering access frequencies with temporal variations

Abstract: 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.

Scheduling methods for broadcasting multiple continuous media data

Abstract: Recently, various schemes for broadcasting continuous media data such as music or movies have been studied. These schemes reduce the waiting time for playing the data under the continuity condition, i.e., playing continuous media data without any intermittence until the end of the data. These schemes usually employ multiple channels to broadcast the data. However, most clients are not able to receive data from multiple channels concurrently. In this paper, we propose methods for reducing client waiting time for multiple data via a single channel. In our proposed methods, we divide each data into several segments and produce a schedule that includes the first segment of each data more frequent than the rest. By changing the number of segments according to the playback ratio, client waiting time is effectively reduced.

A System for Generating Background Scenes of Karaoke Using an Active Database System

Abstract: In recent years, it has become popular to use multimedia data for building presentations. In cases of real-time contents are built, a powerful mechanism is necessary for extracting materials suited to the situation from a large amount of multimedia data. In this study, as an example of such a mechanism, we constructed the Active Karaoke system, which generates background scenes for karaoke using an active database. An active database is a database system that processes prescribed actions automatically in response to the occurrence of an event. We show that Active Karaoke can extract appropriate multimedia data from the database in response to the change of music tones and contents of lyrics, and display them as background scenes. Since an active database is used for storing and managing data, the system behavior can be easily and flexibly described using ECA rules, which are the behavior description language of an active database.

A System for Presenting Background Scenes of Karaoke using an Active Database System.

Abstract: In recent years, it has become popular to use multimedia data for building presentations. In cases of real-time contents are built, a powerful mechanism is necessary for extracting materials suited to the situation from a large amount of multimedia data. In this study, as an example of such a mechanism, we constructed the Active Karaoke system, which generates background scenes for karaoke using an active database. An active database is a database system that processes prescribed actions automatically in response to the occurrence of an event. We show that Active Karaoke can extract appropriate multimedia data from the database in response to the change of music tones and contents of lyrics, and display them as background scenes. Since an active database is used for storing and managing data, the system behavior can be easily and flexibly described using ECA rules, which are the behavior description language of an active database.

Design and implementation of an active database system for receiving broadcast data

Abstract: Satellite-based data broadcasting has been the focus of increasing attention in recent years due to launches of new broadcasting or communications satellites and the initiation of new services. The popularization of these kinds of broadcasting systems has led to a dramatic increase in both the broadcast volume and types of services. As a result, a system is needed that will enable an ordinary user to efficiently extract, store, and reuse required information from the massive amount of data that is broadcast. In response to this request, the authors propose a super active database system (SADB) and describe its design and implementation. The proposed SADB is an adaptation of an active database, which is an event-triggered database, to a broadcasting system. Since the SADB must quickly process the massive amount of data that is sent to it, the reception actions and reception data processing were designed independently of the rule processor. This paper evaluates the performance of an implemented system and shows the data volume that it can handle. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 86(9): 87–99, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.10111

Dynamic construction mechanism of a trigger graph on active databases in mobile computing environments

Abstract: As a result of the rapid development of wireless communications and computer hardware technologies, we can now access various information anywhere using handy terminals. To support the integrative use of data held by mobile hosts in this environment, we proposed the AMDS (Active Mobile Database System) as the kernel system for data management. The behavior definition language of this system, ECA (event-condition-action) rules, has a high description capability that enables users to define complicated behavior. However, the execution of the ECA rules may fall into a chain of unexpected behaviors. In general, a directed graph, called a trigger graph, is used for detecting chains. Since the trigger graph highly depends on network topology, it is difficult to employ the trigger graph in a mobile computing environment. In this paper, we propose a method that reconstructs the trigger graph dynamically to adapt to changes in network topology. Using this mechanism, mobile applications with ECA rules can be used more safely.

A web contents sharing system with contents delivery control functions

Abstract: In this paper, we propose a web contents sharing system which allows a user to save web contents presented on internet and share them on P2P (peer to peer) network. In this system, a user can use the URL, the last update date and time, the size or some other information in order to search web pages. In addition, a user can get web pages that have existed and do not currently exist if they are stored in other systems. Furthermore, we realized a mechanism for authors to control contents delivery, such as the prohibited of forwarding the contents and notification to the authors on forwarding contents. Keyword Peer-to Peer, Web, Date Sharing, Contents Delivery, Delivery Control

Design and Implementation of Tools with Monitoring and Tuning Mechanisms for Scheduling and Caching Strategies in Push-based Broadcast Systems

Abstract: Recently, there has been an increasing interest in research of push-based information systems that de- liver data using broadcast in both wired and wireless envionments. In this paper, we design server and client tools with monitoring and tuning mechanisms for scheduling and caching strategies in push-based broadcast systems. These tools enable server administrators and client users to monitor visually the behavior of the system and the perfomance criterias such as response time and to tune scheduling and caching strategies based on the monitoring results. As a result, they can improve the performance of the system according to the system environment and each user's requirements. We also describe our implementation of the prototypes of the designed tools.

An Adaptive Query Processing Method according to System Environments in Database Broadcasting Systems.

Abstract: In the recent evolution of wireless communication technology, there has been an increasing interest in the database broadcasting system where a server periodically broadcasts contents of a database to mobile clients such as portable computers and PDAs. There are three query processing methods in the database broadcasting system: the on-demand method, the client method, and the collaborative method which we have proposed. The performance of these methods is strongly affected by environmental conditions such as query generation intervals and size of query results. Since the system condition keeps changing, it is difficult to choose the optimal method statically. In this paper, we propose an adaptive query processing method which dynamically chooses a method which gives the best performance at the moment. Our method chooses a method according to query generation intervals in order to reduce the response time and to increase the query success rate. We also show simulation results regarding performance evaluation of our method.