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

OLSRv2 is being standardized in the IETF MANET (Mobile Ad hoc Network) working group. OLSRv2 uses the common packet format, that is also being standardized in the MANET WG. It is necessary to validate the OLSRv2 protocol specification by implementing OLSRv2. In addition, OLSRv2 has a great capability to reduce message size compared to OLSR. This is due to address compression. The change of control message size directly affects the total network performance, but how much it affects the various parameters are dependent on the network scale, number of nodes, and address compression implementation. In this context, we have implemented the OLSRv2 protocol, which can run as a real-time protocol or in the QualNet simulator. In addition, we added link disconnection feedback function from MAC layer to OLSRv2 modifying wireless LAN device driver. In this paper our OLSRv2 implementation detail is introduced, and OLSRv2 performance is compared with OLSR by using both a 50 node testbed built in Niigata university and also in the Qualnet simulator. In addition, IP address compression effect is analyzed in the simulator, and the performance of OLSRv2 with link layer disconnection feedback is evaluated in the testbed. Copyright 2007 ACM.

DOI： 10.1145/1280940.1280955

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

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Other Link： http://hdl.handle.net/10191/9089

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

DOI： 10.11348/reajshinrai.28.3_205

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Language：Japanese  

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

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Other Link： http://hdl.handle.net/10191/6536

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

It has been reported in several studies that the probability distribution functions for interarrival times of tasks in multimedia systems cannot be represented by traditional probability distribution functions, such as exponential ones. In this paper we propose an approximation method, based on the Coxian distribution function, to calculate the probability distribution functions used in analyzing multimedia systems. Although the Coxian function can represent arbitrary distribution functions, it is difficult to determine their parameters directly from a given distribution function. In this work, this drawback is remedied by first approximating the given distribution function with a linear combination of Erlang function, and then converting it to a Coxian function. We also present examples of the approximation and evaluate its accuracy. ©2004 Wiley Periodicals, Inc.

DOI： 10.1002/scj.10446

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

This paper provides an extension of the approximation method proposed in the literature [1]-[2], using the Coxian distribution. In the existing method, the probability distribution functions with the monotonic decreasing property can be approximated. The method proposed in this paper uses the combination of hyper-exponential distribution and Erlang distributions, and enables to approximate non-monotonous distributions. We also present some examples to show the usefulness of the approximate method.

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

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Other Link： http://hdl.handle.net/10191/6552

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

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Other Link： http://hdl.handle.net/10191/25835

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

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Other Link： http://hdl.handle.net/10623/28442

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

The rendering cost of the VR space can be reduced efficiently by selecting appropriate fineness of the shape for the observing distance without loss of drawing quality. We proposed a multi-scale modeling method that controls the fineness of the shape locally by dividing space to octree model. Though Marching-Cubes method is known as the way of forming patches in octant, there is a problem that a crack is created between the adjoining patches when the class level of them are different. In this paper, we describe an efficient and inconsistent surface patching method without any additional procedure like the crack-stitching method.

DOI： 10.11485/itetr.26.35.0_31

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

This paper describes a design of group synchronization mechanism for local area network virtual environment and introduces a step synchronization mechanism. We use a football game for evaluate this mechanism. In this football game, users can share a virtual space in where they can move around, dribble and shot. To achieve synchronization among users, a client of the game exchanges data through a server within a certain period time. A problem of such a system is that all users should share the space in the same time for justice competition. But because of the different of capacity of computers and time cost by the communication between clients, it is difficult for all clients to update the virtual space simultaneity. In our systems, we introduce a waiting time synchronization mechanism. To evaluate our proposed architecture and mechanisms, we make a series of experiments in our local area network and then build and analyses the model of our system.

DOI： 10.1109/KMN.2002.1115158

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：THE VIRTUAL REALITY SOCIETY OF JAPAN  

This paper describes a multi-scale modeling method that can display the wide VR space with enhancing the reality. We divide the object existing space into cubes hierarchically, and control the fineness of object shape by the parameter that indicates the complexity value of object shape. Utilizing this parameter, the object shape is simplified smoothly relative to the viewing distance. Moreover, the high-quality and high-reality VR space can be presented because the expression of the detailed shape of corresponding with the viewing distance can be realized. We showed the validity of the multi-scale modeling method in the high-reality wide VR space that has huge quantities of data.

DOI： 10.18974/tvrsj.6.4_281

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Other Link： http://hdl.handle.net/10191/25842

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

This paper considers faults in distributed real-time systems modeled by queuing networks
in particular, a fast method of analysis of transient variation of system performance is proposed. This method involves analyzing queuing networks by means of the tagged-task model. Such an analysis requires repetitive determination of the limit-state probability at varied initial values
however, the computation time can be reduced by using the absorption probability (the probability of arriving at the absorption state). In addition, a fast algorithm is proposed to calculate absorption probability, in which the state set is split into cosets according to arrivability, and the cosets are replaced by representatives as soon as the state probability becomes low. Finally, the effectiveness and accuracy of the proposed method are verified by actual examples. © 2001 Scripta Technica, Syst Comp Jpn.

DOI： 10.1002/scj.1085

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：THE VIRTUAL REALITY SOCIETY OF JAPAN  

This paper describes a multi-scale modeling method that can display the wide VR space with enhancing the reality. We divide the object existing space into cubes hierarchically, and control the fineness of object shape by the parameter that indicates the complexity value of object shape. Utilizing this parameter, the object shape is simplified smoothly relative to the viewing distance. Moreover, the high-quality and high-reality VR space can be presented because the expression of the detailed shape of corresponding with the viewing distance can be realized. We showed the validity of the multi-scale modeling method in the high-reality wide VR space that has huge quantities of data.

DOI： 10.18974/tvrsj.6.4_281

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Other Link： http://hdl.handle.net/10191/25842

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

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

Several probability distribution functions such as exponential distribution function have been used to represent the task arrival process and processing time of tasks for multimedia systems. These distribution functions are simple, memory less, and easy-to-use, however,they are difficult to represent the task arrival process of multimedia stream data or audio data having real-time properties.
This paper proposes a method for obtaining approximate probability distribution functions for given task arrival process for multimedia systems by using the Cox distribution function. The Cox distribution function can represent arbitrary distribution functions but their parameters are difficult to be determined for representing the given function. In the method, first, an objective probability distribution function is approximated by a linear combination of exponential distribution functions and Erlan distribution functions, then the parameters of the Cox distribution function is determined from the linear combination of the functions obtained above. The examples of the approximations show that the method is effective for approximating given prpbability distribution functions.

DOI： 10.1109/PRDC.2001.992717

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

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Other Link： http://hdl.handle.net/10623/28445

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

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley and Sons Inc.  

This paper presents a method for obtaining the probabilities of absorbing states in a Markov chain for a tagged-task model having a small number of absorbing states and a large number of transient states. In the method, the states are first divided into cosets based on reachability between states of the chain
then the cosets are divided into subsets recursively to reduce the memory size required for computation. During the computation of probabilities, cosets are aggregated to a representative when the state probabilities are smaller than a given threshold value in order to reduce computation time. This paper also gives an example of the analysis. Errors, memory size, and computation time for the method are compared with those for the corresponding method without any divisions and aggregations. © 1998 Scripta Technica.

DOI： 10.1002/(sici)1520-684x(19980630)29:7<41::aid-scj5>3.0.co;2-i

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

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

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

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

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

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

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

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

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Language：English  

Fish-eye cameras (cameras with a fish-eye lens) have a very wide view angle of about 180° and a great depth of field, Therefore, it is possible to take pictures of broad scenes with a fixed posture, and it is suitable for uses like 3D modeling and surveillance cameras for indoor and outdoor environments. Geometrical and optical calibration of the internal parameters are necessary for improvement of the measuring accuracy in the real world. In this paper, we address the geometrical calibration problem. Some geometrical methods for calibration of the internal camera parameters of fish-eye cameras force the eye camera into a perspective model that is not applicable in wide views of 180° or more. We propose a calibration method using spherical projection and projection models, which combine the projection function of the fish-eye lens and geometrical distortion models. Pur method can perform calibration quickly and with high accuracy by using patterns of horizontal and vertical parallel lines shown on a liquid crystal display (LCD), which can display such patterns with high accuracy. We show the effectiveness of our method by an experimental evaluation with a fish-eye camera of orthographic projection type, which obtains high resolution near the edges of the imaging area. © 2007 Wiley Periodicals, Inc.

DOI： 10.1002/scj.20685

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

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

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

Network systems processing multimedia data having real-time properties should satisfy given limits for not only average delay time but the variance of it (jitter). This paper proposes a method for evaluating network systems based on delay-jitter analysis using Generalized Stochastic PetriNets (GSPN). Systems are modeled by GSPN, and average delay time and its variance are calculated by using equations derived from a Markov chain of the GSPN model. The paper also shows an example of analysis for a client-server system. The result shows that the average delay time and jitter can be obtained easily, and the method is effective for evaluating network systems.

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

The rendering cost of the VR space can be reduced efficiently by selecting appropriate fineness of the shape for the observing distance without loss of drawing quality. We proposed a multi-scale modeling method that controls the fineness of the shape locally by dividing space to octree model. Though Marching-Cubes method is known as the way of forming patches in octant, there is a problem that a crack is created between the adjoining patches when the class level of them are different. In this paper, we describe an efficient and inconsistent surface patching method without any additional procedure like the crack-stitching method.

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Language：Japanese  

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

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Language：Japanese   Publisher：日本信頼性学会  

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

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Language：Japanese   Publisher：日本バ-チャルリアリティ学会  

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

This paper presents a method for analyzing the dynamic performance of distributed real-time systems. A tagged-task-model is used for analyzing the systems represented by queuing networks. And task loss ratio when a processor fault occurs is calculated using absorption probabilities of the model. In order to reduce the time required for calculating probabilities, the set of states of the model is partitioned into cosets based on the reachabilities between states, and the elements in the cosets are aggregated to one state when the sum of the state probabilities in a coset becomes less than the given threshold value. The proposed method is evaluated by the computational complexity for calculating the probabilities. This paper also shows an example of analysis, and errors in the analysis is compared with that when aggregations are not made.

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