This paper describes the concept of an adaptive network, that is, a network environment that can rapidly and autonomously adapt its behavior according to network conditions and traffic status. The user interface of the adaptive network can access any resource in the network as a memory-mapped I/O device, as if it were attached to the local bus of the user's PC. This network concept has several benefits. From the application development viewpoint, no network related programming is required, and applications do not have to be modified even if the network topologies and protocols are changed. Network maintenance and upgrading can be done anytime without having to worry about the application users, because the network itself is concealed from the applications. In addition, the reconfigurable hardware technology functions as an autonomous network control through the use of a lower-layer protocol. We developed a testbed that makes heterogeneous resources available to users and used it to demonstrate the feasibility of our concept by implementing and running some applications over it.

We analyzed the performance of adaptive array antennas with a RAKE receiver by employing a common correlation matrix of the sample matrix inversion (CCM-SMI) algorithm in a multipath Rayleigh fading environment for W-CDMA reverse link. A common correlation matrix is usually used to provide adaptive weights for multiple users and multiple delay paths and can be used in packet communications transmitted using frame units. The proposed CCM-SMI algorithm had a better BER and SINR for lower computational complexity compared with the conventional SMI algorithm, even when using a RAKE receiver in multipath Rayleigh fading environment.

In order to assess the possible impacts of meteors with spacecraft, which is among major hazard in the space environment, it is essential to establish an accurate statistics of their mass and velocity. We developed a radar-optical combined system for detecting faint meteors consisting of a powerful VHF Doppler radar and an ICCD video camera. The Doppler pulse compression scheme is used to enhance the S/N ratio of the radar echoes with very large Doppler shifts, as well as to determine their range with a resolution of 200 m. A very high sensitivity of more than 14 magnitude and 9 magnitude for radar and optical sensors, respectively, has been obtained. Instantaneous direction of meteor body observed by the radar is determined with the interferometry technique. We examined the optimum way of the receiving antenna arrangements, and also of the signal processing. Its absolute accuracy was confirmed by the optical observations with background stars as a reference. By combining the impinging velocity of meteor bodies derived by the radar with the absolute visual magnitude determined by the video camera simultaneously, the mass of each meteor body was estimated. The developed observation system will be used to create a valuable data base of the mass and velocity information of faint meteors, on which very little is known so far. The data base is expected to play a vital role in our understanding of the space environment needed for designing large space structures.

In this paper, we propose a new clock tree synthesis method for semi-synchronous circuits. A clock tree obtained by the proposed method is a multi-level multi-way clock tree such that a clock-input timing of each register is a multiple of a predefined unit delay and the wire length from a clock buffer to an element driven by it is bounded. The clock trees are constructed for several practical circuits. The size of constructed clock tree is comparable to a zero skew clock tree. In order to assure the practical quality of the clock trees, they are examined under the five delay conditions, which cover various environmental and manufacturing conditions. As a result, they are proved stable under each condition and improve the clock speed up to 17.3% against the zero skew clock trees.

A great deal of effort has been concentrated on the longitudinal control for the collision avoidance of moving vehicles. In an emergency as well as in a normal situation, however, the steering control can be a very effective alternative as observed in the practice of manual evasive driving. In the reported methods of steering control, it is found that the dynamic motions of the neighboring vehicles are often ignored, which may result in some danger of 2nd collision. Therefore, it is necessary to assess the surrounding traffic situation to prevent 2nd collision that can occur just after escaping from the 1st collision situation. In this paper, we tackle the collision avoidance problem when steering actuation control is allowed in consideration of the dynamic motion of the neighboring vehicles. Specifically, a hierarchical control scheme is suggested as a feasible solution, and the proposed system is verified via simulation using a software simulator called DevACAS (DEVeolper of Active Collision Avoidance System), which we have developed.

The processes observed in a sound environment inevitably contain additional external noise of arbitrary distribution. Furthermore, the actual sound environment system exhibits various types of linear and non-linear characteristics, and it often contains an unknown structure. In this paper, a method for estimating the input signal for a sound environment system with unknown structure and additive noise of arbitrary probability distribution is proposed by introducing a system model of the conditional probability type. The effectiveness of the proposed theoretical method is confirmed experimentally by applying it to the actual problem of input estimation of the sound environment.

Despite their attractive properties, networked virtual environments (net-VEs) are notoriously difficult to design, implement and test due to the concurrency, real-time and networking features in these systems. The current practice for net-VE design is basically trial and error, empirical, and totally lacks formal methods. This paper proposes to apply a Petri net formal modeling technique to a net-VE: NICE (Narrative Immersive Constructionist/Collaborative Environment), predict the net-VE performance based on simulation, and improve the net-VE performance. NICE is essentially a network of collaborative virtual reality systems called CAVE-(CAVE Automatic Virtual Environment). First, we present extended fuzzy-timing Petri net models of both CAVE and NICE. Then, by using these models and Design/CPN as the simulation tool, we have conducted various simulations to study real-time behavior, network effects and performance (latencies and jitters) of NICE. Our simulation results are consistent with experimental data.

Meteor storms and showers are now considered as potential hazard in the space environment. Radar observations of meteors has an advantage of a much higher sensitivity over optical observations. The MU radar of Kyoto University, Japan has a unique capability of very fast beam steerability as well as a high sensitivity to the echoes from ionization around the meteors. We developed a special observation scheme which enables us to determine the orbit of individual meteors. The direction of the target is determined by comparing the echo intensity at three adjacent beams. The Doppler pulse compression technique is applied to improve the signal-to-noise ratio of the echoes from the very fast target, and also to determine the range accurately. The developed scheme was applied to the observation made during the Leonid meteor storm on November 18, 1998 (JST). Estimated orbital distribution seems to suggest that the very weak meteors detected by the MU radar are dominated by sporadic meteors rather than the stream meteors associated with the Leonids storm.

In order to realize universal service access of mobile users on the global telecommunication environment, we have to consider the scalable networking architecute based on the distributed object computing technologies. In this paper, we apply TINA to the promising networking architecture, and propose TINA-based scalable model for realizing personal mobility service, which especially focuses on making access to telecommunication services from any legacy systems that do not support such the new environment, using a downloadable module in an end terminal, as well as considering load balance of a whole system. Our proposed model also focuses on exchanging personal infomation of mobile users between different administrative domains, by separating the already-specified user profile information objects into two parts, which are the domain-common part and domain-specific part, and propose secure exchange procedure.

This paper presents upper bounds on the average bit error rate (BER) of coherent detection of PSK and differential detection of DPSK with adaptive arrays in fading environments. A model where a line of sight (LOS) component and Rayleigh distributed scattering components arrive at a receiver with specific arrival angles is used considering the correlation of signal between multiple antennas. The upper bounds are expressed in a simple matrix form using signal and interference-plus-noise correlation matrices. Examples for the case of 4-element adaptive arrays are given to illustrate the tightness and the application of this upper bounds.

This paper discusses and clarifies effectiveness of data-driven implementation of protocol handling system to access TINA (Telecommunications Information Networking Architecture) network and internet. TINA is a networking architecture that achieves networking services and management ubiquitously for users and networks. Many TINA related ACTS (Advanced Communication Technologies and Services) projects have been organized in Europe. In Japan, The TINA Trial (TTT) to achieve ATM network management and services based on TINA architectures was done by NTT and several manufactures from April 1997 to April 1999. In these studies and trials, much effort is devoted to development of software based on service architecture and network architecture being standardized in TINA-C (TINA Consortium). In order to achieve TINA environment universally in customers and network sides, we have to consider how to deploy TINA environment onto user side and how to use access transmission capacity as efficiently as possible. Recent technology can easily achieve application and environment downloading from the network side to user side by use of e. g. , JAVA. In accessing the network, there are several possible bottlenecks in information exchange in customer side such as PC processing capability, access protocol handling capability, intra-house wiring bandwidth. Authors, in parallel with TINA software architecture study, have been studying versatile requirements for hardware platform of TINA network. In those studies, we have clarified that the stream-oriented data-driven processor authors have been studying and developing have high reliability, high multiprocessing and multimedia information processing capability. Based on these studies, this paper first shows Von Neumann-based protocol handler is ineffective in case of multiprocessing through mathematical and emulation studies. Then, we show our data-driven protocol handling can effectively realize access protocol handling by emulation study. Then, we describe a result of first step of implementation of data-driven TCP/IP protocol handling. This result proves our TCP/IP hub based on data-driven processor is applicable not only for TINA/CORBA network but normal internet access. Finally, we show a possible customer premises network configuration which resolves bottleneck to access TINA network through ATM access.

This paper describes a transaction model for open environments based on mobile agents. Mobile agent-based transactions combine mobility and the execution of control flows with transactional semantics. The model presented represents an approach for providing reliability and correctness of the execution of distributed activities, which fulfills important requirements of applications in Open Environments. The presented transaction model is based on a protocol for providing fault tolerance when executing mobile agent-based activities. This protocol is outlined in this paper. With this protocol, if an agent executing an activity at an agency (logical "place" in a distributed agent environment) becomes unreachable for a long time, the execution of the activity can be recovered and continue at another agency. The fault tolerance approach supports "multi-agent activities," i. e. , activities where some of its parts are spawned to execute and migrate asynchronously in relation to other parts. The described transaction model, called the basic (agent-based) transaction model, is an open nested transaction model. By being based on the presented fault tolerance mechanism, subtransactions can be executed asynchronously in relation to their parent transactions and agent-based transactions can explore alternatives in the event of agent unavailability. The model fulfills requirements for supporting the autonomy of organizations in a distributed agent environment.

The long spikes have been often recorded at the multiples of the electron cyclotron frequency in the ionograms of the topside sounders observed in low latitudes. There has not been sufficient explanation for the physical cause for occourrence of the long spike so far. Here, by interpreting this phenomenon as receiving the trapped cyclotron harmonic wave, some analyses for the length of spike are done not only from the viewpoint of the sweeping property of the frequency spectrum of the transmitted pulse but also from that of the mutual positional relation between the propagation path and the orbit of the sounder. The cause of forming a single spike and a graphical calculation method for the long spike are proposed, respectively. Thus, the cause and the fine structure of long spike consisting of superposed spikes are clarified.

The construction of photo-realistic 3D scenes from video data is an active and competitive area of research in the fields of computer vision, image processing and computer graphics. In this paper we address our recent work in this area. Unlike most methods of 3D scene construction, we consider the generation of virtual environments from video sequence with a video-cam's forward motion. Each frame is decomposed into sub-images, which are registered correspondingly using the Levenberg-Marquardt iterative algorithm to estimate motion parameters. The registered sub-images are correspondingly pasted together to form a pseudo-3D space. By controlling the position and direction, the virtual camera can walk through this virtual space to generate novel 2D views to acquire an immersive impression. Even if the virtual camera goes deep into this virtual environment, it can still obtain a novel view while maintaining relatively high resolution.

When a micromachine works inside a narrow space inside tubes and equipment such as a microfactory, a microdevice that has a visual function is indispensable. To monitor the minute shapes of microfabrication and microassembly process that are impossible to observe, fiber-optic sensors and actuators for environmental recognition devices have been developed. The devices are designed to allow stereoscopic and microscopic observation and to measure the dimensions of microparts. To achieve these goals and to realize minute structures and functions, we developed environmental recognition devices for microfabrication process with functions of far and near field observation, tactile sensing and tip articulation, for microassembly process with functions of stereoscopic observation and tip articulation. The results show that easy and safe environmental recognition is possible in the narrow spaces of a microfactory.

For a wireless communication system to work effectively without interference, the electromagnetic environment needs to be controlled. We experimentally and analytically investigated the requirements for controlling the electrical field strength and delay spread so as to achieve the best communication without electromagnetic interference in selected regions for a 2.4-GHz-band wireless LAN system. To control the coverage, partitions were placed around desks in a test environment and covered on the inside with electromagnetic absorbing board from the top of the desks to the top of the partitions; four indoor environments that combined one of two wall-material types and one of two partition heights were used. The transmission loss and delay spread were measured, then calculated using ray tracing to verify the effectiveness of using ray-tracing calculation. The throughput and BER characteristics were measured for the same environments to clarify the requirements for controlling the coverage. We found that covered and uncovered regions could be created by using partitions with absorbing boards and that the delay spread must be less than 15 ns and the received-signal must be stronger than -75 dBm for a region to be covered. We verified that the delay spread can be calculated to within 5 ns and the received-signal level can be calculated to within 5 dB of the measured data by using ray tracing. Therefore, ray tracing can be used to design antenna positions and indoor environments where electromagnetic environments are controlled for 2.4-GHz-band wireless LAN systems.

Recently, optical loss increases have appeared at high temperatures in some of the optical drop cables, introduced for FTTH field experiments. Optical drop cable is installed from homes to aerial facilities, and consists of an optical fiber cable part and a self-supporting wire part. Fiber micro-bending is caused by cable sheath buckling in high temperature environments when the cable is bent with the cable part inside. Moreover, adhesion between the steel reinforcing wires and the cable sheath is effective in preventing this fiber micro-bending, which induces loss increases. This paper also shows the most suitable range of adhesive ability in terms of both practical construction and environment.

Wireless communication systems are affected by several factors in the indoor environment. The complexity of this environment, however, has hampered the development of methods for analyzing it. Reported here is our investigation of the relationship between the propagation characteristics and performance of a 2.4-GHz ISM-band wireless LAN in various indoor environments. Our objective was to develop guidelines for designing ideal indoor environments for wireless LANs. A booth constructed of a ceiling, floor, and wall materials that could be changed was used for our investigation. The transmission loss and delay spread were measured for four environments; they were calculated by using a ray-tracing method to verify the effectiveness of the ray tracing calculation. The throughput and BER characteristics were measured for the same environments. The following results were obtained. (1) The transmission loss and delay spread could be estimated by using this ray tracing method because the deviations between the calculated and measured data were within 5 dB for the transmission loss and within 10 ns for the delay spread. (2) Reflections from the walls caused a serious interference problem: throughput was 0.0 at more than 30% of the positions along the center line of the booth when the walls were constructed of high-reflection-coefficient material. (3) The throughput and BER were closely correlated with the delay spread; the number of positions meeting a certain throughput was estimated by the method based on the delay spread calculated using the ray tracing method. It was within 10% of the number measured. The results obtained can be used to design ideal indoor environments for 2.4-GHz ISM-band LAN systems.

In the domains involving environmental changes, some knowledge and heuristics which were useful for solving problems in the previous environment often become unsuitable for problems in the new environment. This paper describes two approaches to solve such problems in the context of case-based reasoning systems. The first one is maintaining descriptions of applicable scopes of cases through generalization and specialization. The generalization is performed to expand problem descriptions, i. e. descriptions of applicable scopes of cases. On the other hand, the specialization is performed to narrow problem descriptions of cases which failed to be applied to given problems with the aim of dealing with environmental changes. The second approach is forgetting, that is deleting obsolete cases from the case-base. However, the domain-dependent knowledge is necessary for testing obsolescence of cases and that causes the problem of knowledge acquisition. We adopt the strategies used by conventional learning systems and extend them using the least domain-dependent knowledge. These two approaches for adapting the case-base to the environment are evaluated through simulations in the domain of electric power systems.

We propose a query processing method for amalgamated knowledge bases. Our query processing method is an extension of the magic sets technique for query processing in amalgamated knowledge bases, augmented with the capabilities of handling amalgamated atoms. Through rewriting rules in a given amalgamated knowledge base, our method offers the advantages associated with top-down as well as bottom-up evaluation. We discuss how to handle amalgamated atoms, consider how to check whether an amalgamated atom is satisfiable in a fact set and how to extend a fact set by inserting an amalgamated atom. We also give the transformation procedures for amalgamated knowledge databases and show the correctness of our method.