We have developed a distributed optical fiber strain sensor for detecting the collapse of river embankments. The sensor uses a Brillouin optical time domain reflectometer (BOTDR) and consists of an optical fiber cable and pieces of nonwoven cloth. Pieces of cloth are fixed to the cable at 1.5-meter intervals and it is then embedded in a U-shaped configuration in a river embankment. The pieces of cloth are displaced when there is movement of the soil in which they are embedded. If one of two adjacent pieces of cloth remains stationary while the other moves, the optical fiber between the two pieces is stretched. The collapse of an embankment can be detected by using a BOTDR to monitor any such stretching in the 1.5-m lengths of fiber. The developed sensor operates at a sensitivity of 0.025%/kgf, which is equivalent to 0.067%/mm, and is thus capable of detecting soil movements of a few mm in river embankments. The sensor is also able to provide effective advance warning of the collapse of a river embankment resulting from water penetration. We subjected the sensor system to field tests that demonstrated the effectiveness of its construction and its long-term stability. The developed sensor system is an effective tool for use in river management systems of the very near future.

In modern high-capacity wavelength division multiplexing (WDM) transmission systems, there is increasing demand for large transmission capacity. To achieve this purpose, an L-band (1565-1625 nm) erbium-doped fiber amplifier (EDFA) is very effective method because the conventional silica-based EDF can be used. In EDFAs that used in WDM transmission systems, the gain flatness of EDFA is very important. A passive gain equalizer flattens the gain profile of EDFA. But the gain flatness in L-band deteriorates due to dynamic gain-tilt (DGT) and temperature gain-tilt (TGT) when the operating condition of the EDFA changes, while the EDFAs should maintain the gain flatness even if the operating condition has changed. To solve this problem, we propose an active gain-slope compensation technique for the L-band EDFA using a thulium-doped fiber (TDF). The EDFA actively gain-slope compensated by the TDF compensator keeps the gain profile constant for the wide input power range of more than 8 dB, a wide temperature range of 65 without gain-tilt in a wavelength band between 1575 nm and 1610 nm. Furthermore, the EDFA keeps a low noise figure of less than 7.5 dB.

This paper proposes new recursive fixed-point smoother and filter using covariance information in linear discrete-time stochastic systems. In this paper, to be able to treat the estimation of the stochastic signal, a performance criterion, extended from the criterion in the H estimation problem, is newly proposed. The criterion is transformed equivalently into a min-max principle in game theory, and an observation equation in a Krein space is obtained as a result. The estimation accuracy of the proposed estimators are compared with the recursive least-squares (RLS) Wiener estimators, the Kalman filter and the fixed-point smoother based on the state-space model.

The reverse link bandwidth efficiency of a spectrally overlapped CDMA system with fast transmit power control is evaluated to find the optimum overlapping, where the bandwidth efficiency is defined as the maximum aggregate bit rate of all subsystems per unit bandwidth (bps/Hz). Single and multiple cell environments are considered. Besides the rectangular chip pulse, the impact of a pulse-shaping filter is discussed. It is found that the raised cosine spectrum pulse shaping helps to increase the bandwidth efficiency and strict pulse shaping filter problem can be avoided if a large number of subsystems are overlapped. It is also found that the optimum carrier spacing remains unchanged irrespective of the power delay profile shape of the multipath channel, whether multipath fading exists or not, and whether a single cell or multiple cell system is considered. However, the bandwidth efficiency strongly depends on them and the impacts of the related parameters are discussed.

In this paper, a low-cost radio-on-fiber (ROF) system for a 36 GHz band road-vehicle communication system (RVCS) is proposed and demonstrated. Optical components for 10 Gb/s baseband transmission systems, which are becoming lower in cost, are used for the proposed system. The signal is transmitted in the optical link in the form of an intermediate frequency (IF) signal of the 5.8 GHz band. The third subharmonic of a local oscillator wave (LO) is transmitted simultaneously with the IF signal from the central station to the remote stations (RSs). This scheme enables the realization of RSs without costly millimeter-wave synthesizers. In such a configuration, the influence of intermodulation distortion between the IF signal and the LO subharmonic and degradation of the carrier-to-noise ratio (CNR) could possibly be a problem, and so an analysis and experiments were carried. It was clarified that the compression of dynamic range caused by the simultaneous transmission was small. Frequency tripling of the LO degraded the CNR of the LO; however, this effect was compensated for by increasing the optical modulation index (OMI) of the LO subharmonic. Increasing the OMI of the LO subharmonic proved to have no influence on the IM3 characteristics of the RF signal analytically and experimentally. The proposed low-cost system proved to have sufficient characteristics for millimeter-wave RVCS.

An electronic equivalent to the bank's safe-deposit box service is presented. It is a distributed key safeguarding protocol constructed from an ElGamal threshold cryptosystem. For long-term secrets, a proactive version is also suggested.

Agent-based computing has been advocated by many researchers and software developers as a promising and innovative way to model, design and implement complex Web-related applications. KODAMA (Kyushu university Open & Distributed Autonomous MultiAgent) project, which is described in this paper, is our endeavour to advance both the technology and engineering of well-known multiagent systems. In particular, we have noted that software agents might be the potential solution to many problems faced by today's Web. However, building a high-quality, large-scale multiagent system, which can operate in open environments, is a great challenge. So far, we have devoted a lot of effort to design and implement a generic agent architecture, a hierarchical agent community structure, and an independent network communication middleware. To ensure that KODAMA can be used to create Web-agent applications, its network communication performance and a prototype distributed database retrieval system have been tested. The result shows that KODAMA is suitable for developing network-aware applications.

A parallel file system is normally used to support excessive file requests from parallel applications in a cluster system, whereas prefetching is useful for improving the file system performance. This paper proposes dynamic file prefetching scheme based on file access patterns, named table-comparison prefetching policy, that is particularly suitable for parallel scientific applications and multimedia web services in a VIA-based parallel file system. VIA relieves the communication overhead of traditional communication protocols, such as TCP/IP. The proposed policy introduces a table-comparison method to predict data for prefetching. In addition, it includes an algorithm to determine whether and when prefetching is performed using the current available I/O bandwidth. Experimental results confirmed that the use of the proposed prefetching policy in a VIA-based parallel file system produced a higher file system performance for various file access patterns.

In this paper, we consider a switching system modeled by a discrete-time flow model. By simulation, it is shown that a lot of border-collision bifurcations occur since the system is piecewise linear. By using its characteristics, we classify its dynamics into modes, and we define blocks and a kind of Poincare map based on the modes. We calculate occurrence conditions of each block and all the Poincare points by computer-assisted analysis. We consider two bifurcation phenomena, and we show that a Poincare point hits a boundary of the occurrence conditions of a block. So, both bifurcations are indeed border-collision bifurcations.

We propose a set of Fabry-Perot etalons integrated in a planar lightwave circuit (PLC-FPE) designed for a unified system for broadcasting and communication. A PLC-FPE containing four etalons having different cavity lengths is fabricated and their loss and frequency characteristics are investigated. The total loss and the maximum finesse were found to be 8 dB and 34, respectively.

Spatial multiplexing, or BLAST, is a signaling technique for multiple-input multiple-output (MIMO) channels in which multiple independent data streams are transmitted in parallel in space. The independence between streams, unfortunately, limits the diversity advantage. In this paper we present a space-time code design, using the linear dispersion code framework, for MIMO Rayleigh fading channels. Our design provides codes that have the same ergodic capacity performance as spatial multiplexing but allows for improved diversity advantage. We present a technique for finding good codes based on successive projection. Monte Carlo simulations illustrate performance improvements over spatial multiplexing in terms of bit error probability.

In distributed systems, the provision for failure-recovery is always a hot design issue, whereas no fault-tolerant feature has been extensively considered in the current RMI, CORBA and other OODP environments. As a result, application developers have to implement their own fault tolerant mechanisms. In this paper, we propose a fault-tolerant development environment based on one kind of RMI, called FT_HORB, as a Java extension for the reliable distributed computing with checkpoints and rollback-recovery mechanism. The FT_HORB is implemented on the Sun Ultra10 workstations connected through a 100 Mbps network. We observe that experimental applications on the FT_HORB can continue their operations in spite of hardware and software failures. Three benchmark models such as the nqueens problem, the traveling salesman problem and the gaussian elimination problem are experimented with the FT_HORB to evaluate its performance. The results show the performance of FT_HORB is acceptable. In addition, experiments demonstrate its possibility of extension to fully support our optimal design goal.

We propose a new decidable subclass of term rewriting systems (TRSs) for which strongly normalizing (SN) property is decidable. The new class is called almost orthogonal inverse finite path overlapping TRSs (AO-FPO-1-TRSs) and the class properly includes AO growing TRSs for which SN is decidable. Tree automata technique is used to show that SN is decidable for AO-FPO-1-TRSs.

With the emerging technology of photonic networks, careful design becomes necessary to make most of the already installed fibre capacity. Appropriate numerical tools are readily available. Usually, these are based on the split-step Fourier method (SSFM), employing the fast Fourier transform (FFT). With N discretization points, the complexity of the SSFM is O(N log2N). For real-world wavelength division multiplexing (WDM) systems, the simulation time can be of the order of days, so any speed improvement would be most welcome. We show that the SSFM is a special case of the so-called collocation method with harmonic basis functions. However, for modelling nonlinear optical waveguides, various other basis function systems offer significant advantages. For calculating the propagation of single soliton-like impulses, a problem-adapted Gauss-Hermite basis leads to a strongly reduced computation time compared to the SSFM . Further, using a basis function system constructed from a scaling function, which generates a compactly supported wavelet, we developed a new and flexible split-step wavelet collocation method (SSWCM). This technique is independent of the propagating impulse shapes, and provides a complexity of the order O(N) for a fixed accuracy. For a typical modelling situation with up to 64 WDM channels, the SSWCM leads to significantly shorter computation times than the standard SSFM.

As a center of mobile multimedia of the 21st century, it is very much looking forward to explosion of R&D and business of the next generation of mobile communication systems and the ITS (Intelligent Transport Systems) because ITS will enable information-oriented in the field of the road, traffic and vehicles, by using the most advanced technologies of mobile communications and devices, for the various purposes such as decrease of the traffic accident, the reduction of traffic jam, the increase in efficiency of the logistics and the harmony with the earth environment. This invited paper will first briefly introduce evolution of mobile communications and ITS in ministries, industries and academia in Japan. Then core communication technologies for ITS will be overviewed such as spread spectrum CDMA, adaptive antenna array, and software radio or software defined radio. Demands of SoC (System on a Chip) to carry out the core technologies will be addressed.

Sophisticated and robust resource management is an essential issue in future wireless systems which will provide a variety of application services. In this paper, we employ an adaptive-network-based fuzzy inference system (ANFIS) to control the resource allocation for mobile multimedia networks. ANFIS, possessing the advantages of expert knowledge of fuzzy logic system and learning capability of neural networks, can provide a systematic approach to finding appropriate parameters for the Sugeno fuzzy model. The fuzzy resource allocation controller (FRAC) is designed in a two-layer architecture and selects properly the capacity requirement of new call request, the capacity reservation for future handoffs, and the air interface performance as input linguistic variables. Therefore, the statistical multiplexing gain of mobile multimedia networks can be maximized in the FRAC. Simulation results indicate that the proposed FRAC can keep the handoff call blocking rate low without jeopardizing the new call blocking rate. Also, the FRAC can indeed guarantee quality of service (QoS) contracts and achieve higher system performance according to network dynamics, compared with the guard channel scheme and ExpectedMax strategy.

In this paper, we consider optimal mirror allocation problems for the purpose of load balancing in network servers. We focus on constructing high-reliability networks and propose the optimal mirror allocation model such that the system reliability is maximized subject to costs and delays, in view of the trade-off between the reliability and cost. This optimization model is capable of dealing with various kinds of network topologies, although for simplicity, we assume the read-only situation. We formulate this optimization problem into a 0-1 integer programming model, and we use an approximate method for numerical analysis in order to analyze more large-scale systems. Our objective is to find the optimal mirror allocation by solving this model, and to show quantitatively the general characteristics of the load balancing and the improvement of the system reliability by the distributed mirror allocation.

Recently, Kasahara and Murakami proposed new product-sum type public-key cryptosystems with the Chinese remainder theorem, Methods B-II and B-IV. They also proposed a new technique of selectable encryption key, which is referred to as 'Home Page Method (HP Method).' In this paper, first, we describe Methods B-II and B-IV. Second, we propose an effective attack for Method B-II and discuss the security of Methods B-II and B-IV. Third, applying the HP Method to Methods B-II and B-IV, we propose new product-sum type PKC with selectable encryption key. Moreover, we discuss the security of the proposed cryptosystems.

The C166S V2 is Infineon Technologies' latest generation 16-bit microcontroller core, member of the C166 family. This new core architecture is a huge step forward in performance and DSP capabilities: With its single cycle engine and enhanced MAC unit running at up to 200 MHz it more than doubles the performance of the fastest C166 based controllers (C166S V1) running at the same speed. Furthermore the instruction set is fully compatible with the previous C166 cores. This architecture is specifically suited for real-time embedded systems with high requirements for performance and signal processing functionality with tight cost and power budgets. As a fully synthesizable core, and with a large selection of peripherals available, the C166 V2 provides a straightforward path to the required specific systems-on-chip.

In this paper, we investigate self diagnosable systems on multi-processor systems, known as one-step t-diagnosable systems introduced by Preparata et al. Kohda has proposed "highly structured system" to design diagnosable systems such that faulty processors are diagnosed efficiently. On the other hand, it is known that Cayley graphs have been investigated as good models for architectures of large-scale parallel processor systems. We investigate some conditions for Cayley graphs to be topologies for optimal highly structured diagnosable systems, and present several examples of optimal diagnosable systems represented by Cayley graphs.