The field supported by multilayered periodic waveguides is well characterized by only one or two discrete leaky waves, rather than by a more complicated field representation that includes continuous spectra. The rigorous leaky-modes coupled in multilayered geometry can be then treated by relatively simpler and analytic model that describes the operation of practical optoelectronic devices in terms of leakage effects. To complement our modeling, we discuss and emphasize novel mathematical formulations based on the field orthogonality conditions of TE and TM modes coupled in multilayered periodic structures. In addition, to show the validity of our approach we numerically evaluate new physical meanings to illustrate quantitatively and rigorously the coupling efficiency of grating-assisted directional couplers (GADCs). The results reveal that the systematic and effective technique yields phenomenologically useful interpretations.

We have quantitatively and systematically investigated the effect of parasitic inductance on rapid single flux quantum (RSFQ) circuits by numerical simulation. While a parasitic inductance in parallel to a junction has virtually no effect on the circuit performance, a parasitic inductance in series with a junction significantly reduces the operating margins and speeds of circuits that have been optimized with the assumption that no parasitic inductance exists. To improve the reduced margins and speeds we have re-optimized the circuits for operation with parasitic inductance. While the speeds are sufficiently improved by the re-optimization procedure, the margins do not reach those without the parasitics. This suggests that the parasitic inductance shrinks the operating regions of the circuits and improvement of the margins by changing only the values of the parameters is limited. For further improvement of the margins it is important to employ processes and layouts that minimize the series parasitic inductance.

This paper proposes a group key distribution scheme with a user exclusion. The user exclusion is how to distribute an encryption key over a broadcast channel shared by n users so that all but d excluded users can get the group key. In the broadcast channel such as Pay-TV, Internet multicast and a mobile telecommunication for a group, a manager should exclude a dishonest user or an unauthorized terminal as soon as possible to protect the secrecy of the group communication. However, it takes a long time for the user exclusion on a large group, if the distributor distributes the group key to each user except the excluded one. We propose a scheme in which the amount of transmission and the key storage of each user do not depend on the number of users of the group. Moreover, our scheme does not require a fixed and privileged distributor.

Efficient ID-based key sharing schemes are desired worldwide in order to obtain secure communications on the Internet and other related networks, and Key Pre-distribution System (KPS) is one of the majority of such key sharing schemes. The remarkable property of KPS, is that, user need only input the partner's identifier to the secret KPS-algorithm in order to share a key between them. Although this is just a small part of many advantages KPS has in terms of efficiency, an enormous amount of memory is always required to achieve perfect security. While the conventional KPS methods can establish communication links between any pair of entities in a communication system, in most of the practical communication environment, such as in a broadcast system, not all links will be required. In this article, we achieved a desirable method to remove the unnecessary communication links between any pair of entities in a communication system. In our scheme, required memory size per entity was just proportional to the number of entities of the partner's, while that in conventional KPS, it is proportional to the number of entities of the whole communication system. As an example, if an entity communicates with only 1/r others, the memory requirement is reduced to 1/r of the conventional KPS's. Furthermore, it was proven that the obtained memory size was optimum. Overall, our scheme confirmed greater efficiency to achieve secure communication particularly suited in large-scale networks.

ID-based key sharing scheme is one of the important topics in Key management, and the Key Predistiribution System (KPS) is one of the major divisions of such key sharing schemes. In KPS, in order to share a common key between the participants, one of the participants need to simply feed-in his partner's identifier value into their secret-algorithm. In contrast to its such remarkable property and its high contribution to the field of key management for digital signature, it has downsides as well. In this paper, we propose an efficient signature scheme on the KPS infrastructure that can overcome such difficulties that are faced. It is shown that if an ID-based key sharing system belonging to KPS is provided, the new digital signature scheme can be used straightforwardly. Moreover, this signature scheme is proven to be secure if the discrete logarithm is reasonably complex. There already exists other digital signature scheme which are also based on KPS, but they contain inevitable flaws: its verifier is restricted and a tamper resistant module(TRM) is required. Our method resolved these problems. In our signature scheme, it is an ensured fact that, all signatures are authenticated by any entity, which is based on the inherence behavior of key generator and not of some common key. Moreover, TRM is not required in our scheme. In order to describe our new scheme, a new concept of "one-way homomorphism" is introduced.

This paper describes an efficient k-out-of-n threshold digital signature scheme for a smart card based system where a signer uses multiple cards so that the signature can be issued in a dependable manner. The main feature of our method is that it does not require a secret communication path among these cards in the signature issuing protocol, and that it requires low communication and computational complexity. Former is an advantage under the current export control regulation which makes hard to export more than 56-bit cipher techniques, and latter is advantage over so-called robust signature.

System LSI is a new principal product of semiconductor industry and also a key component of Information Technology (IT). Design of a system LSI contains two different characteristics, system design and LSI design. It is keen issue to establish a design methodology of system LSIs in which designers have much freedom on their design from system level to device level and also can control various design parameters to optimize their design. In this paper, considerations on markets of system LSIs and requirements from each application are summarized. Some proposals on new directions of design methodology are also surveyed.

An aspect of the diverse developments of digital signal processing (DSP) over the last decade are summarized. The current progress of some core fields from the widespread fields are treated in this paper. The selected fields are filter design, wavelet theory and filter bank, adaptive signal processing, nonlinear filters, multidimensional signal processing, intelligent signal processing, and digital signal processor. Through the overview of recent research activities, the interdisciplinary character of the DSP should be proved. Some challenging research direction is described in the last section.

In this paper, we investigate the performance of the orthogonal frequency division multiplexing (OFDM) system based on a configuration of pilot symbol arrangement under a time-varying fading channel and verify it by simulation. A particular channel of concern is modeled by a wide-sense stationary uncorrelated scattering (WSSUS) Rayleigh fading process and furthermore, the inter-carrier interference (ICI) caused by the fading process is assumed to be Gaussian noise. The current analysis focuses on the performance limit of the pilot symbol-assisted channel estimation, in which a minimum mean squared error (MMSE) channel estimator is employed to exploit both time- and frequency-domain correlation simultaneously. In particular, the optimum pilot symbol arrangement was investigated for the time-varying fading channel, which has been rarely addressed with any analytical approach in previous research. Although the proposed channel estimation scheme is subject to the intensive processing complexity in the receiver, it has been shown that the better BER performance can be achieved as compared with that of the differential detection scheme and the error floor can be removed.

For physically disabled persons, the conventional computer keyboard is insufficient as a useable communication device. In this paper, Morse code is selected as a communication adaptive device for persons with impaired hand coordination and dexterity. Morse code is composed of a series of dots, dashes, and space intervals. Each element is transmitted by sending a signal for a defined length of time. Maintaining a stable typing rate by the disabled is difficult. To solve this problem, a suitable adaptive automatic recognition method, which combines a variable degree variable step size LMS algorithm with a learning vector quantization method, was applied to this problem in the present study. The method presented here is divided into five stages: space recognition, tone recognition, learning process, adaptive processing, and character recognition. Statistical analyses demonstrated that the proposed method elicited a better recognition rate in comparison to alternative methods in the literature.

This paper proposes a method for implementing a metric computation accelerator for fractal image compression using reconfigurable hardware. The most time-consuming part in the encoding of this compression is computation of metrics among image blocks. In our method, each processing element (PE) configured for an image block accelerates these computations by pipeline processing. Furthermore, by configuring the PE for a specific image block, we can reduce the number of adders, which are the main computing elements, by a half even in the worst case.

In this paper, we consider the complexity of recognizing ordered tree-shellable Boolean functions when Boolean functions are given as OBDDs. An ordered tree-shellable function is a positive Boolean function such that the number of prime implicants equals the number of paths from the root node to a 1-node in its ordered binary decision tree representation. We show that given an OBDD, it is possible to check within polynomial time if the function is ordered tree-shellable with respect to the variable ordering of the OBDD.

An electromagnetic wave scattering by a material loaded rectangular trough on a ground plane is approximately analyzed by using standard impedance boundary condition (SIBC). The validity of the derived approximate solution is examined by comparing with the rigorous one not only for the oblique incidence but also for the variation of both the filled material's parameters and the trough dimension. An applicability condition has been derived here for this trough structure.

The diffraction problem of a Gaussian beam by finite number of periodic slots in a parallel-plate waveguide filled with a homogeneous dielectric is considered. The integro-differential equation for the unknown equivalent surface magnetic current density over the slots is derived and solved by the method of moments (piecewise sinusoidal Galerkin method). From some theoretical results for the angular diffraction pattern, the present geometry is observed to simulate well the previous rectangular groove geometry from the viewpoint of scattering behaviour. In addition, two types (resonance and non-resonance types) of Bragg blazing phenomena are discussed. Simultaneous Bragg and off-Bragg blazing is also demonstrated.

A passive branched optical network unified for broadcasting and communication utilizing a set of Fabry-Perot etalons with different cavity lengths is proposed and its basic operation including thermal stability of broadcasting channel is demonstrated. It is confirmed that a high transmission frequency in common for a pair of fiber Fabry-Perot etalons is always found however environmental temperature changes.

The capability of frequency-swept cross-borehole radar to detect an empty rectangular cylinder embedded in a dielectric medium is simulated numerically by employing the boundary element method. The frequency loci providing the strongest double dips in the received signal pattern are plotted as functions of the observation distance and the cross-sectional width. It is found that, regardless of the shape of the rectangular cross-section, the strongest double dips become double nulls in the near-field region.

This paper surveys the research topics and results on nonlinear theory and its applications which have been achieved in Japan or by Japanese researchers during the last decade. The paticular emphasis is placed on chaos, neural networks, nonlinear circuit analysis, nonlinear system theory, and numerical methods for solving nonlinear systems.

This paper describes a random access memory (RAM, sometimes also called an array) test scheme that has the following attributes: (1) Can be used in both built-in mode and off chip/module mode. (2) Can be used to test and diagnose naked arrays. (3) Fault diagnosis is simple and is "free" for some faults during test. (4) Is never subject to aliasing. (5) Depending upon the test length, it can detect many kinds of failures, like stuck-cells, decoder faults, shorts, pattern-sensitive, etc. (6) If used as built-in feature, it does not slow down the normal operation of the array. (7) Does not require storage of correct responses. A single response bit always indicates whether a fault has been detected. Thus, the storage requirement for the implementation of the test scheme is zero. (8) If used as a built-in feature, the hardware overhead is very low.

This paper, for the first time, presents a provably secure signature scheme with message recovery based on the elliptic-curve discrete logarithm. The proposed scheme is proven to be secure in the strongest sense (i.e., existentially unforgeable against adaptively chosen message attacks) in the random oracle model under the discrete logarithm assumption. We give a concrete analysis of the security reduction. When practical hash functions are used in place of truly random functions, the proposed scheme is almost as efficient as the elliptic-curve version of the Schnorr signature scheme and existing schemes with message recovery such as the elliptic-curve version of the Nyberg-Rueppel and Miyaji schemes.

This paper examines similarities between the Decision Diffie-Hellman (DDH) assumption and the Quadratic Residuosity (QR) assumption. In addition, we show that many cryptographic protocols based on the QR assumption can be reconstructed using the DDH assumption.