The boundary integral equation (BIE) on interior walls with surface impedance conditions is implemented to the iterative physical optics method and how to treat the singularities involved in the BIE of an impedance cavity is described. Singular integrals over a rectangular region can be represented by simple elementary functions.

This paper introduces a new digital ATC (Automatic Train Control device) system. In the current ATC, the central ATC logic device calculates permissive speed of each blocking section and controls speed of all trains. On the other hand, in the new digital ATC, the central logic controller calculates each position to which a train can move safely, and sends the information on positions to all trains. On each train, the on-board equipment calculates an appropriate braking pattern with the information, and controls velocity of the train. That is, in the new system, the device on each train autonomously calculates permissive speed of that train. These special features realize ideal speed control of each train making full use of its performance for acceleration and deceleration, which in turns allows high-density train operations.

In this paper, we propose a new type of hybrid ARQ protocol, in which a channel-adaptive variable rate channel coding scheme is combined with a multi-copy retransmission strategy so as to enhance the system performance under the delay constraint of real-time ATM services in broadband radio access networks. The main feature of a multi-copy retransmission strategy in this scheme is to improve the average throughput for a given Forward Error Correction (FEC) rate, subject to the prescribed cell loss requirement of the real-time wireless ATM services, while augmenting the reliability of channel state information required for a channel-adaptive FEC scheme. Our analysis shows that under a harsh fading channel, the proposed approach is useful for achieving the prescribed cell loss performance without significantly degrading the average throughput performance.

We proposed a simple technique for measuring the effective zero-dispersion wavelength. In this study, we measured the effective zero-dispersion wavelength of a 25-km-long dispersion-shifted fiber (DSF) using the four-wave mixing (FWM) of a spectrum-sliced fiber amplifier light source, and then compared our results with other conventional techniques to confirm the validity of our method.

Successful e-commerce presupposes techniques by which autonomous trading entities can interoperate. Although progress has been made on data exchange and payment protocols, interoperation in the face of autonomy is still inadequately understood. Current techniques, designed for closed environments, support only the simplest interactions. We develop a multiagent approach for interoperation of business process in e-commerce. This approach consists of (1) a behavioral model to specify autonomous, heterogeneous agents representing different trading entities (businesses, consumers, brokers), (2) a metamodel that provides a language (based on XML) for specifying a variety of service agreements and accommodating exceptions and revisions, and (3) an execution architecture that supports persistent and dynamic (re)execution.

This paper describes an electromagnetically coupled microstrip divider that provides high output port isolation and DC cutting. The device consists of a parasitic resonator placed above microstrip patch resonators, achieving tight coupling for both input and output ports. FDTD simulation and measurements reveal that the device has a high isolation between output ports. Equal and unequal 2-way and 3-way power dividers are presented in this paper.

Simulation based education and training, especially wargame simulations, are being used widely in the field of defense modeling and in simulation communities. In order to efficiently train students and trainees, the wargame simulations must have both high performance and high fidelity. In this paper, we discuss design and implementation issues for a prototype of a parallel and distributed wargame simulation system. This wargame simulation system is based on High Level Architecture (HLA) and employs some optimization to achieve both high performance and high fidelity in the simulation system. The results show that the proposed optimization method is effective when optimization is applied to 93.5% or less of the moving objects (PFs) within the range of detection (RofD) of both the red and blue teams. Specifically, when each team has 1000 PFs we found that if the percentage of PFs within RofD is less than 50% for both teams, our method is over two times better than for the situation where there is no optimization.

An improved arithmetic coding which provides an encoder with finite calculation precision for source sequences over a countable alphabet is presented. Conventional arithmetic coding theoretically has infinite precision for real variables. However any algorithm implemented on a computer has finite precision. This implies that conventional arithmetic codes can only encode sequences over a finite alphabet. The improved arithmetic coding presented here has a computational complexity which is roughly proportional to the length of the source sequence for a given source.

RC6 is a common-key block cipher that was proposed as one of the AES candidates. Although any weakness of RC6 in the use of the confidentiality is not known, Saarinen pointed out the existence of almost equivalent keys in RC6 with 176-byte keys. This means that the Davies-Meyer hash function based on RC6 with 176-byte keys is not a good collision-resistance function. However, Saarinen could not find a precise collision of it. In this paper, we propose a practical method for obtaining a collision of the Davies-Meyer hash function based on RC6-32/20/176. In other words, there exist equivalent user supplied keys in RC6-32/20/176, and it is possible to obtain them practically. This means that the essential key space of RC6-32/20/176 is smaller than the space provided by 176-byte keys. Our computer simulation shows that a collision can be found in about 100 minutes. We should notice that the result of this paper does not affect the security of the AES version of RC6 because RC6-32/20/176 discussed in this paper is different from the parameter of the AES version.

Recently, Kasahara and Murakami proposed new product-sum public-key cryptosystems using the Chinese remainder theorem as the trapdoor. We proposed 'Yaezakura' as the high-density product-sum PKC applying the method using the reduced bases. In this paper, we propose another high-density scheme with the Chinese remainder theorem trapdoor using the message extension. We also show that the proposed scheme is invulnerable to the low-density attack. In the proposed scheme, the sender can freely select the positions of the dummy messages.

Stability of slotted ALOHA systems with retransmission cutoff, in which a packet is discarded after the certain number of unsuccessful transmissions, is investigated on slow-frequency-hopped channels with the aid of the catastrophe theory. The result of this paper can be viewed as extension of the result derived by Kim. The balance function is first formulated. Then, the cusp point and the bifurcation sets are numerically evaluated. We visualize how retransmission cutoff effects on bistable region. Using the result, we can design parameters of slotted ALOHA systems with retransmission cutoff such that the system operates with the unique stable equilibrium point.

In 2000, Wang et al. proposed a new (t,n) threshold signature scheme with (k,l) threshold shared verification. Meanwhile, integrating the idea of message recovery, they also proposed a (t,n) threshold authenticated encryption scheme with (k,l) threshold shared verification. However, this article will show that both proposed schemes are insecure, because any malicious attacker can obtain the group secret keys from two valid threshold signatures. Thus, the attacker may solely forge or verify a threshold signature. An improvement to overcome the attacks is proposed.

Performance of turbo codes over an impulsive noise channel is analyzed by extending an evaluation method over AWGN channels. Burst noise generation is considered with respect to the noise model by applying a hidden Markov model (HMM). A bound calculation method is derived by using a combined trellis which consists of code trellis and HMM trellis. In the simulation, an iterative decoder using the combined trellis into each component decoder is proposed. By using this method, the simulation results show the expectation of the coincidence with the calculated bounds at larger Eb/N0 for various conditions. Search results of optimum component code using proposed bound are shown.

This paper proposes a bandwidth division type parallel combinatory (PC) spread spectrum (SS) modulation scheme. In the proposed system, a given system bandwidth for the conventional single-carrier PC-SS system is divided into H subbands, and H PC-SS signals are transmitted in parallel. We evaluate the frame error rate (FER) of the proposed system under the asynchronous CDMA environment. We show that the proposed scheme provides a smaller FER than the single-carrier PC-SS system for a given information bit rate. We also show that the proposed scheme attains a higher information bit rate than the single-carrier PC-SS system for a given FER.

This paper proposes a precise method of realizing simultaneous measurement of microscopic defects and the macroscopic three-dimensional shapes of planar objects having specular reflection surfaces. The direction vector field of surface tilt is evaluated directly by the introduction of a moving slit-light technique based on computer graphic animation. A reflected image created by the moving slit-light is captured by a video camera, and the image sequence of the slit-light deformation is analyzed. The obtained direction vector field of the surface tilt recovers the surface shape by means of integration. Two sample objects, a concave mirror and a plane plastic injection molding, are tested to measure the performance of the proposed method. Surface anomalies such as surface dent and warpage are detected quantitatively at a high resolution (about 0.2 [µm]) and a high accuracy (about 95%) in a wide area (about 15 [cm]) of the test object.

Characteristics of the optical feedback noise in semiconductor lasers under superposition of the HF (High Frequency) current were experimentally examined and theoretically analyzed. The feedback noise was mostly suppressed by superposition of HF current, but still remained when frequency of the HF current coincided with a rational number of the round trip time period for the optical feedback in experimental measurement. Theoretical analysis was also given to explain these characteristic based on the mode competition theory of the semiconductor laser.

A new algorithm for the maximum a posteriori (MAP) decoding of linear block codes is presented. The proposed algorithm can be regarded as a conventional BCJR algorithm for a section trellis diagram, where branch metrics of the trellis are computed by the recursive MAP algorithm proposed by the authors. The decoding complexity of the proposed algorithm depends on the sectionalization of the trellis. A systematic way to find the optimum sectionalization which minimizes the complexity is also presented. Since the algorithm can be regarded as a generalization of both of the BCJR and the recursive MAP algorithms, the complexity of the proposed algorithm cannot be larger than those algorithms, as far as the sectionalization is chosen appropriately.

This paper presents a new adaptive blind separation of sources (BSS) method for linear and non-linear mixtures. The sources are assumed to be statistically independent with non-uniform and symmetrical PDF. The algorithm is based on both simulated annealing and density estimation methods using a neural network. Considering the properties of the vectorial spaces of sources and mixtures, and using some linearization in the mixture space, the new method is derived. Finally, the main characteristics of the method are simplicity and the fast convergence experimentally validated by the separation of many kinds of signals, such as speech or biomedical data.

Multisignature scheme realizes that plural users generate the signature on a message, and that the signature is verified. Various studies on multisignature have been proposed. They are classified into two types: RSA-based multisignature, and discrete logarithm problem (DLP) based multisignature, all of which assume that a message is fixed beforehand. In a sense, these schemes do not have a feature of message flexibility. Furthermore all schemes which satisfy with order verifiability designate order of signers beforehand. Therefore these protocols have a feature of order verifiability but not order flexibility. For a practical purpose of circulating messages soundly through Internet, a multisignature scheme with message flexibility, order flexibility and order verifiability should be required. However, unfortunately, all previous multisignature do not realize these features. In this paper, we propose a general model of multisignature schemes with flexibility and verifiability. We also present two practical schemes based on DLP based message recover signature and RSA signature, respectively.

Surface passivation process of GaN utilizing electron-cyclotron-resonance (ECR) excited plasma has been characterized and optimized for realization of stable operation in GaN-based high-power/high-frequancy electronic devices. From XPS analysis, the NH4OH treatment as well as the ECR-N2 and ECR-H2 plasma treatments were found to be effective in removing natural oxide and contaminants from the GaN surface. The SiNx/GaN structure prepared by the ECR excited plasma chemical vapor deposition (ECR-CVD) process showed better C-V behavior compared to the SiO2/GaN structure. Surface treatment process using the ECR plasma improved interface properties and achieved the Dit value of 21011 cm-2 eV-1 or less. An estimate of the valence band offset by XPS showed that the present SiNx/n-GaN structure has a type-I band lineup, suitable for the surface passivation of GaN-based devices. No pronounced stress remained at the SiNx/GaN interface, which was confirmed by Raman spectroscopy.