A novel parallel acceleration technique is proposed based on intrinsic parallelism characteristics of shooting-and-bouncing ray launching (SBR) algorithm, which has been implemented using the MPI parallel library on common PC cluster instead of dedicated parallel machines. The results reveal that the new technique achieves very large speedup gains and could be the efficient and low-cost propagation prediction solution.

The WDM optical networks currently being deployed are opaque optical networks, in which each link is optically isolated by transponders. To reduce the number of expensive transponders and switching ports, a hierarchical optical architecture consisting of all-optical waveband switching and opaque OEO switching has been proposed. Although this architecture requires fewer transponders and ports, it also requires a large number of wavelength (waveband) multiplexers and demultiplexers. Switching the optical path solely at the fiber level (i.e., by using fiber cross-connects, or FXCs) is desirable as a way to reduce the total node cost. If all the core nodes in an optical network are FXCs, however, the grooming of wavelengths for the optical fibers is only possible at the edge nodes. This leads to poor utilization of wavelength resources when there is only demand for small numbers of wavelengths, and as a result, the link cost increases. This problem can be solved by adding an OEO grooming function to some of the FXCs. In this paper, we propose an algorithm for designing optical cross-connect (OXC) functions on the basis of the FXC, thus minimizing the total network cost.

We propose a robust edge detection method based on independent component analysis (ICA). It is known that most of the basis functions extracted from natural images by ICA are sparse and similar to localized and oriented receptive fields, and in the proposed edge detection method, a target image is first transformed by ICA basis functions and then the edges are detected or reconstructed with sparse components only. Furthermore, by applying a shrinkage algorithm to filter out the components of noise in the ICA domain, we can readily obtain the sparse components of the original image, resulting in a kind of robust edge detection even for a noisy image with a very low SN ratio. The efficiency of the proposed method is demonstrated by experiments with some natural images.

A digital/analog hybrid system is presented which implements the cardinal polynomial spline interpolation of arbitrary degree. Based on the fact that the (m-1)st derivative of a spline of degree m-1 is a staircase function, this system generates a cardinal spline of degree m-1 by m-1 cascaded integrators with a staircase function input. A given sequence of sampled values are transformed by a digital filter into coefficients for the B-spline representation of the spline interpolating the sampled values. The values of its (m-1)st derivative with respect to time are computed by the recurrence formula interpreting differentiation of the spline as difference of the coefficients. Then a digital-to-analog converter generates a staircase function representing the (m-1)st derivative, which is integrated by a cascade of m-1 analog integrators to make the expected spline. In order to cope with the offset errors involved in the integrators, a dynamical sampled-data control is attached. An analog-to-digital converter is employed to sample the output of the cascaded integrators. Target state of the cascaded integrators at each sampling instance is computed from the coefficients for the B-spline representation. The state error between the target and the estimated is compensated by feeding back a weighted sum of the state error to the staircase input.

In this letter, we present an efficient stream authentication scheme that is an improvement of SAIDA. It is shown that under the same communication overhead its verification probability is higher than that of SAIDA. Moreover, its computation cost is lower than that of SAIDA.

We study the statistical multiplexing performance of self-similar traffic. We consider that input streams have different QoS (Quality of Service) requirements such as loss and delay jitter. By applying the FBM (fractal Brownian motion) model, we present methods of estimating the effective bandwidth of aggregated traffic. We performed simulations to evaluate the QoS performances and the bandwidths required to satisfy them. The comparison between the estimation and the simulation confirms that the estimation could give rough data of the effective bandwidth. Finally, we analyze the bandwidth gain with priority multiplexing against non-prioritized multiplexing and suggest how to get better performance with the right configuration of QoS parameters.

In a severe frequency-selective fading channel, the bit error rate (BER) performance of orthogonal multicode DS-CDMA is severely degraded since the orthogonality property of spreading codes is partially lost. The frequency-selectivity of a fading channel can be exploited by using frequency-domain equalization to improve the BER performance. Further performance improvement can be obtained by using transmit diversity. In this paper, joint transmit diversity and frequency-domain equalization is presented for the reception of orthogonal multicode DS-CDMA signals in a frequency-selective fading channel. As for transmit diversity, delay transmit diversity (DTD) and frequency-domain space-time transmit diversity (STTD) are considered. The achievable BER performance of multicode DS-CDMA in a frequency-selective Rayleigh fading channel is evaluated by computer simulation. It is shown that the frequency-domain STTD significantly improves the BER performance irrespective of the degree of the channel frequency-selectivity while DTD is useful only for a weak frequency-selective channel.

An ultra wide band channel sounder has been developed and has attained the time delay resolution of 0.5 ns which enables the propagation path discrimination in indoor wireless propagation environments as well as the direction-of-arrival measurements by power delay profile measurements.

In December 2001, the authors started two kinds of experiments on the meteor burst communication (MBC) in Antarctica to study the ability of MBC as a communication medium for data collection systems in that region. In the first experiment, a continuous tone signal is transmitted from Zhongshan Station. The signal received at Syowa Station (about 1,400 km apart) is recorded and analyzed. This experiment is aimed to study basic properties of the meteor burst channel in that high latitude region. On the other hand, the second experiment is designed to estimate data throughput of a commercial MBC system in that region. A remote station at Zhongshan Station tries to transfer data packets each consisting of 10 data words to the master station at Syowa Station. Data packets are generated with five minutes interval. In this paper, we explain the experiments, briefly examine the results of the first year (from April 2002 to March 2003), and put forward the plan for the experiments in the second and third year. From the data available thus far, we can see that 1) the sinusoidal daily variation in the meteor activity typical in middle and low latitude regions can not be clearly seen, 2) non-meteoric propagations frequently dominate the channel especially during night hours, 3) about 60% of the generated data packets are successfully transferred to the master station within two hours delay even though we are now operating the data transfer system only for five minutes in each ten minutes interval, etc.

An empirical formula of resonant frequency of bow-tie microstrip antennas is presented, which is based on the cavity model of microstrip patch antennas. A procedure to design a bow-tie antenna using genetic algorithm (GA) in which we take the formula as a fitness function is also given. An optimized bow-tie antenna by genetic algorithm was constructed and measured. Numerical and experimental results are used to validate the formula and GA. The results are in good agreement.

This paper presents a novel design procedure for class E oscillator. It is the characteristic of the proposed design procedure that a free-running oscillator is considered as a forced oscillator and the feedback waveform is tuned to the timing of the switching. By using the proposed design procedure, it is possible to design class E oscillator that cannot be designed by the conventional one. By carrying out two circuit experiments, we find that the experimental results agree with the calculated ones quantitatively, and show the validity of the proposed design procedure. One experimental measured power conversion efficiency is 90.7% under 6.8 W output power at an operating frequency 2.02 MHz, the other is 89.7% under 2.8 W output power at an operating frequency 1.97 MHz.

In this paper, we present Neighbor Community Finder (NCF, for short), a tool for finding Web communities related to given URLs. While existing link-based methods of finding communities, such as HITS, trawling, and Companion, use algorithms running on a Web graph whose vertices are pages and edges are links on the Web, NCF uses an algorithm running on an inter-site graph whose vertices are sites and edges are global-links (links between sites). Since the phrase "Web site" is used ambiguously in our daily life and has no unique definition, NCF uses directory-based sites proposed by the authors as a model of Web sites. NCF receives URLs interested in by a user and constructs an inter-site graph containing neighbor sites of the given URLs by using a method of identifying directory-based sites from URL and link data obtained from the actual Web on demand. By computational experiments, we show that NCF achieves higher quality than Google's "Similar Pages" service for finding pages related to given URLs corresponding to various topics selected from among the directories of Yahoo! Japan.

A new hybrid formulation has been derived for analyzing biological electromagnetic compatibility (Bio-EMC) problems by combining the frequency-domain Method of Moments (MoM) and the Finite-Difference Time-Domain (FDTD) method. This hybrid form is different from, and more direct than, the method previously proposed by Mangoud et al. Some numerical examples are given for the human head exposure field due to a half wavelength dipole and a one-wavelength loop antenna. Our iterative method is found to have fast convergence. In addition, our method works well for cases when the radiation antenna wires are not aligned with the FDTD lattice.

This paper presents a new method to improve the resonant characteristics of a microstrip resonator. The improved characteristics have been achieved by inserting two dielectric rods between strip conductor and the ground plane. Dielectric rods to be inserted have higher relative permittivity than that of the substrate. Therefore, it is suitable to realize by Low-Temperature Cofired Ceramics (LTCC) technique. Several model of microstrip resonators employing the proposed method are analyzed by a Finite-Difference Time-Domain (FDTD) method, and their resonant characteristics are discussed. One of the advantages of the proposed method is that an attenuation pole (fl or fh) in each side of the fundamental resonant frequency (fr) and improved-spurious responses can be realized together by a capacitive-coupling tapped resonator loaded with dielectric rods. The proposed method is also effective to achieve sharp skirt characteristics and wide stopband of a direct-coupling tapped resonator which can be used either as a wideband lowpass filter or a band-elimination filter. Another interesting feature of the analyzed resonators is that about 60% reduction in resonator's length has been obtained compared to a basic half-wavelength (λ/2) microstrip resonator. Therefore, wide exploitation of the proposed method can be expected in the filter design based on the LTCC technique.

This paper introduces a new type of microwave isolator. The operation is based on the two phenomena; the ferrite edge-mode and the photo-generated plasma on silicon substrate. Conventional ferrite edge-mode isolator has been made of the ferrite and the resistive material. The later is used to absorb the reverse-propagating wave of the isolator. An inadequate choice of the resistive body leads to the imperfect absorption; the isolation ratio decreases. In this paper, the isolation-variable isolator is introduced by using this change of isolation. The control is realized by the change of the surface resistance on the silicon. On this isolator, the frequency response is investigated both experimentally and numerically. The numerical analysis is conducted by FDTD method. The experiment is carried out on the prototype isolator. Both experimental and numerical results have shown that the isolation ratio can be controlled for 39 dB at 12 GHz by the irradiation.

In this study, nonlinear wave phenomena related to transmissions and reflections of the phase-inversion waves around a discontinuity of a coupled system consisting of two kinds of arrays of van der Pol oscillators are investigated. By computer simulations, behavior of the phase-inversion waves around the discontinuity in the coupled system is classified into eight types. Further, the mechanisms of the transmission and the reflection of a phase-inversion wave at the discontinuity are explained. Circuit experiments confirm the simulated results.

This paper proposes dynamic distributed unicast and multicast routing algorithms for multiple classes of QoS guaranteed networks. Each link in such a network is assumed to be able to provide multiple classes of QoS guarantee by reserving various amounts of resource. A distributed unicast routing algorithm, DCSP (Distributed Constrained Shortest Path), for finding a QoS constrained least cost path between each O-D (Originating-Destination) pair, is proposed first. Two class reduction schemes, the linear and logarithmic policies, are develpoed to prevent exponential growth of the number of end-to-end QoS classes. Based on DCSP, two distributed multicast routing algorithms, DCSPT (Distributed Constrained Shortest Path Tree) and DTM (Distributed Takahashi and Mutsuyama), are proposed to find QoS constrained minimum cost trees. Numerical results indicate that DCSP strongly outperforms previously proposed centralized algorithms and it works better with the linear class reduction method. For the multicast routing algorithms, the DCSPT with linear class reduction method yields the best performance of all multicast routing algorithms.

Intensity-noise characteristics of stable multi-mode Fabry-Perot semiconductor lasers are analyzed experimentally and theoretically. Mode-partition noise caused by optical filtering and propagation through optical fibers is investigated by evaluating the relative intensity noise and signal-to-noise ratio. The experimental results indicate that the simplified two-mode analysis provides a good approximation. Suppression of the mode-partition noise by nonlinear gain is experimentally confirmed.

In this paper, we propose the Synchronized Mobile Multicast (SMM) scheme for the real-time multimedia service to achieve three most important characteristics that the traditional Home Subscription (HS) and Remote Subscription (RS) mobile schemes cannot support. First, the SMM scheme supports the scalable one-to-many and many-to-many synchronized multimedia multicast on mobile IP networks to achieves seamless playback of continuous media streams even when both the mobile sender and receivers handoff simultaneously. Second, it analyzes the minimal buffer requirements of the mobile sender, the core router, the foreign agents and the mobile receivers in the multicast tree and formulates the initial playback delay within a handoff Guarantee Region (GR). Further, combined with the fine granularity scalability (FGS) encoding approach in the MPEG-4 standard, the SMM scheme achieves superior multimedia QoS guarantees and unlimited numbers of handoffs of the mobile sender and receivers only at the cost of degraded video quality for a short period after handoff with minimal extra bandwidth.

An iterative method is proposed to solve integral equations (IEs) of the second kind with Picard-kernel in linear complexity, i.e.O(N). The particular IE considered describes the process of scattering of a plane wave incident on an inhomogeneous slab. The collocation method with triangle basis functions is used to derive a linear system of equations, which is solved for a test problem with the BiCGSTAB method. To reduce the number of iterations, an efficient preconditioning operator is introduced.