We study state feedback control of discrete event systems described by the Golaszewski-Ramadge model. We derive a necessary and sufficient condition for the existence of a balanced state feedback controller under partial observations.

This paper reviews recent developments in small-sized broadband antennas for EMI measurements, especially in the microwave frequency region. Transient EMI measurements are also discussed by introducing complex antenna factors and conversion of frequency-domain data into time-domain data. This paper also focuses on considerable improvements achieved in calibration techniques for conventional EMI antennas in VHF/UHF bands.

Recently, a wavelength division multi/demultiplexing system has been viewed with keen interest because it is possible to increase the transmission capacity and system flexibility. An arrayed waveguide grating (AWG) type of Multi/demultiplexer which is one of the key components to realize such a system has been developed by using Planar Lightwave Circuits (PLCs). Newly designed optical circuits have been incorporated into the AWG to control the center wavelength and to expand the pass band width. The 3 dB pass band width is 1.4 times that of a conventional AWG. It is confirmed that the newly developed AWG has low polarization dependence, low temperature dependence and high reliability.

An effective learning method for the fuzzy ARTMAP in the recognition of noisy input patterns is presented. the weight vectors of the system are updated using the weighted average of the noisy input vector and the weight vector itself. This method leads to stable learning and prevents the excessive update of the weight vectors which may cause performance degradation. Simulation results show that the proposed method not only reduces the generation of spurious categories, but aloso increases the recognition ratio in the noisy environment.

Microwave oven interference much degrades the performance of digital radio communication systems, and, in order to obtain a good error performance under microwave oven interference environment, the digital radio communication systems should be newly designed for microwave oven interference environment. In this paper, using the Middleton's canonical class-A impulsive noise model, we propose a statistical model of microwave oven interference and discuss the performance improvement achieved by an optimum reception based on this statistical model. As the results, although the first order statistic of microwave oven interference can be modeled by class-A impulsive noise, because of the burst high level interference, the performance of optimum receiver designed for class-A noise cannot achieve a good error performance under microwave oven interference environment. In order to eliminate the effect of burst high level interference, we introduce sample interleave scheme and show that the performance of optimum receiver can be much improved by using sample interleave scheme.

In audio-frequency magnetotelluric surveys, electromagnetic radiation from worldwide thunderstorm activity is used as an energy source for geophysical exploration. Owing to its origin, such a signal is inherently transient and short lived. Therefore, special care should be taken in the detection and processing of this transient signal because the interval of time between two successive transient events contains almost no information as far as the audio frequency magnetotellurist is concerned. In this paper, a wavelet transform detection, processing and analysis technique is developed. A complex-compactly-supported wavelet, known as the Morlet wavelet, is selected as the mother wavelet. With the Morlet wavelet, lightning transients can be easily identified in the noisy recordings and the magnetotelluric impedance tensor can be computed directly in the wavelet transform domain. This scheme has been tested on real data collected in the archipelago of Svalbard, Norway as well as on five sets of synthetic data contaminated with various kinds of noise. The results show the superior performance of the wavelet transform transient detection and analysis technique.

This paper compares signal classification performance of multilayer neural networks (MLNNs) and linear filters (LFs). The MLNNs are useful for arbitrary waveform signal classification. On the other hand, LFS are useful for the signals, which are specified with frequency components. In this paper, both methods are compared based on frequency selective performance. The signals to be classified contain several frequency components. Furthermore, effects of the number of the signal samples are investigated. In this case, the frequency information may be lost to some extent. This makes the classification problems difficult. From practical viewpoint, computational complexity is also limited to the same level in both methods.IIR and FIR filters are compared. FIR filters with a direct form can save computations, which is independent of the filter order. IIR filters, on the other hand, cannot provide good signal classification deu to their phase distortion, and require a large amount of computations due to their recursive structure. When the number of the input samples is strictly limited, the signal vectors are widely distributed in the multi-dimensional signal space. In this case, signal classification by the LF method cannot provide a good performance. Because, they are designed to extract the frequency components. On the other hand, the MLNN method can form class regions in the signal vector space with high degree of freedom.

The filtered-x algorithm, which is widely applied to active noise control system, requires setting a small step gain. Such a small step gain reduces the noise reduction effect when the alogrithm is implemented by fixed point processing. This paper presents an experimental result that the 'polarized-g' individually normalized least mean square (INLMS) algorithm can provide almost the same noise reduction effect even in the fixed point processing of 16 bits as that in floating point processing.

A simple method based on the pattern integration method for measuring the power absorption by human model in the vicinity of antennas is proposed. Good agreement between the measured and the numerical results is obtained conforming the validity of the present measurement method. The equipment is useful in the EMC measurement and research of the antennas for the portable telephone.

A new method is proposed for recovering an unknown source signal ,which is observed through two unknown channels characterized by non-minimum phase FIR filters. Conventional methods cannot estimate the non-minimum phase parts and recover the source signal. Our method is based on computing the eigenvector corresponding to the smallest eigenvalue of the input correlation matrix and using the criterion with the multi-channnel inverse filtering theory. The impulse responses are estimated by computing the eigenvector for all modeling orders. The optimum order is searched for using the criterion and the most appropriate impulse responses are estimated. Multi-channel inverse filtering with the estimated impulse responses is used to recover the unknown source signal. Computer simulation shows that our method can estimate nonminimum phase impulse responses from two reverberant signals and recover the source signal.

The Multiple input-output INverse/filtering Theorem (MINT) proves that N + 1 inverse filters are necessary to precisely control sound at N points in a space, and gives the minimum orders of such filters. In this paper, we propose the Indefinite MINT Filters (IMFs) for adding one or more control points to the above framework without increasing the number of inverse filters. Although the controllability of the new point is not sufficient, that of the other points is still maintained high enough by the principle of the MINT. In a two point sound control (using two inverse filters), the IMFs could reduce the squared error to the desired sound up to - 10 dB at the second point which is not controlled by the MINT.

Concatenated codes have many remarkable properties from both the theoretical and practical viewpoints. The minimum distance of a concatenated code is at least the product of the minimum distances of an outer code and an inner code. In this paper, we shall study on a condition that the minimum distance of concatenated codes is beyond the lower bound.

In the measurement of actual random phenomenon, the observed data often contain the fuzziness due to the existence of confidence limitation in measuring instruments, permissible error in experimental data, some practical simplification of evaluation procedure and a quantized error in digitized observation. In this study, by introducing the well-known fuzzy theory, a state estimation method based on the above fuzzy observations is theoretically proposed through an establishment of wide sense digital filter under the actual situation of existence of the background noise in close connection of the inverse problem. The validity and effectiveness of the proposed method are experimentally confirmed by applying it to the actual fuzzy data observed in an acoustic environment.

Photonic integrated circuits (PICs) are required for future optical communication systems, because various optical components need to be compactly integrated in one-chip configurations with a small number of optical alignment points. Bandgap energy controlled selective metal organic vapor phase epitaxy (MOVPE) is a breakthrough technique for the fabrication of PICs because this technique enables the simultaneous formation of waveguides for various optical components in one-step growth. Directly formed waveguides on a mask-patterned substrate can be obtained without using conventional mesa-etching of the semiconductor layers. The waveguide width is precisely controlled by the mask pattern. Therefore, high device uniformity and yield are expected. Since we proposed and demonstrated this technique in 1991, various PICs have been reported. Using electroabsorption modulator integrated distributed feedback laser diodes, 2.5 Gb/s-550 km transmission experiments have been successfully conducted. Another advantage of the selective MOVPE technique is the capability to form narrow waveguide layers. We have demonstrated a polarization-insensitive semiconductor optical amplifier that consists of a selectively formed narrow (less than 1 µm wide) bulk active layer. For a four-channel array, a chip gain of more than 20 dB and a gain difference between TE and TM inputs of less than 1 dB were obtained. We have also reported an optical switch matrix and an optical transceiver PIC for access optical networks. By using a low-loss optical waveguide, a 0 dB fiber-to-fiber gain for the 14 switch matrix and 0 dBm fiber output power from the 1.3 µm transceiver PIC were obtained. In this paper, the selective MOVPE technique and its applications to various kinds of PICs are discussed.

The supervisory control theory of discrete event dynamic systems was proposed in the framework of automata and formal languages. The concept of decentralized supervisory control was developed for the local supervisor Si whose concurrent operation results in the closed-loop language L (Si/G) equal to that of global supervisor, L (S/G). In this letter we extend this concept by considering the problem of optinal combination of decentralized with centralized control in case pure decentralized control happens to be inadequate. We introduce the concept of locally controllable complementary tuple and present an analytical framework for nonhomogeneous decentralized supervisory control systems.

Theoretical values of site attenuation for broadband receiving antenna or the antenna factor of broadband antenna over the frequency range from 30 MHz to 1 GHz have been calculated or measured by some researchers. For a frequency range over 1 GHz, wire antennas or horn antennas should be used. However, the theoretical site attenuation or antenna factor over 1 GHz have never yet been calculated. A CLS (Conical Log-periodic Spiral) antenna is generally used for EMC/EMI measurements in the microwave band as a broadband wire antenna for the swept frequency method. However, this antenna has the defect that its use results in the loss of polarization information. So we proposed an improved CLS antenna which has linear polarization. This new CLS antenna has another wire wound symmetrically to that of the standard CLS antenna. For this reason, we named it a double-wire CLS antenna. The double-wire CLS antenna loses no polarization information. We calculated the height pattern and the frequency characteristics of CSA (Classical Site Attenuation) for the double-wire CLS antenna when used for receiving, or used for both transmitting and receiving, as well as the antenna factor. Moreover, NSA (Normalized Site Attenuation) when the double-wire CLS antenna is used for receiving or used for both transmitting and receiving in free space were calculated.

Approximate maximum likelihood (ML) detection implemented by a reduced state Viterbi algorithm (VA), called the reduced state Viterbi coherent detection (RSVCD) algorithm in this paper, is described for the reception of uncoded M-ary PSK (MPSK) signals transmitted over additive white Gaussian noise (AWGN) channels. An M-state trellis, each state representing one of M signal constellation points, is used. The RSVCD algorithm performs parallel channel estimation based on the per-survivor processing principle (PSPP). Simple decision feedback CD (DFCD) is deduced as a special case of RSVCD. Unified BER expressions are derived for RSVCD, DFCD, and approximate ML detection implemented as an ML-state Viterbi algorithm (referred to as VACD) [6] as well as ideal CD and differential detection (DD). Computer simulation results are also presented and compared with theoretical results.

This paper describes the use of direct wafer bonding technique to implement the novel concept of "free-material and free-orientation integration" which we propose. The technique is applied for various wafer combinations of an In-Ga-As-P material system with lattice- and orientation-mismatches. The properties of the bonded structures are studied in terms of the crystalline and electrical characterization. The high crystalline quality of the bonded structures with those mismatches is proved by transmission electron microscopy, and good electrical conduction was attained in some bonded structures of InP and GaAs. (001) InP-based 1.55-µm wavelength lasers are fabricated on (110) GaAs substrate by direct wafer bonding. The light-current characteristics of the lasers are almost identical to those of lasers fabricated on (001) InP and (001) GaAs substrates, while the turn-on voltage is a little bit higher due to the higher barrier height at the bonded interface. The practicability in those lasers are also examined. Furthermore, we show direct wafer bonding of a (001) InP-based structure and a (110) Si substrate with a GaAs buffer layer, aligning the cleavage planes of the InP and the Si. The results demonstrate the remarkable feasibility of using the direct wafer bonding technique to obtain integrated structures of material- and orientation-mismatched wafers with satisfactory quality.

Butt-joint waveguide couplings are fabricated for use in InP-based photonic integration, and characterized by scanning electron microscopy and optical transmission measurements. Several parameters have been optimized in the characterization study: size and shape of the mask protecting the first waveguide layer during butt-joint regrowth, and the crystallographic direction of the butt-joint interface. The studies show that high-quality butt-joints having negligible optical loss can be made with good fabrication tolerance. Using the optimized butt-joint, DBR-type, gain-clamped SOAs have been fabricated which are free of internal excess reflections. A constant optical gain of 21 dB is obtained up to a signal output power of 25 mW. The devices show CATV grade linearity in a 77 channel CATV linearity test at a distortion level of -55 dB below carrier.

In this paper, we propose a new strategy of estimating correlation dimensions in combination with the method of surrogate data, which is a kind of statistical control usually introduced to avoid spurious estimates of nonlinear statistics, such as fractal dimensions, Lyapunov exponents and so on. In the case of analyzing time series with the method of surrogate data, it is desirable to decide values of estimated nonlinear statistics of the original data and surrogate data sets as exactly as possible. However, when dimensional analysis is applied to possible attractors reconstructed from real time series, it is very dangerous to decide a single value as the estimated dimensions and desirable to analyze its scaling property for avoiding spurious estimates. In order to solve this defficulty, a dimension estimator algorithm and the method of surrogate data are combined by introducing Monte Carlo hypothesis testing. In order to show effectiveness of the new strategy, firstly artificial time series are analyzed, such as the Henon map with additive noise, filtered random numbers and filtered random numbers transformed by a static monotonic nonlinearity, and then experimental time series are also examined, such as wolfer's sunspot numbers and the fluctuations in a farinfrared laser data.