This paper analyzes the performance of the capacity controlled radio system under a frequency selective fading environment. This system controls the number of modulation levels according to the number of active subscribers. In the analysis, we consider the capacity controlled system either with or without adaptive equalizer. As the results of analysis, it is clarified that the system is superior to the conventional fixed capacity system, and can be considered as a good countermeasure for multi-path fading. And it is found that there exists a synergistic effect due to capacity controlling and adaptive equalizing.

This paper reports the influence of optical reflection induced noise and distortion for optical fiber feeder systems for microcellular mobile communication systems. Since the optical feeder requires very wide dynamic range, noise and distortion must be suppressed to an extremely low level. From optical transmission experiments and theoretical analysis, the basic characteristics of the reflection induced noise and distortion were investigated. By using these results, it was estimated that, for currently used analog mobile telephone systems, the number of connectors with 35 dB reflectance must be limited to less than 17, in order to suppress the noise caused by the connector reflections. Moreover, it was confirmed that the reflection induced distortion drastically decreases according to the increase of the length between reflectors. Therefore, the distortion can be suppressed by expanding the connector spacing to more than 7 meters.

The various propagation characteristics of millimeter waves in silicon rib and image guides containing the optically induced plasma region have been investigated. Phase shift and attenuation properties resulting from the presence of plasma are evaluated using the effective dielectric constant method. Experiments have been carried out to demonstrate the optical control of millimeter waves at frequencies ranging from 3350 GHz using high-resistivity silicon illuminated by a high-power Xenon arc lamp and light emitting diodes. Optical control of millimeter wave attenuation of 20dB has been confirmed for a guide of length 90 mm and plasma density of 1021/m3 with average plasma thickness of 20 µm. To increase the sensitivity of optical control, Bragg reflection filter characteristics are studied and its stop band characteristics have been calculated using the transmission line model, and confirmed experimentally. To further develop the Bragg reflection filter, a Mach-Zehnder interferometer guide with one of the arms periodically corrugated is newly proposed and its optical control performance is confirmed by experiments. Finally the field distributions of the Mach-Zehnder configuration of rib waveguides are measured by a simple optical probing technique using the focused laser spot.

We apply Fahlman and Lebiere's (FL) algorithm to network synthesis and incremental learning by making use of already-trained networks, each performing a specified task, to design a system that performs a global or extended task without destroying the information gained by the previously trained nets. Investigation shows that the synthesized or expanded FL networks have generalization ability superior to Back propagation (BP) networks in which the number of newly added hidden units must be pre-specified.

This paper reviews Ti:LiNbO3 and semiconductor optical waveguide modulators. The operating principle of the Ti:LiNbO3 optical waveguide modulator is based on the Pockels effect. On the other hand, semiconductor optical modulators can be operated based on the Pockels effect, the Franz-Keldysh effect, or the quantum confined stark effect (QCSE) by employing multiple quantum wells (MQWs). Ti:LiNbO3 optical waveguide modulators are discussed with emphasis on the velocity-matching and optical waveguides. MQW optical waveguide modulators are discussed in view-point of design of a MQW structure, waveguide and modulation bandwidth.

Research in optical microwave interaction, at its earlier stages, was spured by the desire to make an optically fed and controlled phased array antenna with monolithic microwave integrated circuit (MMIC) transmit/receive (T/R) modules. In the first part of this paper experimental results are presented demonstrating an optically fed phased array antenna operating at C-band in the 5.5 to 5.8 GHz frequency range. The present system consists of two optically fed 14 subarrays with MMIC based active T/R modules. Custom designed fiber optic links have been employed to provide distribution of data and frequency reference signals to phased array antenna. One of the challenges of the future is the development of better interfaces between electronic (microwave) and optical components, including the chip level merging of photonic and electronic components on III-V compounds. This aspect of the research is covered in the second half of the paper.

For a method to control the microwave coupled lines with optically induced plasma effectively, we propose the selective mode-control method, which restricts controlled modes to a selected one. We analyzed the basic characteristics of coupled microstrip lines theoretically by using the spectral domain technique and indicated the effectiveness of this method with the aid of numerical results. Further, we designed an optically controlled change-over switch as an application of this method.

We show the design of the bandwidth and the external quantum efficiency (including the coupling efficency to a single-mode fiber) of p-i-n photodetectors. Based on their design procedures, the performance limits of both conventional surface-illuminated photodetectors and side-illuminated photodetectors are evaluated. We point out that in the ultrawide-band region, optical waveguide photodetectors have great advantages over conventional surface-illuminated photodetectors in terms of the product of the bandwidth and the external quantum efficiency. It is shown that a 100-GHz bandwidth can be achieved with little degradation of the external quantum efficiency by a multimode waveguide photodetector structure. We also present a design concept for overcoming the performance limits of solitary waveguide photodetectors by including an input tapered optical waveguide.

This paper theoretically evaluates the external electro-optic (EO) sampling of high-speed electrical signals using poled polymers as materials for a proximity electric-field sensor. Based on the derivation of the half-wave voltage and the analysis of a static electric field coupled to the polymeric media placed over IC interconnections, invasiveness, voltage sensitivity, and spatial resolution have been discussed. The polymeric sensors have shown to be used in contact with the IC interconnections with negligibly small invasiveness, thus making polymeric sensors provide higher sensitivity and spatial resolution than inorganic crystals such as GaAs and KD*P.

High Tc superconducting (SC) active antennas made from thin films were produced by the magnetron sputtering method. The SC active antennas are found to be good for detecting 50GHz electromagnetic waves. Furthermore, the improvement of the sensitivity of the SC active antennas is demonstrated with the use of a corner reflector.

Theoretical and experimental evaluations of the horizontal rotating and tilting of the base station antenna beam show that these techniques are effective in reducing delay spread. Result show good agreement between predicted and measured values.

Compared to multi-level signature file techniques, PSF (Partitioned Signature File) technique has less processing overhead by its characteristics of a simple file organization. In a multi-processor environment, the PSF technique also has an advantage that queries can be processed in parallel effectively by allocating one or more partitions to each processor. Main point of the PSF technique is a partitioning scheme based on a key selection. In this paper, an n-BFK (n-Bounded Floating Key) partitioning scheme is proposed, in which the number of segments for a key selection is bounded by n. The cost model is developed for the performance evaluation of the proposed scheme. By performance comparison with the existing schemes, the efficiencies of the proposed scheme are shown with respect to a disk access cost, a signature reduction ratio, and an uniformity of workload.

This paper reviews the application of optical technologies to phased array antennas. The performance of the fibre transmission medium and of sources and detectors is reviewed, leading to simple expressions for transmission loss and noise performance. Both coherent and non-coherent beam forming techniques are considered. Future trends, including the use of optical amplifiers and coherent signal generation, will also be discussed.

A field trial was conducted to evaluate the technical performance of land mobile message communication in different environments. The OmniTRACS system and the Ku-band JCSAT satellite were utilized as the mobile communications system and the satellite, respectively. The trial took place in September 1990 at different areas in Japan. Data collected correspond to about 65 hours of operation, during which a large number of messages were sent via the satellite. Two land mobile terminals operated simultaneously, each terminal having a function of generating messages automatically which simulates a large volume of traffic corresponding to about 50 terminals. Thus, the system was evaluated under the condition that 100 mobile terminals were in operation. Obtained data have been analyzed with a particular focus on the message transmission correlating with actual environments. The analysis was done by classifying environments into five categories: overall condition, type of roads, terrain, areas and weather conditions. The average transmission count per message experienced under all conditions is equal to 1.432 for forward messages transmitted from the hub station to mobiles, and 1.157 for return messages transmitted from mobiles to the hub station. With respect to the classification by the type of roads, for enample it becomes obvious that the performance is generally good except along roads of North-South orientation through dense urban areas. It is concluded that the message communications from/to mobiles are feasible in a wide range of environments, with the performance of success essentially depending on the visibility of satellite.

Real-time database systems have the properties of database and real-time systems. This means they must keep timing constraints of transactions as required in real-time systems, and at the same time ensure database consistency as required in database systems. Real-time concurrency control is a general approach for resolving this conflict. In this type of control, a concurrency control technique for database systems is integrated with a task scheduling technique for real-time systems. This paper surveys previous studies on real-time concurrency control and considers future research directions.

This paper describes a new technique for isolated word recognition that uses both pitch information and spectral information. In conventional methods, words with similar phoneme features tend to be misrecognized even if their phonemes are accented differently because these methods use only spectral information. It is possible to improve recognition accuracy by considering pitch patterns of words. Many phonetically-similar Japanese words are classified by pitch patterns. In this technique, a pitch pattern template is produced by averaging pitch patterns obtained from a set of words which have the same accent pattern. A measure for word recognition is proposed. This measure based on a combination of the phoneme likelihood and the pitch pattern distance which is the distance between a pitch pattern of an input speech and pitch pattern templates. Speaker-dependent word recognition experiments were carried out using 216 Japanese words uttered by five male and five female speakers. The proposed technique reduces the recognition error rate by 40% compared with the conventional method using only phoneme likelihood.

The problem of two-dimensional scattering of electromagnetic waves by a grating with several strips arbitrarily oriented in one period is analyzed by means of the Wiener-Hopf technique together with the formulation using the concept of the mutual field. A formulation for the analysis of multiple scattering from the grating is based on the representation of the scattered field by a grating composed of one strip in one period. The Wiener-Hopf equations and a representation of the scattered wave are obtained. The characteristic of the sampling function is used to expand the unknown function associated with the field on the strip into a series, and then the Wiener-Hopf equations are reduced to a set of simultaneous equations. For evaluation of the convergence and the errors in the numerical results, the relative error with respect to the extrapolated value and the square error for satisfaction of the boundary condition are computed. From numerical comparison of the present method with other various methods, it is found that the present method provides us accurate results. Some numerical examples of the reflection coefficients are presented for the reflection grating and transmission gratings.

Surface construction is known as a way to visualize volume data. Although currently used algorithms such as marching cubes have good enough quality for volume visualization, they do not ensure adequate surface topology. These algorithms work well when the surface is rather simple. While when complicated, the surface does not separate the internal and external spaces, that is, there exist some holes on the surface, or exist redundant overlaps or self-intersection. Actually, adequate surface topology is important not only for visualization but for laser stereolithography, which creates real 3D plastic objects. In the present paper, we propose a new method that produces a set of triangular patches from a given volume data. The fact that the set of patches has no holes, no redundancy, no self-intersection, and has orientable closed surface topology is shown.

Theoretical prediction of propagation is required for the future urban mobile communications, in order to make possible precise and universal prediction for arbitrary conditions. The necessity and the fundamental concept of theoretical prediction are introduced, and the theoretical prediction of mean field strength in urban areas is reviewed and discussed. Theoretical method is important particularly in prediction of multipath delay characteristics, in relation to the prediction of error rates in digital mobile radio communications.

Recently, making good use of the advantages of optical fibers such as wide bandwidth and low loss, it has been investigated to apply optical fiber link to microcellular mobile communication systems. This system allows complex equipment to be located at microcell control station, and can simplify the equipment of microcell base stations compared with the conventional systems. In this paper, we analyze the performance of optical fiber link for microcellular mobile communication systems, taking radio link fading and optical link nonlinear distortions into consideration. From the calculated results, it is disclosed that the effect of both items does not generate the significant excess CNR degradation, and the correct CNR can be approximately calculated by using CNR of non-faded case. And it is also disclosed that the degradation of CNR due to optical link nonlinearity is slightly improved by taking adjacent channel signal fade into consideration.