Applying ARQ to real time video communication can significantly increase transmission delay due its retransmission operations. We analyze this delay and propose an adaptive error control scheme that uses acknowledgment from the receiver to reduce the delay. We evaluate this scheme using a computer simulation and show that the proposed scheme can reduce the delay by controlling the amount of video data by changing the quantization step size and video frame skipping. It also offers acceptable video quality as confirmed by a subjective evaluation test.

In this paper a novel narrow-band bandpass filter with an output pair of analytic signals is presented. Since it is based on the complex analog filter, both synthesis and response characteristics of this filter are different from conventional bandpass filters. In the design of this filter, the frequency shift method is employed and the conventional lowpass to bandpass frequency transformation is not required. The analysis and examples show that the output signal pair of the proposed filter possesses same filtering characteristics and a 90 degree phase shifting characteristics in the passband. Therefore, the proposed filter will be used for a single sideband (SSB) signal generator without quadrature generator.

This paper proposes the use, in integrated wireless systems, of the Reserved Idle Signal Multiple Access with Collision Resolution (R-ISMA/CR) protocol for applications in future multimedia mobile communications. It is applied to the integrated voice and data wireless system. Moreover, the consideration is made of the integrated voice and the low-bit video wireless system in R-ISMA/CR. To integrate video we employed not only a packed discard for video packets when the video packet delay is more than a threshold value, but also the connection packet (CP) technique for improving the channel utilization. Finally the integration of voice, data, and low-bit-video wireless system in R-ISMA/CR is considered. The performance are evaluated mainly by simulations.

This paper describes the relation between the structure and the capability on mesh-connected computers with orthogonal broadcasting. It is shown that algorithms of maximum finding for the two-way communication model can be performed on the one-way communication model without increasing the time complexity.

We have been studying on subthreshold characteristics of SOI (Silicon-On-Insulator) MOSFET's in terms of substrate bias dependence using a one-dimensional subthreshold device simulator based on Poisson equation in an SOI multilayer structure for estimating structural parameters of real devices. Here, we consider the quantum mechanical effects in the electron inversion layer of thin SOI MOSFET's, such as the two-dimensionally quantized electron states and transports, with a self-consistent solver of Poisson and Schrodinger equations and a mobility model by the relaxation time approximation. From results of simulations, we found a significant difference between this model and the classical model and concluded that the quantum mechanical effects need to be considered in analizing thin-film SOI devices.

Electric fishes generate an AC electric field around themselves by the electric organ in the tail. Spatial distortion of the field by nearby objects is detected by an electroreceptor array located an over the body surface to localize the object electrically when other senses such as vision and mechanosense are useless. Each fish has its own 'frequency band' for its electric organ discharges, and jamming of the electrolocation system occurs when two fish with similar discharge frequencies encounter. To avoid janmming, the fish shift their discharge frequencies in appropriate directions. A computational algorithm for this electrical behavior and its neuronal implementation by the brain have been discovered. The design features of the system, however, are rather complex for this simple behavior and cannot be readily explained by functional optimization processes during evolution. To gain insights into the origin of the design features, two independently evolved electric fish species which perform the same behavior are compared. Complex features of the neuronal computation may be explained by the evolutionary history of neuronal elements.

With the dramatic rise in the number of Internet users, the expansion of international corporate activity and the arrival of multimedia services, highly-competitive information and communication services are entering a period of severe global change. There is widespread recognition that as these changes take place, it is important to establish operation and management (O&M) that will enable "seamless" end-to-end communication services between any points on the earth. With worldwide trends moving toward automation, the study of automation of O&M is being energetically pursued. This paper describes the requirements for service O&M and gives an overview of the technology believed to be essential to achieve them. The progress of developments is also reported.

This paper proposes the Snow Crystal method, which aims to present the hierarchies of a large-scale telecommunication network on one screen. This will improve the user interface of a network operation system for network operations and management. With the proposed presentation method, locations of nodes are automatically set based on the number of hierarchy levels and the number of nodes. The nodes in the same hierarchy level are located on the same circle at even intervals. The center of the circle that corresponds to the top hierarchy level is set at the center of the screen. The radius of the circle is determined by the number of nodes. The centers of circles that correspond to the second hierarchy levels belonging to the nodes of the top hierarchy level, are located on a larger circle with the same center point as the top level circle at even intervals. The centers of circles that correspond to the third hierarchy levels are located at even intervals on a circle with the same center point as the second level circle, which the third levels belong to. The nodes of the subsequent levels are located in the same way. The proposed presentation method is successfully applied to a large-scale telecommunication network. Moreover, the results of an operating experiment with the proposed method show its effectiveness for presenting hierarchies of large-scale telecommunication networks.

Rapid advancing technology and customer demand for sophisticated services are driving the global telecommunications environment into fully competitive and multi service providers environment. To cope with this new environment successfully, open network and open telecommunication management are essential. Telecommunication management is becoming more and more important to realize flexible and dynamic telecommunication services. This paper first gives a view of the new environment in the telecommunication industry and discusses the direction to be taken by service providers. Then, a concept of multi-domain management is proposed to meet a dynamically changing environment. Finally, the paper describes the subjects for the development of telecommunication management system and suggests that a competition based on harmony between the users, service providers and vendors is needed to make customers satisfied with telecommunication services.

This paper presents the several bifurcation phenomena of harmonic oscillations occurred in nonlinear three-phase circuit. The circuit consists of delta-connected nonlinear inductors, capacitors and three-phase symmetrical voltage sources. We analyze the bifurcations of the oscillations by the homotopy method. Additionally, we confirm the bifurcation phenomena by real experiments. Furthermore, we reveal the effect of nonlinear couplings of inductors by the comparison of harmonic oscillations in a single-phase circuit.

A small-sized three-stage GaAs power module has been developed for portable digital radios using M-16QAM modulation. This module has exhibited typical P1dB of 10 W with PAE of 48% and a power gain of 35 dB at a low supply voltage of 6.5 V in 1.453-1.477 GHz band. The volume of the module is only 1.5 cc, which is one of the smallest value in 10 W class modules ever reported. In order to realize the reduced size and the high power performances simultaneously, the module has employed new power divider/combiner circuits with significant features of the reduced occupation area, the improved isolation properties and the function of second-harmonic control.

Our compact switching converter using a thin-film microtransformer mono-lithically integrated with rectifier diodes represents the first step in developing a monolithic micro-switching converter that can be integrated with semiconductor devices and magnetic components. This converter is a single-ended forward converter with resonant reset and operates successfully at 15 MHz. The maximum output power is 0.5 W.

Users of computer communication systems and their requirements are rapidly increasing and changing. It is desirable to have a development method which helps to make small changes in a design of a system to obtain another system which satisfies new requirement changes. We propose a flexible synthesis method which adopts designers' requirement changes in formal protocol specifications designed in LOTOS.

Recently several dosimetric assessment procedures have been proposed to demonstrate the compliance of handheld mobile telecommuications equipment (MTE) with safety limits. However, for none of these procedures has an estimation of the overall uncertainty in assessing the maximum exposure been provided for a reasonable cross-section of potential users. This paper presents a setup and procedure based on a high-precision dosimetric scanner combined with a new phantom derived from an anatomical study. This allows the assessment of the maximum spatial peak SAR values occurring in approximately 90% of all MTE users, including children, with a precision of better than 25%. This setup and procedure therefore satisfies the requirements of the FCC, as well as those drafted by a CENELEC working group mandated by the European Union.

This paper optimizes a hierarchical image transmission system based on the hierarchical modulation scheme in a band-limited Rayleigh fading channel. Authors analyze relations between hierarchical parameters and the image quality, and show that the existence of optimum hierarchical parameter that maximizes the received image quality.

A two-dimensional receiver OEIC array having an address selector for highly parallel interprocessor networks has been realized. The receiver OEIC array consists of two-dimensionally arranged 1616 (256) optical receiver cells with switching transistors, address selectors (decoders), and a comparator. Each optical receiver comprises a pin PD and a transimpedance-type HBT amplifier. The HBT has an InP passivation structure to suppress the emitter-size effect, which results in the improvement of current gains, especially at low collector current densities. The receiver OEIC array was fabricated on a 3-inch diameter InP substrate with pin/HBT integration technology. Due to the function of address selection, only one cell is activated and the other cells are mute, so the receiver OEIC array shows low crosstalk and low power consumption characteristics. The array also shows a 266-Mb/s data transmission capability. This receiver OEIC array is a most complex InP-based OEIC ever reported. The realization of the two-dimensional receiver OEIC array promises the future interprocessor networks with highly parallel optical interconnections.

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.

Extremely compact multi-mode interference (MMI) devices using central wide-angle coupling of input and output waveguides are proposed. It is shown that MMI can be used to change the propagation direction of light without the need for corner mirrors or bent waveguides. The concept can also be used for very compact power splitters which are even smaller than conventional MMI power splitters. Coupling between waveguides at wide angles is discussed and a number of regularities are found. The results can be useful for the design of more compact integrated circuits by a reduction of the number of bent waveguides which usually take up the largest part of the area of a photonic integrated circuit.

Wavelength Division Multiplexing (WDM) technology provides many options to the design of flexible alloptical networks. To exploit these options to their full potential, Photonic Integrated Circuits (PICs) for wavelength routing and switching will be indispensable. One of the basic building blocks of such PICs is the planar phased-array (PHASAR) wavelength demultiplexer. The monolithic integration of PHASARs with photodetectors, amplifiers, and other waveguide-based (passive) components is discussed.

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.