Existing MultiCode-CDMA MAC protocols perform only single dimensional access control either in the code or time domain. In this paper, we propose a MAC protocol, called SCTAC which can perform simultaneous code-time access control to achieve better system utilization. Also, SCTAC intends to provide service differentiation among different traffic classes. In order to simultaneously control access in both the code and time domain, SCTAC decouples the function of transmission ordering from the function of packing the scheduled transmissions in the resource space. As such, different transmission scheduling algorithms can be adopted without altering the MAC protocol. A water filling approach is used for efficient transmission packing where each of the scheduled transmissions is treated as a rectangular capsule with an arbitrary size and the resource space is viewed as a water container. In addition, SCTAC uses different request sending probabilities with an improved probability update algorithm to achieve service differentiation. Simulation results indicate that SCTAC is capable of providing different performances to different traffic classes. The results also confirm that SCTAC can achieve higher throughput compared to single dimensional access control protocols. Therefore, SCTAC is a better MAC protocol.

This paper presents the concepts and methodology of knowledge-based information modeling based on Cognitive Science for realizing the autonomous humanoid service robotic arm and hand system HARIS. The HARIS robotic system consists of model-based 3D vision, intelligent scheduler, computerized arm/hand controller, humanoid HARIS arm/hand unit and human interface, and aims to serve the aged and disabled on desk-top object manipulations. The world model, i.e., a shared knowledge base, is introduced to work as a communication channel among the software modules. The task scheduling as well as the 3D-vision is based on Cognitive Science, i.e., a human's way of vision and scheduling is considered in designing the knowledge-based software system. The key idea is to use "words" in describing a scene, scheduling tasks, controlling an arm and hand, and interacting with a human. The world model plays a key role in fusing a variety of distributed functions. The generalized frame-based knowledge engineering environment ZERO++ has been effectively used as a software platform in implementing the system. The experimental system is working within a limited situation successfully. Through the introduction of Cognitive Science-based information modeling we have learned useful hints for realizing human-robot symbiosis, that is our long term goal of the project.

This paper discusses solutions that provide forward link power allocation based on 3GPP (FDD) standardization reports and that meet the Eb/No required for forward link channels. In addition, we determine the forward link user capacity under a mixed service environment. Cell coverage is derived using the solutions from the forward link user capacity problem and an urban propagation model. These results are achieved with the introduction of various factors, such as the number of users, service types, macro/microcell environments, and others. Our study shows that for IMT-2000 systems offering a mixed service environment, forward link power should be carefully allocated depending on the ratio of users occupied by each service type if one is to achieve optimal cell planning.

The urgent tasks of MOSFET modeling for circuit simulation are easy adaptation to new physical phenomena arising for advancing technologies, and, of course, sufficient simulation accuracy. Approaches currently being pursued for developing such MOSFET models are summarized. Their capabilities for accomplishing these tasks as well as the important remaining problems are discussed. Main focus is given on the model HiSIM, the first commonly available model based on the drift-diffusion approximation developed for 0.10 µm MOSFET technology node.

Optical disk systems have been used in a wide range of applications and the performance of these systems has been improving rapidly. The optical integration is one of the important technologies of the progress of the optical pickup head in the system. It can make the optical pickup head miniature, light sized, ease to assemble, cost reduced and reliable during long time operation. In this paper, at first, merits and features of the optical integration for optical disk systems are briefly reviewed. Then, our activities on the development of the various hybrid-integrated optical devices, "Laser Couplers" are reported. Especially, the most recent results on the "Two-wavelength-beam Laser Coupler," are described in detail. It has two-wavelength laser emission/detection functions and easily realizes an ultimate solution of the optical pickup head for the DVD/CD system, now being used in "PlayStaion2. " To simplify the structure and the fabrication of this device, a new monolithic-integrated two-wavelength laser diode, called a visible and infrared laser diode, has been developed, which can be easily fabricated using only two steps of metal organic chemical vapor deposition. The structures and characteristics of this device are reported. Lastly, other recent technologies of the optical integration, including monolithically integration, near field optics and so on, are reviewed.

Nowadays, the World Wide Web is continuing to expand at an amazing rate as a medium for conducting business in addition to disseminating information, and Web users are remarkably increasing. Human activities in virtual space as the Web are producing large volumes of data, and Web data mining to extract information from Web data has become an important research area. In this paper, we examine the features of Web log data and propose a method for transaction identification. We also introduce a new problem of user segmentation and present a method for solving this problem.

This paper presents a historical review of fiber technologies from the 1970s till now, focused on design, transmission characteristics, and reliability assurance of silica optical fibers. Discussion is made by dividing the period into two phases; the first phase closing nearly at the end of the 1980s and the second one starting at the same time. As for the first phase, we present designs of graded-index multimode fiber and single-mode fiber, and development of dispersion shifted fiber. Mechanical reliability assurance and loss increase phenomena due to hydrogen are also described. Development of an optical fiber amplifier triggered the start of the second phase. Due to the introduction of WDM transmission systems as well as demand on high bit-rate transmission, fiber dispersion and nonlinearity have become indispensable factors to be taken into consideration for system design and performance evaluation. We discuss novel non-zero dispersion shifted fibers and dispersion compensating fibers, developed to meet the requirements for long distance and high bit-rate WDM transmission systems. Finally, discussions are made on the future research and development items, which are necessary to realize anticipating photonic networks.

We demonstrate a single high-order transverse mode surface emitting laser (VCSEL) with narrow trenches formed on a top surface. The design and the fabrication of a single high-order mode 850 nm GaAs VCSEL with micromachined surface relief are presented. Stable single-mode operation with a side-mode suppression ratio of over 40 dB was obtained in an entire measured current range. We obtained the maximum single mode power of over 3.5 mW and a record low series resistance of below 50 Ω. In addition, a single-lobe far field pattern is demonstrated even under high-order transverse mode operation by loading phase-shift on the top surface. A coupling efficiency with optical fibers is dramatically improved.

This paper proposes a quasi-coherent equivalent-time sampling method to acquire repetitive wideband waveform signals with high throughput. We have already proposed a new sampling system which incorporates the pre-trigger ability and the time jitter reduction function for a fluctuated input signal while maintaining the waveform recording efficiency. The quasi-coherent sampling method proposed in this paper can be adopted to it in order to improve its data acquisition throughput significantly. Numerical simulation results show effectiveness of our proposed method.

In this paper, we propose the multirate repeating method for alias free subband adaptive filters (AFSAFs) and consider its convergence property. It is shown that we can adjust the convergence speed and the final error of the adaptive filters by varying its two parameters according to the requirements of the applications where the method is applied. The proposed method has two parameters, namely, the number of channel and the number of repetition. We show that by increasing the number of channels we can reduce the final error, and this property is preferred when the signal-to-noise ratio (SNR) is low. On the other hand, we show that the convergence speed of the AFSAF approaches to that of the affine projection algorithm (APA) by increasing the number of repetition. Through the computer simulations, we show the effect of the proposed method.

Low cost optical subscriber systems and effective operation are indispensable to the construction and maintenance of greatly expanded optical fiber networks. An optical fiber line monitoring system is essential for reducing maintenance costs and improving service reliability in optical access networks. To promote cost-effective optical fiber line operation, we propose an extended automatic optical fiber operations support system (AURORA) with a remotely installed fiber selector. We suggest a configuration for extended AURORA and design the dynamic range of the system. We confirmed that testing could be carried out on an extended optical network section of 10 km in length by using extended AURORA when the optical trunk line was less than 15 km. We also discuss the effect on the maintenance cost of optical fiber cables in access networks. We calculated the annual maintenance cost for periodic tests in actual operation areas, and confirmed that this cost could be reduced by 30% compared with that for a conventional system.

In this paper an analytical parametric formulation of total degradation in Orthogonal Frequency Division Multiplexing (OFDM) systems including High Power Amplifiers (HPA) is presented. Two classes of non-linear devices are considered: Traveling Wave Tube Amplifiers (TWTA) and Solid State Power Amplifiers (SSPA). In the results the accuracy of the proposed method is checked and the impact of coding to mitigate non-linear distortion is easily assessed.

The electronically steerable passive array radiator (ESPAR) antenna is one kind of the parasitic elements based single-port output antennas with several variable reactances. It performs analog aerial beamforming and none of the signals on its passive elements can be observed. This fact and one that is more important--the nonlinear dependence of the output of the antenna from adjustable reactances--makes the problem substantially new and not resolvable by means of conventional adaptive array beamforming techniques. A novel approach based on stochastic approximation theory is proposed for the adaptive beamforming of the ESPAR antenna as a nonlinear spatial filter by variable parameters, thus forming both beam and nulls. Two learning rate schedule were examined about output SINR, stability, convergence, misadjustment, noise effect, bias term, etc., and the optimal one was proposed. Further development was traced. Our theoretic study, simulation results and performance analysis show that the ESPAR antenna can be controlled effectively, has strong potential for use in mobile terminals and seems to be very perspective.

In computer-aided drafting and design, interactive graphics is used to design components, systems, layouts, and structures. There are several approaches for using automated graphical layout tools currently. Our approach employs a genetic algorithm to implement a tool for automated 3D graphical layout design and presentation. The effective use of a genetic algorithm in automated graphical layout design relies on defining a fitness function that reflects user preferences. In this paper, we describe a method to define fitness functions and chromosome structures of selected objects. A learning mechanism is employed to adjust the fitness values of the objects in the selected layout chosen by the user. In our approach, the fitness functions can be changed adaptively reflecting user preferences. Experimental results revealed good performance of the adaptive fitness functions in our proposed mechanism.

The detection of timing constraint violation is crucial in reactive systems. A method of detecting deadline violation based on Floyd-Warshall shortest path algorithm has been proposed by Chodrow et al. We extend this method to detect the violation of minimum delay time in reactive systems where the repetition of event sequences frequently occurs.

We describe hybrid integration technologies that employ silica-based planar lightwave circuit (PLC) platforms, and report several high-performance optical components based on these technologies. First, we describe the requirements for optical integrated circuits. Then, we discuss the technologies used in hybrid integration, namely optical coupling between a semiconductor optical device and a silica waveguide, electrical signal transmission to the semiconductor optical device, and high quality optical signal processing. In addition, we describe optical integrated circuits developed for short- and long-haul networks. We realized these high-performance integrated components by combining appropriate hybrid integration technologies.

Using a full-vector finite element method (FEM) with curvilinear hybrid edge/nodal elements, a single-mode nature of index-guiding photonic crystal fibers, also called holey fibers (HFs), is accurately analyzed as a function of wavelength. The cladding effective index, which is very important design parameter for realizing a single-mode HF and is defined as the effective index of the infinite photonic crystal cladding if the core is absent, is also determined using the FEM. In traditional fiber theory, a normalized frequency, V, is often used to determine the number of guided modes in step-index fibers. In order to adapt the concept of V-parameter to HFs, the effective core radius, aeff, is determined using the actual numerical aperture given by the FEM. Furthermore, the group velocity dispersion of single-mode HFs is calculated as a function of their geometrical parameters, and the modal birefringence of HFs is numerically investigated.

This paper proposed an automated segmentation algorithm for MR brain images through the complementary use of T1-weighted, T2-weighted, and PD images. The proposed segmentation algorithm is composed of 3 steps. The first step involves the extraction of cerebrum images by placing a cerebrum mask over the three input images. In the second step, outstanding clusters that represent the inner tissues of the cerebrum are chosen from among the 3-dimensional (3D) clusters. The 3D clusters are determined by intersecting densely distributed parts of a 2D histogram in 3D space formed using three optimal scale images. The optimal scale image results from applying scale-space filtering to each 2D histogram and a searching graph structure. As a result, the optimal scale image can accurately describe the shape of the densely distributed pixel parts in the 2D histogram. In the final step, the cerebrum images are segmented by the FCM (Fuzzy c-means) algorithm using the outstanding cluster center value as the initial center value. The ability of the proposed segmentation algorithm to calculate the cluster center value accurately then compensates for the current limitation of the FCM algorithm, which is unduly restricted by the initial center value used. In addition, the proposed algorithm, which includes a multi spectral analysis, can achieve better segmentation results than a single spectral analysis.

We investigate a method to suppress the polarization-dependent loss (PDL) of long-period fiber gratings (LPFGs). We study the origins of the PDL and propose an azimuthally isotropic UV exposure to suppress the UV-induced birefringence and to realize low-PDL LPFGs. By using this technique and a low birefringent fiber together, the PDL of LPFGs can be reduced to a sufficiently low level required in high performance communication systems. Moreover, the validity of our theoretical modeling is confirmed by the experimental results.

In order to construct optical access networks economically for fiber to the home (FTTH), it is important to reduce the cost of optical fiber cable installation. Optical fiber and cable costs have been reduced over the past ten years, however there have been few reports describing installation cost reduction. In this paper, we describe the design of high-density optical fiber cable that reduces the required installation time. To achieve this we have reduced the optical fiber cable weight and the friction coefficient of the cable sheath. We reduced the cable weight by using polyethylene foam and a non-metallic tensile strength member made of a new material, PBO. These two approaches reduce the cable weight by a total of about 30%. We also added a lubricant to the polyethylene sheath of this cable and this reduced the pulling force required for the additional cable by 30%-50%.