Since mobile communication systems using optical rays (optical mobile communication systems) do not radiate radio waves from the mobile terminals, they are expected to be used in environments containing sensitive electronic equipment. However, the placement and direction of the optical receivers must be suitably determined for mobile communication because light has high directivity. In optical mobile communication systems, the communication quality varies with the direction of the mobile terminal. Therefore, we examined the angle over which communication is possible at various measurement points and defined it as the communication angle. The mean opinion score (MOS) was obtained to assess the communication quality using the communication angle as a parameter. In this paper, the two situations, walking and sitting down, was considered the way optical mobile communication systems actually used. We found that for walking, when the communication angle was over 180 degrees, the MOS was over 3 and over 50% of users could communicate usefully. When used sitting down, the communication quality did not depend on the communication angle, but only on whether or not the user could communicate in the direction he/she was facing. Thus, if the communication angle in the service area is over 180 degrees, it is possible to communicate in practical situations, even while walking.

A comprehensive analysis methodology allowing investigation of the RF performance of Si and strained Si:SiGe MOSFETs is presented. It is based on transient ensemble Monte Carlo simulation which correctly describes device transport, and employs a finite element solver to account for complex device geometries. Transfer characteristics and figures of merit for a number of existing and proposed RF MOSFETs are discussed.

This paper proposes a fast and simple adaptive algorithm for MMSE (Minimum Mean Square Error) adaptive array antenna or MMSE combining diversity. This algorithm can be implemented with as a small operation as LMS since it is based on VS-LMS (variable step size LMS) for which the step size is provided with a fixed profile. Computer simulation results show that the proposed algorithm has much better convergence behavior and BER performance than LMS.

An ultra low-noise and highly selective, experimental 2-GHz band cryogenic receiver front end (CRFE) has been newly developed for cellular base stations. It utilizes a high-Q superconducting filter, a very low noise cryogenic amplifier, and a highly reliable cooler that is very compact. Fundamental design of the CRFE is investigated. First, the equivalent noise temperature of the CRFE and the effect of improving CRFE sensitivity on base station reception are discussed. Next, essential technologies and fundamental characteristics of each component are described. Finally, influence of antenna noise, such as ground noise and man-made noise, is estimated through field tests both in urban and suburban areas.

This paper proposes a novel configuration of an elevated base station using an adaptive array for TDMA systems, which can simultaneously decrease the CCI (co-channel interference) and form a circular cell. The proposed base station comprises two sets of transceivers and antenna arrays, and an adaptive beam control unit. The transceivers work in different time slots. The circular cell that suppresses the interference is achieved by integrating the pattern control of the two antenna arrays. The effectiveness of the proposed base station configuration is evaluated by field measurements using an adaptive array testbed. We confirm that the proposed base station achieves a channel capacity that is approximately 30% greater than that of a base station employing an omni-directional antenna and generates an omni-zone with reduced CCI in an actual microcell system. Furthermore, we confirm by computer simulation that the proposed base station establishes a communicable area that is approximately 1.8 times larger than that of a base station employing an omni-directional antenna.

We examine the detection of coded hybrid direct-sequence frequency-hopped spread-spectrum signals in the presence of narrowband interference. Since blind interference suppression requires a reliable estimate of the data, while at the same time data decoding requires interference suppression, we advocate an iterative ("turbo") detection scheme whereby information is exchanged between the interference suppressor and the soft-input soft-output decoder. Several suppression schemes are examined and compared. Simulation results show that this new scheme is robust, i.e., exhibits good performance under a modicum of assumptions on the interference structure. Turbo codes and convolutional codes are compared, showing that the former perform better.

The ATM Wireless Access (AWA) System allows portable terminals such as notebook PCs to provide up to 10Mbits/s to each user. AWA will be one of the last hops of the fiber system; it seamlessly provides wireless terminals with most of the services available in the fiber system. A prototype is developed to confirm system realization and the technical feasibility of the radio transmission rate of 80 Mbit/s, the highest yet reported in wireless access systems, by employing ATM technology to support multimedia communication with different communication quality requirements. The prototype uses TDMA as the multiple access method. This paper proposes the system concept and technical issues of the AWA system. The design and performance of the AWA prototype are clarified. It is confirmed that the target performance of the prototype can be achieved and technical issues are feasible.

We have developed an IP-over-Ethernet-based ultra high-speed multimedia wireless LAN prototype operating in the 60-GHz band. It employs a media-access-control (MAC) protocol based on reservation-based slotted idle signal multiple access (RS-ISMA), which was implemented in the former prototype, for supporting various IP traffic such as real-time AV traffic and best-effort web traffic. The protocol also has a new function called NACK sensing for the efficient retransmission of wireless multicast packets. It was demonstrated that the prototype can provide the world's fastest radio transmission speed of 128 Mbps for two-way communications. We have measured the throughput and latency of the prototype LAN for Ethernet-frame transmission in a point-to-point baseband-connected environment. The measurement showed that the prototype LAN provides a maximum throughput of 30 Mbps, and that the measured throughput agrees with the theoretically predicted throughput. It also showed that the maximum latency, which includes switching and routing latency in the wired part, is below 1 msec.

A Schottky contact model was implemented as a boundary condition for Monte Carlo device simulations. Unlike the ideal ohmic contact, the thermal equilibrium is unnecessary around the Schottky contact. Therefore, the wide region with high impurity concentration around the contact is not required to maintain the thermal equilibrium, which means that it is possible to avoid assigning a lot of particles to the low-field region. The validity of the present boundary condition for contacts was verified by simulating a rectifying characteristic of a Schottky barrier diode. As an application example using the present contact model, we simulated transport in n+nn+ structures with sub-0.1 µm channel lengths. We observed direction dependence of the electron velocity dispersion, which indicates that the direction dependence of the diffusion constant or the carrier temperature should be taken into account in the hydrodynamic simulation for sub-0.1 µm devices.

This work presents the first comprehensive full-band Monte Carlo model for the simulation of silicon/silicon-germanium devices with arbitrary germanium profiles. The model includes a new CPU and memory efficient method for the discretization of the Brillouin zone based on adaptive nonuniform tetrahedral grids and a very efficient method for transfers through heterointerfaces in the case of irregular -space grids. The feasibility of the FB-MC simulation is demonstrated by application to an industrial HBT with a graded germanium profile and different aspects of the microscopic carrier transport are discussed. Internal distributions of the transistor are calculated with a very low noise level and high efficiency allowing a detailed investigation of the device behavior.

We study the joint optimization problem of a transmitter with multiple transmit antennas and a receiver with multiple receive antennas in a narrow-band communication system. We discuss the problem of designing a pre-filter at the transmitter, a post-filter at the receiver, and a bit allocation pattern to multiple symbols in the sense of minimizing the average bit error rate. With the optimized filters and the bit allocation, we could realize high efficiency and high data rate in band-limited channels.

In this article, an efficient vector quantization (VQ) scheme called side-match finite-state vector quantization with adaptive block classification is presented for image compression. It makes use of edge information contained in image in additional to the average values of blocks forming the image. In order to achieve low bit rate coding while preserving good quality images, neighboring blocks are utilized to predict the class of current block. Image blocks are mainly classified as edge blocks and non-edge blocks in this coding scheme. To improve the coding efficiency, edge blocks and non-edge blocks are further reclassified into different classes, respectively. Moreover, the number of bits for encoding an image is greatly reduced by foretelling the class of input block and applying small state codebook in corresponding class. The improvement of the proposed coding scheme is attractive as compared with other VQ techniques.

This letter empirically evaluates the way how to calculate the complexity of methods, that is used in the definition of WMC(Weighted Method per Class), one of the Chidamber and Kemerer's metrics. With respect to the results of our experiment, Halstead's Software Science metric is the most appropriate one to evaluate the complexity of the methods.

Appropriate meshes are crucial for accurate and efficient 3D process simulation. In this paper, we present a set of tools operating on surface and interface triangulations. These tools allow the improvement of the accuracy of interfaces, the reduction of the number of triangles, and the removal of obtuse not coplanarily compensated triangles. The first tool is used within integrated topography simulation environments based on different data structures, e.g. cell-based and segment-based. The latter two are particularly important for providing appropriate input to mesh generation for 3D process simulation.

The individually normalized least mean square (INLMS) algorithm is proposed as an adaptive algorithm suitable for the fixed point processing. The convergence property of the INLMS algorithm, however, is not yet analyzed enough. This paper first derives an equation describing the convergence property by exploiting the technique of expressing the INLMS algorithm as a first order infinite impulse response (IIR) filter. According to the equation derived thus, the decreasing process of the estimation error is represented as the response of another IIR filter expression. By using the representation, this paper second derives the convergence condition of the INLMS algorithm as the range of the step size making a low path filter of the latter IIR filter. This paper also derives the step size maximizing the convergence speed as the maximum coefficient of the latter IIR filter and finally clarifies the range of the step size recommended in the practical system design.

A generalized algorithm for designing an optimum VQ source codec in systems with channel coding is presented. Based on an AWGN channel model, the algorithm derives the distribution of the channel decoder soft-output and substitutes it in the expression for the system end-to-end distortion. The VQ encoder/decoder pair is then optimized by minimizing this end-to-end distortion. For a Gauss-Markov source, the proposed algorithm outperforms the conventional SOVQ source coding scheme by 5.0 dB in the decoded source SNR. Application of this algorithm for designing optimum low-bit-rate speech codec is given. A 4.0 kbps VQ based CELP codec is designed for performance evaluations, where all the CELP parameter encoder/decoder pairs are optimized by minimizing their end-to-end distortions, respectively. As a result, the speech distortion over the noisy channel is minimized. Subjective tests show that the proposed algorithm improves the decoded speech quality by 2.5 MOS relative to a regular SOVQ CELP speech coding system. The performances of the algorithm under channel mismatch conditions are also shown and discussed.

Silicon self-interstitial atom diffusion and implantation induced damage were studied by using molecular dynamics methods. The diffusion coefficient of interstitial silicon was calculated using molecular dynamics method based on the Stillinger-Weber potential. A comparison was made between the calculation method based on the Einstein relationship and the method based on a hopping analysis. For interstitial silicon diffusion, atomic site exchanges to the lattice atoms occur, and thus the total displacement-based calculation underestimates the ideal value of the diffusivity of the interstitial silicon. In addition with calculating the diffusion constant, we also identified its migration pathway and barrier energy in the case of Stillinger-Weber potential. Through a study of molecular dynamics calculation for the arsenic ion implantation process, it was found that the damage self-recovering process depends on the extent of damage. That is, damage caused by a single large impact easily disappears. In contrast, the damage leaves significant defects when two large impacts in succession cause an overlapped damage region.

Learning process is essential for good performance when a neural network is applied to a practical application. The backpropagation algorithm is a well-known learning method widely used in most neural networks. However, since the backpropagation algorithm is time-consuming, much research have been done to speed up the process. The block backpropagation algorithm, which seems to be more efficient than the backpropagation, is recently proposed by Coetzee in [2]. In this paper, we propose an efficient parallel algorithm for the block backpropagation method and its performance model in mesh-connected parallel computer systems. The proposed algorithm adopts master-slave model for weight broadcasting and data parallelism for computation of weights. In order to validate our performance model, a neural network is implemented for printed character recognition application in the TiME which is a prototype parallel machine consisting of 32 transputers connected in mesh topology. It is shown that speedup by our performance model is very close to that by experiments.

The gate oxide of sub-0.1 µm MOSFETs channel length is expected to be reduced beyond 3 nm in spite of an increasing direct tunneling gate current. As tunnel injection modeling into SiO2 is expected to depend on the electron transport model adopted for the device description, a critical comparison is made in this paper between gate currents obtained from simulators based on Drift-Diffusion, Energy-Balance, and Monte Carlo models. The studied device is a 0.07 µm channel length n-MOSFET with 1.5 nm thick gate oxide. It is shown that positive drain voltage is responsible for two opposite effects on DT leakage: a carrier heating and a potential barrier hardening along the channel. It is proved by a careful study of Monte Carlo microscopic quantities that, contrary to what holds for thicker gate oxide transistors, the balance is favorable to the potential barrier effect. Injection into SiO2 is then dominated by near-thermal carriers injected at the channel beginning. For this reason, the gate current decreases when increasing the drain bias, with the maximum leakage obtained for (Vgs=Vdd, Vds=0), and a correct agreement is obtained between the Drift-Diffusion, Energy-Balance, and Monte Carlo approaches of gate current calculation, in spite of very different physical descriptions of transport at the microscopic level.

An approach for analysis of the small signal response of the carriers in semiconductors is presented. The integro-differential equation, describing the phenomenon in the time domain is transformed into a Fredholm integral equation of the second kind. The response of the carrier system to a small signal of a general time dependence can be calculated by the knowledge of the response to an impulse signal, defined by a delta function in time. For an impulse signal, the obtained integral equation resembles the basic structure of the integral form of the time dependent (evolution) Boltzmann equation. Due to this similarity a physical model of the impulse response process is developed. The model explains the response to an impulse signal in terms of a relaxation process of two carrier ensembles, governed by a Boltzmann equation. A Monte-Carlo method is developed which consists of algorithms for modeling the initial distribution of the two ensembles. The numerical Monte-Carlo theory for evaluation of integrals is applied. The subsequent relaxation process can be simulated by the standard algorithms for solving the Boltzmann equation. The presented simulation results for Si and GaAs electrons serve as a test of the Monte-Carlo method and demonstrate that the physical model can be used for explanation of the small signal response process.