This paper presents a novel four-sector shaped-beam antenna suitable for base station antennas in 60-GHz wireless local area networks (LANs). The antenna has a plateau configuration, whose four side walls have four linearly arranged microstrip antennas. Each trapezoidal facet excites a shaped beam in the elevation plane in order to meet link-budget requirement between base station and remote terminal, taking account of directional patters of remote terminal antennas. Low-loss curved microstrip-line is applied to connect the three-dimensional antennas with active circuits mounted on a flat carrier plate. This antenna has been adopted as the base station antenna in 60-GHz wireless LANs. The first-stage transmission experiment confirms the usefulness of shaped-beam antennas in the 60-GHz band.

This paper presents a new approach to computer image generation via three proposed methods for translating the evolution of a Petri net into fractal image synthesis. The idea is derived from the concept of fractal iteration principles in the escape-time algorithm and chaos game. The approach uses a Petri net as a powerful abstract modeling tool for fractal image synthesis via its duality, deadlock, inhibitor arc, firing sequence and marking reachability. The objective of this approach is to enhance the analysis technique of a Petri net and use it as a novel technique for fractal image synthesis. Generating fractal images via the dynamics of a Petri net allows an easy and direct proof for the similarity and correspondence between the dynamics of complex quadratic fractals by the recursive procedure of the escape-time algorithm and the state of a Petri net via a reachability problem. The reachability problem will be manipulated in terms of the dynamics of the fractal in order to generate images via three proposed methods. Validation of our approach is given by discussion and an illustration of some experimental results.

Novel memory and several logic circuits utilizing the chaotic oscillations produced in SQUIDs are proposed. First, the oscillation modes that can be produced in a SQUID circuit are analyzed. The results of simulation for the SQUID show that there exist four types of oscillations: periodic, subharmonic, chaotic and relaxation oscillations. The bifurcation diagram of oscillation waveforms reveals that the hysteresis phenomena in the relation between the terminal voltage or the current and the external flux appear and that these phenomena can be used for a memory operation. Secondary, novel digital circuits such as memory, Exclusive-OR and full adder circuits are proposed by utilizing the chaotic oscillations. In these digital circuits the chaotic oscillations are made correspond to the logic "1," while the periodic and subharmonic oscillations are made to the logic "0." In order to investigate how these digital circuits perform their functions, computer simulations are made. The simulation results show that the right operations can be achieved.

In this paper, the performance of some communication systems using chaos synchronization is evaluated and compared. A new channel model taking the attenuation, impedance mismatch and noise into account, is proposed for the performance evaluation. The evaluation of bit error rate is done for both ideal and non-ideal conditions using the channel model. It is confirmed that some chaos-based communication systems have a good performance compared with conventional analog communication schemes.

A novel dual-band internal antenna similar in size to the single-band internal antenna for cellular handsets is proposed. Our approach to realize a small and low-profile dual-band internal antenna is to use the dominant mode (TM10 mode) and the higher-order mode (TM30 mode). In order to use this approach for recent dual-band cellular systems it is necessary to lower the resonant frequency of the higher-order mode (TM30 mode). This motivated our development of a new antenna configuration with a slot on the radiation element of a quarter-wavelength shorted microstrip antenna to lower the resonant frequency of the TM30 mode. In this paper, the experimental and the analytical results for this antenna are presented. In the results, by adjusting the location and the length of the slot, the dual-frequency operation can be achieved with the frequency ratio (TM30 mode/TM10 mode) from 2 to 3. In addition, the enhancement of bandwidth is presented.

Tradeoffs between efficiency, power and reliability were analyzed for the GaAs MESFETs with variable recess structures. The MESFET process can be optimized for either best power/efficiency performance or best reliability by varying the width of the first recess. If the first recess width is increased by 0.4 µm, an estimated order of magnitude increase in device lifetime, limited by hot-electron-induced degradation, can be achieved at the expense of 3% in power-added efficiency and 20 mW/mm in output power. The reported hot-electron reliability highlights include maximum sustainable reverse gate current stress of 100 mA/mm and (Stress)(Lifetime) figure of merit of 12.5 Ahr/cm which advances the present state of the art by approximately an order of magnitude. The introduced (Stress)(Lifetime) figure of merit is essential for design-for-reliability of high efficiency power amplifiers.

The conductor-backed asymmetrical coplanar waveguide or micro-coplanar strip (MCS) line has been analyzed. The conformal mapping method is used to calculate the quasi-static effective permittivity εeff and characteristic impedance Z0. The computed results of the present work are found to be in good agreement when compared with the results obtained using the method reported by Yamashita et al. [1] and experimental values reported in [2]. A novel MCS end-coupled half-wavelength long resonator filter is designed to illustrate an application of the present work. The designed filter has 4% bandwidth at a center frequency of 10.5 GHz. The measured insertion loss is approximately 3.4 dB. One of the main advantages of the MCS filter compared to the CPW filter is that bond wires do not have to be used to maintain both coplanar ground at the same potential. The MCS filter is also easily integrable with other planar components and does not require a complicated transition to microstrip.

By integrating three networks, namely, Public Switched Telephone Network (PSTN), Personal Handy-Phone System (PHS) and Intelligent Network (IN) to work together as a Personal Communication Telephone (PCT) service to be offered in the Bangkok metropolis area, the PCT service enables the advent of three new concepts, first, using the same telephone number as that of the fixed line to become a "Personal Number," second, a cell coverage designed to cover larger areas than that of the PHS (by changing hand-out threshold level from 33 dBµV to 30 dBµV and hand-in threshold level from 30 dBµV to 25 dBµV) in order to reduce the muting time during the handover process and provide higher mobility at up to 60 kilometers per hour, and third, a technique of "2 carriers per area" to reduce "call drop." All these techniques will be described in this paper.

The feasibility of a dynamic zone configuration technique has been investigated. To make it easy to implement this technique in wireless communication systems, a simplified method for determining a suitable weight vector by using the least squares (LS) methods was developed. Simulations showed that the developed system is more effective than the present omni-directional zone system. Moreover, combining dynamic zone configuration technique with dynamic channel assignment strategy reduced blocking rate, forced call termination ratio, and required transmission power.

In wireless ATM networks, the condition of the transmission channel fluctuates significantly as a result of many causes such as multipath, shadow phasing, and so forth. Several schemes have been proposed to take care of transmission errors. Some schemes are suitable for favorable channel conditions, while others are more suitable for unfavorable channel conditions. Thus, using a fixed error control scheme regardless of channel conditions is destined to be inefficient. This paper presents a dynamic error control scheme that dynamically selects an appropriate error control scheme according to the conditions of the transmission channel. Using this method, we can decrease both errors and the overhead of redundancy.

This letter proposes a diffusion model that considers both mobility and multimedia based on the user population process to examine the effects of multimedia in mobile communications. As an application example of this model, the shared bandwidth that can be used by one user in packet communications is evaluated. In this model, the user speed and variation in the number of users in a cell are interrelated with respect to mobility. By examining the shared bandwidth behavior based on multimedia teletraffic characteristics, assuming that the number of simultaneously-communicating users within a cell have self-similarity, we found that shared bandwidth and its variance are not dependent on self-similarity but that variance in the shared bandwidth is dependent on user speed.

This paper proposes a new design method of nonlinear filtering and fixed-point smoothing algorithms in discrete-time stochastic systems. The observed value consists of nonlinearly modulated signal and additive white Gaussian observation noise. The filtering and fixed-point smoothing algorithms are designed based on the same idea as the extended Kalman filter derived based on the recursive least-squares Kalman filter in linear discrete-time stochastic systems. The proposed filter and fixed-point smoother necessitate the information of the autocovariance function of the signal, the variance of the observation noise, the nonlinear observation function and its differentiated one with respect to the signal. The estimation accuracy of the proposed extended filter is compared with the extended maximum a posteriori (MAP) filter theoretically. Also, the current estimators are compared in estimation accuracy with the extended MAP estimators, the extended Kalman estimators and the Kalman neuro computing method numerically.

Newton based adaptive algorithms are among the algorithms which are known to exhibit a higher convergence speed in comparison to the least mean square (LMS) algorithms. In this paper we propose a simplified Newton based adaptive algorithm for an adaptive infinite impulse response (IIR) filter implemented using cascades of second order allpass filters and a finite impulse response (FIR) filter. The proposed Newton based algorithm avoids the complexity that may arise in the direct differentiation of the mean square error. The analysis and simulation results presented for the algorithm, show that the property of convergence of the poles of the IIR ADF to those of the unknown system will be maintained for both white and colored input signal. Computer simulation results confirm an increase in convergence speed in comparison to the LMS algorithm.

This paper presents two man-machine reliability models. A system consists of one machine unit, one operator, and one event detecting monitor. The machine unit has three states, normal, abnormal, and failed. The event detecting monitor may fail in two ways. If a machine unit becomes abnormal, the event detecting monitor sends a signal, and the operator takes necessary actions. If the operator fails in the action in the cause of human error, the machine unit goes down. The condition of the operator is classified into two types, good and bad. The time to repair, and the human error rate both depend on the condition of the operator. The MTTF is obtained by using a Markov model and numerical computation. Furthermore, the optimal operating period which minimizes the overall cost is decided by using computer methods. Some numerical examples are shown.

In this paper, we consider the Integrate-and-Fire Model (ab. IFM) with two periodic inputs. The IFM outputs a pulse-train which is governed by a one dimensional return map. Using the return map, the relationship between the inputs and the output is clarified: the first input determines the global shape of the return map and the IFM outputs various periodic and chaotic pulse-trains; the second input quantizes the state of the return map and the IFM outputs various periodic pulse-trains. Using a computer aided analysis method, the quantized return map can be analyzed rigorously. Also, some typical phenomena are confirmed in the laboratory.

In this paper, a general formula of disparity estimation based on Bayesian Maximum A Posteriori (MAP) algorithm is derived and implemented with simplified probabilistic models. The formula is the generalized probabilistic diffusion equation based on Bayesian model, and can be implemented into some different forms corresponding to the probabilistic models in the disparity neighborhood system or configuration. The probabilistic models are independence and similarity among the neighboring disparities in the configuration. The independence probabilistic model guarantees the discontinuity at the object boundary region, and the similarity model does the continuity or the high correlation of the disparity distribution. According to the experimental results, the proposed algorithm had good estimation performance. This result showes that the derived formula generalizes the probabilistic diffusion based on Bayesian MAP algorithm for disparity estimation. Also, the proposed probabilistic models are reasonable and approximate the pure joint probability distribution very well with decreasing the computations to O(n()) from O(n()4) of the generalized formula.

When designing microwave amplifiers, it is the task to select values of the source (input generator) and load reflection coefficients for the transistor, to achieve certain amplifier performance requirements and ensure stability. For unconditionally stable transistors, simultaneous conjugate matching can be achieved using well-known design formulae. Under this condition, the gain is maximised, and the input and output ports are matched. On the other hand when the transistor is conditionally stable, source and load reflection coefficients are selected using graphical design methods, involving gain and stability circles. To eliminate the reliance on graphical techniques, this paper shows the derivation of explicit design formulae that ensure maximum gain for a minimum specified safety margin, with one port matched. In this work, the safety margin is the distance between the chosen source or load reflection coefficient and its respective stability circle. In a production environment, where the circuit and transistor parameters are subject to random variations, the safety margin therefore makes allowance for such variations. This paper shows that the design problem for conditionally stable transistors can be reduced from the selection of values for two complex variables (port terminations) to the selection of the value for just one scalar variable.

This paper describes a forward subchannel control of multi-carrier scheme intended to compensate for phase/amplitude distortions under frequency selective fading. The forward subchannel control scheme is used for a Time Division Duplex (TDD) multi-carrier system on up-link. The forward subchannel control scheme provides forward subchannel control of phase/amplitude variation and subchannel assignment control. These controls are applied before transmission of an up-link signal. The forward control parameters are estimated by a preamble down-link signal. Simulation results clarify that the BER performance with the forward subchannel control scheme shows a superiority of more than one order at the condition of 22 dB of Eb/N0 and 400 Hz of fading frequency.

49-GHz operation for a state-of-the-art static frequency divider using FETs is achieved with high-performance 0.1-µm-gate InAlAs/InGaAs/InP HEMTs and high-speed double-layer interconnections with a thick low-permittivity BCB inter-layer dielectric film. An experiment shows that the propagation delay for the upper-layer line in the double-layer interconnections is less than half of that for the conventional single-layer interconnections directly on InP-substrate. The frequency divider with the double-layer interconnections is about 20% faster than the conventional one with the single-layer interconnections. A delay time analysis reveals that this speed increase is due to the decrease in interconnection propagation delay.

A GaAs linear power amplifier operating with a single 3-V supply has been developed for 5.8-GHz ISM band applications. Two kinds of refractory WNx/W self-aligned gate MESFETs, a P-pocket MESFET and an asymmetric MESFET with a buried p-layer (BP- MESFET ) have been compared in terms of DC characteristics, small signal characteristics and power performances at 5.8 GHz. To obtain both high gain and high efficiency in the case of single 3-V supply operation at 5.8 GHz, we used a highly efficient and linear P-pocket MESFET for the output-stage power FET and a high-gain asymmetric MESFET with a buried p-layer (BP- MESFET ) for the driver-stage FET. The bias condition for 1-mm output-stage P-pocket MESFET was set near class-AB, so as to obtain sufficient output power with high PAE. The two-stage power amplifier MMIC module which can include all matching and biasing circuits, has been designed and fabricated. The amplifier exhibits a high power gain of 17.9 dB and a high power-added efficiency of 25.7% with a sufficient output power of 18.7 dBm at the 1-dB compression point. This self-aligned gate GaAs MESFET technology is promising for near-future 5.8-GHz applications, because of such good power performance and good mass-producibility.