Mobile databases will play an important role in mobile computing environment, to provide data storing and data retrieval functionalities which are needed by most applications. In mobile computing environment, the wireless communication poses some problems, which require us to minimize its use. Replication is a database technique that is commonly used to fulfill the requirement in minimizing network usage. In this paper, we propose two replica allocation strategies, called primary-copy tracking replica allocation (PTRA) and user majority replica allocation (UMRA), which are better suited to the mobile computing environment. Their proposals are intended to cope with cost performance issues in data replication due to user mobility in mobile computing environment. To investigate their effectiveness, we provide access cost analysis and comparison on these strategies and the static replica allocation (SRA) strategy. We show that our proposed strategies outperform the SRA strategy when user mobility (inter-cell movement) is relatively low as compared with data access rate.

This paper proposes a time-interval data model in which all temporal representation and operations can be expressed with time intervals. The model expresses not only real time intervals, in which an event exists, but also null time intervals, in which an event is suspended. We model the history of a real-world event as a composite time interval, which is defined in this paper. Operations on the composite time intervals are also defined, and it is shown how these operations can be used to express temporal constraints with time intervals.

We present a new scheduling policy named Value-based Processor Allocation (VPA-k) for scheduling value-based transactions in a multiprocessor real-time database system. The value of a transaction represents the profit the transaction contributes to the system if it is completed before its deadline. Using VPA-k policy, the transactions with higher values are given higher priorities to execute first, while at most k percentage of the total processors are allocated to the urgent transactions dynamically. Through simulation experiments, VPA-k policy is shown to outperform other scheduling policies substantially in both maximizing the totally obtained values and minimizing the number of missed transactions.

In this paper, a design concept that offers ATM-VP connections with different protection levels is presented. The users have the choice to select the protection level they wish, the network transport service they need, and the worst cell loss they can tolerate at call set up time, and pay accordingly. Besides, an advanced adaptive traffic control scheme that simplifies call and cell processing is also presented. Many important functions such as call admission, VC-bandwidth reservation, cell-level congestion control, etc. are efficiently performed at the boundary of the backbone network. In this way is given a suitable answer to the important question: "How can future telecommunication networks based on ATM provide services with customized availability ?" A platform that outlines the potential interaction between restoration methods and congestion avoidance schemes is also obtained.

An MMIC variable-gain amplifier, which improves the transmission phase deviation caused by gain control, is presented. At first, it is shown that by controlling both the common-gate FET's gate bias voltage and the common-source FET's gate bias voltage, the transmission phase deviation caused by gain control of the variable-gain amplifier using a cascode-connected FET is greatly improved. In this case it is not desirable to control both of the gate bias voltages independently, because of the complexity. Thus we propose two simple gate bias voltage control circuits controlling both of the gate bias voltages, in which only one of the two gate bias voltages is controlled independently and the other is controlled dependently. Then we apply these circuits to the 1. 9-GHz-band variable-gain amplifier using the cascode-connected FET. One of the control circuits is the gate bias voltage control circuit using two resistors. It is confirmed that, by applying the newly proposed circuit, phase deviation is suppressed, from between 0and 30to between 3and 5, with 25-dB gain control. The other circuit is the gate bias voltage control circuit using the FET's nonlinear characteristics. It is confirmed that, by applying the newly proposed circuit, phase deviation is suppressed, from between 0and 44to between 6and 3 with 30-dB gain control. This is a promising technique for reducing the transmission phase deviation caused by gain control of the amplifiers used in active phased array antennas.

This paper presents two types of two-dimensional (2-D) adaptive beamforming algorithm which have high rate of convergence. One is a linearly constrained minimum variance (LCMV) beamforming algorithm which minimizes the average output power of a beamformer, and the other is a generalized sidelobe canceler (GSC) algorithm which generalizes the notion of a linear constraint by using the multiple linear constraints. In both algorithms, we apply a 2-D lattice filter to an adaptive filtering since the 2-D lattice filter provides excellent properties compared to a transversal filter. In order to evaluate the validity of the algorithm, we perform computer simulations. The experimental results show that the algorithm can reject interference signals while maintaining the direction of desired signal, and can improve convergent performance.

S-boxes (vector output Boolean functions) should satisfy cryptographic criteria even if some input bits (say, k bits) are kept constant. However, this kind of security has been studied only for scalar output Boolean functions. SAC (k) is a criterion for scalar output Boolean functions of this type. This paper studies a generalization of SAC (k) to vector output Boolean functions as the first step toward the security of block ciphers against attacks which keep some input bits constant. We first show a close relationship between such Boolean functions and linear error correcting codes. Then we show the existence, bounds and enumeration of vector Boolean functions which satisfy the generalized SAC (k). A design method and examples are also presented.

This paper focuses on competitive learning algorithms for WTA (winner-take-all) networks which perform rotation invariant pattern classification. Although WTA networks may theoretically be possible to achieve rotation invariant pattern classification with infinite memory capacities, actual networks cannot memorize all input data. To effectively memorize input patterns or the vectors to be classified, we present two algorithms for learning vectors in classes (LVC1 and LVC2), where the cells in the network memorize not only weight vectors but also their firing numbers as statistical values of the vectors. The LVC1 algorithm uses simple and ordinary competitive learning functions, but it incorporates the firing number into a coefficient of the weight change equation. In addition to all the functions of the LVC1, the LVC2 algorithm has a function to utilize under-utilized weight vectors. From theoretical analysis, the LVC2 algorithm works to minimize the energy of all weight vectors to form an effective memory. From computer simulation with two-dimensional rotated patterns, the LVC2 is shown to be better than the LVC1 in learning and generalization abilities, and both are better than the conventional Kohonen self-organizing feature map (SOFM) and the learning vector quantization (LVQ1). Furthermore, the incorporation of the firing number into the weight change equation is shown to be efficient for both the LVC1 and the LVC2 to achieve higher learning and generalization abilities. The theoretical analysis given here is not only for rotation invariant pattern classification, but it is also applicable to other WTA networks for learning vector quantization.

This paper proposes a 6.4-kbit/s extension to G.729 (conjugate structure algebraic code excited linear prediction: CS-ACELP). Each G.729 module was investigated to determine which bits could be removed without hurting the speech quality, then two coders that have different bit allocations were designed. They have two different algebraic codebooks (a 10-bit algebraic codebook that has two pulses and an 11-bit algebraic codebook that has two or three pulses). This paper also proposes a conditional orthogonalized search for a fixed codebook to improve the speech quality. The conditional orthogonalized search chooses, one of two search methods (orthogonalized or non-orthogonalized) based on the optimum pitch gain. The quality of the two coders was evaluated using objective measurements (SNR and segmental SNR) and subjective ones (mean opinion score: MOS and a pair-comparison test). The selected coder was evaluated under practical conditions. Subjective test results have indicated that the quality of the proposed coder (10-ms frame length) is equivalent to that of the 6.3-kbit/s G.723.1 coder, which has a 30-ms frame length.

The efficiency and reliability of an ultrasonic motor, operating in longitudinal-torsional degenerate-mode, are investigated. It is essential to miniaturize both longitudinal and torsional mode piezoelectric ceramic elements, in order to produce low-cost ultrasonic motors, and to realize a motor with low battery power consumption. The ultrasonic motor is designed with an accurate mechanical equivalent circuit, which can produce high design precision notwithstanding low computation cost. It is important in this design that the resonant frequencies of longitudinal mode and torsional mode coincide with each other under the pertinent rotor pressing force and longitudinal and torsional mode piezoelectric ceramic elements are located in the vibration nodes for the longitudinal mode and the torsional mode, respectively. As a result, the fabricated motor, whose rotor diameter was 12 mm, produced 480 r.p.m. no-load revolution speed, 0.55 kgfcm maximum torque, 50% maximum efficiency, 2.5 W consumed power and a lifetime over 1000 hours with continuous rotation.

This paper extends left-incompatible term rewriting systems defined by Toyama et al. It is also shown that the functional strategy is normalizing in the class, where the functional strategy is the reduction strategy that finds index by some rule selection method and top-down and left-to-right lazy pattern matching method.

This paper proposes high-speed similitude retrieval schemes for a viewpoint-based similarity discrimination system (VB-SDS) and presents analytical and experimental performance evaluations. The VB-SDS, which contains a huge set of semantic definitions of commonly used words and computes semantic similarity between any two words under a certain viewpoint, promises to be a very important module in analogical and case-based reasoning systems that provide solutions under uncertainty. By computing and comparing similarities for all words contained in the system, the most similar word for a given word can be retrieved under a given viewpoint. However, the time this consumes makes the VB-SDS unsuitable for inference systems. The proposed schemes reduce search space based on the upper bound of a similarity calculation function to increase retrieval speed. An analytical evaluation shows the schemes can achieve a thousand-fold speedup and confirmed through experimental results for a VB-SDS containing about 40,000 words.

This paper presents a distributed power control scheme for next-generation multiservices CDMA systems. CDMA has inherent capability to control the quality-of-service (QoS) requirements by assigning different power levels to each traffic type. Toward this, optimum power control schemes have been investigated. The main drawback of the previously proposed algorithms is that they would require all users' transmission state necessiating a complicated control process or peak-rate badnwidth allocation. To overcome this, we exploit the Markovian property to obtain the statistics of the traffic. The statistical formulation is presented for allocating power distributedly so as to keep the "collision" probability below a predefined probability. Numerical examples show that the distributed power control scheme allows better utilization of wireless resources through statistical multiplexing than peak-rate bandwidth assignment, and it does not require a complicated control process while keeping total transmitted power at slightly greater than optimum power control.

Recently, progress has been made in the area of electrical modeling of conductors embedded in arbitrary dielectrics using circuit oriented techniques. These models usually occur in conjunction with VLSI type circuits. Many different applications exist today for such models in the EMI, EIP (Electrical Interconnect and Package) analysis as well as for the microwave circuit area. Practical problems involve a multitude of hardware components and they demand a wide spectrum of both time as well as frequency domain solution techniques. In this paper we consider circuit oriented techniques for the solution of these problems. Specifically, we give an outline of the three dimensional Partial Element Equivalent Circuit (PEEC) full wave modeling approach and review the recent progress in this area.

This paper describes an efficient and simple coding algorithm of universally optimal codes for stationary (ergodic) sources and noiseless channel with unequal symbol costs. The symbol cost indicates the required time (or space) for the transmission (or storage) of that symbol, and the cost of any code symbol depends only on that symbol. The proposed coding algorithm mainly consists of two parts. The first part is based on the well-known Ziv-Lempel coding algorighm proposed in 1978 (sometimes called LZ78), and the second part is based on the Varn coding algorithm. The coding algorithm asymptotically achieves an optimal average cost of codes for stationary sources, and also achieves an optimal cost of codes for stationary ergodic sources with probability one. Furthermore, the computational complexity of the proposed coding algorithm is linear with respect to the length of source sequence and coded sequence.

A method for recovering the LPC spectrum from a microphone array input signal corrupted by less directional ambient noise is proposed. This method is based on the subspace method, in which directional signal and non-directional noise is classified in the subspace domain using eigenvalue analysis of the spatial correlation matrix. In this paper, the coherent subspace (CSS) method, a broadband extension of the subspace method, is employed. The advantage of this method is that is requires a much smaller number of averages in the time domain for estimating subspace, suitable feature for frame processing such as speech recognition. To enhance the performance of noise reduction, elimination of noise-dominant subspace using projection is further proposed, which is effective when the SNR is low and classification of noise and signals using eigenvalue analysis is difficult.

Equivalence of physical optics (PO) and aperture field integration method (AFIM) in the full 360 observation angle is discussed for polyhedron approximate reflectors; the necessary conditions of integration surface in AFIM for the equivalence to PO are presented. In addition to the condition that complete equivalent currents consisting of both geometrical optics (GO) reflected fields from the reflector and direct incident fields from the feed source are used, the integration surface should cap the reflector perfectly and should be in the illuminated region of the GO reflected field. Validity of the conditions is numerically confirmed for a two-dimensional (2-D) strip reflector, 3-D corner reflectors and a 2-D polyhedron approximate reflector.

We consider the problem of estimating one- and two-dimensional direction of arrivals for arbitrary plane waves in an incoherent/coherent source environment. For the one-dimensional case, we use matrix pencil (MP) method developed by Y. Hua for signal-poles estimation. We then extend this method to estimate the two-dimensional direction of arrivals (2D-DOA), resulting in the "Extended Matrix Pencil" (EMP) method. This method can be applied successfully as much for an incoherent source environment as for a coherent source environment. To study the performance of these methods, in both cases results are compared with the "Total Least Squares-Estimation of Signal Parameters via Rotational Invariance Techniques" (TLS-ESPRIT) and the "Spatial Smoothing-TLS-ESPRIT" (SS-TLS-ESPRIT) methods. The results show that the MP method estimates the DOA more accurately and better than the TLS-ESPRIT and the SS-TLS-ESPRIT, even with few snapshots. Simulation results show that the EMP method, presented in this paper, estimates the 2-DOA better than the other two methods used for comparison.

In this Letter, we investigate the loss performance of a discrete-time single-server queueing system with periodic vacations, with which we are often confronted in traffic control, such as cell scheduling or priority control schemes, at ATM nodes. Explicit expressions are derived for the cell loss ratio in terms of the distribution of the buffer contents in an infinite capacity queue.

We present here the Controlling Value Boolean Matching based on fault analysis. The problem is to match a Boolean function with don't cares on library cells under arbitrary input permutations and/or input-output phase assignments. Most of the library cells can be represented by tree structure circuits. The approach presented here is suitable for these structures and computes the Boolean matching better than the structural matching used in SIS. It can handle library cells with a general topology and reconvergent paths. The benchmark test shows that the Controlling Value Boolean Matching can be as facter as the structural matching used in SIS.