This paper describes an oversampling analog-to-digital converter (ADC) suitable for PCM codes. Non-linear 5-level quantizer is implemented to noise-shaping modulator. This ADC meets the specifications of ITU-T G.712, in spite of using first order delta-sigma modulator, and realizes low power operation. This chip is fabricated in 0.8 µm double-poly and double-metal CMOS process and occupies a chip area of 15 mm2. Maximum power consumption is 12.8 mW with a single +3 V power supply including DAC and TONE generator.

A non-invasive method is proposed to estimate the location of intracranial vascular disease using several sensors placed on the forehead. The advantage of this method over earlier measurements with a single ocular sensor is the abilty to localize the region of abnormal vascular tissue. A weighted least mean square procedure is applied to estimating the time difference between the sensor outputs using the phase distribution in the cross-spectrum. It is possible to estimate time differences shorter than sampling period. Computer simulation and clinical experiments demonstrate that a distance difference of around 20 times shorter than the wavelength can be obtained.

This paper proposes a hardware architecture of programmable controller based on Petri nets. The suggested architecture achieves sufficiently rapid processing even as demands on PCs become increasingly more complex. The architecture's speed and efficiency are derived from an automatic and dynamic super scalar computing capability that executes bit instructions and data handling instructions simultaneously without preprocessing, due to the properties of Petri nets. Specific characteristics for both architectural memory-based implementation of Petri nets and evolution algorithms are suggested and classified by the net structure. Analysis of the suggested architectures and effects on performance are also given with mathematical formulas and a computer simulation.

The performance of decision-feedback equalization combined with maximum-likelihood detection (DFE/ML) using the fixed-delay-tree-search/decision feedback (FDTS/DF) algorithm was estimated analytically in terms of the length of the feedback-filter and the depth of the ML-detector. Performance degradation due to error propagation in the feedback-loop and in the ML-detector was taken into account by using a Markov process analysis. It was quantitatively shown that signal-to-noise-ratio (SNR) performance in high-density magnetic recording channels can be improved by combining an ML-detector with a feedback-filter and that the error propagation in the DFE channel can be reduced by using an ML-detector. Finally, it was found that near-optimum performance with regard to channel SNR and error propagation can be achieved, over the channel density range from 2 to 3, by increasing the sum of the feedback-filter length and the ML-detector depth to six bits.

This paper describes a simulation technique of start-up characteristics that considers a nonlinearity of the drive level of quartz crystal resonators. A nonlinear resonator model for SPICE where the resonant resistance varies with the voltage added to a resonator is proposed. In an examination using a transistor Colpitts oscillator, the simulation using this technique agreed with the experimental results very well.

In this paper, we discuss an abstraction method for Petri nets based on an equivalence of firing sequences of a specified subnet or a specified subset of transitions. Specifically, a method is presented to generate an equivalent net which preserves firing sequences of a specified subnet or a specified subset of transitions. The abstraction can be applied to an efficient behavioral analysis of concurrent systems constructed by composition of modules such as communication networks and Flexible Manufacturing Systems (FMS).

Due to the large and complex information processing systems, formal description methods are needed for specification of systems and their efficient and reliable designs. During the early stage of system design, it is often necessary to modify or change system requirements which may influence the whole system design. We have proposed a new flexible description methodology, which copes with the modifications or changes in the system requirements, in order to obtain the formal specification of the system. We have also shown that function requirements can be modeled by a Logical Petri Net (LPN), which is a kind of extended Petri Nets, in order to derive the formal specification. In this paper, we propose a verification method of system requirements that contain some kinds of logical errors. Further, we show a method to decompose and refine a requirement description hierarchically, and discuss how to derive a formal specification from a requirement description flexibly along our refinement method against the changes of the requirement description in the system.

A fast pitch search algorithm using the skipping technique is proposed to reduce the computation time in CELP vocoder. Based on the characteristics of the correlation function of speech signal, the proposed algorithm skips over certain ranges in the full pitch search range in a simple way. Though the search range is reduced, high speech quality can be maintained since those lags having high correlation values are not skipped over and are used for search by closed-loop analysis. To improve the efficiency of the proposed method, we develop three variants of the skipping technique. The experimental results show that the proposed and the modified algorithm can reduce the computation time in the pitch search considerably, over 60% reduction compared with the traditional full search method.

This paper addresses approaches to enhancement of performance of the CMA (Constant Modulus Algorithm) adaptive array antenna in multipath environments that characterize the mobile radio communications. The cost function of the CMA reveals that it has an AGC (Automatic Gain Control) procedure of holding the array output voltage at a constant value. Therefore, if the output voltage by the initial weights is different from the object value, then the CMA may suffer from slow convergence because suppression of the multipath waves is delayed by the AGC behavior. Our objective is to improve the convergence characteristics by adopting the differential CMA for the adaptive array algorithm. First, the basic performance of the differential CMA is clarified via computer simulation. Next, the differential CMA is incorporated into the eigen-beamspace system in which the eigenvectors of the correlation matrix of array inputs are used in the BFN (Beam Forming Network). This BFN creates the optimum orthogonal multibeams for radio environments and works helpfully as a preprocessor of the differential CMA. The computer simulation results have demonstrated that the differential CMA with the eigen-beamspace system has much better convergence characteristics than the conventional CMA with the element space system. Furthermore, a modified algorithm is introduced which gives the stable array output voltages after convergence, and it is confirmed that the algorithm can carry out more successful adaptation even if the radio environments are changed abruptly.

The tandem structure of a matched filter (MF) and a maximum likelihood sequence estimator (MLSE) using the Viterbi algorithm (VA) has been considered to be an optimal receiver for digital pulse-amplitude sequences in the presence of intersymbol interference (ISI) and additive white Gaussian noise (AWGN). An adaptive array antenna has the capability of filtering received signals in the spatial domain as well as in the temporal one. In this paper, we propose a receiver structure using an adaptive array antenna, a digital filter and the VA that is spatially and temporally optimal for multi-user detection in a direct sequence code division multiple access (DS/CDMA) environment. This receiver uses a tapped delay line (TDL) array antenna and the VA, which provides a maximum likelihood sequence estimate from the spatially and temporally whitened matched filter (ST-WMF) output. Performance of the proposed receiver is evaluated by theoretical analysis and computer simulations.

This paper proposes and investigates a tap selectable Viterbi equalizer for mobile radio communications. When the multipath channel is modeled by a tapped delay line only, the taps which may seriously affect the data sequence estimation are selected and used to calculate the trellis metric in the Viterbi algorithm. The proposed equalization algorithm can reduce the number of path metric calculations and the number of path selections in the Viterbi algorithm. Moreover, we propose an extended equalizer which has antenna diversity. This equalizer calculates the path metric using the antenna outputs and results of channel estimators. Computer simulation is used to evaluate the BER performance of the proposed equalizer in a multipath radio channel.

Signal processing antennas have been studied not only for interference suppression but also for high-resolution estimation of radio environment such as directions-of-arrival of incident signals. These two applications are based on the common technique, that is, null steering. This tutorial paper reviews the MUSIC algorithm which is one of the typical high-resolution techniques. Examining the eigenvector beam patterns, we demonstrate that the high-resolution capability is realized by steering nulls. The considerations will be useful for understanding the high-resolution techniques in the signal processing antennas. We then describe a modified version of MUSIC (Root MUSIC). We show the performance and robustness of the method. Furthermore, we introduce radar target identification and two-dimensional radar target imaging. These study fields are new applications of the signal processing antennas, to which a great deal of attention has been devoted recently.

Queries to generate a map from geographic detabases are too large and complex for users to specify all components in it. Thematic parts of the map should be described by users as ad hoc queries. However, background parts of it should be inferred from users' queries corresponding to the thematic parts. Furthermore, it is important for the map systems to lead users' constructing their ad hoc queries and to infer visualization methods applied to the data retrieved by the ad hoc queries. This paper discusses a framework to infer supplemental queries and visualization methods in order to make the retrieval results into a feasible map using geographic domain hierarchical levels, geographic domain thesauruses and existing example queries. The framework allows users to know mismatches of components in queries, inappropriate queries for maps, and deriving candidates for additional components in queries.

Analyzing multipath propagation structure is important to develop anti-fading techniques for high-speed digital radio systems. Several techniques have been employed to measure delay profiles and/or arrival angles. This paper presents a simultaneous estimation method of delay times and arrival angles of indoor multipath waves. We obtain frequency-domain data at different receiving antenna positions using a network analyzer. We estimate the propagation parameters by means of a two-dimensional MUSIC algorithm. In order to obtain reliable results, a two-dimensional discrete inverse Fourier transform and a gating technique are employed before the MUSIC algorithm. Simulation and experimental results show that the proposed method can estimate the propagation parameters properly.

A two-dimensional recording method that achieves double recording density by reducing the track pitch is described. This method uses a flat disk and the data are recorded with circular marks on lattice points. Two-dimensional interference consisting of crosstalk and inter-symbol interference is reduced by two-dimensional equalization. To minimize the two-dimensional interference, the optimum equalization coefficients are calculated dynamically with the reproduced signal of the training marks. Reproduction was simulated and this showed that the signal-to-noise ratio of the processed signal was 24.3 dB under ideal conditions and 19.8 dB under worst-case conditions with the usual magneto-optical media using double recording density. These simulation results were checked by a recording/reproduction experiment. The experimental result for the signal-to-noise ratio of the processed signal was 23.6 dB with an areal density of 2.3 Gbit/in2.

When signal subspace techniques, such as MuSIC, are used to locate a number of incident signals, an exhaustive search of the array manifold has to be carried out. This search involves the evaluation of a single cost function at a number of points which form a grid, resulting in quantization-error effects. In this paper a new algorithm is put forward to overcome the quantization problem. The algorithm uses a number of cost functions, and stages, equal to the number of incident signals. At each stage a new cost function is evaluated in a small number of "special" directions, known as characteristic points. For an N-element array the characteristic points, which can be pre-calculated from the array manifold curvatures, partition the array manifold into N-1 regions. By using a simple gradient algorithm, only a small area of one of these regions is searched at each stage, demonstrating the potential benefits of the proposed approach.

The evolution of heterogeneous and autonomous databases research has been slow compared to other areas of research. Part of the problem resides in the fact that bridging data semantics has been a difficult problem. Sharing data among disparate databases has mostly been achieved through some form of manual schema integration. The complexity of making autonomous heterogeneous databases smoothly interoperate is dependent on addressing two major issues. The first issue to address is what adequate levels of autonomy databases are guaranteed to keep. The second issue to address is what overhead cost is required to bridge database heterogeneity. The complexity of these two issues are closely dependent on how scalable multidatabase systems are. In this paper we introduce the FINDIT architecture which uses information meta-types to provide a basis for such an organization and, consequently, provides a platform for inter-operability. A distinction is made between the information and inter-node relationship spaces to achieve scalability. Tassili language primitives are used for the incremental building of dynamic inter-node relationships based upon usage considerations.

Documents stored in a database system can have complex internal structure described by languages such as SGML. How to take advantage of this structure presents challenges for database system implementors. We classify the types of queries that need to be supported by SGML-conformant database systems. We then describe several data models that have been proposed for representing documents in a database system and discuss the support these models provide for SGML. Finally we consider query evaluation.

This paper discusses the reliability of the Modified EBU method compared with the EBU and DSCQS methods where the small and different levels of impairments exist in the coded HDTV sequences. The subjective evaluation tests are carried out in the full and limited impairment ranges. And it is shown that the Modified EBU method is most reliable for both ranges.

In this paper, electromagnetic scattering by infinite double two-dimensional periodic array of resistive upper and lower elements is considered. The electric field equations are solved by using the moment method in the spectral domain. Some numerical results are shown and frequency selective properties are discussed.