The paper describes the design considerations, fabrication process and performance of the newly developed 1-K ECL gate array implemented with fully self-aligned AlGaAs/GaAs hoterojunction bipolar transistors (HBTs). This gate array consists of 960 three-input OR/NOR ECL basic gates. It contains about 7,600 transistors in a chip area 8.15-mm8.45-mm. The basic (FI=FO=1, wiring length L=0-mm) and loaded (FI=FO=3, L=1-mm) gates exhibit delay times of 33-ps and 82-ps, respectively, with 8.5-mW/gate power dissipation. From the measured values, fan-in, fan-out and wiring delay times of 9-ps/FI, 7-ps/FO and 17-ps/mm are estimated, respectively. These results are in good agreement with the designed results obtained using "SPICE" simulation.

The paper proposes a combined delay model to manipulate the variance of the delay time of logic elements and a new timing verification method based on the theory of regular expressions. With the delay time of logic elements such as TTL SN7400, the minimum delay time (dm), the maximum delay time (dM), and the typical delay time are specified in the manual, and the delay time of an element is one in the interval between dm and dM. Here we assume a discrete time, and we manipulate the variance of the delay time as a set of output strings corresponding to each delay time. We call the model as the combined delay model. Since many output strings are generated with a single input string, the usual timing simulation method cannot be applied. We propose a timing verification method using a behavior extraction method of logic circuits with respect to a time string set: with respect to the specified input set, the method extracts the output string set of each element in the circuit. We devised (1) a mechanism to keep the correspondence between a primary input string and an output string with respect to the primary input string, (2) a mechanism to manipulate the nondeterminism included in the combined delay model, and (3) an event-driven like data compaction method in representing finite automata. We focused on the hazard detection problem and the verification of asynchronous circuits, and show the effectiveness of our method with medium sized circuit with 100 elements or so. The method includes the state explosion, but the data compaction method and the extraction for only the specified input set are useful to control the state explosion.

OGIS Research Institute and Osaka Gas have developed two intelligent tutoring systems (ITSs): PCTS (Process Control Training System) and PDTS (Power Distribution Training System). This paper describes a basic concept of an ITS for plant operation based on the experience of their development. The topics include: (1) The features and structure of PCTS (i.e., text based training and model based training, a simulation model based on OOP, an intelligent authoring system). (2) What kinds of stages are needed for training systems from the view point of cognitive science (i.e., verbal learning multiple discrimination learning, rule learning, compound rule learning problem solving). (3) How to detect trainees' missing operational steps and misoperations using the perturbation method.

The effectiveness of traffic shaping for VBR traffic is analyzed. Evaluation results prove that traffic shaping can improve link efficiency for most forms of bursty VBR traffic and that link efficiency gains of more than 250% can be expected without the shaping delay imposing any significant QOS deterioration. Traffic shaping increases the link efficiency to about 80% for traffic with short burst repetition periods. The traffic shaping techniques and analytical results described herein can be employed in the traffic management of future B-ISDN/ATM networks.

Air-bridge metal interconnection technology is used for upper level power supply line interconnections in GaAs LSI's to reduce the signal propagation delay time. This technology reduces both parasitic capacitance between the signal line and the power supply line, and propagation delay in the signal line to about 10% and about 50%, respectively, compared to conventional 3-level interconnections without air-bridges. Under standard load conditions (FI=FO=2, length of load line=2 mm), the air-bridge technique leads to gate propagation delays which are about 60% of those in conventional interconnections. We fabricated 2.1-k gate Gate Arrays and 4-kb SRAM's using the air-bridge structure to interconnect power supply lines. For a Gate Array with 0.7 µm gate Buried P-layer Lightly Doped Drain (BPLDD) FET's, the typical gate propagation delay under standard load conditions was about 110 ps with a dissipation power of 1.4 mW/gate. SRAM's with 05 µm gate BPLDD's had typical access time (tacc) of 1.5 ns with a dissipation power of 700 mW/chip.

This paper proposes a test case generation method for testing concurrent programs as a black box. Typical applications are system testing for switching systems and inter-operability testing for OSI products. We adopt a two-step approach: first generate the control flow graph which represents global behaviors of a given concurrent program, and then apply conventional test case generation methods for the control flow graph. To generate a control flow graph without state space explosion, the black-box equivalence between system behaviors is introduced. The proposed algorithm generates a minimal control flow graph which consists of representatives of equivalence classes. Two practical techniques for the second step are discussed for a case study using a commercial digital PBX. The results show the feasibility of the proposed method.

The subject of the paper is to propose two approximation algorithms FM_SPLA, FM_DPLA for priority-list scheduling in timed Petri nets. Their capability is compared with that of existing algorithms SPLA, DPLA through experimental results, where SPLA and DPLA have previously been proposed by the authors.

A laser/microwave method using two lasers of different wavelengths for carrier excitation is proposed to evaluate Si surfaces. These constitute a He-Ne laser (wavelength=633 nm, penetration depth=3 µm) and a YAG laser (wavelength=1060 nm, penetration depth=500 µm). Using a microwave probe, the amount of excited carriers can be detected. The carrier concentration is mainly dependent on the condition of the surface when carriers are excited by the He-Ne laser, as well as on the condition of the bulk region when carriers are excited by the YAG laser. Microwave intensities detected under the He-Ne and the YAG lasers illumination are referred to as the surface-recombination-velocity-related microwave intensity (SRMI) and the bulk-related microwave intensity (BRMI), respectively. The difference between SRMI and BRMI is called relateve SRMI (R-SRMI), and is closely related to the condition of the surface and surface active region. We evaluate the surfaces of the samples after plasma and wet etching to remove the photoresist layer. And we evaluate the surfaces of the samples after heat or HF treatment which is done to recover the damage introduced by plasma etching. It was found that the R-SRMI method is better suited to surface evaluation than conventional lifetime measurements.

Isotope dilution secondary ion mass spectroscopy (ID-SIMS) using 30Si as a spike is investigated as a quantitative analysis method for trace amounts of Si. For a standard solution of Si, the relateve standard deviation of results using this method is 5% for 0.2 µg Si, and the determination lower limit is 18 ng. Using this method, the amount of Si deposited on the Ge(100) surface by the self-limited adsorption of SiH2Cl2 is determined to be about 1.00.2 monolayer.

In the maximum-likelihood decoding under a non-Gaussian noise, the decoding region is bounded by complex curves instead of a perpendicular bisector corresponding to the Gaussian noise. Therefore, the error rate is not evaluated by the Euclidean distance. The Bhattacharyya distance is adopted since it can evaluate the error performance for a noise with an arbitrary distribution. Upper bound formulae of a bit error rate and an event error rate are obtained based on the error-weight-profile method proposed by Zehavi and Wolf. The method is modified for a non-Gaussian channel by using the Bhattacharyya distance instead of the Euclidean distance. To determine the optimum code for an impulsive noise channel, the upper bound of the bit error rate is calculated for each code having an encoder with given shift-register lehgth. The best code is selected as that having the minimum upper bound of the bit error rate. This method needs much computation time especially for a code with a long shift-register. To lighten the computation burden, a suboptimum search is also attempted. For an impulsive noise, modeled from an observation in digital subscriber loops, an optimum or suboptimum code is searched for among codes having encoders with a shift-register of up to 4 bits. By using a code with a 4-bit encoder, a coding gain of 20 dB is obtained at the bit error rate 10-5. It is 11 dB more than that obtained by Ungerboeck's code.

Subscriber network opticalization is the key issue for the next generation network. Fiber-optic systems have been limited to mainly big business applications, so far. Massive opticalization including home and small business customers remains the ultimate goal. Opticalization of the subscriber network needs an enormous investment and a long construction period. In order to achieve smooth evolution towards B-ISDN, the subscriber network must be effectively opticalized well in advance of full B-ISDN deployment. This paper presents the development concept of optical subscriber network. It also describes the design concept and configuration of fiber-optic subscriber systems. Deployment strategies and the developing technologies for the future subscriber network are also addressed.

In this paper, a type hybrid ARQ scheme with Adaptive Forward Error Correction (ARQ/AFEC) using BCH codes is proposed and analyzed. The basic idea in the proposed type hybrid ARQ/AFEC scheme is to increase the error-correcting capability of BCH code according to channel state using incremental redundancy. The incremental redundancy is the remainder ai(x) of an information frame f(x) of length n divided by a minimum polynomial mi(x) of α2i-1, where α is a primitive element of finite field GF(2l). Let gi(x) be the product of mj(x) (j=1, 2, , i) and let ci(x) be the remainder of f(x) divided by gi(x). The polynomial ci(x) is obtained from the remainders ai(x) and ci-1(x) since mi(x)and gi-1 (x) are relatively prime. Since f(x) + ci(x) is divided by gi(x), f(x) + ci(x) is the codeword of an i-error-correcting BCH code when n2l-1. So, the errors less than or equal to i bits in f(x) can be corrected if ci(x) has no error.

Although individual segments of a natural language such as words have different importance on human interpretation of the meaning, every segment has been uniformly protected by an error-correcting code. If the importance of individual segments is defined by considering their meaning in the sentence, we can adaptively control the level of error-protection for each segment according to its importance in order to reduce errors on human interpretation of the meaning. In this paper, we propose an error-control scheme based on the varying importance of each word. We first introduce a method which determines the importance of each word and then propose an error-control scheme in which several error-correcting codes are alternately used to protect each word according to its importance. Probablity of semantic errors, that is, errors on human interpretation of the meaning, is defined and used as a criterion in mapping error-correcting codes to words possessing different importance. We theoretically formalize the problem of obtaining an optimum mapping which minimizes the probability of semantic errors under some constraint. Given a certain probability distribution of the importance of words and set of error-correcting codes, we can derive the optimum mapping. The proposed error-controlling scheme is theoretically evaluated by comparing its probability of semantic errors with that of a conventional scheme in which every word is uniformly protected by a single error-correcting code. Results show that the proposed scheme can considerably raduce the probability of semantic errors while retaining the same average transmission rate or redundancy.

The purpose of our research is to get further improvement in the performance of order statistic filters. The basic idea found in our research is the use of a robust median estimator to obtain median differential order information which the classes of order statistic filter required in order to sort the input signal in the filter window. In order to give the motivation for using a median estimator in the classes of order statistic filters, we derive theorems characterizing the median filters and prove them theoretically using the characteristic that the order statistic filter has the performance for a monotonic signal equivalent with the FIR linear filter. As an application of median operation, we propose and investigate the Median Differential Order Statistic Filter to reduce impulsive noise as well as Gaussian noise and regard it as a subclass of the Order Statistic Filter. Moreover, we introduce the piecewise linear function in the Median Differential Order Statistic Filter to improve performance in terms of edge preservation. We call it the Piecewise Linear Median Differential Order Statistic Filter. The effectiveness of proposed filters is verified theoretically by computing the output Mean Square Error of the filters in parts of edge signals, impulsive noise, small amplitude noise and their combination. Computer simulations also show that the proposed filter can improve the performance in both noise (small-amplitude Gaussian noise and impulsive noise) reduction and edge preservation for one-dimensional signals.

The characteristics of an optical functional integrated circuit and its applications are discussed. This circuit is based upon a Mach-Zehnder interferometer type waveguide device employing thermo-optic effect. This circuit is compact, cost-effective and practical. One proposed application is an optical loopback circuit to test both OCU loop 1 and DSU loop C. This optical loopback circuit with an attenuator and space switches is formed on a common silicon substrate, and using this circuit both loopback and line tests are independently available at the same access point. The other is an optical selector. This optical selector with WDM-MUX/DMUX and space switches is formed on a common silicon substrate, and using this selector, wavelength selection from medium density WDM (MDWDM) signal can be performed. Each MDWDM signal carries both AM and FM-FDM video signals modulated by Subcarrier Multiplexing (SCM) techniques. This selector can be wired in point-to-multipoint configurations to home video appliances.

It often occurs in the acoustic environment that a specific signal is contaminated by the additional noise of non-Gaussian distribution type. In order to extract exactly the various statistical information of only specific signal from the observed noisy data, a stochastic signal processing by use of digital computer is essential. In this study, a stochastic method for estimating the probability function of the specific signal embedded in the additional noise is first theoretically proposed in a suitable form for the quantized level observation. Then, the effectiveness of the proposed method is experimentally confirmed by applying it to the observed data in the acoustic environment.

In power line SS communication system, since available frequency range is limited from 10 kHz to 450 kHz by the law, we can't transmit any components of lower and higher frequency regions. In this paper, we propose a method for improving bit error rate by using the PN sequence coded by the new channel code, FM-V5 code, instead of PE code to have correlation property in the coded PN sequence. Correlation property in the coded PN sequence makes us effectively use Viterbi decoding technique on the receiving side. To enhance correlation property more, we also examine to apply additionally partial response (PR) system, so called PRML system, on the receiving side. The results of computer simulation show the improvement of about 4.5 dB on SNR at bit error rate 10-5 by using FM-V5 code without PR system compared with PE code. In the case of FM-V5 code with PR(1, -1) system, we get the further improvement of about 11 dB on SNR at the same bit error rate 10-5 compared with PE code. As a result, our method can attain SNR improvement about 20 dB compared with conventional simple PN sequence, that is the conventional Direct Sequence/Spread Spectrum (DS/SS), method.

The essential functions of the passive double star (PDS) system are clarified by comparing them to the functions of the single star (SS) and the active double star (ADS) system. A layered structure describing the functional characteristics of the PDS system is proposed for flexible transport capability. The functions of the optical network unit (ONU) on the customer premises are systematically partitioned into four layers. The functions of the optical subscriber unit (OSU) in the central office are described using five layers. Call by call activation and deactivation techniques are described on the basis of a layered architecture. The reduction of ONU power consumption by adopting activation and deactivation control is also discussed.

Optical fiber cable systems are being developed in many countries for subscriber loops as the infrastructure to realize B-ISDN (Broadband Integrated Services Digital Network). The present systems are DLC (Digital Loop Carrier) systems which provide leased lines, POTS (Plain Old Telephone Services), and N-ISDN (Narrowband ISDN) services. Before FTTH (Fiber To The Home) networks can be implemented, their construction cost must be lowered to the level of the current metallic network. The FTTH network must also be easy to operate and maintain. In this paper, we describe optical fiber cables, splicing, and testing technologies used in the NTT cable networks, and introduce the technologies being developed to construct FTTH networks.

A new image restoration filter based upon a physical model of an image degradation is constructed. By means of this filter, signal dependent noise and blur can be suppressed. In particular, image degradation noise can be modeled in generalized form. Noise suppression and deblurring are performed separately. This filter has additional applications when used in conjunction with the degradation model, such as real photographic images and photoelectronic images. Simulation results show that this filter gives a superior performance in restoring an image degraded by signal dependent noise and blur.