In this paper, a multiuser receiver using a Hopfield network (Hopfield network receiver) for asynchronous codedivision multiple-access systems is proposed. We derive a novel likelihood function for the optimum demodulation of a data subsequence whose length is far shorter than that of the entire transmitted data sequence. It is shown that a novel Hopfield network receiver can be derived by exploiting the likelihood function, and the derived receiver leads to a low complexity receiver. The structure of the proposed receiver consists of a bank of correlators and a Hopfield network where the number of units is proportional to both the number of users and the length of a data sequence demodulated at a time. Computer simulation results are presented to compare the performance of the proposed receiver with those of the conventional multiuser detectors. It is shown that the proposed receiver significantly outperforms the correlation receiver, decorrelating detector and multistage detector, and provides suboptimum performnace.

In this paper, the bit error rate (BER) performance of the Spread Spectrum communication system with Constrained Spreading Codes (SS-CSC) is analyzed. The BER of the SS-CSC system is the same as that of the Bi-orthogonal system. Moreover, the frequency utilization efficiency of the SS-CSC system is better than that of the Bi-orthogonal system when K 10 and N = 3.

In this paper, we discuss both effective approaches in specification process, formal specification and reuse, and focus on providing an integrated and systematic supportbased on them. Preparing the specification model which mediates an image of the designer and another representation of it in formal method, the designer can specify the target system incrementally and smoothly. As for the specification model, we employ LTS on the early step of specification process because of its understandability for the designer. Moreover, reuse of specification leads to reduction of the cost and time, defining retrieval mechanism of reusable cases from database by mathematically calculating similarity of them. For the reuse mechanism, we define a new concept of similarity on LTS as the criterion of case retrieval, which enables more flexible matching between the besigner's requirement and the existing case than any other traditional schema on LTS, and show the case retrieval algorithm. Integration of two approaches brings us the great improvement of the productivity on system development.

In this paper we propose a method for generating Prolog program code and skeleton C code from a specification of requirements written in DFDs (Data Flow Diagram) and DD (Data Dictionary). This generation of code takes two transformation steps. The specification is transformed into a Prolog program and the transformed Prolog is used for generating skeleton C code so that the specification is directly expendable in the conventional programming environment. This work makes it possible to rapidly have a prototype by executing Prolog programs and remove the design stage from the software development life cycle. This has been implemented on UNIX workstation environment with a data flow diagram editor START system.

We propose a method to fuse auditory information and visual information for accurate speech recognition. This method fuses two kinds of information by using Iinear combination after calculating two kinds of probabilities by HMM for each word. In addition, we use full-frame color image as visual information in order to improve the accuracy of the proposed speech recognition system. We have performed experiments comparing the proposed method with the method using either auditory information or visual information, and confirmed the validity of the proposed method.

In this paper, we propose a camera calibration method that estimates both intrinsic parameters (perspective and distortion) and extrinsic parameters (rotational and translational). All camera parameters can be determined from one or more images of planar pattern consists of parallelogramatic grid points. As far as the pattern can be visible, the relative relations between camera and patterns are arbitrary. So, we have only to prepare a pattern, and take one or more images changing the relative relation between camera and the pattern, arbitrarily; neither solid object of ground truth nor precise z-stage are required. Moreover, constraint conditions that are imposed on rotational parameters are explicitly satisfied; no intermediate parameter that connected several actual camera parameters are used. Taking account of the conflicting fact that the amount of distortion is small in the neighborhood of the image center, and that small image has poor clues of 3-D information, we adopt iterative procedure. The best parameters are searched changing the size and number of parallelograms selected from grid points. The procedure of the iteration is as follows: The perspective parameters are estimated from the shape of parallelogram by nonlinear optimizations. The rotational parameters are calculated from the shape of parallelogram. The translational parameters are estimated from the size of parallelogram by least squares method. Then, the distortion parameters are estimated using all grid points by least squares method. The computer simulation demonstrates the efficiency of the proposed method. And the results of the implementation using real images are also shown.

We present a topological framework of stepwise specification for concurrent systems in this paper. Some of description techniques can make topologies on the system space. Such topologies corresponds to abstract levels of those description techniques. Using a family of such description techniques, one can specify systems stepwisely. This framework allows to bridge various DTs and modularizing, so that global properties and module properties of systems become to be related to each other. Within this framework, we show derivation of a LOTOS cpecification from temporal logic formulae. An extended version of LOTOS with respect to concurrency is used in this paper. A semantics including concurrency is introduced to do this in this method. The method presented in this paper is applied to mobile telecommunication.

We analyzed the operation speed of the resonant tunneling logic gate, MOBILE, using a simple equivalent circuit model and varying parameters of I-V characteristics and capacitance of RTTs(resonant tunneling transistors). The switching time for large peak-to-valley(P/V)current ratios is smaller at small Vbmax(maximum bias voltage), but larger at large Vbmax than that for small P/V ratios in the case of present I-V characteristics with flat valley current. It is also demonstrated that the MOBILE operation fails if the bias voltage rises too fast, when the capacitance of the load and the driver is different due to the displacement current through the capacitance. These behaviors can be explained by considering the potential diagrams of the circuit.

Progress made in the field of high speed networking technology has led to the planning and prototyping of true high-bandwidth applications with very high throughput and low delay requirements. In this study we approach the problem of high throughput demand from the aspect of protocols and introduce the handling of error control in the application layer level as opposed to the transport layer since the eventual destination of data is the application itself. This scheme, called ACER (Application Conscious Error Recovery), is proposed and defined for bulk data transfers. A simple analytic throughput comparison of the sliding window scheme with go-back-N, and ACER is given later, Also, a prototype implementation of ACER for bulk data transfer and experimental measurement results are presented. Besides, we investigate the performance of the scheme by simulation for various network models. Finally, we present a discussion of extending the scheme to different traffic patterns and applications.

To improve the demodulated signal-to-noise ratio, SNR, for colored noise environments, we present a new direct-sequence spread-spectrum receiver system, whose construction is based on the concept of Shaped M-sequence Demodulation (SMD). This receiver has the function for shaping the local dispreading-code waveform. This method can modify the frequency transfer function from a received input to the damp-integrated output according to the power spectrum of colored noise added in the transmission process. SMD performs the combined function of a whitening filter and a matched filter, which can be used to implement an optimum receiver. For the case when the additive colored-noise power spectrum is known and the transmission channel is non-band-limited, a design theory is derived that provides the maximum SNR by choosing the best dispreading-code sequence corresponding to a given signature spreading-code sequence. The noise power component produced in the receiver damp-integrated-output is anayzed by introducing the auto-correlation matrix of the additive noise. The SNR performance of systems, one using non-optimized codes and the other using optimized codes, is examined and compared for various noise models. It is verified by analysis and computer simulation that, compared to a conventional system using non-optimized codes, remarkable SNR improvements can be achieved due to the whitening effect acquired without producing inter-symbol interference. In contrast, if a transversal whitening filter is front-ended, it produces inter-frame interference, degrading the SNR performance. The band-limiting effect of the transmission channel is also analyzed, and we confirmed that the codes optimized for the non-band-limited channel can be applied to the band-limited channel with little degradation of SNR. SMD is inherently tolerant of fast-changing noise such as fading, due to its frame-by-frame operation. Considering this function as a general demodulation scheme, it may be called "Local Code Filtering."

The dipole-dipole interaction in the quantum mechanical treatment of the matter-radiation dynamics, is shown to give rise to split energy levels reminiscent of the nonlinear coupled spectral features as well as a self-sustained coherent modes. Wiener's theory of nonlinear random processes is applied to the second harmonic generation (SHG), leading also to coupled spectral pulling and dipping features, due to the dual noise sources in the fundamental and the harmonic polarizations. Furthermore, the nonlinear spectral features are suggested to be applied to implement quantum (qubit) gates for computation.

In order to apply formal design verification, it is necessary to describe formally and correctly the specification of the circuit under verification. Especially when we apply conventional OBDD-based logic comparison method for verifying combinational circuits, another correct" logic circuits or Boolean formulae must be given as the specification. It is desired to develop an efficient automatic design verification method which interprets specification that can be described easier. This paper provides a new verification method which is useful for combinational circuits such as arithmetic circuits. The proposed method efficiently verifies whether a designed circuit satisfies a specification given by recurrence equations. This enables us to describe easily an error-free specification for arithmetic circuits. To perform verification efficiently using an ordinary OBDD package, an efficient truth-value rotation algorithm is developed. The truthvalue rotation algorithm efficiently generates an OBDD representing f(x + 1 (mod 2n)) from a given OBDD representing f(x). By experiments on SPARC station 10 model 51, it takes 180 secs to generate an OBDD for designed circuit of 23-bit square function, and additional 60 secs is sufficient to finish verifying that it satisfies the specification given by recurrence equations.

Finite-difference time-domain (FDTD) analysis is performed to evaluate the distributions of specific absorption rate (SAR) in a human head during use of a handheld portable telephone. A heterogeneous head model has been assumed which is comprised of 273 108 cubic cells 2.5 mm on a side, with the electrical properties of anatomical equivalents. A handset model has been assumed to be a metal box with either a quarter-wavelength monopole or a half-wavelength dipole operating at 900 MHz or 1.5 GHz. The maximum local SARs in the head are evaluated under various exposure conditions. The dependence of the maximum local SARs on the difference in the structures or parameters of the model, i.e. the distance between the antenna and the head, the heterogeneity of the head, the antenna type, the volume of the smoothing region of the local SAR value, skin electrical constants, and the presence or absence of auricles, are examined. It is shown that the heterogeneity of the head barely affect the maximum local SAR when the telephone is located sufficiently close to the head. It is also shown that the electrical constants of skin which has lower conductivity provide the lower maximum local SAR in the head while the maximum local SAR within the brain is not significantly affected. The auricle which lies in closest proximity to the antenna is shown to have significant effect on the maximum local SAR. It is suggested that the presence of the auricle enhances the maximum local SAR by a factor that is 1.7-2.4 larger than the model without auricles.

Spread-spectrum (SS) sharing with comb spectrum structure in a microcell/macrocell cellular architecture in order to increase spectral efficiency is proposed. Such method employs a filter in the code division multiple access (CDMA) transmitter to feature comb spectrum structure, and suppress interference with a narrowband time division multiple access (TDMA) system in using together in SS sharing. The relationship between microcellular capacity and macrocellular capacity of the system is explored and compared to those of conventional SS sharing and orthogonal sharing. To be concrete, we investigate two cases, i.e., using no power control and ideal power control in the TDMA system. In both cases, the proposed SS sharing gives better capacity results than the conventional SS sharing and in the comparison when ideal power control is used in th. TDMA system, it even has the property to oppose the orthogonal sharing in ideal condition without interference.

Hybrid image coding method is one of the most promising methods for efficient coding of moving images. The method makes use of jointly motion-compensated prediction and orthogonal transform like DCT. This type of coding scheme was adopted in several world standards such as H.261 and MPEG in ITU-T and ISO as a basic framework [1], [2]. Most of the work done in motion-compensated prediction has been based on a block matching method. However, when input moving images include complicated motion like rotation or enlargement, it often causes block distortion in decoded images, especially in the case of very low bit-rate image coding. Recently, as one way of solving this problem, some motion-compensated prediction methods based on an affine transform or bilinear transform were developed [3]-[8]. These methods, however, cannot always express the appearance of the motion in the image plane, which is projected plane form 3-D space to a 2-D plane, since the perspective transform is usually assumed. Also, a motion-compensation method using a perspective transform was discussed in Ref, [6]. Since the motion detection method is defined as an extension of the block matching method, it can not always detect motion parameters accurately when compared to gradient-based motion detection. In this paper, we propose a new motion-compensated prediction method for coding of moving images, especially for very low bit-rate image coding such as less than 64 kbit/s. The proposed method is based on a perspective transform and the constraint principle for the temporal and spatial gradients of pixel value, and complicated motion in the image plane including rotation and enlargement based on camera zooming can also be detected theoretically in addition to translational motion. A computer simulation was performed using moving test images, and the resulting predicted images were compared with conventional methods such as the block matching method using the criteria of SNR and entropy. The results showed that SNR and entropy of the proposed method are better than those of conventional methods. Also, the proposed method was applied to very low bit-rate image coding at 16 kbit/s, and was compared with a conventional method, H.261. The resulting SNR and decoded images in the proposed method were better than those of H.261. We conclude that the proposed method is effective as a motion-compensated prediction method.

A new type of noncausal stochastic model is proposed to represent a random image with double peak spectrum. The model based on the assumption that the double peak spectrum is expressed by a product of two spectra located at two symmetric positions in the 2D spatial frequency space. Estimation of model parameters is made by means of minimizing the "whiteness" which was proposed in authors' previous work. In a simulation for model estimation we make use of computer-generated random images with double peak spectrum. Comparing this with the estimation by a causal model, we demonstrate that the present method can better estimate not only the spectral peak location but also the spectral shape. The proposed model can be extend to an image model with multl-peak spectrum. However, Increase of parameters makes the model estimation more difficult We try a model with triple peak spectra since a real texture image usually possesses a spectral peak at the origin besides the two peaks. A result shows that the estimation of three spectral positions are good enough, but their spectral shapes are not necessarily satisfactory. It is expected that the estimation of multi-peaked spectral model can be made better by improving the process of minimizing the "whiteness."

This paper presents the scattering characteristics of a TE electromagnetic plane wave by metallic strip gratings on an optically plasma-induced silicon slab at millimeter wave frequencies. The characteristics were analyzed by using the spectral domain Galerkin method and estimated numerically. We examined to control the resonance anomaly by changing the optically induced plasma density, and the metallic strip grating structures were fabricated on highly resistive silicon. The optical control characteristics of the reflection, and the forward scattering pattern by the grating structures, were measured at Q band and are discussed briefly with theory.

This paper is concerned with the study of fast-frequency-hopped spread-spectrum multiple-access (FFH-SSMA) digital systems employing antenna diversity and noncoherent binary frequency-shift-keying (FSK) modulation operating through an indoor radio multipath Rayleigh channel. The diversity technique of equal gain combing (EGC) is considered in our study. It is assumed that the frequency-hopping rate is equal to the bit rate.

In this study, we analyze the system which simultaneously transmits spread-spectrum signals with different processing gains. The main purpose of this study is to give an analytical framework that describes the influence of the interfering signals with different processing gains. For this purpose, we define a crosscorrelation function between the spreading sequences with different code lengths, and discuss the effects of interaction between the signals. As the results, we show that the power of the interference component after despreading procedure, the power ratio of the desired to undesired components, and thus the bit error rate are not constant but vary symbol by symbol.

For direct sequence spread spectrum systems, the performance of PN sequence acquisition can be significantly affected if data modulation is present. However, the data modulation often exists during the reacquisition of a PCS radio channel. This study proposes and analyzes two shemes which are designed to improve acquisition process for PN sequence under data modulation. Both designs are based upon a PN acquisition receiver with parallel I-Q matched filters. The first scheme employs a serial search strategy with verification mode. The second scheme, which is still based upon the same parallel acquisition receiver, employs the parallel search strategy. We show that the second scheme is capable of providing faster acquisition under data modulation than the first serial search scheme using the same number of I-Q matched filter. We believe it should become a very good alternative for the acquisition of data modulated PN sequences in personal communications.