In this paper, we analyze a multi-stage hard-decision bounded-distance decoding method for multi-level block modulation codes. Each stage of the decoding is performed by a combination of a hard-decision for each received symbol and an algebraic decoding for a component code. Error performance of multi-level block modulation codes is analyzed for a memoryless additive channel based on the multi-stage decoding algorithm presented here. Formulas are derived for the probability of erroneous decoding and that of decoding failure. Then these probabilities are computed for some specific 8-PSK block modulation codes.

We have recently extended one of the conceptions of the lossless universal pattern-matching coding, viz. the concept of coding via copying, to multi-dimensional lossy coding, and applied the extended concept to intraframe compression of still images. The work herein applies the extended concept of lossy coding via copying to interframe low-rate video compression, thus developing a novel low-rate interframe PMIC (pattern-matching image coding) technique, which produces the effect of generalizing the definition of a search area used in the existing block-matching motion compensation. We have experimentally shown the performance gain provided by the generalization within the framework of lossy coding via copying, and demonstrated that the interframe PMIC technique is usefull and potential as a basic means for low-rate video compression.

We propose five classes of variable length codes for encoding positive integers: One is a class of codes having constant Hamming weight. The other four classes of codes have a prefix and a suffix in a codeword. The prefix indicates the weight or the length of the suffix and variable length constant weight codes are used for the prefixes and the suffixes of some of these codes. For encoding of these codes we can use Schalkwijk's algorithm. It is shown that some of the proposed codes are universal and asymptotically optimal in the meaning that P. Elias has defined. We compare them with other known codes from the viewpoints of the length of the codewords corresponding to integers 2M (M=0, 1, , 30) and the average codeword length for two sources: 26 letters in English sentences and the geometrically distributed positive integers. The results shows that some of the proposed codes which are universal and asymptotically optimal are more efficient than the known codes.

Decision tree design is an important issue because decision trees have many applications in, for example, fault diagnosis and character recognition. This paper describes an algorithm designing a probabilistic decision tree, in which a test applied to a state produces different outcomes with non-zero probability. The algorithm strictly minimizes the tree cost, which is defined as the weighted sum of expected loss and expected test execution time. The lower bound of the cost is utillized to remove the excessive computing time needed to search for the exact optimum. This lower bound is derived from information theory and is transformed to an easily computable representation by introducing a network model. The result of a computational experiment confirms the time efficiency of the proposed method.

When the alphabet of a source is very big, existing universal data compression algorithms fail to show their expected performances. The purpose of this paper is to provide an efficient coding algorithm even for sources with such a big alphabet size. We assume that the source has an independent identical smooth distribution but the distribution itself is unknown to us, and that the source symbols have a linear order. The algorithm is described in an adaptive enumerative coding flavor. Let Sn denote the set of observed past n samples and we are to encode a new sample x noiselessly. We look into Sn and decide the positional index of x among the ordered past n samples. This can be done by Cover's enumerative formula. Sn is divided into k groups of equal size according to that order. Then the probability that x falls into any particular group being almost equal to 1/k, the group number of x is encoded in fixed length, log k bits. Source alphabet is also partitioned into k sub-alphabets in accordance with the groups in Sn. Then the positional index of x in the selected sub-alphabet is encoded in variable length. The computational time complexity of the algorithm is linear to the input data length. The experimental analysis and discussion show superiority of our algorithm to existing ones for the sources in question. A modification to the base algorithm is also proposed for implementation purposes.

A new trial of statistical evaluation for an output response of a stochastic linear system on an energy scale is proposed as a prediction method of its probability distribution function by using differential operator with respect to a distribution parameter. As the differential operator is independent of system variable, the statistical features like the nonstationarity, non-gamma property and various type linear and non-linear correlations of input signal reflected in the differential operator and the system dynamics can be treated independently of the system variable. Hence, the probability distribution of transmitted power is easily derived by operating nonstationary operator to the basic probability distribution of output response obtained by a pre-experiment with a test signal of standard gamma type. As an application to the actual noise environment, the proposed evaluation method is employed for the evaluation on a sound insulation system of double walls with sound bridge excited by a non-stationary road traffic noise.

This paper proposes () an algorithm that dynamically constructs an asymptotically-balanced binary tree to store successively-given keys without knowledge of the distribution of key occurence, and () another algorithm for quick key search over the constructed tree such that: If the tree has in memory at least a key that is inside the Δ-neighbor (in a Hamming space) of a reference key, then the algorithm can find one of such Δ-neighbor keys almost with probability 1. The memory capacity required to describe a tree in the tree construction algorithm is of order being proportional to the number l of keys already processed. For an independently and idenically distributed binary source of generating keys, the mean computation time required to update a tree for every key input can be of an order being a little higher than (log2l)2log2(log2l), and that required to search a Δ-neighbor key can be of an order being a little higher than (log2l)3.

A major problem in Doppler ultrasound has been the lack of quantitation of the magnitude of the blood velocity vector, particularly in intracardiac flow where the flow direction can't be estimated. This paper derives a new flow-mapping system for visualizing the two-dimensional blood velocity vector. The resultant velocity vector is the projection of the three-dimensional velocity vector on the beam scanning plane.

This paper presents a useful numerical approach based on a self-consistent finite-element method for solving stationary properties of third-order nonlinear guidedwave phenomena in a planar optical waveguide which supports nonlinearly coupled transverse-electric and transverse-magnetic modes. This method can be useful for the stability analysis as well by tracing intermediate solutions generated through iterative processes. Depending on the transitional behavior of the intermediate solutions we can identify the nonlinear excitation under consideration to be absolutely stable, quasi-stable, or unstable.

In this letter, the relations between the generalized beams with the different parameters are investigated by using the formula for the Hermite polynomials and that for the generalized Laguerre polynomials. The adjoint functions for the generalized Laguerre-Gaussian beam functions are also derived concretely. It is shown that the generalized beam is represented by a finite number of another generalized beam with the different parameter.

Electromagnetic wave scattering from a perfectly conducting indented body of revolution is analyzed both in the frequency and time domains. The three-dimensional (3-D) scattering process and the effect of polarization on scattering characteristics are revealed. A well-defined scattering matrix representation is adopted for investigating the polarimetric property of the 3-D scattering. First, the scattering cross sections are calculated in the frequency domain by using the Yasuura method (Mode-Matching Method) which is a powerful and reliable numerical method for solving electromagnetic boundary value problems. Next, co-polarization and cross-polarization components of the pulse response waveforms are calculated from the scattering matrix by using the Fourier synthesis technique. It is found out from the numerical results that the pulse responses from the indented objects can be interpreted as three distinctive waves: conventional specularly-reflected wave, creeping wave and complex specularly-reflected wave which is reflected from a complex specular reflection point. These scattering processes are consistently explained by employing the extended ray theory. And the radar polarimetries of these three distinctive waves are clearly observed both in co-polarization and cross-polarization components of scattering cross sections and pulse responses.

Five channel optical waveguides are investigated numerically by using mode-matching method. The precise numerical results of the dispersion relations near the cutoff and the field distributions are presented for the lowest five HE modes. When the geometric parameters of the waveguides can be optimized so as to satisfy the phase-matching condition, it is shown that the five channel optical waveguides operate as power divider.

This paper discusses on the methods and their numerical simulation results of the one-dimensional profiling of dielectric targets in the direction of electromagnetic wave incidence. Two different inverse profiling algorithms are proposed. First method is based on the Rayleigh approximation. The inverse profiling is carried out by performing the Fourier transformation of the backscattered field in frequency domain. In this method, the dielectric constant of the target is assumed as known beforehand. The second method is based on the extended physical optics (EPO) method. The EPO method was proposed for calculating the backscattering cross section for a conducting scatterer, however, we apply the EPO method to the inverse problem of the dielectric target whose dielectric constant is not known. The validity and limitation of each method are tested numerically for spherical and spheroidal targets.

Tohoku University has been constructing the academic information-exchange network TAINS (Tohoku University Academic/All-round/Advanced Information Network System) to link its widely spread campuses and to meet several demands for an intrauniversity network. TAINS, the first network based on OSI, became operational in April 1988. The primary function of TAINS is to connect all the geographically dispersed locations of the university via a high-speed digital network in order to facilitate an easy and efficient interconnection among the various computers, terminals and other scientific equipment. TAINS is constructed as a large-scale local area network of hierarchical structure. In the hierarchical network of TAINS, a backbone network, consisting of two 100 Mbps optical fiber rings, interconnects several small-scale IEEE802.3 networks, each of which span a building or a part of a building. This paper describes the background, the basic design concept and the constitution of TAINS. In TAINS, the inhouse network protocol is OSI-based, and the ring network protocol is based on FDDI. The use of these communication protocols are reviewed and the protocol matching adopted for TAINS is described. Finally, a method for estimating the stable operation of a 2-layer hierarchical network using traffic analysis is given.

Tunable fiber lasers with ring resonator structure were reported in this paper. A tunable fiber directional coupler links the rear-earth-doped single-mode fiber to from a ring resonator. Laser oscillation should occur in the fiber ring cavity when the rear-earth ions in the fiber are excited by a pumping light. The losses of the directional coupler and rear-earth-doped fiber are very small so that the fiber ring laser has low threshold and high slope efficiency. In this fiber ring laser, the directional coupler plays three functions of transmitting pumping light, coupling lasing oscillation and tuning laser wavelength. We have used both Nd3+-doped and Er3+-doped single-mode fiber to fabricate the tunable fiber ring lasers. An argon ion laser was used as the pump source. For the Nd3+-doped fiber ring lasers with cavity lengths of 3 meters and 5 meters, the lasing threshold were 0.8 mW and 4.9 mW respectively at the lasing wavelength of 1.088 nm. The highest slope efficiency was about 30%. The laser wavelength could be tuned continuously in the Nd3+ fluorescent spectrum and the tunning range is greater than 60 nm. The Er3+-doped fiber ring lasers had the cavity lengths of 1 meter and 8 meters, lasing at 1550 nm with a tuning range of about 70 nm, the thresholds were 1.9 mW and 14.2 mW and the slope efficiencies were 6.1% and 10.2% respectively. A novel fiber ring laser with single-longitudinal-mode output was demonstrated. This fiber laser has a composite resonator which is composed of two subrings. Longitudinal mode is selected in the subrings coupled each other. A laser linewidth less than 40 MHz was got from the Nd3+-doped fiber ring laser.

The diffraction of a plane electromagnetic wave by a perfectly-conducting finite sinusoidal grating is analyzed using the Wiener-Hopf technique combined with the perturbation method. Assuming the depth of the grating to be small compared with the wavelength and approximating the boundary condition on the grating surface, the problem is reduced to that of the diffraction by a flat strip with a certain mixed boundary condition. Introducing a perturbation expansion for the unknown scattered field under the small-depth approximation, the problem is formulated in terms of the zero order and the first order Wiener-Hopf equations, which are solved exactly in a formal sense by a factorization and decomposition procedure. Applying a rigorous asymptotics, explicit high-frequency asymptotic solutions are further obtained for the width of the grating large compared with the wavelength. Scattered far field expressions are derived by taking the inverse Fourier transform are applying the saddle point method. Representative numerical examples of the far field patterns are given for various physical parameters, and the scattering characteristics of the grating are discussed.

A mode-matching method in the sense of least squares is applied for analyzing grating couplers having various groove shapes. These couplers are formed on surfaces of core regions of the thin-film waveguides and their periodic parts extend finitely. The grating couplers are analyzed for the plane wave incidence when the Bragg condition is satisfied. The discussion is developed about the grating coupler which is formed on the asymmetric waveguide and has arbitrary triangular grooves. However various couplers, which have triangular, rectangular and sinusoidal grooves and are formed on asymmetric and symmetric waveguides, are analyzed and results for them are presented in this paper. The approximate scattered fields of each region of the coupler are described by the superpositions of the plane waves with band-limited spectra, respectively. These approximate wave functions are determined by the minimization of the mean-square boundary residual. This method results in the simultaneous Fredholm type integral equations of the second kind for these spectra. Results of analyses based on the first order approximate solutions are presented. The comparison between each coupling efficiency derived by the present method for couplers having sinusoidal, triangular and rectangular grooves is presented in this paper.

This paper discusses an efficient numerical calculation technique for scattering from three dimensional bodies of perfect conductors and dielectric materials. The key of this method is to express the scattering fields by the field generated by the distributed hypothetical dipoles (or the equivalent sources). Since the scattered field should be analytic in each homogeneous sub-domain of general scattering bodies, the equivalent sources to be used for expressing the scattered field in one of those sub-domains should be distributed outside of this space domain. Unknown vector currents of equivalent dipoles are solved by the generalized mode-matching method. Example scatterers discussed here are finite conducting and dielectric cylinders with rotationary symmetry. The results are discussed with comparative data obtained by other numerical method and also with experiments that we took.

An analytical theory of the quasi LP-modes in anisotropic optical fibres with a homogeneous circular core and homogeneous cladding is developed. Analytical expressions for the quasi LP-mode fields are obtained by the separated variable method and by the perturbation method under the following conditions. The Cartesian permittivity tensors of the core and cladding are diagonal and have the same orientation in the crosssection of the fibre. The longitudinal components of these permittivity tensors are equal, and the differences between the transversal and longitudinal components of these tensors are sufficiently small. The transversal components of the quasi LP-mode fields are derived from Maxwell's equations in the linear approximation on these differences. Solutions of the mode characteristic equation for the quasi LP-modes are reduced to the known solutions of the characteristic equation for the LP-modes in the isotropic optical fibre.