In this paper, we examine a new initial symbol acquisition method for M-ary spread-spectrum (M-ary/SS) signals that are affected by large carrier frequency offset. By the effect of the carrier frequency offset, preamble signal energy is dispersed to the undersired outputs. The proposed method is based on the collection of such dispersed signal energies by using reference patterns. The reference patterns are constructed by using the characteristic of Hadamard code sequences. The effectiveness of the proposed method is evaluated in terms of mean acquisition time.

In this paper we discuss the binary spreading sequences whose spectral distributions are DC free and spectral distribution's shapes can be easily controlled by a certain parameter denoted by δ. The newly developed sequences, referred to as modified antisymmetric M-sequences, are modified-versions of the conventional antisymmetric (AS)M-sequences. The proposed sequences are designed to increase the varieties of spectral distribution's shapes and improve the correlation properties when compared to those of the FM coded M-sequences which have already proposed by Tsuzuki et al. Some typical line coded M-sequences, i.e. the (differential) Manchester coded M-sequences and the FM coded M-sequences, and the conventional AS M-sequences are included in the set of proposed sequences. The improvement of the average BER (bit error rate) performance for asynchronous DS/SSMA (direct sequence/spread spectrum multiple access) systems using the proposed sequences in comparison to the system using the conventional AO/LSE (auto-optimal phase with least sidelobe energy) M-sequences is also shown.

In circuit simulation, dc operating points of nonlinear circuits are obtained by solving circuit equations. In this paper, we consider "hybrid equations" as the circuit equations and discuss the stability of dc operating points obtained by solving hybrid equations. We give a simple criterion for identifying unstable operating points from the information of the hybrid equations. We also give a useful criterion for identifying initial points from which homotopy methods coverge to stable operating points with high possibility. These results are derived from the theory of dc operating point stability developed by M. M. Green and A. N. Willson, Jr.

A rigorous radar cross section (RCS) analysis is carried out for two-dimensional rectangular and circular cavities with double-layer material loading by means of the Wiener-Hopf (WH) technique and the Riemann-Hilbert problem (RHP) technique, respectively. Both E and H polarizations are treated. The WH solution for the rectangular cavity and the RHP solution for the circular cavity involve numerical inversion of matrix equations. Since both methods take into account the edge condition explicitly, the convergence of the WH and RHP solutions is rapid and the final results are valid over a broad frequency range. Illustrative numerical examples on the monostatic and bistatic RCS are presented for various physical parameters and the far field scattering characteristics are discussed in detail. It is shown that the double-layer lossy meterial loading inside the cavities leads to the significant RCS reduction.

In this paper a new class of single error-correcting fixed block-length (d, k) codes has been proposed. The correctable error types are peak-shift error, insertion or deletion error, symmetric error, etc. The basic technique to construct codes is a systematic construction algorithm of multilevel sequences with a constant Lee weight (TALG algorithm). The coding rate and efficiency are considerably good, and hence the proposed new codes will be very useful for improving the reliability of high density magnetic recording.

We investigate an importance sampling (IS) simulation of MMPP/D/1 queueing to obtain an estimate for the survivor function P(Q > q) of the queue length Q in the steady state. In Ref.[11], we studied the IS simulation of 2-state MMPP/D/1 queueing and obtained the optimal simulation distribution, but the mathematical fundation of the theory was not enough. In this paper, we construct a discrete time Markov chain model of the n-state MMPP/D/1 queueing and extend the results of Ref.[11] to the n-state MMPP/D/1. Based on the Markov chain model, we determine the optimal IS simulation distribution fo the n-state MMPP/D/1 queueing by applying the large deviations theory, especially, the sample path large deviations theory. Then, we carry out IS simulation with the obtained optimal simulation distribution. Finally, we compare the simulation results of the IS simulation with the ordinary Monte Carlo (MC) simulation. We show that, in a typical case, the ratio of the computation time of the IS simulation to that of the MC simulation is about 10-7, and the 95% confidence interval of the IS is slightly improved compared with the MC.

Let {Xk}k=- be a stationary and ergodic information source, where each Xk takes values in a standard alphabet A with a distance function d: A A [0, ) defined on it. For each sample sequence X = (, x-1, x0, x1, ) and D > 0 let the approximate D-match recurrence time be defined by Rn (x, D) = min {m n: dn (Xn1, Xm+nm+1) D}, where Xji denotes the string xixi+1 xj and dn: An An [0, ) is a metric of An induced by d for each n. Let R (D) be the rate distortion function of the source {Xk}k=- relative to the fidelity criterion {dn}. Then it is shown that lim supn-1/n log Rn (X, D) R (D/2) a. s.

Scattering data from radar targets are analyzed in the time-frequency domain by using wavelet transform, and the scattering mechanisms are investigated. The wavelet transform used here is a powerful tool for the analysis of scattering data, because it can provide better insights into scattering mechanisms that are not immediately apparent in either the time or frequency domain. First, two types of wavelet transforms that are applied to the time domain data and to the frequency domain data are defined, and the multi-resolution characteristics of them are discussed. Next, the scattering data from a conducting cylinder, two parallel conducting cylinders, a parallel-plate waveguide cavity, and a rectangular cavity in the underground are analyzed by using these wavelet transforms to reveal the scattering mechanisms. In the resulting time-frequency displays, the scattering mechanisms including specular reflection, creeping wave, resonance, and dispersion are clearly observed and identified.

Coupling in time domain between two non-parallel transmission lines of finite length is analyzed by using a circuit concept. Coupling equations based on the Maxwell's equations for lossless transmission lines in a homogeneous medium are written by a set of non-homogeneous differential equations including distributed source terms produced by external electromagnetic fields. The forcing terms are expressed by vector potentials generated by currents in the line section and at the transitions. A set of solutions in frequency domain is obtained by a four-port network expression with regard to the terminal voltages and currents, and can be applied to estimation of the frequency-domain crosstalk. Utilizing the inverse fast Fourier transform (FFT), the crosstalk responses between the lines is studied in time domain. Comparison of theoretical and experimental results shows the validity of the method.

This paper deals with the scattering and diffraction of a plane wave by a randomly rough half-plane by three tools: the small perturbation method, the Wiener-Hopf technique and a group theoretic consideration based on the shift-invariance of a homogeneous random surface. For a slightly rough case, the scattered wavefield is obtained up to the second-order perturbation with respect to the small roughness parameter and represented by a sum of the Fresnel integrals with complex arguments, integrals along the steepest descent path and branch-cut integrals, which are evaluated numerically. For a Gaussian roughness spectrum, intensities of the coherent and incoherent waves are calculated in the region near the edge and illustrated in figures, in terms of which several characteristics of scattering and diffraction are discussed.

The present paper gives a new formulation for rough surface scattering in terms of a stochastic integral equation which can be dealt with by means of stochastic functional approach. The random surface is assumed to be infinite and a homogeneous Gaussian random process. The random wave field is represented in the stochastic Floquet form due to the homogeneity of the surface, and in the non-Rayleigh form consisting of both upward and downward going scattered waves, as well as in the extended Voronovich form based on the consideration of the level-shift invariance. The stochastic integral equations of the first and the second kind are derived for the unknown surface source function which is a functional of the derivative or the increment of the surface profile function. It is also shown that the inhomogeneous term of the stochastic integral equation of the second kind automatically gives the solution of the Kirchhoff approximation for infinite surface.

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.

In this paper an algorithm for numerical investigation of the transmission line having a generalized polygonal cross-section and open interface is proposed. Solution of the eigenmode problem is based on the method called the domain product technique, which employs a Mathieu function expansion and provides an efficient technique to the analysis of the structures with multiangular boundaries. An agreement at the obtained numerical results with existing data confirms the applicability of the theoretical analysis given in the paper.

The capture effect caused by some of power assignment, Rayleigh fading, and near-far effect, can improve the performance of random-access techniques in mobile radio environment. Moreover, if we consider the overall effect of them, the system performance can be noticeably improved. In this paper, the combined effect of fixed power assignment scheme, Rayleigh fading, and near-far effect on the performance of slotted ALOHA are studied. Plus, the performance degradation caused by AWGN is also investigated. The type of signal capture to be considered is the one that a signal involved in a collision survives if its power level exceeds the sum of the other signals participating in the same collision. Numerical calculations are used to demonstrate the degree of improvement and degradation.

This paper deals with a probabilistic formulation of the diffraction and scattering of a plane wave from a periodic surface randomly deformed by a binary sequence. The scattered wave is shown to have a stochastic Floquet's form, that is a product of a periodic stationary random function and an exponential phase factor. Such a periodic stationary random function is then represented in terms of a harmonic series representation similar to Fourier series, where `Fourier coefficients' are mutually correlated stationary processes rather than constants. The mutually correlated stationary processes are written by binary orthogonal functionals with unknown binary kernels. When the surface deformations are small compared with wavelength, an approximate solution is obtained for low-order binary kernels, from which the scattering cross section, coherently diffracted power and the optical theorem are numerically calculated and are illustrated in figures.

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.

To reduce the memory access latency on sharedmemory multiprocessors, several prefetching schemes have been proposed. The sequential prefetching scheme is a simple hardware-controlled scheme, which exploits the sequentiality of memory accesses to predict which blocks will be read in the near future. Aggressive sequential prefetching prefetches many blocks on each miss to reduce the miss rates and results in good performance for application programs with high sequentiality. However, conservative sequential prefetching prefetches a few blocks on each miss to avoid prefetching of useless blocks, which shows better performance than aggressive sequential prefetching for application programs with low sequentiality. We analyze the relationship between the sequentiality of application programs and the effectiveness of sequential prefetching on various memory and network latency and propose a new adaptive sequential prefetching scheme. Simply adding a small table to the sequential prefetching scheme, the proposed scheme prefetches a large number of blocks for application programs with high sequentiality and reduces the miss rates significantly, and prefetches a small number of blocks for application programs with low sequentiality and avoids loading useless blocks.

A novel neural network architecture for image texture classification is introduced. The proposed model (Kernel Modifying Neural Network: KM Net) which incorporates the convolution filter kernel and the classifier in one, enables an automated texture feature extraction in multichannel texture classification through the modification of the kernel and the connection weights by the backpropagation-based training rule. The first layer units working as the convolution kernels are constrained to be an array of Gabor filters, which achieves a most efficient texture feature localization. The following layers work as a classifier of the extracted texture feature vectors. The capability of the KM Net and its training rule is verified using a basic problem on a synthetic texture image. In addition, the possibilities of applying the KM Net to natural texture classification and biological tissue classification using an ultrasonic echo image have been tried.

Logic operations in principle have been demonstrated based on the planar high-Tc Superconducting QUantum Interference Device (SQUID). Two kinds of logic gates were produced by using the focused ion beam (FIB) superconducting weak links fabricated in NdBa2Cu3O7-δ (NBCO) thin films. Logic gates investigated in this paper are (1) an rf-SQUID based logic gate which utilizes threshold characteristics, and (2) a dc-SQUID based logic gate which is an elementary gate of RSFQ circuits. Elementary logic operation such as (1) AND/OR logic and (2) SET-RESET flip-flop operation were successfully obtained in the logic gates. In addition to the present experimental results, some problems and future prospects are also discussed.

Recent progress of highly sensitive magnetmeter utilizing high Tc dc superconducting quantum interference device (SQUID) is reviewed briefly. Performance parameters of the SQUID magnetometer, such as field resolution, dynamic response and usability in unshielded environment, are focused on. Relationship between these performance parameters and SQUID characteristics are discussed quantitatively, and key factors which dominate each performance are clarified. With this result, design principle to obtain high performance SQUID magnetometer operating at T77K is shown. Present status on the performance of the magnetometer is discussed by comparing experimental results with theoretical predictions. Issues to much improve the performance of the high Tc SQUID magnetometer are also discussed.