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When an adaptive array antenna is used in cellular and other mobile communication base stations for the purpose of improving SINR, the array antenna itself sometimes falls into a fading valley, resulting in failure to obtain an adequate improvement effect. While this problem can be solved by increasing the aperture length of the array antenna, simply increasing the aperture length alone increases the number of antenna elements, so that a large-scale adaptive array antenna becomes required, leading to the problem of failure of the weighting to track changes in the environment during fast fading. In this paper, we try to solve the first issue by making the element spacing nonuniformly aligned, reducing the number of elements. For the second issue, the weighting is divided into two layers, resolving the problem through both use of MMSE to eliminate interference and use of EGC for diversity combining. In a slow fading environment, however, favorable characteristics can be obtained when the entire weighting is controlled by MMSE. In this paper, we estimate the fading speed by the amount of envelope fluctuation in the desired signal after elimination of interference by the initial layer MMSE, and propose during slow fading the use of MMSE batch control, and during fast fading a control that incorporates both MMSE and EGC diversity combining. Finally, we use a computer simulation to evaluate the validity. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 13–21, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20397 [ABSTRACT FROM AUTHOR]

The demand for video service in mobile communications systems is increasing. In response to this demand, wireless P-MP (Point-to-MultiPoint) video transmission, in which a given video is transmitted to several moving terminals via a single channel, has been studied. This scheme can make effective use of bandwidth, power, and spreading codes. In this paper, as wireless P-MP video transmission schemes effective in the CDMA system, we propose MCAP (MultiCode Assignment algorithm for P-MP transmission) and the P-MP video transmission system. In MCAP, the mobile terminals receiving the identical video are divided into two groups, high quality and low quality, based on the channel quality. By performing transmission power and transmission rate control for each group, the transmission rate can be improved. Also, by using multicode transmission, transmission rate control and the channel allocation are carried out in a unified fashion. In this paper, by means of simulations, it is demonstrated that the proposed scheme can substantially improve the transmission rate without increasing the number of spreading codes and the power. Several schemes are compared as power control base selection schemes needed for MCAP. An optimum scheme is determined from the comparative evaluation results. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(8): 14–25, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20280 [ABSTRACT FROM AUTHOR]

The authors previously proposed a TDMA with parallel transmission (TDMA/PT) system in which several terminals can send packets in parallel in the TDMA system by controlling the transmission power of each terminal. In TDMA/PT, packets can be transmitted in parallel unless the packet sent by a terminal collides with that transmitted by the preceding terminal. Each terminal understands the positions of other terminals and can obtain transmission information about the preceding terminal. Hence, if a directional antenna is used in the TDMA/PT, it is possible to improve the performance by increasing the probability of parallel transmission. In this paper, a transmission algorithm is proposed in which directional antennas are used in conjunction with TDMA/PT. In TDMA/PT, only the parallel transmission of two terminals with contiguous IDs is considered, so that the probability of parallel transmission cannot be made very high. In this paper, a transmission algorithm allowing the parallel transmission of more than three terminals is proposed, and its performance improvement effect is discussed. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(1): 11–21, 1999 [ABSTRACT FROM AUTHOR]

Research and development have been carried out extensively on the MUSIC and ESPRIT algorithms, based on the eigenfunction expansion of the correlation matrix, for high-resolution direction-of-arrival estimation using array antennas. A factor hindering the best performance of these high-resolution algorithms in real array antennas is nonuniformity of the element patterns caused by element coupling in an array configuration. In this paper, it is assumed that the array antenna is operated in a single mode and that the initial deviations of the transmitted amplitude and phase of the feed system and errors such as interelement coupling can be represented by a single coupling matrix with complex elements. Under such assumptions, this paper proposes a method for compensating the error of the center of rotation of the rotating table on which the device under test for calibration data measurement is installed, and estimates the coupling matrix. By computer simulation in the case of a receiving array antenna, it is found that the coordinates of the rotating center and the coupling coefficient can be estimated and that received signals with the initial deviation and interelement coupling compensated can be obtained by multiplying by the inverse of the coupling matrix estimated for the received signals. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(3): 59–73, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10126 [ABSTRACT FROM AUTHOR]

In order to more accurately extract desired signals, it is necessary to suppress interference such as reflection and clutter more strictly. This paper discusses a method of suppressing sidelobes adaptively by placing a receive-only array around a high-gain array. The output power minimization method (DCMP) has been proposed as an adaptive clutter suppression method. When this method is applied to a high-gain array, there is a danger of destroying the directivity of the high-gain array. In this paper, a constraint on the weight not destroying the receiving pattern of the high-gain array is added to the DCMP, resulting in a norm-constrained DCMP (DCMP-CN). By using this method, adaptive sidelobe suppression is possible regardless of the intensity of the input signals. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(3): 11–18, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10178 [ABSTRACT FROM AUTHOR]

Recently, the superresolution method has attracted significant attention as a high-resolution method of estimation of the electromagnetic wave propagation environment for mobile communications as well as various kinds of wireless communications. With regard to the array shape used in the estimation problem of direction of arrival, various array configurations in addition to equally spaced arrays have been studied. Weiss and colleagues have proposed a method of realizing a virtual equally spaced array by applying the EM method and the IQML method to nonuniform arrays. In this paper, the EM-MODE method based on this algorithm is proposed for estimation of the direction of arrival of the coherent wave by a nonuniform array and for improved processing. It is shown that improvement of the estimation success rate is possible by applying the improved processing in cases where estimation by the conventional EM-MODE method is difficult. The errors in estimation of the direction of arrival when this method is applied are studied. It is shown that much better characteristics can be obtained than when real elements are equally spaced. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(8): 47–56, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1117 [ABSTRACT FROM AUTHOR]

This paper proposes a method that calculates the approximate cross-correlation between two discrete sequences with high speed. The method is evaluated by applying the idea to range compression in the SAR image reconstruction process. When the sequences are very long, tremendous computation time is required, even if the cross-correlation function is calculated through the frequency domain. This is a problem when real-time processing is required. In such a case, however, it is often more important to determine the approximate value with high speed than to determine precisely the value of the cross-correlation function. From this viewpoint, this paper proposes a method in which the wavelet transform is applied to the two sequences, and the correlation function for the obtained short sequences is defined as an approximation to the original correlation function. By forming a hierarchy of wavelet functions, a hierarchy of approximate values is formed according to their accuracy. It is also possible, by successively improving the accuracy starting from a coarse approximation, to finally obtain the accurate value. The algorithm for such an idea is presented. Then, by applying the idea to the SAR range compression, the proposed method is experimentally evaluated. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(6): 10–20, 2000 [ABSTRACT FROM AUTHOR]

An efficient scheme for establishing a multicast route in packet networks is constructing a tree-shaped path in which multicast packets are replicated at specific branching nodes, called “copy nodes,” by the packet copy function and are forwarded to downstream nodes. This scheme leads to the efficient usage of network resources, but needs multicast routing control. To realize rapid multicast routing, it is suitable and realistic to restrict the number of copy nodes in calculating the multicast route. However, even in this approach we need to adequately select a limit on the number of copy nodes which satisfies the conditions of both priority for multicasting and geographical distribution. In this paper, a new copy-node allocation algorithm is proposed. This heuristic algorithm makes some “copy node functions” move on the network map sequentially according to attraction and repulsion determined by several conditions and finally makes them converge on the switching nodes suitable as copy nodes. In addition, the performance of this algorithm is evaluated by a computer simulation. This algorithm is applicable to various other server assignment problems. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 83(1): 87–96, 2000 [ABSTRACT FROM AUTHOR]

This paper proposes an application method of the cooperative distributed multiagent model in multipath allocation algorithm and confirms its valid calculation results by realizing this model in a distributed computer environment. The multiagent model in this paper is an environment where each agent has the same function of asynchronous and parallel calculation and no globally controlling agents exist. To realize this model, this paper proposes an appropriate dividing method of the multipath allocation problem for asynchronous and parallel calculation, a unifying method of each agent's answers end interagent communication protocols. It also compares the required calculation time and the number of allocated paths of a single agent with that of the multiagents end shows the practical calculation ability of the multiagent model. [ABSTRACT FROM AUTHOR]

Vector quantization is known widely as a highly efficient coding for image and speech signals. The algorithm proposed by Linde, Buzo, and Gray (the LBG algorithm) is the most fundamental design procedure for this kind of quantizer. However, the LBG algorithm usually gives only the local minimum of the distortion measure based on the quantization error. With such a background, this paper introduces the simulated annealing procedure into the design of the vector quantizer based on the LBG algorithm, which is known as the effective method for the NP-complete probabilistic combinational optimization problem. The widely employed mean-square error is adopted as the distortion measure. Various approaches are considered to derive the global minimum of the measure. In other words, this paper is based on the LBG algorithm and presents a design procedure for the vector quantizer (more generally, the vector quantizer considering the channel error) by introducing simulated annealing. By this approach, a vector quantizer with a better performance than the traditional design as well as a more ideal highly efficient coding is realized. A simulated experiment is executed for the standard image data (SIDBA), and it is demonstrated that the simulated annealing is useful in the design of the vector quantizer. [ABSTRACT FROM AUTHOR]

The control of the cell contention is a technical problem in the input queueing ATM cross-connect switch. This paper considers this problem and proposes a scheduling control method which dynamically assigns the cell transmission time. A construction of the distributed scheduling circuit also is proposed based on Batcher's sorting network. The proposed method processes the cells in the order of their arrivals, as in the conventional three-phase algorithm but has an advantage in that the throughput can he increased by approximately 26 percent without increasing the number of control processes per cell. Mother merit is that multirate ports can directly be contained in the switch. In this paper, the approximate model for the proposed method is constructed, and the mean delay and the cell loss probability are calculated theoretically. The actual operating performance is evaluated by a computer simulation. By combining the proposed method with the conventional self-routing spatial switch, a distributed switching circuit can he constructed as a whole, which is useful in developing an economical large- capacity ATM cross-connect switch. [ABSTRACT FROM AUTHOR]

In high-efficient motion picture coding such as systems to compress moving image information below several 100 kbit/s, some visible spatial and temporal distortions are unavoidable. The spatial distortion is perceived by humans as a spatial degradation or noise on the image. On the other hand, the temporal distortion, which is caused by frame dropping, occurs as unnaturalness of motions in the processed image sequence. Here, spatial and temporal distortions are in a trade-off relationship. Finding the visually best point from this trade-off is a key feature of good codees. This paper describes a newly developed coding control algorithm aimed at keeping spatial and temporal distortions in a good balance. In the algorithm, the trade-off relationship is calculated first from generated information amount vs. the SNR characteristics of the current input frame. Next, an optimal distribution is determined from the viewpoint of human perception. Finally, a coding parameter set is chosen for realizing the distribution and reproduces visually good images. This paper shows the principal of the coding control algorithm and describes an application of the algorithm to an MC-DCT coding system and simulation results. [ABSTRACT FROM AUTHOR]

This paper considers the semiconductor integrated circuit, and proposes a solution to the decision problem for the optimum design, where circuit-element values are determined so that the yield is maximized. The spherical surface random number is employed in the calculation of the yield. Although various nonlinear programming methods can be applied to the optimization problem, this paper applies Newton's algorithm to the optimization algorithm. It is shown that the first- and the second-order derivatives of the yield to the design value, which are needed in the calculation of the search vector in Newton's method, can also be derived using the spherical surface random numbers. I is also shown that the center of the element value determined by the design specification can be calculated using the spherical surface random hi, hers, and the optimization can be performed efficiently using the center as the initial point for the optimization. Applying the proposed method to the 5th-order leap-frog-type switched-capacitor filter, the processing time is reduced to approximately one-fourth compared with the case of the Monte­Carlo method. [ABSTRACT FROM AUTHOR]

Radon discussed the reconstruction problem of a two-variable function from its line integrals and the algebraic representation of this problem. He also discussed the reconstruction from curved-line integrals curved-line integrals and extended the discussion to the reconstruction problem of a multivariable function from its hyperplane integrals. For the first two of these problems, reconstruction algorithms have been developed. They have been applied to X-ray CT (Computed Tomography). The third problem has been studied in connection with ultrasonic CT. On the other hand, very little engineering development has been reported on the fourth problem. However, in a practical problem, it is desired to find a three-dimensional structure based on its projections measured as plane integrals. Also, in statistical analysis, a joint probability density function of multiple variables is often desired based on its marginal distributions. Moreover, the reconstruction problem in multidimensional spaces is of mathematical interest. In this paper, a foundation to this problem and theoretical formulas for a filtered back-projection method for reconstruction are given in a simple form based on a discussion similar to that in CT. For numerical calculation filtering is usually implemented by convolution in CT. In this paper, extensions of the kernel functions for convolution to the multidimensional problem are also presented. [ABSTRACT FROM AUTHOR]

The existence problem for solution of a nonlinear resistive circuit and the problem of identifying the number of the solutions are classic and basic problems in circult theory. In their paper "On the application of degree theory to the analysis of resistive nonlinear networks" (int. J. Cir. Theor. Appl., 5, pp. 35-68 (1977)), Cbua and Wang presented a unified theory for the existence of solutions for nonlinear circuit equations. That is, on the basis of the degree theory the existence of solutions of many nonlinear resistive circuits can be guaranteed in a unified manner by showing that the circuit equations are homatopic to certain odd fields. Their arguments are, however, not constructive. In this paper, an algorithm based on the fixed-point algorithm theory is presented and it is proved that by this algorithm at least one solution can always be constructed for nonlinear circuit equations whose solutions are guaranteed to exist by Chua and Wang's theorems. Usefulness of the algorithm is also demonstrated by a few examples. [ABSTRACT FROM AUTHOR]

Distributed databases in general-purpose business software such as groupware widely use a method for simultaneously updating the replicas of other databases owned by each database according to the replication routing schedule. In this paper, a replication routing schedule is discussed in which the time required for updating the replica is the minimum in the distributed database. Specifically, an optimization problem is first formulated for deriving the replication routing schedule with minimum update time. Next, in the cases of even and odd numbers of distributed databases, an algorithm providing a replication routing schedule as an optimum solution is presented in the even case, while a heuristic algorithm providing an approximate solution is shown for the odd case. These algorithms are extremely simple and are practical since the required amount of computational processing is small. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 11–20, 1999 [ABSTRACT FROM AUTHOR]

As a method of solving the electromagnetic scattering by perfectly conducting cylinders, the discrete singularity method is discussed. For this method, a finite number of singular points is distributed within the scatterer and the wave function composed of a linear combination of solutions (each of which is derived from a helmholtz equation with each single singularity among the many) is matched with the incident wave function on the boundary. The remaining important problem in this method is how to distributed these singularities in order to obtain the accurate solution with faster convergence and with fewer number of singular points for an arbitrary configuration of the scatterer. The purpose of this paper is to present a reasonable solution to this problem. The essential of the method is that by making as unknown quantities, not only the unknown amplitude coefficients involved in the linear combination of the solutions, but also the coordinates of the singularities, the scattered wave is matched on the boundary in the sense of the least squares. This problem is linear in the amplitude coefficient but nonlinear in the singularity coordinate. Thus we solve this problem by using the algorithm by marquardt et al, of a nonlinear optimization process. This paper considers the general description and indicates its effectiveness by showing a few examples of the scattering problem of rectangular cylinders. [ABSTRACT FROM AUTHOR]

This paper presents a polynomial-time algorithm which can determine the multicommodity flows in a planar undirected graph G. It is assumed that G remains planar if an edge is added between each source-sink pair. Given positive and real demand to each source-sink pair, the algorithms determines whether or not there exists a multicommodity flow in G realizing the specified demand, i.e., feasibility, and if it exits, the multicommodity flow is determined. It is shown that by solving the maximum-weight matching problem once for a graph which is a modification of the graph dual to the given graph G, the feasibility is determined, and by solving the problem for 0(kn) times, the multicommodity flows are determined. Consequently, if G has a vertices and k source-sink pairs, the computation time required to determine the feasibility is 0(n² log n), and the time required to determine the k-commodity flow is O(kn³ log n). The memory storage required is 0(kn). It is known that the maximum-flow min-cut theorem exists for the case of planar graph considered in this paper. [ABSTRACT FROM AUTHOR]

To achieve efficient and highly reliable network operation requires a mechanism to monitor and control the states of remote a mechanism to monitor and control the states of remote terminals (nodes) automatically by control operation system (OpS). This paper is an attempt to obtain such a mechanism. Operation and maintenance (OAM) cell is defined that contains the connection information for remote monitoring and the control path to be set. By successively transferring OAM cells according to the connection information, remote monitoring and control virtual paths (VPs) can be obtained autonomously. Based on the proposed idea, this paper discusses the structure of the OAM cell, the functions to be provided in the cross-connect system, and transmission algorithms for the OAM cell. The proposed system well utilizes the unique feature of the ATM cell. The cell routing information (VPI) is transferred within itself. [ABSTRACT FROM AUTHOR]

In the communication system using a constant modulus signal, a constant modulus algorithm (CMA) adaptive array antenna is effective for elimination of the frequency-selective tiding generated in multiple propagation paths. On the other hand, in the system in which CMA adaptive loops are installed for each antenna element in an array with mare than 10 elements used for mobile satellite communication, the computing time and the amount of hardware become excessive. in this paper, a beam-space CMA adaptive array antenna (BSCMA) is proposed in which a portion of the multibeam output is selected to form a CMA adaptive array. In the BSCMA, first, a multibeam is formed by means of a fast Fourier transform (FFT) and only the beams whose output power exceeds a threshold level are selected. An adaptive process is carried out with the CMA as a guiding principle only for the selected beam outputs. The BSCMA has an advantage of carrying out the capture of the desired wave and the elimination of the interference wave effectively with degrees of freedom corresponding to the number of arriving waves. The method is effective for an adaptive antenna system applied to an array antenna constructed with many antenna elements. In this paper, the configuration of the BSCMA is shown and its characteristics are investigated by the numerical simulation. [ABSTRACT FROM AUTHOR]

This paper discusses the multipath allocation problem in the communication network and proposes a multipath allocation algorithm suited to the distributed environment. The multipath allocation problem is a problem where multiple paths arc to be allocated without a conflict. This problem has been difficult to solve in the distributed environment since relations among various routes must be considered. The algorithm proposed in this paper solves this point by realizing the asynchronous path search. In this paper, the basic characteristics of the proposed algorithm are described through the comparison between the proposed and the traditional algorithms for the case of serial computation under the centralized control. Then the proposed algorithm is applied to several kinds of distributed cooperative multiagent models, and it is demonstrated that the proposed model can easily be applied to the distributed environment. A simulation is executed actually using several workstations, and it is shown that the proposed algorithm is desirable as a solution method for the multipath allocation problem m the distributed environment. [ABSTRACT FROM AUTHOR]

Multipath fading is a (actor degrading the communication quality in mobile communications. It has been reported that an adaptive array antenna can enable elimination of the effect of delayed signals by an appropriate control of the radiation pattern. In this paper, it is recognized that an optimum weight of the array antenna can be computed if the direction of arrival and the signal to-noise ratio of the received signal are known. By using the spatial frequency derived by the discrete Fourier transform (DFT) of the received signal which is spatially sampled by the array antenna, an algorithm is proposed in which the directions of arrival and the signal-to-noise (SN) ratio of the desired and interference waves are estimated and an optimum weight coefficient of the antenna is computed. This algorithm is different from those in the conventional adaptive digital filter algorithms such as the LMS algorithm. It requires no reference signal and can follow quickly changes in the communication channel. Further, a method is proposed to improve the estimation accuracy of the direction of arrival and the SN ratio with a limited number of elements by using the property of the DFT. To confirm the principle of the proposed algorithm, the basic characteristics are evaluated by computer simulation. [ABSTRACT FROM AUTHOR]

In cellular mobile communication, the same channel is shared by a number of cells. Up to now, the model has been considered where the same channel is used with a sufficient separation, so that the radiowave interference is sufficiently small for any call generated in the cell. Recently, on the other hand, a model has been proposed where the same channel is assigned independently of the specified cell separation, as long as the carrier-interference ratio is above a certain value. Although the assignment algorithm has been discussed for the traditional model, no report has been made on the detailed assignment procedure for the new model. With such a situation as the background, this paper proposes an application of Hopfield's neural net as an approach to the channel assignment in the new model and derives the energy function. Several results of computer simulation are shown where the proposed neural net is applied to the mobile communication model. It is not always true that the neural net produces the optimal solution, but it is interesting that an unexpected improvement of the channel utilization is observed in the communication traffic as far as the result of computer simulation is concerned. [ABSTRACT FROM AUTHOR]

Strong international effort has been made toward the realization of a B-ISDN based on ATM techniques. This paper proposes self-healing techniques for enhancing ATM network reliability. Self-healing is defined here as failed path restoration with distributed control mechanism by using cross-connects. First, the characteristics of virtual paths (VPs) are compared with those of digital paths in STM networks. It is clarified that VP benefits can be exploited for network restoration upon failure. Two high-speed self-healing algorithms that make the best use of VP characteristics are then proposed for restoring single-link failures. A technique for multiple-link failure restoration also is proposed. Finally, restoration performance is evaluated by computer simulation. It is confirmed that the proposed algorithm enables faster restoration than that possible using the existing algorithm for STM networks. [ABSTRACT FROM AUTHOR]

Recent construction of corporate communication networks with the use of high-speed digital links, etc., is becoming popular. Economical and reliable networks must be designed. Few papers have been published on the design of corporate communication networks. Moreover, some need improvement. This paper proposes a new topological design algorithm for efficiently constructing economical and reliable corporate communication networks. This algorithm achieves effective network design by utilizing the correct network information. The triangle network configuration, which provides higher reliability than two-connected networks with only a small additional cost, is proposed. Moreover, this paper proposes a new idea at a lower cost (cost lower bound) that evaluates the results obtained by various heuristic algorithms. Superiority of the proposed algorithm is verified by means of this cost lower bound. [ABSTRACT FROM AUTHOR]

In this paper, a link capacity assignment algorithm for a packet switched communication network is presented. This algorithm, called max-delay-link algorithm, prevents sharp performance degradation in a network even m case of link failures. An optimal link capacity assignment can be obtained with respect to link cost minimization, subject to the constraint that the average packet network transmission delay does not exceed a predetermined value. Robust networks against failures can be, designed by assigning large capacities to links where overflow traffic and packet delay are expected to increase in case of a failure. Several numerical examples also are shown to examine the effectiveness of the algorithm in comparison with the conventional capacity assignment algorithm where link failures are not taken into account. [ABSTRACT FROM AUTHOR]

For high-efficiency image compression, previously, an SVD (singular value decomposition)-based coder was developed using vector quantization, called SVD-VQ. This paper proposes an improved quantization SVD-VQ scheme. For every input subblock, the SVD- VQ coder scalar-quantizes a singular value and vector-quantizes two singular vectors, separately. The SVD-VQ decoder reproduces a subblock as the product of these quantization outputs, but does not necessarily produce a reconstruction with the minimum distortion in an image space. This paper develops a quantization scheme where the minimum-distortion reconstruction is always provided in the original image space and presents its design algorithm. The improved SVD-VQ shows A/N performance improvement of 0.5 - 1.0 dB over the conventional SVD-VQ, and is similar in performance to the adaptive DCT (discrete cosine transform) coder. [ABSTRACT FROM AUTHOR]

This paper presents a method of numerical analysis by the multiple input describing function for the self-excited oscillation in a nonlinear system with hysteresis. In the traditional analysis by the describing function, the decribing function for the hysteresis is determined in an analytic form, and a very complex calculation is required to perform a highly accurate analysis including the harmonic components of the self-excited oscillation. Consequently, in practice, it has been impossible to determine analytically the describing function for the multiple input. Furthermore, the calculation is impossible for the describing function, where the hysteresis characteristics contain a minor loop. From such a viewpoint, this paper proposes a method and algorithm for the analysis of self-excited oscillation. In the proposed method, the describing function is determined numerically by the digital simulation of the hysteresis, and the discrete Fourier transform and its inverse are applied to the result. But this method, the describing function can be determined numerically even for the cases of multiple input and the case with a minor loop. Thus, the self-excited oscillation can be analyzed considering the harmonic components and the multiple mode. As an example, the self-excited oscillation of the nonlinear system is analyzed for the case where the linear part is represented by a second-order transfer function or by a sum of such functions. [ABSTRACT FROM AUTHOR]

For the steady-state analysis of nonlinear oscillatory circuits, the Newton algorithm proposed by Aprille and Trick is well known. However, often the conventional algorithm needs too many iterations or may not converge, because of the discretization error of numerical integration. This paper discusses in detail the Newton algorithm for the steady-state analysis, and proposes an efficient algorithm which retains the quadratic convergence in the presence of the error of numerical integration. First, a method of computing the exact Jacobians of the functions obtained by numerical integration is proposed. Then it is shown that the quadratic convergence of the Newton algorithm is retained by suitably controlling the truncation errors of the inner Newton iterations for the corrector equations. The proposed Newton algorithm converges to a solution quadratically even if the step length of the numerical Integration is large. Utilizing this property, a mesh refinement strategy is proposed which improves the computational efficiency of the 81goritha by determining first an inaccurate solution which is computed by using a large steplength. Then this approximate solution is used for the starting point of the next Newton iteration with a smaller steplength to obtain an accurate numerical solution. Also, it is shown that the foregoing technique can also be applied to the Newton algorithm for computing the bifurcation value of the periodic solutions. The validity and the effectiveness of the proposed method are also verified by numerical examples. [ABSTRACT FROM AUTHOR]

This paper proposes the systolic decoder for Reed-Solomon (RS) codes based on systolic algorithms. Three steps of decoding procedures for RS codes can be reduced to simple repetitive algorithms and thus can be realized by one-dimensional systolic arrays, each operated by simple controls. The decoding system is a cascade connection of these cell arrays in one dimension. In this paper we also design three types of cells building arrays for RS codes on GF(28). Each cell has a size that permits its integration in a one-chip LSI and we can determine the number of cells according to the error correcting ability for codes. [ABSTRACT FROM AUTHOR]

This paper describes a theoretical analysis of the heuristic algorithm for the efficient solution of (the linear) assignment problem defined on a plane. The evaluation function, or assignment cost, in the assignment problem discussed in this paper is defines as the square-sum of Euclidean distances between points included in the two points sets. A heuristic assignment algorithm, based on a vertical or horizontal partitioning of the given plane, is presented. Then the average-case analysis is performed for the algorithm, assuming that the points are distributed uniformly on the unit square plane. Letting the site of the point set be n, the number of partitioned stages in the algorithm be hm and the average assignment cost for n → ε be Î, it is seen as a result of analysis that the rate of increase of Î in regard to n decreases monotonously with the increase of hm. It is also seen that when hm is maximum, Î is (¼)) log2 n. The result of theoretical analysis is compared with the result of experiment. [ABSTRACT FROM AUTHOR]

This paper presents a polynomial-time algorithm for finding multicommodity flows in planar graphs. Suppose that G is an undirected planer graph and that some of the source-sink pairs are located on the boundary of the outer face and all the other pairs share a common sink located on that boundary. The algorithm determining whether G has multicommodity flows each from a source to a sink and of a given demand, and if it does, actually finds them. Let n be the number of vertices in G and b be the number of edges on the boundary of the outer face. Then the time complexity of the algorithm is G(n(b2 + T+(n)), where T+(n) is the time required to find the shortest paths from a vertex to the others in a planar-directed graph with n vertices and nonnegative real weighted edges. In the class of planar networks treated in this paper, it is shown that he so-called "Max Flow - Min Cut theorem" holds. [ABSTRACT FROM AUTHOR]

In a packet switching network it is important to route traffic flow so as to minimize message delay. This problem is formulated as a multicommodity flow problem with a nonlinear objective function and it is solved by the steepest descent method. It is also necessary to control the traffic demand at each node so that the total message delay is below a certain level. This paper presents an algorithm to obtain the region vectors consisting of traffic demand at each node which can be transmitted simultaneously under the given delay time. Despite its importance this region has not been adequately considered. A nonlinear T-cut condition is introduced by which the region is obtained. This paper is a non-linear extension of the authors' recent work. [ABSTRACT FROM AUTHOR]

This paper proposes a universal information source code (improved ZL code) based in the Ziv-Lempel (ZL) incremental parsing algorithm. It is known that a ZL code is asymptotically optimum for a stationary ergodic information source, although it does not utilize the source structure. Its convergence, however, is very slow and it cannot provide efficient compression for an input string of limited length. This paper considers the redundancy of ZL code, high is the reason for the slow convergence. In order to eliminate the redundancy coding scheme is presented in which only the substring obtained by incremental parsing is used in the next stage. When the substrings of the incremental parsing are separately coded the improved ZL code obtained by the proposed scheme is the least redundant in the sense that the mean code length for the substrings is minimized. In the coding a data structure called modified ZL tree is introduced and its properties discussed together with two coding algorithms based on that structure. The coding is actually performed for the output string from a memoryless binary source and binary Markov source. It is shown that sufficient compression is realized for a binary code string length of 10³ to 104, indicating the possibility as a practical data compression algorithm. [ABSTRACT FROM AUTHOR]

Newtonm's method is well known for finding the fixed point of the Poincaré mapping for steady-state analysis of nonlinear oscillatory circuits. However, in particle, quadratic convergence of this method is not ensured due to the discretization error of the numerical integration and the errors of the approximate solutions for nonlinear equations which are solved at each time-step of the numerical integration. This paper proposes a new method for the steady-state analysis of nonlinear nonautonomous and autonomous systems which takes account of the numerical integration error stated above. In this method, the system of equations which includes a Poincaré mapping is discretized and reexpressed is a system of finite difference equations to which an iterative decomposition method is applied. Although this approach is essentially equivalent to the environment Newton method based on the Poincaré mapping, it has the advantages that the Jacobian matrix can always be computed exactly for an arbitrary time-steplength and that the local quadratic convergence of the algorithm is guaranteed. Considering these advantages, this paper also proposes a strategy to improve the computational efficiency of the algorithm in which initially, a large time step is used to find a rough solution which is then used as the starting value in the subsequent Newton iteration. Numerical examples are given to verify the relevant theorems and to show the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In the field of system modeling, circuit synthesis and filter design, it is very important to approximate a given characteristic function by a rational function of an appropriate order. Padé approximation has been known for a long time and is one of the rational function approximation methods used extensively because of its simplicity. This paper proposes to investigate N-point Padé approximation, from the system-theoretic viewpoint. The N-point Padé approximation is a rational function interpolation including the derivative of arbitrary order and, compared to regular Padé approximation and rational Hermite interpolation. In this paper we discuss the following subjects on rational function approximation of given characteristic function: its explicit form, minimal order realization problem, Nuttall's compact form, its relation to continued fractions, and the numerical efficient iterative algorithm. These are more general discussions, even including regular Padé approximation. Also, we give numerical results of the approximation of a transfer function for continuous and discrete systems as an example of application of N-point Padé approximation. [ABSTRACT FROM AUTHOR]

This paper examines whether a circuit is realizable on a single-layer printed wiring board. Linear time algorithms for this problem have been proposed under the constraint that no wiring is permitted below the mounted modules. However, this problem becomes NP-complete when wiring below the mounted modules is permitted and the number of wires available between adjacent pins of a module is given. This paper presents an algorithm for this problem under the constraint that wiring is permitted under modules but no wires are allowed to pass between adjacent pins. The time complexity of this algorithm is proportional to the total number of pins of the circuit. [ABSTRACT FROM AUTHOR]

A generalized mode vector that simultaneously uses the differential coefficient component of the mode vector has been proposed for estimating the direction of arrival of incident waves having angular spread. In this paper, the authors first examined this generalized mode vector and proposed a gradient-type MUSIC algorithm that uses the differential coefficient component of the mode vector independently for estimating the direction of arrival. Then they used a computer simulation in which the waves having angular spread were considered to be a group of scattered waves to compare this algorithm with regard to the performance for estimating the direction of arrival with an integral-type MUSIC algorithm that uses simple integration, which they proposed separately. To improve the estimation precision degradation that occurs when the signal correlation is low among scattered waves that exist within the angular spread when using the integral-type MUSIC algorithm, the authors proposed a combined-type MUSIC algorithm that incorporated the gradient-type MUSIC algorithm in the integral-type MUSIC algorithm and used this to examine the performance for estimating the direction of arrival and angular spread again. The results of the comparison of the gradient-type MUSIC algorithm and integral-type MUSIC algorithm confirmed that the two algorithms have conflicting properties related to the signal correlation among scattered waves that exist within the angular spread. Also, the investigation related to the combined-type MUSIC algorithm indicated that estimation precision degradation that occurs when the signal correlation is low among scattered waves when using the integral-type MUSIC algorithm was reduced as expected. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(6): 53– 64, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20208 [ABSTRACT FROM AUTHOR]

A Virtual Output Queuing (VOQ) input buffer type switch provided with a buffer in each input port is proposed in this paper as an input buffer type switch that avoids Head-of-Line (HoL) blocking. A scheduling algorithm for a multiple VOQ input buffer type switch is also proposed. As a representative algorithm we use a Two-Dimensional Round Robin (2DRR) scheduling algorithm that achieves low-delay and has iSLIP to avoid starvation as well as high fairness between ports. This paper also proposes a layered scheduling algorithm for a VOQ input buffer type switch with an objective of fairness between ports and switching with lower delay. The frequency of packets not being output is reduced regardless of whether an output port is empty by using up patterns of all I/O pairs in N input N output switches. The N input N output switching is divided into smaller units. Fairness between the units is achieved by successively shifting the order of priority of each unit that will be switched. Simulations were used to evaluate the effectiveness of the proposed scheduling algorithm. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(6): 43–52, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20313 [ABSTRACT FROM AUTHOR]

Hidden terminals can significantly lower the throughput of such competitive MAC protocols as CSMA. Therefore, a large number of MAC protocols that implement different hidden terminal strategies have been developed. In this paper we propose an algorithm for generating evaluation networks with different ratios of hidden terminals in order to evaluate the effect of hidden terminals on competitive MAC protocols. In addition, we use the same algorithm to report results that elucidate the characteristics of throughput as the ratio of hidden terminals that exist in a network is varied for both CSMA, a representative competitive MAC protocol, and MACA, a MAC protocol that makes use of RTS/CTS control, a representative hidden terminal strategy. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(4): 46–55, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20343 [ABSTRACT FROM AUTHOR]

With direction-of-arrival estimation by the ESPRIT method, this paper investigates the effect of short spacing between the transmitter and receiver and of mutual coupling and array manufacturing error on the estimation error. A simulation model is presented. The effect of these errors on direction-of-arrival estimation is quantitatively presented. It is shown that the maximum estimation error is inversely proportional to the distance between the transmitter and receiver and that the ranges and the standard deviation of the estimation errors can be reduced in the range of 0° <θ1 <60° if the manufacturing error is reduced. Further, the validity of the simulation is confirmed by experiments in an anechoic chamber. It is also confirmed that mutual coupling and manufacturing error in the array antenna are the main causes of the estimation error in the direction-of-arrival estimation experiment. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(9): 68–76, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10230 [ABSTRACT FROM AUTHOR]

In this paper, we applied combination channel assignment using the genetic algorithm (GA) to the channel assignment problem in mobile communications and performed evaluation tests. Combination channel assignment is a method combining the three assignment methods of repetition channel assignment, grouped channel assignment, and maximum channel assignment. A computer simulation tested a model with four patterns of the number of requested channels for 49 cells. In addition, the three assignment methods independently performed the channel assignment and at least two combined methods performed the channel assignment. The result showed that the number of channels used could be reduced by combination channel assignment compared to independent channel assignment using GA. And we demonstrated the ability to assign channels with hardly any effect on the assignment time when the number of cells was increased. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(7): 20–28, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20183 [ABSTRACT FROM AUTHOR]

As a means of flexibly providing large-capacity access infrastructure at a low cost, the broadband fixed wireless access (BFWA) system using millimeter-wave and quasi-millimeter-wave frequencies is promising. In general, wireless channel quality variations are significant due to rainfall in wireless systems using millimeter-wave and quasi-millimeter-wave frequencies. Hence, deterioration of the channel working rate is a problem. In this paper, a multihop wireless access system with a mesh configuration is proposed that can deploy a millimeter- and quasi-millimeter-wave BFWA system at a high quality and a high density. In the proposed system, deterioration of the channel working rate due to wireless channel quality variations is avoided. In addition, the capacity is maximized by adaptively assigning the network resources for variations of the traffic demand and wireless channel transmission capacity. Further, as an adaptive control used in the proposed system, wireless channel assignment for a wireless link and load distribution among several paths within the mesh network are discussed. The problem is formulated as a mixed nonlinear optimization problem. In addition, a heuristic solution is proposed for solving the problem within a realistic time for a network of the anticipated size. The proposed algorithm is applied to a mesh network and the behavior and the performance of the algorithm are evaluated to prove its effectiveness. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(6): 22–33, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10133 [ABSTRACT FROM AUTHOR]

An important problem of the adaptive array antenna proposed previously in regard to its installation is the increased equipment size. This is because the adaptive array antenna requires as many RF circuits as the number of antenna elements. In this paper, in the case where there is an input in one system, we study an adaptive array antenna with sequential processing (AAA-SP) in which the MMSE (minimum mean square error) criterion is used to control array weights by means of sequential processing of sampled signal data. Since there is only one input system in this case, it is found that the SINR is degraded due to reduction of correlation among elements if the conventional MMSE criterion is used as the adaptive control algorithm. Hence, in order to improve the deterioration of the SINR, a tapped-delay-line adaptive array antenna with sequential processing (TDL-AAA-SP) is proposed in which oversampling and a TDL-AAA are combined. It is theoretically proven that the TDL-AAA-SP improves the SINR by recovering from reduction of correlation by means of correlation on the time axis. A computer simulation demonstrates that the proposed scheme is effective. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(2): 59–67, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10142 [ABSTRACT FROM AUTHOR]

As the Internet continues to spread and equipment performance improves, the typical operation has been to assign multiple Internet Protocol (IP) addresses to one node. At this type of node, whether the node is the destination of the received packet must be efficiently determined. Conventionally, a Berkeley Software Distribution (BSD) system used an algorithm that performs a linear search for the address of the node. As described in this paper, the Widely Integrated Distributed Environment (WIDE) Project conducted R&D on an improved method using a routing table algorithm. Later an original improvement using a hash table was introduced into Internet Protocol Version 4 (IPv4) implementation in NetBSD and BSD/OS. In this paper, we explain these three methods and evaluate their performances using actual equipment. From the evaluation results, a decision method based on the routing table or the hash table is clearly an improvement over the conventional technique based on a linear search. In addition, the performance of the decision method using the routing table algorithm does not degrade even if the number of addresses increases similar to a conventional routing lookup. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(9): 1–8, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10110 [ABSTRACT FROM AUTHOR]

To use finite spectral resources more efficiently, the cellular mobile communications method reuses frequencies (radio channels) repeatedly. With the cellular method, channel assignment that efficiently allocates radio channels to each base station while guaranteeing fixed communication quality becomes harder as the number of base stations grows, making it difficult to achieve optimization in a short time. This paper looks at the autonomous function for learning the channel used by each base station in autonomous distributed channel assignment and proposes a new channel assignment algorithm for determining channel assignments from the results that are obtained. It also clarifies the application results in a channel assignment system that incorporates the proposed algorithm. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 59–71, 2003; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/ecja.1162 [ABSTRACT FROM AUTHOR]

AntNet was reported to exhibit an undesirable effect called “Routing Lock.” If a link is congested or down, a node can select another link easily with the ability to cancel the effect quickly. As means of canceling the effect, the decay method and the negative feedback method were proposed. However, the decay method is not effective in balancing the cancellation of the effect with the learning speed of network traffic statistics. Also the negative feedback method requires ants to move on at least one congested link so that it takes a long time to cancel the effect. In this paper, we propose an improvement algorithm, BntNetL, which cancels the effect indirectly by giving ants the ability to update routing tables bidirectionally. BntNetL shows better performance than its competitors in simulations. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(9): 31–41, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1123 [ABSTRACT FROM AUTHOR]

This paper considers an ATM switching network in a self-routing system for line switching, and proposes a Batcher Banyan network with a cell copy preparation network. The idea of this switching network is to consider the upper layer line in a communication network with a hierarchical structure, and to note that the traffic of a multicast connection is much smaller than the traffic of a one-to-one connection. The hardware scale is greatly reduced by allowing a small amount of blocking. More precisely, the Batcher Banyan network is used as the basic structure, and a cell copy preparation network with a small amount of hardware and a simple cell transfer algorithm is connected before the Batcher Banyan network. The cells are copied in the cell copy preparation network and the Batcher network. Routing is executed in the Batcher network and the Banyan network. The amount of hardware is greatly reduced compared to the conventional configuration in which the structure is divided into the copying network and the routing network. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(9): 54–63, 2001 [ABSTRACT FROM AUTHOR]

The strong resolving capacity of the superresolution method is effective for the analysis of local scattering of electromagnetic waves. In this paper, as an example of scattering phenomena in which a scattered wave with frequency dispersion is included, backscattering from a circular waveguide is discussed. The accuracy of estimation of the parameters related to frequency dispersion by the improved Root-MUSIC method is discussed. In particular, a new form of postprocessing is proposed in addition to the preprocessing used as a data correction method in the improved Root-MUSIC method. The advantages of postprocessing are discussed. Further, by numerical calculation and experiment, it is demonstrated that the estimation accuracy of the present method can be improved by including a notch filter in the time domain. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(5): 48–56, 2001 [ABSTRACT FROM AUTHOR]

This paper considers the network design and control for multipoint-to-multipoint communications. We propose a new routing control method which includes the member connection method and the route setup algorithm. The former implies that each member has its own route to send information to other members. Thus, it can avoid traffic concentration in a particular route. Further, in the route setup algorithm, all routes are generated in parallel, by adding links which have lower cost and lower load one by one, based on grouping by the number of destination nodes on the route. An interesting feature of the proposed algorithm is that every route can be established with a unified algorithm, even when newcomers join ongoing communications. In addition to the above method, we also propose a network design algorithm. It can make the proposed routing control method more effective. Simulation experiments show that the proposed framework is suitable for multipoint-to-multipoint communications. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(2): 18–26, 2001 [ABSTRACT FROM AUTHOR]