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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]

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]

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]

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]

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]

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]

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]

In high speed multimedia networks, numerous communication quality requirements must be satisfied. In this paper, a tunable routing method for quality of service (QOS) is proposed. In this method, a cost value is given to each link. For these cost values, the routing selection is made by a minimum cost route selection algorithm from graph theory. However, the routing cost value is determined by a tunable cost function that depends on the service class for the quality of service. The cost function proposed in this paper has sorting parameters whose values are determined by the network delay and required quality of service. The proposed method is evaluated for a class in which network delay requirements are strict and for forgiving classes (class 2 or 3) in which the network delay requirement is not so strict. Using simulation, we show that this method makes it possible to select the route for different network delay requirements (targeted QOS) unlike the conventional method in which a uniform cost function is used for every condition. Furthermore, using the proposed condition, a network load equalizing effect can be expected. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(5): 30–40, 1998 [ABSTRACT FROM AUTHOR]

As a coding algorithm in which picture processing can be applied directly to the compressed data, the author has proposed a surface-fitting method (B-spline coding) for the variation of the pixel values using the B-spline surfaces. It was shown that the performance of the new algorithm is equal to or better than the one in the DCT system, even for the compression efficiency. On the other hand, in some compression coding systems dealing with picture data, it is required that the coding is completed for one picture at a predetermined rate. Such problems of controlling the coding rate have not been studied for B-spline coding. In this paper, a method is proposed for dealing with the above problems. In addition, an effort is made to enhance the performance of B-spline surfaces as a compression tool. In this paper, the number of coded bits of each block is controlled by adaptive feedback, depending on the fineness of the picture pattern and the actual number of coded bits generated. A performance evaluation shows that the deviation of the actual number of coded bits from the specified number can be kept within 1%, while the compression performance (better than that of the DCT system) is maintained, and that coding rate control is possible in B-spline coding. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(6): 59–68, 1997 [ABSTRACT FROM AUTHOR]

This paper discusses a multitarget tracking algorithm for use in a dense environment, where there exist other targets or clutter near the tracking target. It is currently one of the most important technical problems in the air traffic control. The joint probabilistic data association (JPDA) algorithm, considered to be a promising multitarget tracking algorithm, has the deficiency that the tracking of the multiple maneuvering targets in a dense environment is difficult. This paper proposes an algorithm in which the multiple motion models are obtained by using different constant acceleration vectors under the JPDA approach; six-dimensional motion models composed of the position and the velocity of the target in three-dimensional space are used in parallel. In this algorithm, the fuzziness due to the nonuniqueness of the motion model when the target maneuvers can be expressed in the calculation of the gain matrix, the covariance matrix and the motion states of the target. In addition, it is possible to adjust the prediction region for the observed vector (center and spread), according to the maneuvering of each target. Simulations indicate a remarkable improvement in the rate of tracking success by the proposed algorithm, reaching several times to ten times larger than that obtained in JPDA. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80 (5): 23–34, 1996 [ABSTRACT FROM AUTHOR]

This paper discusses the tracking filter that estimates the true values of the states of the target such as position and velocity by Cartesian coordinates with the target position used as the observation value of the radar. A typical example is a Kalman filter or an α-β filter. A Kalman filter has a good tracking accuracy but a heavy computational load, whereas the α-β filter has a light computational load and is practical, although it has a problem in tracking accuracy. If the α-β filter with a light computational load has a tracking accuracy similar to the one for a Kalman filter, this filter becomes even more practical. Therefore, in this paper, the conditions are discussed where the α-β filter can approximate a Kalman filter. In this paper, the radar coordinates, where the target position vector is one axis, is used for calculation of the smoothing values (estimated values of the states for target motion at the present sampling time). It is proven that the α-β filter can approximate a Kalman filter if the angular velocity of the target and the rotation of the radar coordinates with the coordinate axis rotated with the target motion are infinitesimal and the process noise (a parameter indicating the ambiguity of the target motion model) is independent and the same between the coordinates. This result indicates that the α-β filter can approximate a Kalman filter if the target is at a low speed, the target range is large, or the target is proceeding toward the radar in a straight line. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(3): 67–77, 1997 [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]

It is known as generally impossible to generate automatically the test cases for arbitrary LOTOS expression containing data parameters. A subclass of LOTOS, called P-LOTOS, is defined. In P-LOTOS, the data type is restricted to be integer and Boolean and the operation on the integer is restricted to be the addition/subtraction and comparison. This paper presents an algorithm for automatic generation of the test cases for this class of LOTOS descriptions. Algorithms also are presented solving the detection problems for the deadlocks, the unexecutable edges, sad the nondeterministic branches, The proposed algorithm is applied to a simplified OSI session protocol, and the result is reportod in this paper. [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]

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]

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]

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]

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 proposes a high-efficiency coding algorithm realization of a 64 kbit/s video coding equipment. A prototype equipment constructed shows a high quality performance for video conferencing and video- phones. For high efficiency coding for video conferencing a coding algorithm combined with motion-compensated interframe prediction and the orthogonal transform coding or vector quantization is usually employed. It is known theoretically that the latter has an excellent characteristic which approaches the rate-distortion bound. However, another coding system is desired which not only has a high coding efficiency, but a small-scale hardware and easy control of information generation. This paper proposes an adaptive tree-search vector quantization in which the size of a code book can be varied according to the local property of an image. The improvement of the coding efficiency due to this idea is demonstrated by a computer simulation compared with a conventional system with a fixed size code book. A 64 kbit/s video-coding system having the resolution of 384 (horizontal) × 240 (vertical) pixels per frame was constructed. Using the coding system with the proposed algorithm, a temporal resolution of 5 to 7.5 frames/s was obtained, confirming the satisfactory results for practical applications such as video conferencing and videophones. [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]

A short-time Fourier transform can be derived by low-pass filtering of the product of an input signal and exp(j2πft). According to this method, called the Running Fourier Transform (RFT) in this paper, running power spectra with arbitrary center frequencies and arbitrary Q values can be obtained. This paper proposes a fast algorithm of discrete RFT (FRFT). In the FRFT, a first-order lag system is adopted as the low-pass filter (LPF), and by approximating the impulse response of the LPF with a step function, the amount of multiplications is reduced. The calculation of the complex exponentials is omitted by referring to a table of sin(2πk/K) (k = 0, …, K). [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]

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 presents a new synthesis method for ARMA digital lattice filters. These filters are obtained by a fast algorithm for estimation of ARMA parameters. Some fast algorithms for such estimation have already been proposed in which approximation models are derived using the input and output signals and can be applied to arbitrary input signals. Among these methods, the Mullis-Roberts algorithm estimates the parameters by the autocorrelation coefficients and impulse response of observed signals. The method is similar to the parameter estimation using white Gaussian process for the input signals. Though the Mullin-Roberts algorithm can estimate the parameters with less calculation cost than other algorithms, it is not suitable for designing different orders of the AR and MA parts. The fast algorithm proposed in this paper estimates the parameters with the same calculation cost as in the Mullis-Roberts algorithm when the input signal is restricted to a white Gaussian process and obtains the ARMA parameters as the AR and MA orders are independently increased. The new ARMA lattice filter is synthesized by three prediction errors defined in the new algorithm and consists of a simpler structure than the usual filters of this type. By processing time series signals using the algorithm and the lattice filter, we show the feasibility of estimating the minimum realization for an ARMA model. [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]

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]

The cause of the error in the FFT is due mostly to the quantization error of the input data, the round-off error in arithmetic operation, and the computation error of Wnk = exp (-j2πnk/N). Of these, the error of Wnk is complex, and this error is approximated in the reported error analysis by the truncation error by finite bits. This paper examines the actual computation error of Wnk is much larger than the truncation error by the finite bits, and can produce instability in the algorithm. Then to solve the problem, this paper proposes a method to improve the computation accuracy of Wnk. The proposed method can be executed without increasing greatly the processing time and the memory, compared with the direct FFT computation. By using the proposed processing, the error analysis is made more reliable than in the past and the error accompanying the FFT is reduced. Finally, the effectiveness of the proposed method is verified by several example. [ABSTRACT FROM AUTHOR]

Recently, extensive studies have been carried out on the algorithms which constructively determine the solution of nonlinear equations, These algorithms are in general attraction lies in the global convergence. However, fixed-point algorithms have been a problem in the execution speed is decreased greatly with the increase of the size of the system of equations to consider. This paper proposes a decomposition method and acceleration techniques as a means to improve the computational efficiency of the fixed point algorithms. Kevorkian's method is used in this paper as decomposition. Since the method includes errors in the decomposed equations and function value, it is important to discuss the convergence of the solution algorithm and to improve the convergence speed taking the effect of the those errors into consideration. This paper shows a solution algorithm in which the system of equations is decomposed by Kevorkian's method, and then Merril's method, a typical fixed-point algorithm, is applied. Accuracy of simplicial approximation and convergence properties of the algorithm are discussed, indicating that the algorithm exhibits local quadratic convergence under some suitable conditions. By numerical examples, it is verified that the algorithm exhibits quadratic convergence. The method is compared with the past methods, indicating the effectiveness of the propose method. [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]

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]

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]

To date, for the tomographic signals obtained in cross-borehole radar measurement in which transmitting and receiving antennas are scanned independently, a position estimation method for the isolated reflector has been studied by applying the transmission and reception array MUSIC method. However, when the operating wavelength and the size of the conducting cylinder cannot be neglected, as in the case of buried pipes, there is an error in the estimated position in the conventional method when the scattered wave from the point scatterer is used as the steering vector for position estimation. In this paper, the steering vector obtained from rigorous solution of scattering from a conducting cylinder is used. It is shown that the position estimation accuracy is improved by taking into account the effect of the elimination of the direct wave. It is also shown that the cylinder position and the radius can be estimated simultaneously by using the cylindrical radius as an estimation parameter. The effectiveness of multifrequency synthesis is discussed. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(8): 26–36, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20271 [ABSTRACT FROM AUTHOR]

An algorithm using electrical edge routers as shared buffers is studied as a packet collision avoidance method in optical packet routers that switch variable-length packets of light. In this algorithm, packets in contention on the output lines of an optical packet router are switched to an electrical edge router placed at the same location, electrically converted temporarily, and buffered. If few packets are electrically processed by buffering compared to the total, since most of the packets are transferred as light, the optical packet router can have an extremely large processing capacity with respect to the limit of the processing capacity of the electrical router. In this paper, we propose an edge traffic control algorithm to improve the performance of the optical packet router. The edge router used as a buffer is positioned at the same location as the optical router. The traffic transmitted from this location can be controlled in response to the state of the optical router. In the proposed control algorithm, transmissions from the edge are controlled when the output lines of the optical router are congested to ease congestion. The performance of this optical packet router is improved by this control, and the application range of the optical packet router satisfying fixed performance conditions clearly expands. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(12): 61–70, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20190 [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]

With the spreading use of cellular phones in recent years, there has been an increasing demand for various services based on location information. The location-dependent information to be used in location estimation can be the TOA (time of arrival), TDOA (time difference of arrival), signal strength, and AOA (angle of arrival). In third-generation cellular phones, whose widespread use is expected, the communications data rate will be increased. The chip resolution will also be improved, making it possible to measure the signal arrival time with higher accuracy. Consequently, this paper presents an evaluation and discussion of the location estimation performance of a TDOA system. An exponential distribution is assumed for the signal delay profile, and the location estimation algorithm is formulated on the basis of maximum likelihood estimation. Then the accuracy of location estimation is compared by simulation for maximum likelihood estimation in the TDOA system and the existing method. The accuracy of location estimation by maximum likelihood is also evaluated for various environments. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(6): 47–54, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20155 [ABSTRACT FROM AUTHOR]

This paper is concerned with the backoff algorithm for a random access system on the basis of slotted ALOHA. The performance of the algorithm in which the backoff counter is reset after the packet transmission success (conventional scheme), and the performance of the algorithm in which the backoff counter is successively decremented (modified scheme), are analyzed for the unsaturated condition. Based on the concept of equilibrium point analysis, the packet transmission failure probability, the throughput, the average transmission delay, and the uniformity of the transmission delay variation are evaluated. It is shown by a numerical example that the modified scheme exhibits better performance than the conventional scheme, even in the unsaturated condition, as well as in the saturated condition, with appropriate setting of the backoff window width. In addition, the modified scheme is shown to be better from the viewpoint of uniformity, in the sense that the packet transmission delay variation is smaller, even if the parameters are set to values that degrade the throughput. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(4): 32–43, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20176 [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]