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This paper gives a suboptimal layout for minimizing the virtual wiring length of a given circuit which is one of the design problems in the circuit module placement. The connective relations among circuit modules are represented by a circuit hypergraph and then by a circuit graph. A graph space method is proposed in which the modules are placed so that the pair with strong affinity is close and the pair with weak affinity is distant. Based on such a graph, the modules are assigned to the two-dimensional slots. It is shown that even when there is a restriction that some of the module placements are already specified, the placements of other modules can be performed without affecting the overall connective relationships. The effectiveness of the method is verified by a computer simulation. [ABSTRACT FROM AUTHOR]

This paper proposes a reduction method for the D-section which realizes the complex attenuation poles in the wave digital filter (WDF) design. The reduction is based on the lumped/distributed network. First, an approximate lumped network (called A2-section) is introduced for the transmission line (UE) with the length T where Richard's variable μ = tanh τ is replaced by the rational function qτs/(p² + τ²s²) (p ... 1.6, q ... 2.8). The A2-section has a set of complex attenuation poles if the values τ, p, q are chosen so far as the attenuation pole s = (± γ ... j ...)/2(γ = q/τ, δ = p/τ) is complex. In this case, the A2-section is called the A2-section. Then it can be shown that the cascade connection 2-port of two GA2-sections and series coils is equivalent to the D-section, and the D-section is also approximately, equivalent to the 2-port composed of two UE's and LC elements. By applying the well-known WDT realization method by Fettweis and Swammy, simultaneously, an approximate but very simple D-section of WDF is obtained. When the length of UE is small, the deviation of WDF response from the design specification is small. As an example, the design of the WDF bandpass filter is shown and the low coefficient sensitivity property compared to the conventional cascade synthesis method is verified. [ABSTRACT FROM AUTHOR]

When maritime satellite communication is conducted at low elevation angles, fading due to sea surface reflection becomes a problem. For suppression of the fading, space diversity and frequency diversity may be employed. This paper studies the correlation characteristics of multipath fading due to sea reflection in the spatial and frequency domains in L-band operation. This is important in investigating the diversity effect. First, from the theoretical model of sea surface reflection, the correlation scattering cross sections of the coherent and incoherent components of the reflected wave are obtained. Next, from numerical calculations, the correlation characteristics are obtained with the antenna elevation angle and the height over the sea as the parameters. It is found that in space diversity good diversity effects can be expected from two antennas separated in the vertical direction by about 40 cm. It is also seen that fading reduction cannot be expected with frequency diversity in the case of narrowband communications such as in maritime satellite communications. The effects of various fading reduction measures in the up and down links are considered. [ABSTRACT FROM AUTHOR]

The minimum energy signal is defined as a band-limited signal of minimum energy that has the sample values of the original waveform and its derivative at prescribed sampling points. This paper proposes an approximation method for band-limited signals given over a specified time interval. The proposed method selects each new sampling point so that it minimizes the square error between the minimum energy approximation waveform and the actual waveform. It does not require complicated integration and/or transformation as in the conventional methods. Therefore, there is no error caused by such computations. When the number of sampling points approaches infinity the proposed method yields an approximation waveform which converges to the actual waveform. Furthermore, if the sampling points are allowed to deviate within a certain limit from the optimum sampling points then the approximation waveform can be obtained without using the derivative signal, and yet retains its convergence characteristics. [ABSTRACT FROM AUTHOR]

This paper considers the nondeterministic operator G defined on the direct product space of a completely matrizable linear space X and a metric space Y; G is introduced as a projective set G (x, y) ⊂ X for arbitrary x ε X and y ε Y. Relating to the completely continuous operator f(x) with Y as the range, a fixed-point theorem is given for the generalized operator equation x ε G (x, f(x)). This mathematical theory is applied to the analysis of deviation of the output response when a nondeterministic fluctuation is imposed on the internal structures, internal parameter or input signal of a system. As a result, clear definitions are given for the tolerability and quasitolerability of the system fluctuation, the stability and quasitability of the system, and the tolerability and quasitolerabiity of the system model and simulation by it. An aspect of the system's sensitivity analysis is also discussed. Of particular importance in this paper is the new proposal of the new concepts of quasitolerability and quasistability, which suggests that these concepts should be utilized more widely the notions of the system and its model by developing the computing abilities. [ABSTRACT FROM AUTHOR]

The charge simulation method has the Following characteristics compared with other approximate methods for the scattering problems: (1) Only the zeroth and first-order Hankel functions are used; (2) no processing of the singularities on the boundary is needed; (3) no numerical integration is necessary. As a result, it is an extremely simple method. However, the arrangements of the sources and contour points are arbitrary and such arrangements affect the accuracy of the approximate solutions. Previously, the source arrangements by the boundary contractions have been used in the charge simulation method. This choice provides good results if the shape of the scatterer is close to a circle or is a circle itself. The accuracy becomes poorer as the shape deviates more from the circle. Also, it is not possible to determine beforehand the arrangement that provides the best result. Hence, the boundary contraction is an important arrangement method. In this paper, arrangement of the sources and contour points is determined by means of the conformal mapping that transforms the boundary to a circle. Numerical calculations have been performed for typical convex shapes. It is found that the charge simulation method based on the present arrangement has the following properties. It exhibits much better accuracy than the arrangement by boundary contraction. The arrangement minimizing the error is found from the conformal mapping. Scatterers with edges on the boundary cannot be analyzed. [ABSTRACT FROM AUTHOR]

The controllers of the majority of existing stored-program control switching systems employ architecture of Von Neumann. Shortcomings associated with such architecture include high OS overhead in multiprocessing, and difficulties in understanding the relationship between the control structure and the data flow of sequential programming. To overcome these problems this paper proposes a data flow architecture for controlling the switching system and describes the implementation of a prototype DATAFLEX-1 (data flow exchange-1). The basic operators of this prototype are implemented to approximate the task macro of the cell processing programs by using seven Z80A microprocessors to provide the necessary functions for intra-office switching. The self-documentary feature of the proposed programming technique, the clarity of data flow, the architectural modularity, the expandability of both the control functions and the scale of the proposed scheme are verified. [ABSTRACT FROM AUTHOR]

This paper describes the trial production results for two linearizers, one being a compact, lightweight MIC linearizer developed to improve the input-output nonlinear characteristics of an earth station HPA and the other being a new soft-limiter linearizer (SL-LRZ) followed by an amplitude limiter. The symmetric construction of the MIC linearizer is easily implemented with MIC techniques, operates over a wide frequency band and its nonlinearities can be controlled electrically. Also, the transfer characteristics of a TWTA with SL-LRZ are such that its amplitude response is linear up to saturation, it maintains constant output level beyond saturation and phase shift is not likely to occur. The TWTA in amplification of multiple carriers and can improved transmission performance when a band-limited PSK signal is amplified at close to saturation. The test-fabricated SL-LRZ is sufficiently small and lightweight for on-board application. [ABSTRACT FROM AUTHOR]

The demand of facsimile transmission of printed matter as well as photographs is becoming strong daily as the variety of information is increasing. The disadvantage of the previous methods is that the character quality is deteriorated because in the case of artificial half-tone reproduction using black and white recording, the resolution is sacrificed and tonal reproduction is performed. In this paper, a method to solve this problem is reported in which each block consisting of multiple picture elements is distinguished as bilevel region or gray-scale region, and the processing suitable to each region is performed. This paper also describes the results of computer simulation obtained by applying this method to reproduce the characters and photographs, Moreover the case of gray-scale region lying inside the character region is discussed and it is shown that a simple region correction method is very effective. [ABSTRACT FROM AUTHOR]

Various proposals have been made in recent years with regard to hybrid power supply systems for communication system applications. The main common feature of such system applications. The main common feature of such systems is the incorporation of two or more kinds of power sources. In this paper we first discuss the concept of hybrid systems and then describe experimental results obtained with a triple hybrid system incorporating a wind-power generator, solar cells and Diesel generating equipment. It is then shown that the continuous time distribution of natural energy in the nonenergized state follows an exponential function. We apply a mathematical model which id in good agreement with the experimental results an develop a theory for derivation of the required storage battery capacity as well as the power to be applied by the Diesel generators. Then, applying this design method to various systems, we present a quantitative analysis of the complementary relationship between wind power and solar illumination and show that the triple hybrid system is most economical. [ABSTRACT FROM AUTHOR]

The problems of testing the planarity of a graph and of embedding a planar graph in a plane arise in many applications. This paper presents a simple linear algorithm for the latter problem. The algorithm is based on the 'vertex-addition algorithm' of Lempel, Even and Cederbaum for planarity testing and is a slight modification of Booth and Leuker's implementation of the testing algorithm using a PQ-tree. Compared with the embedding algorithm known as the 'path-addition; algorithm of Hopcroft and Tarjan, our algorithm is conceptually simple and easy to understand or implement. [ABSTRACT FROM AUTHOR]

The internal loss modulation of a semiconductor laser has a very rapid response because it depends on the photon lifetime in an optical cavity. This technique is applicable to high-frequency modulation and generation of short light impulses which could not be possible by means of ordinary current modulation. The present paper describes some results of small-signal and large-signal sinusoidal modulation which are obtained by applying a rate equation to a lateral field coupling control (LFCC) semiconductor laser. It is found that modulation at frequencies higher than 10 GHz is possible and that light impulses with 10-ps half width can be obtained at several GHz. These results are applicable to other lasers with internal loss modulation. [ABSTRACT FROM AUTHOR]

A problem inherent in discussing the antenna radiation mechanism is that the electromagnetic energy flux density can not be deterministically defined. The practice has been to interpret the Poynting vector as the flux density vector and to use it to explain the various phenomena. In this paper, as the equivalent of the Poynting vector, the Nukiyama vector derived from the energy theorem is interpreted as the flux density vector. This interpretation is applied to the radiation mechanism of a perfectly conducting antenna, and it is shown that the radiation can be explained as "an exchange of energy between the electromagnetic wave radiated into space and the conductor on which the power is impressed, with the energy exchange taking place as the energy transverses the conductor." It is also shown that the new concept of locally-stored energy derived from Nukiyama's vector for use in this exposition is a broad concept which also encompasses the representation of observable stored energy as defined by Rhodes. [ABSTRACT FROM AUTHOR]

This paper proposes &Rtilde;(t), an approximation for the auto-covariance function of virtual waiting time in an M/G/1. Calculation by &Rtilde;(t) is much easier and faster than the exact formula R(t). By the use of this approximation, not only the computation for arbitrary model becomes possible, but also the computation time can be reduced below 10-3 time even for the model which can be calculated by the exact formula, such as M/M/1. Comparisons between &Rtilde;(t) and R(t) for several models show that &Rtilde;(t) approximates R(t) closely enough for practical use. We have applied &Rtilde;(t) to the accuracy estimation of waiting time measurement by test calls (test call method) and obtained several important results for waiting time measurement. They are: i) the accuracy is improved as the interval of test calls is set shorter, but is hardly improved even if the interval is set shorter than ten times the mean waiting time (saturation characteristic); ii) better measurement accuracy is obtained by the test call method if the interval of test calls is properly set than by the real call method; and iii) the coefficient of variation of service time distribution greatly affects the measurement accuracy. [ABSTRACT FROM AUTHOR]

This paper proposes a method of constructing an RC active network to realize a voltage transfer function matrix without using an integrator. The method is based on the fact that an m-input system of multi-variable controllable canonical form can be decomposed into m subsystems of controllable canonical form using state feedback and input transformation. The required m-input p-output voltage transfer function matrix is constructed using m passive RC networks and (m + p) summers. The network has the following structure. The capacitor edge voltage of the passive RC network is taken out as the state variable, and the state differential equation is realized by the feedback through the input-side summers. The output equation is realized by the feedforward through the input-side summers. The output equation is realized by the feedforward through the output-side summers. The feature of the proposed method is that it is applicable to any proper rational transfer function matrix of any size, not only of the square form. Another feature is that the transfer function matrix can be realized with a fewer number of active elements. [ABSTRACT FROM AUTHOR]

A shaping filter for a stationary stochastic process can be viewed as the open-circuit voltage transfer function of a resistant-terminated reactance 2-port. Further, Levinson's theory regarding spectral analysis (AR analysis) based on the autoregression model of a stationary stochastic process is equivalent to Ricca's theorem in network theory. Using these facts, from the digital lattice filter which is developed from the AR analysis, we can determine the impulse response of the inverse of the reflection coefficient at the output of the resistance-terminated reactance 2-port corresponding to the stationary stochastic process which is analyzed. In this paper we present a technique in which an AR analysis is performed on an autoregressive, moving average process (ARMA process), the impulse response is approximated by a rational function as described above and, by determining the open-circuit voltage transfer function, the ARMA coefficients are derived. Also, we present two different regression methods for determining the rational function approximations to the impulse response. In general, there is no guarantee that the rational function approximations determined by these methods will be physically realizable transfer functions, but it has been verified by modeling tests that, for an ARMA process of finite degree, by this technique we can determine ARMA coefficients which are better than those obtained by AR analysis to approximate the power spectrum. [ABSTRACT FROM AUTHOR]

In this paper we consider the problem of resizing figures in a digitized XY coordinate plane. The figures are regions closed by line segment parallel to the X or Y axis or line segments at 45° angles to the axes. By resizing we mean that, given the closed regions and a change width, we expand or contract the input regions by the change width. After first proving some theorems on resizing, we response an algorithm solving the problem in running time 0 (n log n), where n is the number of vertices in the regions. For particular applications we consider examples using the algorithms for verifying compliance with design rules for the smallest feature size and spacing in a mask pattern, and also the compensation for characteristic machine error in pattern generators, apertures, etc. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method for decreasing cross-polarization in the tilt plane by optimizing the dielectric substrates of dual-polarized patch antennas. At the same time, we clarify the limit values for the cross-polarization level. First, we use a cavity model of the patch antenna to find cross-polarization dielectric characteristics in the tilt plane. We learn from this that the direction of cross-polarization increase or decrease in relation to the dielectric is reversed during horizontal polarized excitation and vertical polarized excitation. Therefore, if the cross-polarization level during horizontal polarized excitation and vertical polarized excitation is the same dielectric, the lowest cross-polarization level can be obtained in conditions where both horizontal polarization and vertical polarization are decreasing cross-polarization. Next, we investigate the case where parasitic elements are mounted on the patch antenna, and use the FDTD method and test to show that our method is valid. In addition, if the patch is positioned perpendicularly to the horizontal plane, we show that the optimum dielectric remains virtually unchanged in the tilt plane up to about 15° from the horizontal plane. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(8): 1–9, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20393 Copyright © 2004 Wiley Periodicals, Inc.Copyright © 2007 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

While independent provision of service results in normal operation, operation in tandem with other services causes defective operation to occur. These defects are called ‘feature interactions.’ Our investigation of the international benchmark for detection of feature interactions revealed that feature interactions not occurring in real systems (called ‘lsquo;seeming interactions’) were being detected. Analysis of the cause showed that a conventional state transition model was being used unchanged for the service specification execution model. Seeming interactions are an important issue for increasing the man-hours used to solve feature interactions. In this paper, we propose a trigger point model that clarifies the service specification trigger point as the specification execution model. Through use of this model, we were able to eliminate as seeming interactions about 60% of the feature interactions listed in the international benchmark, confirming the validity of the proposed model. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(4): 23–34, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20349 [ABSTRACT FROM AUTHOR]

This paper notes that the modulation scheme used in MIMO (multiple-input multiple-output) system has only discrete spectral efficiency, which in addition has an upper limit from the viewpoint of implementation. A capacity-controlled MIMO adaptive modulation scheme is proposed. In contrast to the conventional MIMO adaptive modulation, which aims at maximization of channel capacity based on the water-filling theorem, the proposed scheme assigns the minimum necessary transmitted power satisfying the required QoS (quality of service) while maintaining constant transmission capacity by applying mode-selective adaptive modulation based on a LUT (look-up table). The algorithm of the proposed system is very simple, since the parameters for the adaptive modulation and the transmitted power control are determined by a single step. It is useful in the sense that the control part can easily be constructed in hardware. Furthermore, the overhead of the adaptive modulation is decreased by applying mode-selective adaptive modulation. An evaluation by computer simulation is presented, and it is shown that the proposed system is useful in reducing the transmitted power while maintaining the specified transmission capacity. Furthermore, the proposed system is better in environments in which the fading variation in the channel has high spatial correlation. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(8): 1–13, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20282 [ABSTRACT FROM AUTHOR]

This paper shows that the integral of the current flowing on a parasitic dipole can be made to vanish by supplying a reactance with an appropriate value. When a reactor is placed at the center of a half-wave dipole with a thickness of 0.02 wavelength, the reactance value making the integral of the current vanish is about +450 Ω. The state in which the integral of the current is zero is not affected by other elements and minimizes the electrical influence on other elements. Hence, this state is considered electrically invisible. A reconfigurable (structurally variable) ESPAR antenna is proposed in which a variable reactance is placed on a parasitic dipole and the combination is adequately made electrically invisible. A method of calculation is proposed in which the admittance of the array configuration without a specific dipole element is obtained from the admittance in the presence of such an element by making it electrically invisible. Further, by this calculation method, the behavior of the admittance of an array with symmetrically placed elements is obtained. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(3): 21–35, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20262 [ABSTRACT FROM AUTHOR]

In this paper, we show that the current distribution along the parasitic dipole elements loaded by variable reactors varies greatly depending on the variable reactor value. Thus, when the directionality of an Electronically Steerable Passive Array Radiator (ESPAR) antenna constructed from parasitic dipoles is calculated, we must consider the changes in the current distribution along these elements. Therefore, we propose a method where the current weight is the value of the vector effective length of each element multiplied by the current value at the port. We also show that when the dipole length is less than approximately the half wavelength, the vector effective length is calculated for the most part by the ratio of the port voltage to the port current. From this relationship, even if the current distribution along an element is not determined, the vector effective length of a parasitic element can be calculated from the value of the variable reactor loading the element. Thus, the current distribution along the elements can be easily considered when calculating the directionality of the ESPAR antenna. We present a method that calculates the directionality of the feed dipole array antenna having mutual coupling among the elements that considers the current distribution along the element where not only the port current but also the port voltage are set as the weights. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(2): 22–35, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20232 [ABSTRACT FROM AUTHOR]

The rotating element electric field vector (REV) method is an extremely effective measurement technique for calibration of a phased array. However, if there is any error in the excitation amplitude and phase of each element antenna, the measurements will contain an error. In this paper, the relationship between the error of the excitation amplitude and phase of each element and the measurement error of the REV method is obtained by means of probabilistic analysis theory. In the derivation of the theoretical equation, we study the error in the combined power of the array antenna (to be called the array combined power) when the excitation phase of the element is varied in accordance with the measurement principle of the REV method. Then, the error from the ideal condition without any error in the excitation amplitude and phase is expressed in terms of probability density profile. Next, the relationship between the error in the array combined power and the measurement error of the REV method is given by an approximate formula. As a result, it is clarified that the error of the excitation amplitude and phase of each element and the measurement error of the REV method can be related by a simple theoretical equation. The effectiveness of the derived theoretical formula is verified experimentally, indicating that the measurement accuracy of the REV method is amenable to analysis. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(1): 22–33, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20239 [ABSTRACT FROM AUTHOR]

To improve the volume search efficiency of a bistatic radar with the transmitting antenna and the receiving antenna positioned apart, a known beam scanning method is pulse chasing that scans the receive beam at high speed in response to the propagation of the transmitted pulses. However, in normal pulse chasing, the receive beam width cannot be narrower than some value in order to receive all of the transmitted pulses without losses. In other words, a limit is the antenna gain cannot be increased. The problem is the receive signal-to-noise ratio (SNR) decreases compared to when pulse chasing is not performed. In this paper, we propose multibeam pulse chasing, a beam scanning technique using multiple receive beams based on digital beam forming, as the solution. We show that even if the transmitted pulse width is relatively long, if the number of multibeams is increased, the received SNR does not exhibit a decrease. Furthermore, we study a method to decrease the number of multibeams by dropping a portion of the receive pulses when pulse compression is applied as the transmission and reception methods, and present the computational result of the relationship between the number of multibeams and the received SNR when the Taylor window is applied. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(1): 11–21, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20240 [ABSTRACT FROM AUTHOR]

The adaptive array antenna (AAA) can suppress interference waves. It is also possible to realize a large space diversity effect by increasing the spacing between antenna elements. In a TDD system, when an AAA is installed in the base station, the characteristics of both the up- and down-links can be improved by using the weights determined for the up-link. This paper considers a feedback-type AAA in an FDD system in which the AAA is installed only in the base station, and analyzes its characteristics. The following properties are identified by computer simulation. If the fading has a period which is slow compared to the control delay, the FDD system can deal with both fading and co-channel interference, and performance can also be improved for fast fading by applying linear extrapolation. Furthermore, by applying a feedback-type AAA to site diversity, the error rate can be improved. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(11): 9–20, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20225 [ABSTRACT FROM AUTHOR]

The adaptive array is an effective measure in OFDM systems against intersymbol interference caused by delayed waves outside of the guard intervals. In this paper, we studied a technique that suppresses only delayed waves outside of the guard intervals and not delayed waves in the guard intervals by examining the temporal changes in the amplitude spectrum of the received OFDM signal caused by intersymbol interference. This technique is applicable if the signal points of the modulation of each subcarrier have a constant amplitude, and can be implemented by a relatively simple circuit because control is possible without the need for a known reference signal and estimation of the transmission path. Here, we proposed a method that compares in the time domain because the configuration is simpler. We also proposed a method that emphasizes the error portions with respect to a reference signal and improves the convergence speed as a measure against the slower convergence speed due to the interference components included in the standard signal. The simulation results verified the effective operation of the proposed method in a static multipath environment and a Rayleigh fading environment assumed in mobile communications. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(10): 35–44, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20201 [ABSTRACT FROM AUTHOR]

Multiuser detection using decorrelating detectors in CDMA systems have favorable performance when a few channels are in the synchronized state. However, when there are many channels, the performance degrades due to the effect of intersymbol interference in the unsynchronized state and the effect of noise emphasis. In this paper, we propose a method that reduces the effects between adjacent symbols by adding a guard chip interval while not increasing the processing computational load of the decorrelating detector even in the unsynchronized state. In addition, we propose a method that applies quasi-maximum likelihood estimation, a simplification of maximum likelihood estimation, to reduce the degradation in the noise emphasis. The result of an evaluation of the BER performance by a computer simulation verified the removal of interference nearly equal to the synchronized state even in the unsynchronized state. Even if the performance is degraded by the effect of noise emphasis with many channels, we verified that the performance can be improved to some degree by applying quasi-maximum likelihood estimation. [ABSTRACT FROM AUTHOR]

As an optical multiplexing system to be applied to the uplink of a passive optical network, the authors propose short pulse amplitude modulation as a form of optical CDM. Although this method has the attractive feature that no timing control and wavelength control is necessary, the number of multiplexed optical signals is limited by the optical beat interference. In this paper, the signal-to-noise ratio and the number of optical signals that can be multiplexed are theoretically discussed when digital signals are transmitted with short pulse amplitude modulation in the case where the DFB-LDs with identical wavelengths are used as the optical sources and the optical beat interference is generated within the signal bandwidth. It is found that the number of optical signals that can be multiplexed is 8 when the signal speed is 100 Mb/s and the amount of chirp in the LD is 280 MHz/mA. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(4): 35–41, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10075 [ABSTRACT FROM AUTHOR]

Antennas for private mobile communications are required to have enhanced performance and miniaturization in order to deal with high-performance mobile communications for the next generation. In this paper, with regard to the polarization diversity H antenna using the correlation between polarizations proposed as a base station antenna, the results of an analysis of the structure, characteristics, and effectiveness of the polarization diversity H-type antenna in an actual environment obtained from field experiments are presented. The polarization diversity H antenna has a turnstile H element for the horizontal polarization and a dipole for the vertical polarization. The optimum shapes of each polarization antenna are derived. Also, in the diversity configuration, a structure optimizing the directivity and mutual coupling is derived. A field experiment is carried out at 150 MHz, the frequency presently used for operations. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(4): 10–18, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10078 [ABSTRACT FROM AUTHOR]

This paper presents the general cross-polarization elimination condition for multireflector offset antennas consisting of one primary horn and many reflectors. It clarifies that the derived condition is a frequency-independent geometrical relationship. We apply this condition to an offset parabolic antenna, a dual reflector offset antenna, a trireflector offset antenna, and a four-reflector offset antenna, and show that a trireflector offset antenna is consistent with the already derived relationship. Furthermore, the configurations for the reflector system obtained by applying this condition to a four-reflector beam waveguide feed are shown, and the general broadband characteristic condition is derived, which is especially important for the broadband design. To determine the validity of the theory, a design example is presented for a beam waveguide feed satisfying the cross-polarization elimination condition and the broadband characteristic condition, and minimizing the spillover loss within the structural restriction of using a four-reflector beam waveguide feed. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(12): 1–12, 2001 [ABSTRACT FROM AUTHOR]

Due to their great fabrication flexibility, multilayered conductive thin films are used as a shielding material by thin film metal plating on a dielectric body. In the simulation of the shielding effect of these multilayered thin conducting films by the FDTD method, it is necessary to use a cell size less than the conductor thickness in direct modeling. However, since the shield material generally is much thicker than the metal thin film, the number of cells needed in such modeling is prohibitive and calculation becomes difficult. In this paper, as a subcell method in the FDTD approach, an infinitesimally thin resistive film that has a transmission coefficient equivalent to the multilayered conducting thin film is introduced. By this technique, modeling becomes possible without increasing the number of cells unnecessarily. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(12): 22–31, 2001 [ABSTRACT FROM AUTHOR]

Scan synthetic aperture radar (SAR) is a synthetic aperture radar technique that observes a wide elevation width by conducting observations while successively switching the antenna orientation direction in the elevation direction. In this paper, we propose a method to increase the signal-to-ambiguity ratio (S/A ratio) in the azimuth direction of the image by adjusting the Scan SAR observation sequence. In addition, the procedure for planning the observation sequence by this method is presented and its effects are evaluated. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(12): 32–40, 2001 [ABSTRACT FROM AUTHOR]

The defocused feed reflector antenna with a phased array is promising as a mobile communication antenna on board a satellite because electronic beam reshaping and beam scanning are possible. In this paper, (1) an electrical design of the phased array feed, (2) test fabrication of the 31 radiating element array and beam forming network as the principal components of the feed, and (3) the measured results of the primary radiation pattern combining the above are described. By comparing the secondary radiation pattern computed using this measured result with the designed value, the validity of the electrical design of the phased array feed used for a defocused feed reflector antenna is verified. It is shown that the phased array feed using the verified design method can accomplish more than 42 dBi of area gain and more than 20 dB of isolation between the beams by combining it with a reflector having an aperture diameter of 13 m. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(6): 22–31, 2001 [ABSTRACT FROM AUTHOR]

To achieve a fair share of buffer memory among the output queues in a shared buffer ATM switch, a maximum allowable queue length (a threshold) for each queue should be set. In this paper, to analyze a transient behavior of the buffer state in such switches, we perform a discrete-time transient analysis of a queuing model and then approximately derive time-varying queue length distribution and cell loss probability. In numerical examples, we discuss the validity of our analytical approach by comparison with simulation results. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(6): 1–10, 2001 [ABSTRACT FROM AUTHOR]

Automatic repeat request (ARQ) is very effective in error control, and among various ARQs, selective repeat gives the best throughput characteristics where infinite-capacity buffers are theoretically required in the transmitter and receiver stations. Therefore, in practice, a modified selective repeat request method with a finite-capacity buffer must be devised. In this paper, a selective repeat method is proposed where multiple frames corresponding to a message may continuously be sent. Based on the error rate, number of repeats, and round-trip delay time, the appropriate number of multiple transmissions for maximum throughput in the case of a finite-capacity buffer is derived. It is shown that good throughput characteristics can be achieved in the proposed method with an appropriate number of multiple transmissions. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(6): 68–76, 2001 [ABSTRACT FROM AUTHOR]

The M3JPDA (multiple maneuver model joint probabilistic data association) system is a multiple target tracking algorithm that can cope with maneuvering targets. The system includes a straight-line constant-velocity movement model as well as multiple accelerated movement models, to be used in parallel, where the models are utilized according to their reliability. It sometimes happens in M3JPDA, however, that when the targets move in straight lines with constant velocities, the multiple tracking performance is worse than in the conventional JPDA using the straight-line constant-velocity movement model. This paper proposes adaptive M3JPDA to remedy this point. In this method, the target acceleration is estimated and is smoothed. If the resulting value is large, the conventional M3JPDA is used. If the value is small, the reliability of each motion model is calculated and the choice of models is based on the difference between the reliabilities of the conventional M3JPDA accelerated motion models and the straight-line constant-velocity motion model. Using the proposed algorithm, the reliability of the straight-line constant-velocity motion model is improved when the target executes straight-line constant-velocity motion. As a result of evaluation by simulation, it is seen that the proposed algorithm is capable of tracking two crossing targets in straight-line constant-velocity motions, as well as two targets rapidly maneuvering with 7 g accelerations, in contrast to JPDA based on the straight-line constant-velocity motion model and M3JPDA. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 83(2): 61–73, 2000 [ABSTRACT FROM AUTHOR]

Applying feedback control to a flyback converter in discontinuous conduction mode causes instability by virtue of a jump phenomenon under some snubber circuit conditions. In this paper, we clarify this jump phenomenon, analyze stability, and discuss circuit constants to avoid the phenomenon. We propose current-mode control without relying on circuit constants. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 21–29, 1999 [ABSTRACT FROM AUTHOR]

Weibull distribution and log normal distribution among others have been used to describe the amplitude distribution in clutter. The K-distribution, proposed more recently attracts attention because its parameters are able to explain the physical nature of clutter. The relationship between the K-distribution parameters and the nature of geographical features is clarified in this paper. Differences in experimental conditions and small amounts of non-object clutter in the geographical features influence the parameters. We show that this influence can be reduced by a limiter related to average electric power. We show that the distribution, obtained by pulse integration and unification processing, and using a limiter several times, conforms to a gamma distribution. In these experiments, this method, using the same radar, is applied to clutter from various geographical features to obtain the K-distribution parameter. The K-distribution parameter is used to compare the relation between various geographical features. Finally we show that the power distribution before pulse integration or the clutter voltage distribution conforms to a K-distribution with the same shape and scale parameter as the gamma distribution. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 57–65, 1999 [ABSTRACT FROM AUTHOR]

Series resonant dc-dc converters possess the advantage of high efficiency for a relatively wide load range because their circulating energy is small. However, it is often observed that the switching frequency varies greatly when the input voltage and load current change, and in particular that the switching frequency enters the audible frequency range when the load current decreases. A half-bridge type series resonant dc-dc converter with auxiliary switches has been designed in order to prevent this lowering of the switching frequency under light load conditions. This paper analyses the performance characteristics of a half-bridge type series resonant dc-dc converter with auxiliary switches, including operation of the control circuit. The relationship among the circuit parameters, the operation modes, and output characteristics is clarified, and the regulation mechanism of the output voltage is defined. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 74–81, 1999 [ABSTRACT FROM AUTHOR]

As mobile communications such as mobile phones spread, biological effects of electromagnetic waves become a concern. Though many calculations of the specific absorption rate (SAR) by various human models have been reported, most of them relate to the case where one human model is isolated in free space. However, in real situations, it needs to consider that more than two persons are exposed to the EM waves. In this paper, the average SAR and the local SAR of two cylindrical human models exposed to a plane wave or located near a line source are calculated. The results show that the SAR for two models is 1.5 times that of the isolated case. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(10): 1–8, 1998 [ABSTRACT FROM AUTHOR]

This paper discusses new pulse compression codes in which the modulation phase is monotonoically increased or decreased and the phase difference between the neighboring modulated codes is compressed to polyphase. In the proposed coding system, the sidelobe is small when the compression ratio is relatively low. Even in the high Doppler frequency region in which the pulse shape of the 13-bit Barker codes is largely deformed, the shape of the compressed pulse is stable and the sidelobe is always smaller than in the 13-bit Barker code. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(10): 41–49, 1998 [ABSTRACT FROM AUTHOR]

Slotted nonpersistent CSMA with an adaptive array is known to obtain high throughput when a number of terminals transmit data packets to a base station over a common radio channel. However, in this scheme, the terminals cannot begin to use a channel while the interfering packets are transmitted, even if the transmission of the acquired packet is complete. This causes throughput degradation. In this paper, we propose a slotted nonpersistent CSMA with an adaptive array and canceling signals to improve throughput performance. In the proposed model, the base station transmits a canceling signal to the terminals at the end of the transmission period of the acquired packet or at the time a failure occurs. The terminals cancel transmitting packets as soon as the terminals receive the canceling signal. We evaluate the throughput S and the average number of transmissions and schedulings G/S by theoretical analysis and computer simulation. It is shown that the proposed model attains higher S and smaller G/S than the conventional slotted nonpersistent CSMA with an adaptive array. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(10): 60–70, 1998 [ABSTRACT FROM AUTHOR]

This paper discusses the use of cell interleaving (CI) to compensate for cell losses in VBR video transmission. To bound the delay due to CI, we propose a CI method with variable interleave unit length. Since the effectiveness (gain) of CI depends on the additional redundant information amount (redundancy) and delay, the optimum redundancy which maximizes the gain and the relation between the delay and the gain need to be studied. Thus, the gain of the proposed CI when it is applied to VBR video transmission is analyzed as a function of redundancy and delay tolerance. The analysis yields the following results: In the case where 50 VBR video sources are multiplexed, the tolerated delay should be larger than 20 ms to yield positive gain, and provided that tolerated delay is 33 ms (one video frame interval), the optimum redundancy is achieved at around 0.22 and the maximum gain is 0.091. The gain becomes smaller as more video sources are multiplexed. In case 200 sources are multiplexed, the gain is negative even if tolerated delay is 33 ms (one video frame interval). © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(10): 81–90, 1998 [ABSTRACT FROM AUTHOR]

Numerous broadcast ATM switching networks have been proposed and studied so far, but most of them are constructed with symmetric switches, which have the same number of input and output ports. Transit switching networks may be symmetric, but local switching networks must be asymmetric, because the numbers of input ports and output ports of local switching networks are different. An asymmetric broadcast ATM switch can be constructed with copy networks and routing networks, which consist of a number of symmetric switches. Another type of broadcast ATM switch uses output buffer ATM switches. This type of switch can establish point to multipoint connections easily, and it can also be extended to an asymmetric switching network. This paper proposes an asymmetric switching network using output buffer switches and not using copy networks. Conventionally, an output buffer switch has good switching performance, but it requires large amounts of hardware. This paper proposes to reduce the switching network hardware size using concentrators, and by applying newly developed bus interface switches. It also presents the traffic performance and reduction of switching hardware for concentrating traffic. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(8): 59–67, 1997 [ABSTRACT FROM AUTHOR]

A cavity-backed slot antenna is thought to be one of the most suitable antenna elements for microwave energy transmission in solar power satellites. The objective of the work presented in this paper is to establish an effective design method by which we develop cavity-backed slot antennas used as elements in energy transmission antennas. For this purpose we use the finite-difference time-domain (FDTD) technique. Discretization schemes for the problem space, including an analyzed model in the FDTD method, make it possible to fully characterize antenna performance, including input impedance and the far field pattern. Compared with other techniques, the method takes account of the geometry of the antenna and the feeding element located in the cavity. In the paper we point out several problems in the FDTD analysis of the cavity-backed slot antenna and give solutions for them. Further, we discuss FDTD parameters in order to carry out the accurate analysis and evaluation of the antenna performance. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(7): 14–22, 1997 [ABSTRACT FROM AUTHOR]

Extensive research has been carried out on transform coding using the discrete cosine transform (DCT) for compression of digital video data. Improvement of the video quality has been brought about by an increased number of pixels, such that a reduction of the time required for coding per pixel is highly desirable. When the multiplier coefficients in the coding operation or the values of the basis coefficients of the DCT are expressed as binary numbers, it is possible to reduce the operating time and simplify the process by using as few bits as possible. It is necessary to consider the constraint that the picture quality of the reconstructed video image should not be degraded by the reduction of the number of bits. In this paper, it is shown that the number of bits of the basis coefficients can be reduced under this constraint if quantization of the transform coefficients is taken into account. Also, the limiting value of the decrease of the number of bits in specific coding examples such as JPEG is determined. Finally, it is confirmed that the quality of the reconstructed video image changes very little even if the basis coefficients are represented by fewer bits than in previous schemes, provided that the reduction is within the limit presented in this paper. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(8): 81–91, 1997 [ABSTRACT FROM AUTHOR]

This paper describes theoretically and experimentally the outer electromagnetic field of the two-layered helical coaxial line which is constructed on the ground. First, the relationships between a transmission constant, material, and the structural parameter of the two-layered helical coaxial line were formulated. Then the outer electromagnetic field was presented with a coupling impedance defined in each E and H mode. Although the effect of earth conductivity can be expressed with an equivalent current image of the earth, this paper proposes a new approximated formula, which can be applied to a surface wave mode having a large effective wavelength ratio. The H-mode has a smaller effect due to the earth conductivity compared with the E-mode. Thus it is obvious that large magnetic permeability of a magnetic core which excites the H-mode is effective in the enhancement and stabilization of an electromagnetic field. The convergence of an electromagnetic field along a line which is the feature of the to-layered helical coaxial line and the effectiveness of the approximated formula in this paper, were confirmed by the experiments taken for an externally constructed long line. [ABSTRACT FROM AUTHOR]

This paper discusses the hysteresis generator which is drawing attention as an autonomous chaos generator. However, this generator has not been discussed theoretically for its chaos generation mechanism. A fundamental hysteresis chaos generator is proposed deriving analytically the condition that chaos is generated in the circuit. The analysis of the circuit is performed by mapping procedure, and the Poincaré mapping is derived analytically as a one-dimensional mapping form the fact that the circuit is a second-order piecewise-linear differential equation. By calculating based on the mapping, the generation condition for the chaos is represented explicitly for the parameters. In this paper, the definition for the chaos is that the derived mapping has a unique absolutely continuous invariant measure and is ergodic. The generation of the chaos is verified by experiment. [ABSTRACT FROM AUTHOR]

This paper discusses the problems associated with the state equation approximation of linear shift invariant systems when a multi-input/multi-output system is given. First we present the approximation method to obtain the state equation for the system and then we present a method for stabilizing a rational function which is not physically stable. By iterative application of the approximation method we can always obtain a controllable, observable and physically stable system. The approximation method presented in this paper first considers a system which has multiple inputs and one output sequence and then makes minimum-order estimates of the sequences to the desired precision and arranges the output sequences in increasing order. We then approximate the state equations which satisfy the output sequence of lowest order and the multiple input sequences. This is a method of approximating the state equation for the second and subsequent output sequences by effectively employing the state variable already obtained. If at the approximation stage a physically unstable rational function is obtained, one can use the technique of first shifting the pole to form a stable function and then determine the coefficients of the numerator polynomial so as to minimize the squared sum of the errors in the output sequence. [ABSTRACT FROM AUTHOR]

Problems occur in the automatic routing for a gate array LSI. These include the logically equivalent terminals to be used for a net to be connected to any one of such terminals, and the vertical track of feed-through cell to be used for a net assigned to the feed-through cell. Since the routing area in such as LSI chip is predetermined, these problems are important in attaining 100% interconnection in each horizontal channel. This paper describes a heuristic algorithm for these problems, and experimental results of the algorithm are also shown to reveal its performance. [ABSTRACT FROM AUTHOR]