bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning characteristics of spherical dome antenna composed of arcing dipole array antennas including the effects of mutual coupling between elements
Authors: Maeda Tadahiko , Sawaya Kunio , Adachi Saburo , Mushiake Yasuto
Published: July 2007

For a beam scanning at high speed over a wide angle, a dome antenna has been proposed. Past research on the dome antenna treated the dome parts as an ideal lens. However, the concrete arrangement of antenna elements outside and inside the dome and their mutual coupling have not been considered. Based on our past work on the electromagnetic field inside a concave spherical surface, this paper describes the results of analysis performed on the most fundamental dome antenna composed of arcing array antennas. For the array elements we considered dipole antennas. We obtained the radiation characteristics considering the mutual coupling among the elements of the radiators on the convex surface, the elements of the collector on the concave surface, and the coupling between the elements of the collector and the elements of the primary radiator. We determined the excitation currents in the elements of the primary radiator so that the currents in the elements of the radiator become co‐phase and uniform amplitude along the direction of the main beam. We obtained the radiation characteristics, and confirmed that over the range from 0 to 110°, beam scanning at almost a constant gain was possible. Next, we suppressed the levels of the sidelobes. We showed that up to a maximum of 18 dB, we suppressed the levels of the sidelobes compared to the co‐phase excitation. Finally, we discussed the influence of the mutual coupling between the elements of the radiator and the elements of the collector on the directivity.
Time sidelobe suppression for coded pulse compression via nonlinear optimization method
Authors: Nishimoto Shinkichi
Published: July 2007

In the pulse compression radar, it is necessary to suppress the time sidelobes which can cause a false alarm so that reliability of target detection is improved. For the pulse compression system to be adaptable for radar management which is considered to be important in recent years, it is indispensable that the radar waveforms be controlled flexibly by means of pulse compression. A method to this end can be provided by the pulse compression system using several random binary sequences with maximum entropy. However, since a coded sequence generated with a probabilistic manner is used in this method, both the time sidelobes and the mismatch loss tend to increase. Therefore, it is necessary to reduce both of them. From the forementioned viewpoint, in the case that the number of stages of the pulse compression filter is set equal to the code length, a method for deriving the filter coefficients realizing the minimum value of the peak time sidelobe level is analyzed as an optimization problem in the nonlinear programming. The pulse compression characteristics obtained by this method are described.
Multiring local area network system
Authors: Kanada Yoshihisa , Ikeda Tetsuo
Published: July 2007

The network interconnection technique is one of the keys for expansion of a local area network. This paper gives a performance evaluation of the multiring local area network system which consists of several token ring networks interconnected by using this technique. The result shows that this network system is better than the single‐ring network system, which is an ordinary token ring network, at heavy load operation. This paper also gives a performance comparison among three network interconnection topologies, “MESH connection,” “RING connection,” and “BUS connection,” and the optimum regions for these network interconnection topologies are suggested.
Low‐frequency crosstalk loss characteristics of balanced cables
Authors: Tomita Nobuo , Ohmura Makoto
Published: July 2007

The low‐frequency crosstalk loss characteristics are analyzed by a statistical method which derives the mean square of the crosstalk coupling. The theoretical formulas are derived for the near‐end and far‐end crosstalk losses in which mismatch terminations are taken into consideration. From both the theoretical and experimental viewpoints, the frequency dependence, terminal impedance dependence and cable length dependence of the crosstalk loss are studied. At low frequencies below a few tens kilohertz, both the near‐end and far‐end crosstalk losses decrease at the rate of 20 dB/decade for an increasing frequency. In the case of the terminal impedance of about 100 ω, the near‐end crosstalk loss decreases at the rate of 20 dB/decade for the increase of the terminal impedance. The far‐end crosstalk loss has a larger decreasing characteristic than this. Further, in the near‐end crosstalk, the crosstalk component at the far‐end due to the reflection at the cable end causes the cable length dependence in which the crosstalk loss decreases at 10 dB/decade for the increase of the cable length. In the case of far‐end crosstalk, the crosstalk of the forementioned far‐end is superposed on the intrinsic crosstalk. Therefore, the crosstalk attenuation decreases at the rate of 20 dB/decade.
A wideband sidelobe canceller for an earth station antenna
Authors: Takao Kazuaki
Published: July 2007

As Earth stations for satellite communication become smaller, the problem of interference with existing communication links becomes more serious. This paper proposes a technique to apply cancelling sidelobes to suppress such interference. A detailed examination of the location of auxiliary antennas was made to realize favorable characteristics to suppress the interference over a wide bandwidth. For an analytic study, a uniformly excited circular aperture antenna was assumed. Its characteristics for different sizes were obtained numerically. First, a case of the known arrival direction of the interfering waves was considered where only two auxiliary antennas are needed. However, their placement must be determined exactly depending on the arrival direction of the interfering waves and the diameter of the main antenna. If the arrival direction of the interfering waves is unknown, five auxiliary antennas are needed to achieve a fairly favorable interference suppression. To decide the optimum location of the auxiliary antennas, a normal projection of the two properly chosen antennas in the arrival direction of the interfering waves is required to coincide as closely as those for two antennas used in the case of the known arrival direction.
Analysis of microstrip antenna
Authors: Morishita Hisashi , Hirasawa Kazuhiro , Fujimoto Kyohei
Published: July 2007

A microstrip antenna is divided into an interior region and an aperture region contributing to the radiation. The structure is then analyzed by applying the transmission line model to the interior and the magnetic and electric currents are assumed at the aperture where the moment method is used. In the interior, transmission lines are combined into triangular meshes so that the loading of a circuit element is easily done, and the method can be applied to an arbitrarily shaped microstrip antenna. At the aperture, the magnetic current distribution is obtained by the moment method so that the effect of the external electromagnetic field can be taken into account. Computations are carried out for four types of antennas on an infinitely large ground plane. For the input impedance characteristics, magnetic current distributions and radiation patterns, the computed results agree well with measured data.
Rayleigh fading compensation method for 16qam modem in digital land mobile radio systems
Authors: Sampei Seiichi
Published: July 2007

To cope with the increasing demands for the land mobile communication with a limited frequency band, it is necessary to improve the spectral efficiency beyond the present state. QAM (quadrature amplitude modulation) is one of the effective means for this purpose. When QAM is applied to land mobile communication, however, a great distortion is produced in the envelope and the phase due to fading fluctuation. Because of this property, few discussions have been made on the application of QAM to land mobile communication. This paper proposes the following system for such an application. The fading distortion is measured from the periodically inserted known frame symbol. By interpolating the obtained time‐series, the fading distortion for all symbols is estimated. Then the distortion is compensated. The performance when the proposed method is applied to 16QAM is examined by computer simulation. It is seen as a result that the fading distortion can be compensated with high accuracy, making 16QAM applicable to land mobile communications.
A burst error tolerant synchronization method in an asynchronous transport system
Authors: Kitami Tokuhiro
Published: July 2007

This paper proposes a burst error tolerant synchronization method in an asynchronous transport system. In this method, the received original cell stream is branched off into several streams and these branched streams are then delayed differently so that the bursty errored periods in the resulting streams rarely coincide. The synchronization pattern is detected using these streams based on N‐out‐of‐M logic.

This technique is applicable to cell alignment using empty cells with synchronization pattern, as well as to frame alignment. The analyses include synchronization pattern detection probability, alignment recovery time, and misalignment probability performance. This method has the following advantages.

(1) It yields a highly tolerant performance against long burst errors because processing with signals at different time positions is introduced.

(2) Degradation caused by burst errors is reduced regardless of the synchronization pattern insertion probability.

(3) Alignment performance is considerably improved even for a simplified configuration with a majority‐logic synchronization pattern detection for only three branched streams.
Design of a multistage self‐routing switch with a distributed cell sequence control
Authors: Obara Hitoshi
Published: July 2007

As a technique for constructing the switch fabric in the ATM (asynchronous transfer mode) communication system, the self‐routing switching network has been proposed where the buffered Banyan network is used as the distribution network as well as the routing network. The features of this kind of switch are that it is of a distributed structure, being suited to the modular construction, the large capacity system can easily be realized, and the performance is stable for diversified traffic. On the other hand, it has a problem in that the order of the transmitted information (cells) is not preserved.

This paper proposes anew a switch construction with time stamps attached to the cells. The cell sequence is preserved by controlling the sequence of the time stamps, and the system can be controlled in a distributed way. The feature of the method is that the cell sequence is preserved while maintaining the self‐routing property of the traditional multistage buffered switch.

Also, the principle and the optimal construction are described. Basic system parameters such as the required word length for the time stamp signal are determined. The delay characteristics of the proposed system for various kinds of traffic are evaluated by a computer simulation.
Analysis of call admission control in the atm network
Authors: Arai Hideaki , Kawarasaki Masatoshi , Nogami Shinya
Published: July 2007

In the ATM network, where multimedia information such as voice, video, and data are transmitted in a unified way, it is very important to establish a control technique to secure the required network quality for the traffic with various speeds and bursti‐ness. A discussion is made for the ATM network to introduce the call admission control function based on the loss probability, instead of the flow control within the network.

This paper considers the situation where traffic with varous speeds and bursti‐nesses arrive, and discusses the call admission control for each call, to suppress the cell loss probability below a certain value.

First, a method is considered in which multimedia information is divided into the high‐speed and low‐speed media, and the two media are multiplexed. The cell loss probability is analyzed.

As the analysis model, MMPP/D/1/(1 +N) is employed, where the arrival follows the Markov‐modulated Poisson process. It is shown as a result that the peak‐bit‐rate of the high‐speed calls and the mean‐bit‐rate of low‐speed calls have greater effects on the cell loss probability.

It is shown also that the cell loss probability can be approximated by that of M/D/1/(1 +N) with the sum of the two fore‐mentioned parameters as the input traffic. Finally, a call admission algorithm is proposed and evaluated based on the result derived. The feature of the control method using this algorithm is that it is simple and easy to realize.
Channel assignment in a cellular mobile communication system and an application of neural networks
Authors: Sengoku Masakazu , Nakano Keisuke , Yamaguchi Yoshio , Abe Takeo , Shinoda Shoji
Published: July 2007

In cellular mobile communication, the same channel is shared by a number of cells. Up to now, the model has been considered where the same channel is used with a sufficient separation, so that the radiowave interference is sufficiently small for any call generated in the cell.

Recently, on the other hand, a model has been proposed where the same channel is assigned independently of the specified cell separation, as long as the carrier‐interference ratio is above a certain value. Although the assignment algorithm has been discussed for the traditional model, no report has been made on the detailed assignment procedure for the new model.

With such a situation as the background, this paper proposes an application of Hopfield's neural net as an approach to the channel assignment in the new model and derives the energy function. Several results of computer simulation are shown where the proposed neural net is applied to the mobile communication model. It is not always true that the neural net produces the optimal solution, but it is interesting that an unexpected improvement of the channel utilization is observed in the communication traffic as far as the result of computer simulation is concerned.
Object‐oriented switching program structure
Authors: Maruyama Katsumi , Kubota Minoru
Published: July 2007

Public switching systems are severely real‐time and multiprocessing, very large, long‐lived, and frequently modified. Programs that control switching systems therefore are required not only to have run‐time efficiency but also to be easy to maintain and expand.

This paper proposes a concurrent object model and an object‐oriented switching program structure. The concurrent object model ensures simple and efficient real‐time multiprocessing. Also, it allows logical switching components to be implemented as “objects” in software, and the structure of the program coincides with the structure of the logical model. The program structure proposed here uses distributed call processing, which allows building‐block structured switching systems. A prototype switching program confirmed the effectiveness of this approach and showed that the static and dynamic overheads are within the capacity of present VLSI technology.
Design of a folded banyan switching network with by‐pass links using a distribution cell sequence control
Authors: Okamoto Satoru
Published: July 2007

The asynchronous transfer mode (ATM) is considered to be important as a key technology in realizing a broadband ISDN that can handle diversified services in a unified way. The high‐speed burst multiple transmission system using ATM is proposed. This paper considers the folded Banyan network with by‐pass links which is proposed as a cross‐connect switch to be applied to the cross‐connect MUX of the high‐speed burst multiple transmission system. A routing method that preserves the time sequence of cells also is proposed and its cell transfer performance is analyzed.

The proposed routing method is realized by a distributed control. It is shown that the method can be applied at the same time preserving the features of the folded Banyan network with by‐pass links, which are the unified modularity and the expansion without interruption. For the performance evaluation, a method of analysis is presented which improves the approximation of the traditional analysis of the cell loss rate.
Polarization diversity detection performance of 2.4 Gbit/s CPFSK heterodyne system
Authors: Hayashi Yoshihiro , Ichihashi Yasutaka , Imai Takamasa , Yanai Daisuke , Ito Takeshi
Published: July 2007

In the practical implementation of the coherent optical transmission system, it is important to establish the techniques for stabilizing the optical frequency considering the actual environmental condition, as well as a technique for compensating for the variation of the state of polarization in the usual single‐mode optical fiber cable.

This paper considers the application of the polarization diversity receiver to the CPFSK heterodyne delay detection in the 2.4‐Gbil/s band and discusses the construction and performance. The regenerative repeater equipment is designed in a compact form to be implemented in a commercial rack (INS cabinet rack). Using the designed equipment and the existing trunk fiber transmission route, an experiment in the actual site is conducted and the results are shown.

The first part of this paper presents the construction of both the automatic frequency control (AFC) system and the automatic gain control (AGC) system suited to the polarization diversity system. The design guides are presented for the required frequency response speeds of AFC and AGC, the required frequency stability of AFC, and the response performance to the fluctuation of polarization. A high‐output, high‐sensitivity 2.4‐Gbit/s regenerative repeater equipment (with repeater gain above 48 dB) is realized with the overall performance that the variation of optical received sensitivity against the polarization fluctuation can be suppressed to within 0.5 dB.

Finally, the stable operation of the equipment is verified by the experiment at the actual site, and the practical usefulness is indicates.
Cost‐effective configuration for large‐scale optical distribution system utilizing optical fiber amplifiers
Authors: Matsuura Masaaki
Published: July 2007

This paper investigates the cost‐effective optimum configuration of large‐scale optical distribution systems utilizing optical fiber amplifiers.

First, the relation between network topology and the number of equipment is discussed. It is shown that in low‐loss optical fiber distribution systems, the tree configuration is more advantageous than the bus configuration from the viewpoint of required optical fiber amplifiers.

Next, the relation between the network topology or distribution scale and the cost of each equipment is investigated. It is shown that when the cost of the fiber amplifier dominates, the tree distribution system with multilayer structure divided properly into subsystems is the optimum one. It is clarified that the structure with a large number of layers and the minimum number of segments in each layer is the economical configuration.
A study on a TDMA system with dispersive delay lines
Authors: Miyauchi Kazuhiro , Hangai Seiichiro , Mizoguchi Masato
Published: July 2007

This paper discusses a satellite TDMA system with two dispersive delay lines of opposite characteristics in earth stations and in the satellite transponder to reduce the peak transmitting power of the earth stations. Reduction effect is estimated for available SAW devices and the reduction in peak transmitting power of about 27 dB is achieved in the single‐pulse transmission mode.

In actual TDMA systems, however, burst pulses must be transmitted and bursts of about 1000 symbols in length are used. Since only relatively short bursts (about 20 symbols long) are allowable in this system, various study subjects are discussed to realize it, such as the increase of burst length, reference time establishment at earth stations, modulation/demodulation and clock recovery.

The effects of several kinds of system impairments, such as residual response of modulator, effect of characteristic deviation of dispersive delay lines, and dynamic range of receiver amplifier of transponder are studied.
Performance of CMA adaptive array optimized by the marquardt method for suppressing multipath waves
Authors: Fujimoto Mitoshi , Kikuma Nobuyoshi , Inagaki Naoki
Published: July 2007

Constant modulus algorithm (CMA) adaptive array has been proposed as a countermeasure to frequency selective fading; but since the evaluation function is nonlinear with respect to weight, the conventional steepest gradient method is being used for optimization. However, if there is a large variation in the eigenvalue of the correlation matrix of the input, then the convergence becomes very slow.

In this paper, Marquardt's method of optimizing the CMA adaptive array is proposed. This method is based on a nonlinear least‐square algorithm, and its dynamic characteristics are clarified by computer simulations.

First, the fundamental characteristics of the algorithm are investigated. It is shown that this algorithm gives satisfactory convergence even for those cases where the convergence performance of the conventional steepest gradient method has degraded and where waves approach by multiple paths.

Next, the performance of the algorithm is studied under the influence of Doppler shift or in the case where the wave conditions vary and satisfactory performance is obtained under frequency selective fading environment.
A multimedia intelligent message communication system for distributed coordination environments
Authors: Hattori Shinmi , Kuramoto Keisuke , Nakazawa Minoru
Published: July 2007

This paper proposes a new multimedia message communication system. This system is strongly integrated with deskwork operation by multiple polymorphism of object‐oriented construction in a distributed computer resource OA environment consisting of networks, personal computers, and workstations.

Here, a message communication system and desk‐work system are regarded as a means of processing mail with undecided/decided boxes as start/end points. Further, automated generation of an individual action schedule and response mail has been implemented by using a distributed coordination algorithm of 1: N conversation element module with knowledgebase of individual action status, and its application to automated and personalized secretary work in OA environments has been studied.
Generation of efficient test sequences from lotos specifications
Authors: Okazaki Naonobu , Noguchis Shoichi , Takahashi Kaoru , Shiratori Norio
Published: July 2007

LOTOS is a formal description technique (FDT) developed by ISO. This paper proposes a formal technique for generating test sequences from a LOTOS specification. In the proposed technique, test sequences correspond to a finite “tree” which is represented as a TreeLOTOS expression which is a subset of LOTOS. A labelled transition system (LTS) with variables called VTS is introduced to generate test sequences, which is useful not only for compactness of expression but also for effective selection of test sequences at the execution of tests. Furthermore, the concept of the reduced form of a VTS is introduced and, by using this concept, efficient test sequences can be obtained.
Switched snubber for high‐frequency switching converters
Authors: Sakamoto Hiroshi , Noguchi Seiichi , Haradas Koosuke
Published: July 2007

This paper proposes a switched snubber circuit for the switching converter. The switched snubber is made of a series connection of a switch and a capacitor. The switched snubber can suppress the surge over a wide range of duty ratio and is basically lossless. The switched snubber features zero‐voltage switching. A PWM controllable and low‐stress converters are developed by replacing the resonant capacitor with a switched snubber in the voltage‐mode resonant converters. Also, the region where the output voltage increases abnormally is narrow in the converters with a switched snubber.
Analysis of parallel plate mode in slot‐coupled microstrip antenna
Authors: Iwasaki Hisao , Shoki Hiroki , Kawabatas Kazuaki
Published: July 2007

In the electromagnetic slot‐coupled microstrip antenna in which a triplate transmission line is used and a patch antenna is fed via a slot on the ground plane, a parallel plate mode (TEM wave) propagating between the ground planes is excited so that a power leakage causes unwanted coupling and radiation.

This paper studies the Poynting power and the electric field of this parallel plate mode. The amount of the parallel plate mode generated and the propagation behavior are investigated analytically by means of the Spatial Network Method. The method for installing shorting pins known for their suppression of the parallel plate mode is studied in its relationship to the generation of the parallel plate mode.

A method for placing pins with a least number of pins is proposed. The relationship between the resonance of the parallel plate mode and the external dimensions of the dielectric substrate comprising the triplate transmission line is studied experimentally. It is found that the resonance of the parallel plate mode coincides with that of an open resonator with its dimensions identical to a finite dielectric substrate comprising the triplate transmission line.
Error performance of two decision schemes for frequency‐detector gaussian minimum shift keying (gmsk) on a frequency‐selective fading channel
Authors: Shibata Koji
Published: July 2007

In high‐speed digital mobile communication systems, one of the most spectrally efficient modulation methods is Gaussian‐filtered minimum shift keying (GMSK). In this paper, two decision schemes of frequency‐detected GMSK under frequency‐selective fading are compared theoretically from the viewpoint of bit error rate (BER) performances.

The GMSK signal which is encoded differentially has an eye pattern with three levels; and, by using the characteristic, the offset decision is made. The BER performances of the offset decision method are compared with those of the conventional one which is based on the eye pattern with two levels.

Under the frequency‐selective fading, which is characterized by a two‐ray model, the BER performances for BbT = 0.20 with the offset‐type decision are superior to those with the conventional one when normalized rms delay spread (τ/2T for two‐ray model, τ: delay spread) is less than 0.10.

By using the post‐detection selection diversity with two diversity branches, we can reduce the degradation of signal energy per bit to noise power spectral density ratio with the offset decision greater than that with the conventional one for τ/2T < 0.20.
Diffraction control and improvement of interference characteristics by beam shaping
Authors: Yonehara Satoshi , Takano Tadashi
Published: July 2007

The diffraction phenomenon usually degrades the extinction and signal‐to‐noise (S/N) ratios of optical devices which utilize the interference of light beams. In this paper, the use of spatial filters to shape the field distribution in the cross section is proposed as the method by which the degradations due to diffraction effects can be reduced. The beam shape and the diffraction characteristics are shown experimentally to be improved due to two types of filters with Gaussian and trapezoidal transmission profiles in radial direction.

In fabrication of the filters, due to the difficulties in the control of the deposited film thicknesses, the transmission characteristics are deviated from the designed ones. However, the extinction ratio is shown to be almost doubled using the realized filters.
Optical fiber amplifiers for optical amplitude‐modulated vestigial sideband transmission systems
Authors: Shigematsu Masayuki , Kashiwada Tomonori , Nishimura Masayuki , Kanamori Hiroo , Okitas Toshio
Published: July 2007

An optical fiber amplifier for an optical amplitude‐modulated vestigial sideband (AM‐VSB) transmission system has been developed. Various pumping methods in an Er‐doped optical fiber for a high‐power and low‐noise performance are discussed. The bidirectional pumping method was found to be the best. A high‐performance Er‐doped optical fiber has been fabricated, and an optical amplifier has been made with it. The loss budget of 14 dB was obtained in 40‐channel transmission with 51‐dB carrier‐to‐noise ratio (CNR) by using this prototype optical amplifier, which is 6 dB better than before.
High‐speed lan architecture based on b‐isdn technology
Authors: Takiyasu Yoshihiro , Amada Eiichi , Hatakeyama Yasuhiko
Published: July 2007

Multimedia backbone local area networks (LAN) have recently become key components of private networks as fiber distributed data interface (FDDI) backbone LANs. This paper discusses the architecture of loop‐type high‐speed multimedia backbone LANs (MBLANs) based on B‐ISDN technology as the next generation LAN targeting the introduction stage of the B‐ISDN age and its realization.

This paper highlights problems to be solved with respect to the adoption of B‐ISDN technologies, such as synchronous digital hierarchy (SDH) and asynchronous transfer mode (ATM) technology, to MBLANs and proposes some solutions. It also presents high‐speed MBLANs with transmission rate of 622 Mbit/s and the basic hardware implementations of the system.
Signal‐detection characteristics in trellis‐coded modulation system under impulsive noise environment and its optimum reception
Authors: Miyamoto Shinichi , Morinaga Norihiko , Katayama Masaaki
Published: July 2007

This paper investigates the performances of the trellis‐coded modulation (TCM) systems under impulsive noise environment. Conventionally, receivers for a TCM system have been designed based on Euclidean distances between signal sequences assuming their use under Gaussian noise environments. These receivers are not suitable for impulsive noise environments having statistics significantly different from Gaussian noise and thus designs based on the statistics of impulsive noise are needed. The error event probability characteristics of TCM signals received by conventional‐type receivers have been obtained, and it has been clarified that coding gain is obtained even under impulsive noise when the carrier‐to‐noise power ratio (CNR) is sufficiently large, and there is a range of CNR at which the error event probability characteristics of TCM signals become worse than those of uncoded signals.

Next, it is shown that the error event probability characteristics of TCM signals are inferior to those of the case in which uncoded signals are received by optimum receivers designed by considering impulsive radio noise. In addition, it has been shown that optimum receivers for TCM systems under impulsive radio noise can simply be constructed by adding a number of circuits to conventional‐type TCM receivers, and their performances exceed those of the case in which uncoded signals are received by optimum receivers at any CNR and great coding gain is obtained.
An er‐doped fiber active switch controlled by coded pump light
Authors: Sato Yoshiaki , Aida Kazuo , Nakagawa Kiyoshi
Published: July 2007

In this paper, a new optical matrix switch using Er‐doped fiber amplifiers is reported. The Er‐doped fiber amplifier acts as an optical gate, depending on the presence or absence of the pump light. The pump light may be a pulsed light whose repetition period is shorter than the fluorescence lifetime. Here the pump light contains interconnection information as a code, and an optical matrix switch where the pump light is distributed through an optical decoder to multiple optical gates is proposed. As a result, an optical matrix switch where the interconnections may be changed by changing the code became possible.

In experiments, first, a basic optical gate characteristics were investigated. Using a 20‐mW pump light, the isolation for ON/OFF was 35 dB in the optical gate. In optical gates pumped by pulsed light, it was clarified that there was no influence on the signal light when the repetition rate of the pump light is above 5 kHz. Next, from the above conditions, a 1 × 2 optical switch using an acousto‐optical deflector for the optical decoder was constructed and the switching operation controlled by a coded pump light was demonstrated. The extensibility of matrix size was also investigated; and, by a combination of the proposed switch configuration and Clos‐network construction, it was found that a realization of a 225 × 225 optical matrix switch was possible.
Optimized bandwidth of optical filter in optical preamplifier
Authors: Kinoshita Susumu , Okiyama Tadashi , Kuwahara Hideo
Published: July 2007

It has been demonstrated that the receiving sensitivity in the direct detection scheme is significantly improved by using an optical preamplifier. The bandwidth of an optical filter plays an important role in the characteristics of such an optical preamplifier. Therefore, in this paper, a method to optimize the optical filter bandwidth by taking into account the wavelength tolerance is presented. First, the noise figure is found to increase due to the relative increase of the ASE power compared to the signal optical power on detuning, if we consider the tolerance of the wavelength and the spectrum of the filter. Second, the increase in the noise figure is expressed in terms of the equivalent noise bandwidth of the ASE‐ASE beat noise and is compared with the experimental result obtained for the various detuning values. The optimized bandwidth which keeps the preamplifier noise level low even for the maximum detuning is determined. For example, for a Lorentzian‐type optical filter spectrum, the full‐width at half‐maximum (FWHM) is 3.46 times larger as compared to that at the maximum detuning. Also, a preliminary study on the intersymbol interference due to the detuning in a 2.4 Gbit/s intensity modulation‐direct detection system was conducted; it was found that the intersymbol interference can be neglected for a Lorentzian‐type filter spectrum with FWHM 1 nm.
A mathematical model for evaluation of overload traffic in communication networks
Authors: Ohta Masataka
Published: July 2007

With the advent of the information age, congestion of communication networks due to natural and social phenomena occurs more easily, and coping with this overload traffic is necessary.

In this paper, a mathematical model for evaluating overload traffic is presented, and methods for using this model to evaluate overload traffic are shown. Since the state of a congested network varies with time, the transient behavior of the traffic needs to be analyzed. However, it is impossible to conduct the analysis by means of existing methods because of the enormous amount of computations required. Therefore, by regarding the traffic in a congested network as deterministic, an approximate solution, by means of deterministic equations, is proposed in this paper.

The transient analysis of the throughput and overflow rate of networks with finite resources can be evaluated by means of this approximate solution. In accordance with the proposed model, the methods to compute the call blocking probability, which is used to evaluate the network robustness against temporary overload, and the throughput in circuit‐switched networks are shown. It is possible to compute the number of resources (i.e., buffers) which is appropriate for a given blocking probability considering the robustness of the network against congestion. The maximum throughput of the network can also be evaluated with transient analysis of the throughput.
Transient response of resistively loaded dipole antennas for pulse radar
Authors: Kominami Masanobu , Takagi Tohru , Sawa Shinnosuke , Kikuta Takashi
Published: July 2007

To improve the coverage and the resolution of the baseband pulse radar system, it is important to predict accurately the characteristics of the transmitting and receiving antennas due to a pulse and the electromagnetic transient field scattered by a target.

In this paper, a moment method and Fourier transform are presented to solve the problem of transient coupling between two orthogonally and resistively loaded dipole antennas and a thin‐wire target, both placed in free space.

Numerical results show that if resistances with optimum values are loaded in both arms of the dipoles, the multiple reflections arising between their ends and their feeder can greatly be suppressed. Based on these results, the coverage method for such a pulse radar system using resistively loaded dipoles as well as the near field patterns at the first resonant frequency are examined.
A radial line slot antenna without a slow wave structure
Authors: Member Katsuei Ichikawa , Takada Jun‐Ichi , Ando Makoto , Goto Naohisa
Published: July 2007

The radial line slot antenna is a thin circularly polarized antenna intended for satellite broadcast reception, and is expected to be highly efficient in principle. To improve the efficiency, it is necessary to suppress the grating lobe in the 90‐deg direction by means of a slow‐wave structure in the antenna. To this end, styrofoam is mainly used. However, it is more appealing to find a structure without any dielectric material from the viewpoint of heat resistance, fluctuation of the permittivity, and fabrication cost.

This paper proposes a radial line slot antenna without a slow‐wave structure in which the wavelength reduction phenomena due to slot coupling analyzed quantitatively are used intentionally. From the analysis, the antenna gain is derived as a function of the antenna thickness (waveguide height), which is the principal parameter for the wavelength reduction effect. It is demonstrated that the grating lobe can be suppressed. Also, by means of an experiment, the antenna efficiency of 61 percent is attained in a hollow configuration so that the viability of this approach is proven.
Throughput analyses of packet radio communications systems
Authors: Hara Shinsuke , Morinaga Norihiko
Published: July 2007

Collision of packets is inevitable and is a problem in contention‐type random access systems. In radio systems, however, the throughput of the systems is improved as a result of the capture effect on power differences between colliding packets caused by propagation characteristics of channels such as fading, shadowing, and distance problems.

In this paper, analyses are made of the capture effect by considering channel characteristics of radio channels and modulating and demodulating schemes. First, a theoretical equation for the packet reception success probability of the ALOHA system under frequency nonselective slow Ray‐leigh fading has been derived, and the validity of this equation has been proven by computer simulation. Thus, throughput characteristics of slotted ALOHA and pure ALOHA system have been analyzed by means of this theoretical formula. In addition, it has been proven theoretically that the channel capacity of the ALOHA system is improved two times by the capture effect for the case of a large number of mobile stations and high mean power versus noise power ratios.
Improvement of traffic bias characteristics and acknowledgement method for MULTISTAR LAN
Authors: Saito Tadao , Aida Hitoshi , Ooi Eng‐Theam , Tomiyama Tadahiro
Published: July 2007

MULTISTAR was proposed as a system to improve header‐driven storageless (HDSL) local area network (LAN) to transmit simultaneously more than one frame, but it has a problem in that the throughput is deteriorated for the high or biased load.

This paper presents two improvements for MULTISTAR LAN: One is that the tournament switch is devised as a means to realize the multiinput arbiter and is used instead of the input arbiter; and the other is that a system is devised where the central node can notify the passage of a packet to the originating side. The performances of those two new MULTISTAR configurations are evaluated by simulation. It is then demonstrated that the system implementing those new ideas exhibits a drastic improvement in the efficiency, compared to the original MULTISTAR LAN.
Coding of motion compensation prediction error signal
Authors: Shishikui Yoshiaki
Published: July 2007

This paper discusses the properties of the motion‐compensating prediction error signal and the appropriate coding scheme. For a high‐efficiency coding of the moving picture, generally, a method combining the motion‐compensating prediction and the spatial coding such as discrete cosine transform (DCT) is used. It is shown that the spatial coding used here is effective for the input picture signal. On the other hand, the motion‐compensating prediction error signal has spatial properties which are considerably different from those of the input picture signal. For example, the correlation between pixels is small, especially in the vertical direction, or the magnitude of the correlation locally fluctuates greatly. Consequently, such signal transformations as the orthogonal transform and subband partition are not effective in the motion‐compensating prediction error signal.

This paper analyzes the correlation between pixels to reevaluate the traditional coding schemes and to propose the adaptive coding scheme with and without signal transformation. It is shown that the proposed scheme can prevent the deterioration of the picture quality found in the traditional schemes while retaining equal or better rate‐distortion performance than that of the traditional scheme.
A method of image reconstruction for snow search radar using an estimated permittivity of snow
Authors: Mitsuhashi Ryuichi , Aoki Yoshinao
Published: July 2007

For the image reconstruction of the snow search radar based on the principle of multifrequency holography method, the values of the relative permittivity of snow to be interrogated are needed. Since the relative permittivity of snow changes by various factors, it was necessary to measure it by some means at the same time as the search. The relative permittivity of the snow with low water content which is the medium of the snow search radar has a strong correlation with the density of the snow. Hence, the relative permittivity was estimated by measurement of the density in the past.

To eliminate such a procedure, it is necessary to estimate the relative permittivity of the snow from the multifrequency hologram which comprises the data obtained by the snow search radar. In the multifrequency hologram, the information along the frequency axis and that on the azimuth axis are recorded independently. In addition, the distance information in each axis varies in the direction opposite to that of the change of relative permittivity. This property was used for automatically estimating the relative permittivity of snow by discriminating the focusing of the reconstructed image.

In this paper, a method is presented for estimating the relative permittivity of snow from the data of the snow search radar. The results are given for processing of actual data.
An atm connecting network—the batcher‐cyclic bus network
Authors: Choi Myung‐Hun , Asano Shoichiro , Ji Yusheng
Published: July 2007

There have been many studies on switching networks using ATM switching machines. With regard to cell loss, methods of reducing the rate of loss of cells within the connecting network, methods of reducing loss of cells by accumulating cells of the same route in buffers introduced to the output circuit line, etc., are being studied. As an example of the latter, knockout networks characterized by buffer control using bus‐type switching networks have been proposed and considered as one of the useful systems. Such knockout networks, however, are known to have the disadvantage of an increased number of switches. In this paper, a new ATM switching network having a smaller number of switches than knockout networks is proposed and its traffic characteristics are clarified.
Adaptive recursive least‐squares maximum‐likelihood sequence estimation with higher‐order state variable model of radio channels—adaptive performance improvement of rls‐mlse
Authors: Fukawa Kazuhiko , Suzuki Hiroshi
Published: July 2007

Superior tracking performance for fast fading mobile radio channels is obtained by extending channel models used in the adaptive recursive least squares maximum likelihood sequence estimation (RLS‐MLSE) derived from the theory of maximum likelihood signal estimation. Conventional adaptive maximum likelihood sequence estimators used the simple Markov model or random walk model to describe fluctuations of the impulse response of a frequency‐selective fading channel.

In this paper, a second‐order Markov model that incorporates the first‐order time derivative of the impulse response is used. This higher‐order state variable approach improves the adaptability of the channel estimation algorithm and gives a significant improvement in signal transmission performance. Computer simulations show that the RLS‐MLSE based on this higher‐order state variable model yields good performance of 40 kbit/s QPSK with the maximum Doppler frequency up to 160 Hz.
Effect of reduction of mobile communications co‐channel interference by transmission power control considering received signal level correlations
Authors: Fujii Teruya
Published: July 2007

In a small‐zone mobile communications system that reuses the same frequencies in geographically different places, the margin for interference required to obtain a required call quality (CIR margin) can be reduced when there are correlations between geographic variations of the desired and interfering waves in comparison to when there are no correlations.

In a sector zone configuration allowing the arrival directions of desired and interfering waves to be the same direction, correlational relationships can be expected in the downlink circuit, while such relationships cannot be expected in the uplink circuit since the topographical and geological factors affecting the mobile stations are clearly different.

In this paper, it has been clarified analytically that when there are correlations between geographic variations of desired and interfering waves of the downlink circuit, the CIR margin can be reduced even in the uplink circuit as well as in the downlink circuit by using adaptive transmission power control (ATPC). Next, the direction connecting the base station and the reception point is defined as the direction of arrival of the electric current and the correlational relationships between the arrival angle difference and the received signal level were studied on the basis of propagation test results, considering the differences in angles of the directions of arrival of desired and interfering waves in the downlink circuit (referred to as the arrival angle differences). In addition, the relationships between the spatial frequency utilization rate (spectrum efficiency) and the sector zone divisions of a wireless zone, closely related to the arrival angle differences, in a six‐wave interfering system having six interfering zones have been clarified.
Performance comparison of high‐speed ring networks with nodes of finite buffer capacity
Authors: Fuwa Yasushi , Tasaka Shuji
Published: July 2007

This paper analyzes the performance of a number of MAC protocols in high‐speed ring‐type networks and determines the suitable region for each protocol. The authors previously have evaluated the slotted rings, register‐insertion rings and register‐insertion‐type slotted rings, and begin with the analysis of the token ring in this report. To compare the results of the various analyses, the models of each MAC protocol are constructed under the same set of conditions and evaluated with the same method (EPA). Since the nodes of each model are assumed to have buffers to finite capacity, the discussion of buffer overflow is made possible. The results obtained from analysis matched closely with simulation results verifying the accuracy of the analysis. The MAC protocols also are analyzed under high‐speed network conditions, and a comparison of the results reveals the most suitable protocols for various environments keeping in mind the issue of buffer overflow.