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This paper discusses a λ/4-type wave absorber for the microwave band made with conductive paper, which is paper with a coating of conductive material. A simplified wave absorber of this type is first designed and constructed for the X band and Ku band. Using the resulting absorption characteristics, experimental formulas are derived for the relative permittivity and surface resistance. These formulas are then used to design and construct a more practical wave absorber, whose absorption characteristics are measured. Excellent absorption characteristics, better than 20 dB, are verified in the intervals from 8.2 to 10.6 GHz and from 14.1 to 17.2 GHz for wave absorption in the X band and Ku band, respectively, although there is a difference of approximately 0.4 dB between the designed matching frequency and the measured value. Design guidelines for such a microwave absorber using a conductive coating are then presented. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(10): 100–107, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1180 [ABSTRACT FROM AUTHOR]

For a system comprised of multiple Web servers that provide the same content, this paper proposes a method for the dynamic selection of servers that process requests, based on periodically obtained load information on servers. Previously proposed methods select servers probabilistically based on the weights calculated from server load information, and consequently, a server with a heavy load is selected by chance, often resulting in decreased performance. In contrast, the present method, instead of employing probabilistic server selection, selects servers by a round-robin scheme after eliminating any difference in load among the servers. A comparison of performance based on simulation studies with the conventional method indicates that the proposed method is immune to the impact of the intervals at which load information is acquired or the number of servers involved, and that it produces a low average response time even under heavy load conditions. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(10): 1–12, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20309 [ABSTRACT FROM AUTHOR]

In feeding parallel plate slot arrays with plane waves propagating between parallel conductor plates, a dielectric plate lens or a parabolic cylindrical reflector is often used to generate the plane waves. Such a lens or a reflector requires a point source at its focus, since these lenses are designed by using a geometrical optics approach and actually are fed by H-plane sectoral horns. However, it is impossible to regard the horn as a point source, because its aperture is generally several wavelengths. Thus it is essential to determine the phase center of the sectoral horn in order to put the feeding system to practical use. Moreover, the lens and reflector are usually placed in the Fresnel region of the horn and are designed to operate at the widest feeding angle possible. In this paper a method to determine the phase center of the horn that is applicable in the wide angle Fresnel region is proposed, and several charts for its location are presented. This method is ascertained to be fully practical by means of several numerical and experimental investigations. A trial-fabricated plate dielectric lens and an offset parabolic cylindrical reflector were tested and found to operate approximately in accordance with the principles of geometrical optics, if their focii are arranged on the phase centers given in this paper. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(3): 28–38, 1999 [ABSTRACT FROM AUTHOR]

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

This paper proposes a beam pattern selection diversity technique using an adaptive array antenna. In the system using an adaptive array antenna, beam control in the uplink is carried out for all terminals in the cell. Hence, it is necessary to determine the antenna weights for all terminals at the base station, so that the amount of computation is increased and the base station configuration becomes complex in a cellular system that seeks to be capable of handling as many terminals as possible. In this paper, the beam patterns are generated only for a limited number of terminals in the cell, while other terminals share the generated radiation patterns, so that the amount of computation can be reduced substantially. In general, in a system using an adaptive array antenna, the interference suppression capability is significantly affected by the angle of arrival of the propagation channel. In this paper, the angle of arrival of the channel is modeled by a normal distribution and the proposed system is investigated in a micro-cell environment. As a result of numerical simulation, it is found that the proposed method can reduce the processing effort by 20% in the micro-cell environment, while the characteristics are sufficiently competitive with the results obtained when optimum radiation patterns are generated for all terminals. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 32–41, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10020 [ABSTRACT FROM AUTHOR]

As a method to obtain the baseband signal from each of several time division multiple access (TDMA) signals that are frequency-multiplexed in the uplink in wireless communication, this paper proposes a method of group demodulation using a multirate filter bank. The proposed method allows demodulation when the TDMA signals are asynchronously received in the uplink. Further, it can be applied to the case in which TDMA signals with different bandwidths are frequency-multiplexed, if the multiple resolution capability of the multirate filter bank is used. Hence, this method is useful in the situation where several different types of signals coexist in such environments as software radio. In the systems discussed in this paper, it is necessary to realize a sharp amplitude response and a linear phase response in the filters of the multirate filter bank with a small computational effort. This is accomplished in this paper by using an infinite impulse response (IIR) filter with approximately linear phase response. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(4): 44–52, 2002 [ABSTRACT FROM AUTHOR]

The packet-switched network design problem can be formulated as a capacity and flow assignment problem (CFAP). The CFAP of an elementary network consisting of one tandem switch (TS) and n local switches (LSs) has been analyzed, and economical configurations shown in previous papers. This paper extends the study to include cases in which there are constraints on circuit discreteness. A large-scale network usually employs a hierarchical structure with elementary networks used as structural units. In addition, the most economical structure of an elementary network in a hierarchical network is ascertained. The first assumption is that circuit speed is restricted to a predetermined discrete number (multiple of unit speed), and either one or no circuit can be installed per link. When the elementary network represents the entire small-scaled network, economical regions of star, mesh and combined star/mesh are complicated. This is because effective traffic packing to a discrete capacity circuit sometimes yields more economical network configurations. When the elementary network is a structural unit in a large-scale network, star occupies most of the economical region because a tandem circuit is always installed for carrying external traffic. The second assumption is that circuit speed is fixed. If a number of circuits can take real numbers, combined star/mesh is always the minimum cost topology in which internal traffic is assigned co the direct circuit, and external traffic through a tandem switch is assigned to the tandem circuit. When the number of circuits is a natural number, it is more economical in some cases to assign some part of the traffic to a tandem circuit because of the integrity of the number of circuits. [ABSTRACT FROM AUTHOR]

When the strip line containing a semiconductor material is illuminated by light with an energy larger than the band gap, the resistivity of the semiconductor changes and the control of the microwave propagation in the line cab be realized. For high-speed control it is necessary to use the semiconductor with short lifetime and to increase the intensity of illuminating light. In this paper, a fundamental study has been performed for the microwave modulator using photoconductivity. Strip lines suitable for this modulator are a coplanar waveguide and a slot line. This paper investigates the coplanar waveguide. An optimum structure is found the provides the strongest microwave attenuation for a given light intensity. The dependence on the frequency of the attenuation constant is also found. The analysis is based on the frequency of the attenuation constant is also found. The analysis is based on the spectral domain method. To confirm the usefulness of the modulator proposed here, the modulator has been made of Si and tested at 10 GHz is possible even with a light source such as a light emitting diode. [ABSTRACT FROM AUTHOR]

Numerous ways to analyze the pull-in range of the phase-locked system have been proposed. These include harmonic balance, the phase plane method and numerical analysis. In most of these methods, however, it was difficult to determine the actual pull-in range with high accuracy. This is because of the limitations in the applicable phase detector characteristics and loop filters, or the need to perform a complex numerical analysis. This paper proposes Galerkin's procedure to determine the pull-in range of the phase-locked system, demonstrating that the pull-in range can be determined with a high accuracy in a relatively simple way. Galerkin's procedure is a method of numerical analysis which can determine the periodic function for the nonlinear ordinary differential equation. By applying the procedure, the periodic solution of the second kind, corresponding to the out-of-lock condition of the system, is determined. From the critical input-output detuning for the solution to exist, the pull-in range is determined. From the critical input-output detuning for the solution to exist, the pull-in range is determined. This method can be applied to any phase-detector characteristics and loop filters, and by taking higher harmonics into consideration, a highly accurate solution can be determined. In this paper, as examples, the pull-in ranges are determined for a wide range of natural angular frequency and damping factor, for the phase detector characteristics which are sinusoidal, triangular, tanlock and sawtooth with fast jilter. [ABSTRACT FROM AUTHOR]

Conventionally, the problem of capacity-flow assignment in packet switching computer networks has been considered mainly for the purpose of improving the network performance and the effective usage of the resources in the networks. The problem of the fair allocation of the network resources to each user (fairness) has been investigated little. Because one of the most important purposes of the computer network is that a plural number are arranged dispersively in the network, we must make sufficient study of fairness in the problem of the flow assignment of the packet and the problem of the distribution of the line capacity. However, no clear definition of the fair allocation has been proposed to data. In this paper, we adopt the "power" (function) as the performance measure and discuss the problem of the network capacity-flow assignment in which maximized network power ensures effective usage of networks, and equalized power for each user realizes the fairness. The results of this study provide a new guideline to solve the problem of distributing the resources effectively and fairly. The method in this paper can be discussed generally without limitation of the network topology. However, since the concrete numerical calculation is so complicated, we take loop networks for the object of the analysis. [ABSTRACT FROM AUTHOR]

This paper discusses structural controllability for non-strongly connected networks, especially an electromechanical network connected by an energy conversion de- vice. The energy conversion device is non- linear and all other associated devices are linear. Thus, this paper considers the linearized state equation for studying the structural controllability in the neighborhood of an equilibrium point. Because of the nonlinearity of the energy conversion device, the coefficient matrix of the equation is decomposed into the product of matrices for graph incidence information and resistances and the matrix for element values other than resistances. The sufficient condition for the structural control- lability is characterized by using only the first of these matrices. It is shown that the sufficient condition for the structural controllability of the electromechanical network is that its equivalent electrical network graph have no capacitor-only cut- sets and no inductor-only loops. [ABSTRACT FROM AUTHOR]

The multifractal nature of traffic volume is known to have significant influence to queuing behavior in network nodes. In the Internet, TCP traffic, which is the major traffic flowing through the Internet has been reported to have multifractal nature. To control the effect of the multifractal nature, the origin of the multifractal nature in TCP traffic needs to be explained. However, it is still unclear what part of TCP control mostly affects the multifractal nature. In this paper, we focus on TCP congestion control from the viewpoint of multifractal nature of generated traffic. We investigate “what component of TCP congestion control mechanism affects multifractal nature of generated traffic?” Our simulation results show that Retransmission Time-Out mechanism plays an important role for multifractal nature of TCP traffic. In addition, our results show that avoiding occurrence of Retransmission Time Out is the best approach to improve TCP performance, i.e., throughput degradation, LRD, and multifractal nature. Random Early Detection (RED), based on the fact that Retransmission Time Out should be avoided, to improve TCP performance are also reasonable from the viewpoint of LRD and multifractal nature. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(1): 68–76, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20277 [ABSTRACT FROM AUTHOR]

An SCM optical FM method can obtain an FM gain, so it is effective on employing an RoF link which transfers a broad-band or multicarrier RF signal. However, the RF signal quality is degraded by intermodulation distortions due to the nonlinearity of LDs and optical frequency discriminator. The nonlinear compensation technique in the RoF link has been investigated in order to obtain a higher RF signal quality. This paper proposes an insertion-type distortion nonlinear compensation. In the proposed scheme, a nonlinear device is inserted between transmitter and receiver and we propose an optical chirp controller as the nonlinear device. The proposed scheme suppresses the higher order intermodulation distortion which degrades RF signal quality in the adaptive transmittance control method. In this paper we theoretically analyze the SFDR of the optical FM method using the optical chirp controller and show that improvement in the SFDR at 9 and 5 dB compared to methods without nonlinear compensation and the adaptive transmittance control method, respectively, can be obtained. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(12): 1–11, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20322 [ABSTRACT FROM AUTHOR]

This paper addresses the cases where a dipole is located near the boundary between two lossless media, and determines the equivalent permittivity for a homogeneous medium with matching the frequency characteristics of input admittance by means of the FDTD method. The paper reveals that the equivalent permittivity of the dipole near the boundary of lossless media consists of a complex number, and describes the behavior where the permittivity changes as a function of the gap between the dipole and the boundary. In particular, as the dipole leaves the boundary toward the medium with a lower permittivity, the equivalent permittivity changes discontinuously, indicating the asymmetric nature of the electric characteristics with respect to the boundary interface. Experimentally, the input admittance was measured when a monopole was placed near the boundary between a finite-size clay and air. Experimental results and the results of theoretical analyses are compared to demonstrate the validity of this paper. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(9): 60–67, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10232 [ABSTRACT FROM AUTHOR]

OFDM AMS/MTPC (OFDM-based Adaptive Modulation Scheme with Multilevel Transmit Power Control) using multilevel transmit power control schemes to set the modulation levels and transmitted power of each subcarrier of an OFDM (Orthogonal Frequency Division Multiplexing) system can significantly improve the throughput in an isolated cell environment. This paper takes advantage of the property that OFDM AMS/MTPC allows high throughput by using the frequency selectivity of the received SINR (Signal to Interference plus Noise power Ratio) in the presence of interference, and a one-cell reuse TDMA (Time Domain Multiple Access) system using simple wireless resource control is proposed. In this system, it is necessary to limit dynamic variations of the interference power level associated with transmit power control in such a way that control of the OFDM AMS/MTPC can be appropriately carried out depending on the interference among the cells. In this paper, it is confirmed that an effective cell reuse value of 1.46 can be achieved by optimization with regard to the application of diversity reception, the control period of adaptive modulation, and the spacing of the required SINR of the modulation level. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(12): 50–60, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20195 [ABSTRACT FROM AUTHOR]

The purpose of this paper is to speed up handover processing. The handover process is first analyzed. Based on the result of analysis, an extension of the protocol is proposed, in which adjustment of the timer value, a mechanism to report the link layer information to the network layer, and a speed-up of DAD processing are considered. The extended protocol is implemented. A problem in the operating system is identified by experiments, and solutions are presented. This paper also presents the tool constructed for the handover experiment, which produces a network shift at the desired time and timing. The handover time was measured and evaluated using the tool in an experimental environment, and it was shown that the handover time is drastically reduced compared to the system based on the standard IPv6 specification. The effect of the handover time on the application was evaluated, and it was demonstrated that the proposed method can realize handover with little effect on the application, although the environment is prepared by emulating wireless communications by cable communications. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(11): 44–53, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20213 [ABSTRACT FROM AUTHOR]

In the video and speech transmission using packets, the media synchronization control is applied, especially in the system for real-time transmission. In the system containing the media synchronization, the allowable time delay is defined, and the packet after this delay limit is discarded. In protocols such as ARQ (automated repeat request), where the packet retransmission is executed for error correction, if the delay or the error rate of the channel is large, the packet delay is greatly increased when an error occurs. The packet is discarded when the packet delay exceeds the allowable delay, which produces degradation of quality. This paper proposes an adaptive protocol relay system considering the allowable delay, in order to cope with this problem. In the adaptive protocol relay system, the protocol relay is executed at the relay node, when a certain condition for each packet is satisfied. By reducing the time spent in the packet retransmission due to the error, the number of packets that do not arrive at the receiving terminal within the allowable delay is reduced. This paper examines the effect of the protocol relay on the packet discard rate, when the proposed method is used. The condition for the adaptive control at the relay node is also discussed. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(8): 50–59, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10031 [ABSTRACT FROM AUTHOR]

FRN (flexible radio network) is an ad hoc network product that can realize a wide-area data collection network. This paper discusses a performance improvement method when TCP is applied to the transport layer in FRN. It is shown that even when the terminal is not moving as in FRN, the throughput can be improved in radio link failure due to noise or obstacles by combining ELFN (explicit link failure notification), which is proposed as a method for TCP performance improvement in ad hoc networks, with routing information. The proposed method is evaluated by simulation in this paper. A further objective is to reduce the performance degradation due to packet collision. The delayed ACK and the ACK retransmission with priority in the case of packet collisions are analyzed and the effectiveness of the method is demonstrated. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(11): 99–107, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10134 [ABSTRACT FROM AUTHOR]

In cellular communication systems, every call is carried through a base station, and when the communication path to the base station is obstructed by buildings or other obstacles, the communication may not be established. It is expected that ad hoc relaying of such an obstructed call will increase the performance of the network as a whole. This paper discusses how to theoretically analyze the communication traffic performance of a cellular system with ad hoc networking and shows that the network performance can be increased even with relatively small range of relaying capability of terminals. This paper also shows by simulation that multihop relaying does not give significantly greater performance improvement than that by two-hop relaying. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(11): 1–10, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10135 [ABSTRACT FROM AUTHOR]

ABT (ATM block transfer) has been considered an efficient protocol for high-burst data transmission in ATM networks. The characteristics of ABT in the ATM service class have already been investigated. For practical applications, however, it is necessary to consider an upper layer having its own congestion-control mechanism, apart from the ABT. This paper analyzes the characteristics of a TCP (transmission-control protocol) for the Internet which has become very popular recently, when this is used for the upper layer of the ABT. It is shown to be possible to separate the congestion control and the error-recovery service, since the congestion control is carried out effectively in the ABT by the retransmission mechanism of TCP, without using the congestion control of TCP. However, for high performance it is necessary to tune the retransmission timer of the TCP as discussed in this paper. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(1): 97–104, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1150 [ABSTRACT FROM AUTHOR]