Search

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]

This paper considers a network in which one of the links is the bottleneck of communication, and the speed of that link is upgraded. A simple method of calculation is proposed for the effect of the upgrading on the throughput of the TCP communication passing through the link. As the first step, a formula for the TCP communication throughput is proposed, which is a function of the mean window size of the TCP flow control, the round-trip time, and the loss ratio of the packet. The waiting time in the router, which is the major factor determining the round-trip time, is approximated by the M/M/1/m queue. By combining those two expressions, the change of the throughput by upgrading the link speed is calculated. In order to verify the validity of the throughput calculation and the router model, the change of the TCP communication throughput in upgrading the speed of the bottleneck link is calculated, and the result is compared to the result of actual measurement in the experimental network composed of PPP and Ethernet. It is seen that the model proposed in this paper agrees well with the actual measurement although it is simple. The method is applied to the network between Mie University and SINET. The effect of the link speed upgrading on TCP throughput is examined and verified. The result obtained in this paper is expected to be useful in the network design, in estimating the link speed required in dissolving the bottleneck. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(1): 65–73, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1147 [ABSTRACT FROM AUTHOR]

Self-healing has been investigated as a technique for efficient path failure restoration in VP-based networks. This paper discusses self-healing in networks with multiple reliability classes, and evaluates restoration performance of different failure recovery procedures that introduce priority orders in the failure recovery process based on the reliability class for each failed path. The authors present a composite-type restoration procedure in which preplanned-type and flooding-type procedures are combined. This paper also presents a bumping added-type restoration procedure. The authors evaluated the performance of the above proposed techniques assuming various failure modes. The simulation results revealed that the proposed methods show improved performance. In addition, we propose an enhanced technique that introduces a subsidiary priority criterion in the paths belonging to the same reliability class, in order to increase the number of paths to be recovered. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(7): 1–17, 2001 [ABSTRACT FROM AUTHOR]

This paper discusses a cell loss recovery method using FEC. The technique applies VP-based FEC and recovers discarded cells that were lost because of buffer overflow at the ATM nodes in the transport network. This paper presents the FEC code format and analyzes the performance, with emphasis on the design of coding matrix and FEC code. Next, an improved structure is presented in which FEC is applied only to the paths with higher quality requirements. This improves loss recovery performance at higher traffic load and reduces coding matrix size. The analyses also include the aggregate processing delay in the cell multiplexer and FEC codec. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(3): 77–88, 2001 [ABSTRACT FROM AUTHOR]

The information possessed by many individual users connected to a large-scale network can be considered as a gigantic database, termed a superdistributed database. To date, effective methods of searching scattered information in such a superdistributed environment have been proposed. The problems are different between the cases where the number of information items to be searched for in the network is 1 or unknown. For both cases, the method proposed in this paper can measure the search effect in terms of evaluation quantity taking into account the communication cost and the time cost. Accordingly, the search considered most effective at that time point is repeated. In this paper, the optimum nature of the proposed search method when either the communication cost or the time cost is taken into consideration is proven. In addition, the characteristics of this method are analyzed for general cases and it is shown that the communication cost and the time cost can be reduced. Next, the effect of the error in the existence probability of the information to be searched at each node in the network is discussed. It is shown that the effect is small in the proposed method. Further, an approximate search procedure with a reduced amount of computation is proposed. It is demonstrated that the effect obtained is similar to those in the search methods presented to date. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(7): 15–25, 2000 [ABSTRACT FROM AUTHOR]

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

With the development of mobile communication, active research is being done on the small-sized antennas such as microstrip antennas (MSAs). Moreover, MSAs normally are placed on spherical or cylindrical surfaces as a conformal antenna. Conformal MSAs are expected to have different characteristics compared to planar structure. In this case, numerical analysis is needed before the actual experiment. The method of analysis which has wide applications may be considered as efficient for this purpose. One such method is the conformal grids finite-different time-domain method (FD-TD method). In this paper, an MSA on a curved surface is analyzed using the conformal grids FD-TD method. Moreover, comparison with the experimental values also is performed. The experimental results and the analytical results ate in close agreement which shows the validity of the method of analysis. As a result, it is confirmed that in the range of this paper, the input impedance and radiation pattern varies from their values for the planar patch when the patch surface is curved. [ABSTRACT FROM AUTHOR]

The tree-type algorithm has been proposed and investigated widely as a random multiple-access communication protocol. It is a distributed algorithm but shows a stable throughput performance. Several proposals have been made, including Tsybakov's, for the tree-type algorithm with a reservation mechanism to improve farther the throughput performance. This paper proposes new TREE-DTA with reservation mechanism, which is based on the block access method and employs the deterministic Q-ary tree-type algorithm operating on the terminal addresses as the retransmission algorithm. The feature of the reservation mechanism proposed in this paper is that the realization is easy, compared to various other methods that have been proposed. To evaluate the performance of TREE-DTA with reservation mechanism, a mathematical model is used to derive the approximate expression for the relation between the throughput and the average delay. Furthermore, the performances of TREE-DTA with reservation mechanism are examined by a simulation experiment. The robustness to the system error and the application of the priority scheme are discussed. [ABSTRACT FROM AUTHOR]

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

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

This paper discusses the channel assignment problem in the multichannel, high-speed packet network. It is assumed that multiple channels exist between a pair of switches in the network. It is expected that by regarding those channels as a single channel group and executing the packet transmission, a more efficient high-speed and large-capacity transmission will be realized. This paper newly introduces, in contrast to the virtual circuit in the multichannel network, the concept of a channel group-virtual circuit (CG-VC) for the multichannel network, where the packets are assigned to the channels based on the concept of the overflow traffic. To realize the CG-VC system in the high-speed environment, a simple and practical switch structure is proposed. The switch uses optical fibering as the basic module and the system is constructed by superposing the basic modules. Each packet automatically selects an appropriate channel from the set of output channels belonging to the same channel group. It is shown as a result of performance evaluation that, compared to the conventional VC packet switching system, the proposed system greatly improves the transmission delay and utilizes efficiently the channel. [ABSTRACT FROM AUTHOR]

This paper presents a new construction of the distributively controlled homogeneous self-routing space switch network, which is composed of single-kind 2 x 2 unit modules. The feature of the proposed method is that the order is defined among the destination addresses according to their binary representation by the bitwise comparison. The bionic sort is executed based on the order. In the conventional space switch network composed of a single kind of module, the total number of unit modules is of the order of N2 at the minimum, where N is the number of I/O ports. In the space switch network proposed in this paper, the total number of unit modules is of the order of (N log3N). The total number of unit modules in the proposed method is equal to that of the conventional method for N>16. When N = 1024, for example, the total number of unit modules in the proposed method is approximately one-sixth that of the conventional method. Another point is that the processing speed within the 2 x 2 unit module is independent of N, as in the conventional method, and is small. This is advantageous in the high-speed operation. [ABSTRACT FROM AUTHOR]

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

To design a highly efficient video codec, comparisons of available techniques front various viewpoints are necessary so that the coding scheme and parameters are chosen appropriately. In recently presented papers and equipment, many systems use motion-compensated interframe prediction and DCT or VQ schemes for the prediction error coding. A loop filter often is adopted to improve coding efficiency. This paper compares DCT and VQ schemes in an interframe coding scheme, in an optimal blocksize for interframe prediction error signal coding and on the Effect of loop filtering from the viewpoints of coding efficiency and reproduced image quality Simulations using actual. image sequences show that the optimal block size is 4 × 4 or 8 × 8, that the loop filter improves significantly the coding efficiency and reproduced image quality, and that DCT and VQ schemes give nearly the same efficiency with an appropriate loop filter. [ABSTRACT FROM AUTHOR]

When testing communication systems, it is necessary to select the test sequence from the specification. Since the test sequence must be selected manually, the confidence in the testing is low and the testing cost is high. Therefore, we are studying a tool to generate the test sequence automatically from the state table, based on a finite state machine (FSM) model. The PW method and the OS method are presently used to generate a sequence that has a great error detection capability. However both the PW method and the OS method have disadvantages. This paper presents a new method for the generation of the test input sequence for a system based on an FSM. The method is called the SW method (single transition checking method using W set), and uses the state transition checking approach and the characterization set (W set) for state distinction. This paper also presents an evaluation of this method in terms of its generated test sequence length, its error detection capability, and its general applicability. The results of the evaluation show that the SW method improves some of the weak points of the existing PW and DS methods. [ABSTRACT FROM AUTHOR]

This paper describes the behavior of the processing element (PE) generally used in applying the data-flow control scheme to signal processing equipment in the switching system or in the computer system. A performance evaluation is presented in terms of the characteristics based on the theoretical analysis. It is important in this scheme to evaluate the time until the program execution is completed (program execution time) for the given parallelism of the data-flow program and the multiplicity of the program (task). As a preliminary to the estimation of the program execution time, this paper evaluates PE as a whole. First, the matching-store unit of FE is considered. A simple numerical analysis based on the traffic model is presented and the performance is evaluated. The characteristics such as the mean number of waiting calls and the mean waiting time are calculated. Using those results, the whole PE is modeled as a BCMP-type queueing network, and the mean cycle time is derived. Finally, the result of numerical calculation and the result of simulation are illustrated. The range of application is described, together with some discussions. [ABSTRACT FROM AUTHOR]

In this paper we propose a new method for an economical and realizable null synthesis to prevent interference between wireless communication lines and mixing with interfering waves. Existing methods are based on the principle of a subtraction of the directivity of a cancelling beam which has a maximum value along the prescribed null direction from that of the original array. These methods cannot avoid a degradation of the directivity in directions other than the null direction. In this paper we have applied the concept of an array of the arrays. We have synthesized nulls by the array factor of an (M + 1) element array which has M nulls in the directivity of an N element array. In total, we used H + N elements for the array. This method depends on the principle of the products of directivities. As long as the null direction is far removed from the main beam direction, there is, in principle, no degradation of the array directivity. By approximating element weights, we can synthesize nulls by controls ling the weights of only terminal 2M elements. Past methods have noted experimentally a possible null synthesis by controlling the weights of the terminal elements. This paper provides clearly for the first time its theoretical reason and limits. We have applied the present analysis method for cases of Taylor directivity for the side-lobe level -30 dE for &nbar; = 5 in a linear array with elements placed one-half wave- length apart. We show calculations in exams pies for syntheses of cases of one null and two nulls. We found that by synthesizing two symmetric nulls with respect to the main beam, there was almost no degradation of the array directivity. [ABSTRACT FROM AUTHOR]

Transmission channels in mobile communication are extremely unstable due to the effect of multipath fading. Therefore the realization of high-reliability communication necessitates the introduction of error control in the form of error-correction coding. This paper considers the decoding of error-correcting codes that are adapted to digital mobile communication operating under Rayleigh fading conditions. A soft decision Viterbi decoding using the received carrier level is studied for the case of convolutional codes. This soft decision method is based on the level of the received carrier by adaptively determining the metric used in the decoding. In this way a metric is obtained for digital mobile communication. This paper also presents an estimation method using error exponent which provides effective means to realize such a soft decision method. If the channel can be considered memory less due for example to interleaving, then this method provides an easy way to estimate: (1) the figure of merit for quantizing thresholds, and (2) the gains of the soft decision. First, it is shown that using this kind of estimation in the case of channels which can be considered sufficiently memoryless due to interleaving, extremely large gain is obtained by the soft decision method discussed in this paper. Next, simulations are performed and the efficiency of the estimation method is demonstrated. Finally, the bit error rate characteristics are shown for the case when the channel is not made sufficiently memoryless by interleaving. [ABSTRACT FROM AUTHOR]

Ferrite electromagnetic absorbers making use of the frequency dispersion of the ferrite permeability are very superior to other absorbers in terms of thickness and bandwidth. Their basic properties have been found by extensive research in the past. However, no theoretical and systematic explanation has yet been given. This paper discusses the electromagnetic absorbing characteristics based on the material dispersion of the ferrite. It is shown that the previous findings can be derived systematically. Because of a significant dispersion in the permeability, the ferrite absorber becomes reflectionless only for the frequency f and the thickness d (matching point) characteristic to each ferrite material. The traditional methods for determining the matching point are based on the impedance matching and require solution of complex transcendental equations of two variables (f and d). Hence, these methods are not suited for systematic derivation of theoretical explanation. In this paper, the reflection coefficient itself is treated and the equation for the matching condition can be separated into the determining equation for the matching frequency and that of the matching thickness. By means of this new method, the basic absorbing characteristics such as the matching frequency, matching thickness, and relative bandwidth are given in the form of nomographs applicable to any ferrite. In addition, the relationship between the permittivity of the ferrite and the absorbing characteristics is derived. [ABSTRACT FROM AUTHOR]

The radial line slot antenna is a wave- guide slot array and has been studied as a high-gain and high-efficiency planar antenna in which efficiency reduction due to an in- creased aperture size is minimal. If the theoretical efficiency (of more than 80%) is required to be realized, the aperture distribution must be made uniform at the de- signed frequency by controlling the coupling of slots. This paper presents a method for design of the slots for this purpose. By considering the perturbation of the internal electromagnetic field due to coupling, an excellent characteristic with the efficiency of 75 percent (36.3 dBi) is obtained at the designed 12 GHz. [ABSTRACT FROM AUTHOR]

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

This paper considers the highly efficient coding of the gray-level image. The extrapolative prediction-discrete sine transform scheme, which was previously proposed by the authors for the case of one-dimensional coding, is extended to the case of two-dimensional coding. In the proposed method, the image is partitioned into square blocks. The correlations among blocks are eliminated by applying the two-dimensional extrapolative prediction for each block from the restored boundary pixel. The correlations the block is eliminated by applying the orthogonal transformation to the prediction errors. In this paper, the correlation function of the image is assumed as the isotropic exponential function, and a two-dimensional extrapolative prediction method is derived, which can be realized as a simple manipulation. The transformation of the prediction errors is performed by the variable-separation type two-dimensional extrapolative prediction-discrete sine transform, where the one-dimensional extrapolative prediction-discrete sine transform is applied to rows and columns. Then the rate-distortion characteristic is calculated, indicating that the proposed method is useful. It is shown that the proposed method with 4 × 4 block size has almost the same coding efficiency as the discrete cosine transform coding with 16 × 16 block size. A computer simulation was made for the actual image, leading to a result validating the theoretical estimation. The proposed method requires less computation per pixel, compared with the discrete cosine transform coding. The method is especially useful from the viewpoint of hardware implementation, since the block size is as small as 1/16. [ABSTRACT FROM AUTHOR]

The authors have developed a radar to search an object buried in snow based on multifrequency holography. Multifrequency holography has a deficiency in that the quality of the reconstructed image is degraded. This phenomenon is called the range curvature. This paper proposes a method for correcting this phenomenon to obtain a correct image. The experimental results based on this method are presented. Multifrequency holography is based on the principle similar to that of the synthetic aperture radar. In both multifrequency holography and synthetic aperture radar, the range curvature is a problem. This phenomenon is especially significant in the near region. In this paper, this region is studied and the formula for range-curvature correction and the simulation for confirmation of this formula, as well as the experiment, are introduced. Two experiments have been carried out with X-band signals at 8.3 to 9.3 GHz for the object separated from the antenna by about 1 m. One of the experiments used a metal post while another used two metal posts. From these experimental results, it is confirmed that the range-curvature correction is an effective method. [ABSTRACT FROM AUTHOR]

In accordance with the diversification and efficiency promotion of visual communication, various new services have been desired recently. One such service is facsimile which can transmit both black-and-white pictures and photographic pictures. However, it is rather difficult to process these two kinds of pictures with a single algorithm. To fulfill the demand for high transmission efficiency and high quality of the reproduced pictures, it is desirable to segment the documents into two categories and process them separately. For this purpose, the extraction of the photographic area included in documents becomes a very important theme. In this paper an extraction algorithm of the photographic area from the document images using the characteristics of edge elements and background gray levels is proposed. The features of this algorithm are: 1) automatic setting of parameters adaptable for each picture is possible; 2) area segmentation corresponding to the various gray levels of backgrounds is possible; and 3) segmentation accuracy is rather high. In the experiment presented in this paper, 125 document images which consist of 512 × S12 pixels with 7-bit gray levels have been used. The background gray levels of these images are 27, 36, 42, 57 and 77, and into these images photographic images, which occupy 50, 60, 70, 80 and 90 percent of the total area have been inserted. Experimental results show that in every image the photographic areas have been segmented successfully in the sense of practical use. For 93.8 percent of the images, the differences between the inserted areas and extracted areas are only 0–7 blocks (0–27 pixels), and the usefulness of this algorithm has been proved categorically. [ABSTRACT FROM AUTHOR]

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

With the development of such communication networks as INS in recent years, the communication protocol has become more complicated, and efficient description and validation are becoming more important. This paper proposes a new method of description and validation for the communication protocol, which realizes the merits of both the composite state-transition diagram and the high-level language. The method describes the communication protocol using the SL diagram, which is the complete state-transition diagram with built-in logical expressions. Using the SL diagram, it is easy to verify the existence of the deadlock by utilizing its graph-theoretic features. On the other hand, by regarding the SL diagram as a flowchart, the inductive assertion (technique used in proving the validity of the program) can be applied to validate the parameter functions. A method is also shown which can efficiently locate the invalid loop using the SL diagram. In this paper, the loop is defined as invalid if the transfer of a packet is continued without progressing the communication. Furthermore, it is pointed out by applying the proposed method that there exists in invalid loop in the standard protocol HDLC. An improvement of HDLC is proposed to eliminate such an invalid loop. [ABSTRACT FROM AUTHOR]

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

This paper proposes a high-performance noiseless data compression model which can compress strings generated by a binary Markov information source without prior knowledge of the source. The adaptive expression of the existing universal codes is described by a model with separated sampler and encoder, and the learning structure of each code and the encoding process are described. Through such a discussion, the intuitive reasons are clarified as to why the codes, despite their asymptotic optimality, do not compress well at the start, pointing out room for improvement. Then, the MDL criterion is introduced into each encoder, to improve the performance, while keeping the sampler fixed. The MDL criterion is an estimation for the minimum code length, including the representation cost of the parameters. Based on this criterion, the Markov order which is to be assumed for each symbol is adaptively determined. Since the same determination can be made at the time of decoding, the unique decodability is guaranteed. In the second half of this paper, more detailed techniques are discussed, and a remarkable improvement is demonstrated by a computer simulation. tt is also shown that the sampler of the proposed universal code is of a high-performance, realizing two kinds of encoders. [ABSTRACT FROM AUTHOR]

In a coherent optical fiber communication with a single-mode fiber and an optical heterodyne detection for improved receiver sensitivity, degradations of the receiving sensitivity due to fluctuation of the polarization condition of the received light are a problem. As a possible solution to this problem, this paper proposes a polarization diversity system with an error-detecting code or an error-correcting code. Its characteristics are analyzed and optimum design values are obtained. [ABSTRACT FROM AUTHOR]

A gain/shape vector quantizer for orthogonal transform domain has been designed based on a previous paper [11] on a gain/shape vector quantizer for a spherically symmetric random source. Such a design method is used in the design of a discrete cosine transform encoder with gain/shape vector quantizer. This encoder is similar to that described in [7] except in the following: (i) it has a gain/shape codebook; and (ii) its normalized coefficients of discrete cosine transform are modeled as having spherically symmetric distribution. The S/N rendition of this encoder is 1.0 - 2.5 dB better than that of the DCT coding scheme with Max-type scalar quantizer at the same bit rate. Furthermore, in spite of its similarity to the conventional discrete cosine transform coding scheme with vector quantizer [7], the encoder introduced in this paper delivers higher S/N using the same number of multiplications for the quantization of normalized coefficients, and/or the same amount of memory for the codebook. [ABSTRACT FROM AUTHOR]

Quantization error is one of the important measures that determine the performance of the differential PCM. This paper investigates the DPCM quantization error characteristic and the exact determination of the stationary error density. The input signal considered is a time-discrete increment process which is similar to the Wiener sequence, but with Laplacian increments. A system of equations satisfied by the characteristic function of the prediction error is derived first and the exact formulas are derived for error probability distributions. Using these distributions the mean-squared error, the entropy of the quantized outputs, and the probability of granular error are determined. For the obtained optimum quantization step size, it is shown that the granular error exceeds the slope overload error, that the distribution of quantized outputs is nearly geometrical, that the quantization error is almost equal to that of increments for a large number of quantization levels, and that the results agree with rate distortion theory. The present analysis will be useful to performance analysis of DPCM with stationary non-Gaussian autoregressive inputs. [ABSTRACT FROM AUTHOR]