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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]

We explain a tracking method that uses a linear filter to estimate the true values of the position and the velocity with the target position as the radar observation. One rep- resentative example is a Kalman filter for three-dimen- sional space. The α-β filter with its easily analyzed performance is widely used in one-dimensional space. In a tracking method, the tracking precision must be evaluated when sufficient time has elapsed since the initial calculation, that is, in the steady state. The equation for calculating the variance of the errors in the predicted position in the steady state has been reported for radar observations of a constant-velocity linear motion target by an α-β filter. In addition, a Kalman filter can obtain the variance of the errors in the predicted position in the steady state by the Riccatti equation. In this case, however, a premise is the presence of drive noise that indicates the ambiguity of the motion model. There is no equation for calculating the variance of the errors in the predicted position in the steady state for the radar observations of a constant-velocity linear motion target. In this paper, we present an equation for calculating the covariance matrix of the prediction errors in the steady state of the position and velocity for the radar observations of the constant-velocity linear motion target in a 3D spatial linear filter. The results calculated in this paper present an extension of a conventional α-β filter. [ABSTRACT FROM AUTHOR]

Recently there have been many methods for rate control methods as applications of control theory. This paper considers congestion control in an ER system of ABR class in ATM as an example, and proposes a PID-type control rule under the existence of propagation delay. In the ATM switch, we predict the buffer level after time which equals the propagation delay elapsed. Based on the difference between the predicted and target values, a QoS value is calculated. It is stored in the ER field of an RM cell, and sent to each source. The connection sets the transfer rate corresponding to the extent of satisfaction and the QoS service class. We show conditions for the control parame- ters in order to stabilize the buffer level. [ABSTRACT FROM AUTHOR]

The main problem of an indoor infrared (IR) wireless system via diffuse infrared link is bit error rate (BER) performance degradation due to intersymbol interference (ISI) induced by multipath distortion. In the previous study, only a rectangular pulse was employed as a transmitted pulse. However, multipath distortion tends to make the nondirected diffuse indoor IR channel have a low-pass frequency characteristic, and thus a rectangular pulse, whose spectrum has a form of sinc function, induces much ISI. In this paper, we analyze the BER performance of indoor IR wireless system via diffuse link employing different kinds of pulse waveforms, such as a Gaussian pulse and a raised cosine pulse, and consider the effect of ISI. Moreover, we analyze the BER performance employing a return-to-zero (RZ) pulse which has a guard interval in a slot. It is shown that the RZ Gaussian pulse is effective in mitigating the effect of ISI. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(9): 33–43, 2000 [ABSTRACT FROM AUTHOR]

Efficient handover during both mobile telephone and portable telephone communication is a technology essential m implementing ideal mobile communications. However, there exists the possibility of a transmission data slip during the process of circuit switching, which has become a problem in communication using terminal machines such as data modems and FAX machines connected to mobile telephones and portable telephones. In this paper, a transmission data slip accompanying route changes reside digital exchanges in a handover during telephone communications is assumed; it is shown on the basis of this assumption that a lag in synchronism occurs m the receiver terminal equipment. Then a sync lag of the receiver terminal modem during handover has been confirmed by tests using actual analog cellular phones and a transmission data slip has been shown on the basis of the results of the tests. In this paper, a synchronism control method minimizing the sync lag has been studied. The efficacy of this method has been confirmed as a result of applying the method to a mobile telephone FAX modem. [ABSTRACT FROM AUTHOR]

It is important to know the scattering properties of objects buried underground so that the techniques of imaging the buried objects by electromagnetic waves may be established. This paper analyzes numerically the transient scattering characteristics by the finite difference time domain (FDTD) method where an infinitely long perfect conductor of arbitrary cross section is buried in the ground and an infinitely long current source is located above the ground surface parallel to the object. The calculation error resulting from the approximation of the scattering object by square mesh is decreased by introducing the field interpolation which satisfies the boundary conditions of the scattering surface. The spatial distribution of the electromagnetic field at each step of the calculation is shown. Moreover, the propagation characteristics of the wave near the ground surface and the scattering characteristics of various objects are studied and the presence of two types of waves, i.e., direct and lateral, is confirmed between the source and ground and between the object and ground. [ABSTRACT FROM AUTHOR]

This paper proposes a high-accuracy positioning service for terrestrial mobile communication systems which employs the global positioning system (GPS) with the differential method (DGPS). The proposed system provides a high-accuracy navigation service to land-based mobile communication users. The proposed system also provides a comprehensive vehicle control service to the transportation companies when both forward and return links are available in the terrestrial-based mobile communication systems. This paper also assesses the performance of the DGPS method by computer simulations and a field experiment in an urban area to identify the viability of the proposed system under an actual environment. The relationship between average hinging time rate and the average visible number of satellites in various operating environments also is investigated. [ABSTRACT FROM AUTHOR]

This paper aims at improvement of the interbeam connectivity of the multibeam satellite for fixed satellite communications under frequency division multiple access (FDMA) operation and proposes the subchannel switched FDMA (SS/FDMA) system, which is realized by installing the filter matrix on-board the satellite. In the proposed system, each transponder is used to realize multiple interbeam connections and the interbeam connectivity is improved greatly compared to the traditional system. A satellite network among multiple beams can be constructed efficiently. A method is shown in this paper to determine the transmission parameters which maximize the system capacity of the multibeam satellite network and minimize the average transmission equivalent isotopically radiated power (e.i.r.p.) for one career. Example calculations me shown for the power-limited and band-limited systems. In the band-limited system, the number of subchannels and the ratio of bandwidths of the subchannels are important parameters. From such a viewpoint, a method is shown which determines the number of subchannels when the bandwidth ratio of the subchannels is specified. An example calculation is shown taking into account uniform and nonuniform traffic distribution patterns. [ABSTRACT FROM AUTHOR]

This paper considers a slotted ALOHA network which consists of a central base station and many mobile terminals. In classical performance analyses of random access networks, a channel between the station and a terminal is assumed to be always in a good state. However, this is not the case in mobile radio networks since the channel suffers from many factors such as fading, shadowing, and so on. Moreover, the channel condition changes with the terminal location. In this paper, a simple channel model is used to consider the effects of time-varying channels in a random access network. The channel model assumed in this paper has three states: shadowing, good, and bad. The transitions between the channel states are described by a Markov chain. The dynamic performance of a slotted ALOHA network over such time-varying channels is evaluated by means of the equilibrium point analysis. Then the influence of the time-varying channel on the throughput performance of a slotted ALOHA network is studied. [ABSTRACT FROM AUTHOR]

This paper describes an adaptive array antenna using a signal processing system which is implemented by a systolic array processor (SAP), SAP-AA. Computer simulations show the behavior of the SAP-AA against multipath fading. The SAP realizes a parallel pipelined processing by regularly placing many SAP cells with identical functions and structures so that it achieves the high throughput rate in the data processing. Also, the SAP has many desirable features for very large-scale integration (VLSI) system design and enables miniaturization, weight reduction, and mass production of the processing equipment. In this paper, first, the SAP-AA is described which realizes the least squares (LS) algorithm based on the QR decomposition for the input data matrix using the Givens rotations. In addition, the fundamental performances of the SAP-AA are studied including both the transient response and the steady-state behavior in multipath signal environments. To date, there has been no report which treats the multipath signal suppression performance of the SAP-AA. Finally, it is concluded from the discussion that the SAP-AA is effective for unwanted signal suppression in a multipath signal environment. [ABSTRACT FROM AUTHOR]

This paper evaluates a leaky-bucket-type control method as a means of policing control of input traffic in ATM networks. In an ATM network, a user reports parameters specifying traffic characteristics to each traffic source at the time of making a request for a call connection and the network determines whether or not to accept the call on the basis of these parameters. In addition, after the call reception, input traffic after a call connection must be controlled such that the cell arrivals from the traffic source conform with the reported parameters. In this paper, as a method of controlling input traffic, the mean arrival rate and burstiness of input traffic are evaluated quantitatively using the leaky-bucket method and problems associated with introduction of such an input control system to an ATM network are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper considers the Z-channel, which is known as a channel model for photon communication or semiconductor memory. A new decoding algorithm is proposed and discussed. Recently, studies have been made from various viewpoints on the asymmetrical error-correcting code suited to the Z-channel, which is considered interesting. One of the basic problems in the Z-channel is the performance and the decoding method when the cyclic code with various features is applied, but it has been investigated little. This paper presents first a maximum-likelihood decoding algorithm which is highly efficient for the cyclic code on the Z-channel. It is then shown that by providing a certain threshold for the algorithm, a higher-speed decoding is realized. It is shown also that by setting the threshold above a certain value, the computational complexity can be improved without sacrificing the maximum-likelihood property. Finally, it is demonstrated by numerical calculation that the decoding error probability is improved greatly by the decoding algorithm proposed in this paper, together with a drastic improvement in the computational complexity. [ABSTRACT FROM AUTHOR]

This paper proposes a new method for efficient validation of the telecommunication protocol, containing the internal events, including those for the timer and resource management. The proposed validation method first converts the protocol containing the internal event into the equivalent protocol not containing the internal event. Then the original protocol is validated by applying the already-proposed validation method for the protocol not containing the internal event to the result of conversion. This paper discusses mainly the principle and the algorithm of the protocol equivalent conversion. The features of the proposed validation method are that the protocol is validated with the minimum processes and signals, which reduces the processing time and the memory capacity needed in the validation and also improves the efficiency. [ABSTRACT FROM AUTHOR]

The main cause of the absolute positioning error in the Loran-C system is in the occurrence of the propagation time delay error caused by the fact that the propagation speed of the pulse signal on the actual propagation path is different from that assumed in the formation of the Loran-C maritime chart. The propagation path characteristics not only cause the propagation time delay of each received pulse signal but also generates waveform distortion in the received pulse. Hence, it is possible to estimate the propagation delay time by means of this waveform distortion. At present, a measure of the distortion of the pulse waveform distortion of the Loran-C is envelope to cycle difference (ECD). In this paper, as a new measure for the pulse-wave distortion to estimate the propagation time delay, CHACLE, or change of half-cycle length, is proposed. A method for correction of the absolute positioning error is provided based on the estimation of the propagation time delay from the measures of the waveform distortion (CHACLE end ECD) by means of the simplified propagation path for an easy analysis and of the general propagation path. It is demonstrated that CHACLE is superior to ECD in terms of the effect of correction. Further, to confirm the validity of the correction method proposed in this paper, the present method is applied to a propagation path model resembling the mixed propagation path used in the United States to estimate the pulse time delay. It is confirmed that the absolute positioning error can be reduced to less than about 20 percent. [ABSTRACT FROM AUTHOR]

This paper proposes an authentication technique by 3D pattern communication, using terminals with a small-sized screen. 3D pattern communication is a method whereby an arbitrary signal can be transmitted by rewriting the signal patterns on the screen for several times on the terminal screen. The signal is not limited by the display resolution of the screen or the kind of liquid crystal. Con- sequently, any signal can be sent to the destination through the screen, and secure authentication can be realized by using a portable terminal. It is verified that, even if the terminal is inclined to some extent during reading due to the angle of the hand holding the terminal, or an arbitrary picture is overlaid on the pattern, the 3D pattern can be recognized correctly by utilizing error-correcting code and interleaving. The proposed scheme is implemented on cur- rent models of portable phones with TFT, TFD, STN, and organic EL screens. The communication of 1024-bit RSA signature data is successfully performed in 0.33 to 0.44 second, except for a single terminal. Using the proposed 3D pattern communication, an authentication service with a strong security requirement can be provided without adding a special device to existing portable phone terminals. [ABSTRACT FROM AUTHOR]

Communication between an IPv6 host and an IPv4 host requires a name server that makes a mapping between an IPv4 address and an IPv6 address, and a translator that performs IP packet conversion. In this paper, we propose an IPv4­IPv6 bidirectional communication system, implement our proposed method, and present the results of performance evaluation. Our system can provide IPv4 hosts with connectivity to more IPv6 hosts in spite of pooling fewer IPv4 addresses. It is realized by adding a source IPv4 address and a port number to an address mapping with cooperation between a name server and a translator. [ABSTRACT FROM AUTHOR]

In this paper, a typical mobile communication environment is assumed and the eigenvalue distributions of the correlation matrix of a MIMO channel with the spatial correlation of the multipath taken into account are studied by simulation. Based on this study, a simple method is proposed for accurately deriving the probability distribu- tion of the largest eigenvalue of the correlation matrix. The proposed approximation equation is compared with simu- lation results and good agreement is obtained. In order to understand the information transmission capability of MIMO in a multipath fading environment with spatial correlation, the proposed equation is used for studying the effect of the spatial correlation on channel capacity. Finally, the digital transmission characteristics (relationship be- tween the BER and the CNR) with correlation taken into account are obtained. [ABSTRACT FROM AUTHOR]

In array antennas, sometimes the desired radiation pattern cannot be obtained due to coupling between element antennas, reflections from the surroundings, or amplitude and phase error of the power supply circuits or failures. In these cases, it is necessary to regenerate the desired radiation pattern by estimating the excitation amplitude and phase of the array antennas. Among methods of estimation of the excitation amplitude and phase, the rotation element field vector method of element antennas is used for the phased array antenna with variable phase shifters, and the planar near-field measurement method is used for the array antennas with no variable phase shifters. The former is limited to phased array antennas, and the latter requires a large-scale scanner for the measurement and results in increased measurement time with larger-scale array antennas. In this paper, we propose a method of estimation of excitation amplitude and phase using the radiation pattern of array element antennas and the measured radiation pattern of the array antennas. Two methods are proposed here; the first method of estimation is the least-squares method using the electrical field as the measured radiation pattern, and the second is the repeating calculation method using the electrical power as the measured radiation pattern. We describe here the principle and experimental results when the first method is used, and the principle and the effectiveness of selection of the initial value for the second method is confirmed by numerical results. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(9): 102–110, 2000 [ABSTRACT FROM AUTHOR]

As a receiving method suitable for channels with intersymbol interference such as frequency selective fading, a method is proposed in which the soft decision using the hard decision sequence generated from the data after forward error correction (FEC) is alternated with FEC. In the conventional receiver with a serial configuration of the equalizer, deinverter, and decoder, the performance of the equalizer significantly affects the overall receiver characteristics. Hence, the performance of the equalizer is emphasized. On the other hand, in the proposed method the error generated in the initial equalization can be corrected by repetitive soft decision and FEC. Therefore, the method does not strongly depend on the performance of the equalizer used in the initial equalization. Hence, even if an equalizer requiring a smaller amount of process with a somewhat degraded performance is used in the initial equalization in place of a high-performance equalizer, the amount of process for the entire receiver can be decreased without degrading the characteristics of the proposed method very much. In this paper, the characteristics of the proposed method are evaluated by computer simulation. The following are the confirmed conclusions. (1) The proposed method using the maximum-likelihood sequence estimation (MLSE) as the equalization has superior BER characteristics over the conventional method using a maximum a posteriori (MAP) equalizer and MLSE. (2) In a transmission channel with a large delay spread, the degradation of the BER characteristics of the proposed method using the delayed decision-feedback sequence estimation (DDFSE) in place of MLSE is very slight while the amount of processing can be reduced substantially from that in the conventional method using MLSE. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(9): 76–85, 2000 [ABSTRACT FROM AUTHOR]

A small antenna with a size of 1/15 to 1/5 wavelength, consisting of a toroidal coil of fixed length, is proposed. The radiation characteristics of antennas with a limited range of turn numbers and pitch angles are analyzed by the conventional method and the method of moments. The conventional method is based on the assumption of a cosinusoidal current distribution along the antenna element. The results are then compared with experimental results. It is found that the method of moments with correction for the resonant frequency expresses well the characteristics of this small-size antenna, and that fairly good agreement between the results of the conventional method and the experimental results is obtained. For the limited size range adopted in this paper, the proposed antenna offers the advantages of having the same radiation pattern as a one-wavelength loop antenna, allowing easy matching to a coaxial line, and achieving a relatively high gain despite its small size. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(9): 10–19, 2000 [ABSTRACT FROM AUTHOR]

As more and more automotive electronic devices have been employed and the level of sophistication of their functions has tended to increase, the needs for further enhancement of reliability of operation in an electromagnetic environment also have been increasing. This paper discusses laboratory measurement methods of RF conducted noise for automotive electrical and electronic devices. Also described are impedance characteristics with power line of six models of Japanese passenger vehicles, suggesting that the impedance can be characterized in three frequency ranges: 10 Hz to 1 kHz; 1 kHz to several megahertz; and several megahertz to 60 MHz. Characteristics of an artificial network simulated power line of the Japanese passenger vehicles are discussed. This paper proposes measurement methods and systems for conducted emission and susceptibility. The proposed system is functional in the 150 kHz - 60 MHz frequency range. In the emission measurement, a histogram of the noise level produced by EUT in the frequency domain can be measured, whereas in the susceptibility measurement system, malfunction modes with EUT, as well as the level of input to cause the EUT to malfunction, can be characterized. [ABSTRACT FROM AUTHOR]

As radio communication has progressed, reduction of intersystem interference has become a problem. In a conventional interference canceller, the interference signal as a source of cancellation is obtained at the receiving station and the interference component in the desired signal is canceled based on this interference signal. However, the interference signal for cancellation may not be obtained at the receiving station. As a remedy, an extraction and reinjection-type interference canceller has already been proposed. In this paper, a pre-interference canceller is proposed in which, if the transmitting station of the desired signal and that of the interference signal are identical, the interference signal is mixed with the desired signal from the transmitting station beforehand and the interference signal leaking into the desired signal is cancelled at the receiving station. First, the applicable range and the fundamental configuration of the present canceller are presented. Subsequently, the method for determining the amplitude and phase of the interference signal injected into the desired signal of the transmitting station and the method for evaluation of the cancellation effect are presented theoretically. Next, an experiment is carried out with the desired signal of 16 QAM or 256 QAM and the interference, signal of 256 QAM. Interference improvement by about 20 dB is obtained for both the 16 and 256 QAM signals. Also, the response speed of control for the fading is 60 ms. In addition to the validity of the theoretical results, effectiveness of the proposed canceller is shown. [ABSTRACT FROM AUTHOR]

As the broadband integrated services digital network (B-ISDN) become more available for home use, it is expected that the demand for broadcast services, e.g., video distribution from a center to end terminals, will increase. Thus, in the local switching system, the number of output subscriber lines is much larger than the number of input trunk lines. Therefore, an asymmetric broadcast ATM switching network is needed for this service. However, most of the switching networks already proposed In this paper, an asymmetric switching network is realized by partitioning the output and by using existing symmetric switching networks. Furthermore, the size of symmetric switching networks which are used as parts is reduced by placing concentrators in the front. This decreases the total amount of hardware. Since excessive concentration invites cell loss, the relation between the hardware-reduction effect and the cell-loss characteristic also is studied. [ABSTRACT FROM AUTHOR]

A ranging and positioning system using a geostationary satellite has been developed and its performance has been evaluated using an aircraft. This system can be applied to oceanic air traffic control and can be used at a ground station to determine positions of aircraft. An experimental system consists of a geostationary satellite, a ground station, an aircraft, and a pseudo-satellite, which is installed inside the ground station sod used as the substitute for another geostationary satellite. The Engineering Test Satellite V (ETS-V) of Japan was in the experiment. It is known that the positioning error increases a user approaches the equator in a positioning system using two geostationary satellites. This fact has been confirmed in this paper by experiment. It has also been shown that positioning errors can be decreased by using relative positioning m which the position of the ground station is used as a reference station. The use of old orbit elements increases the error of the predicted position of the geostationary satellite and therefore increases the positioning error of the aircraft. This has also been confirmed in the experiment. Furthermore, it has been shown that, in relative positioning, positioning errors do not increase much even with old orbit elements and the epoch of orbit elements does not have much influence on positioning errors. [ABSTRACT FROM AUTHOR]

This paper considers the decision feedback transversal-combining (TC) diversity reception system in the digital mobile communication, and describes experimentally the interference cancelling characteristics of decision feedback equalizer-type (DFE) TC diversity reception through laboratory tests. Three kinds of interference signals are considered: the intersymbol interference (ISI). the cochannel interference (CCI), and the adjacent channel interference (ACI). The exponentially weighted RLS, which executes the least-square method m readtime, is employed m the adaptive control of the combining coefficients. It is shown first that the method for equalization and diversity combining can be classified into the TC and the metric combining (MC), among which TC has the linear interference cancelling effect. By 40 kbit/s quadriphase-shift keying (QPSK) transmission experiments under Rayleigh fading condition, the following properties of TC are shown compared to MC: (1) In ISI, dominant condition in double path model, the average BER performance for average Eb/No values over 20 dB; (2) For CCI, dominant condition BER performance of TC is better than that of MC by 5 dB in average CIR at average BER of 10-2. [ABSTRACT FROM AUTHOR]

In the conventional adaptive discrete cosine transform (ADCT) using the fixed length code, it is known that the source coding performance can be improved greatly by the combined use of the M-transform (MT). This method is called ADCT-MT. The purpose of this paper is w evaluate the effect of the combined use of MT from the viewpoint of the channel coding performance. In the conventional ADCT, as well as in the scene adaptive coding (SAC) using the variable length code, the damage in the reconstructed image due to the channel error often is manifested as the local block distortion. In ADCT-MT, the damage is diffused and distributed uniformly by the inverse MT over a large number of blocks, making the damage less noticeable. A subjective evaluation experiment is conducted (five-step score) assuming the binary symmetrical channel. A simple error-correcting code is applied to the coding data of the additional information and DCT dc component. When the bit-error rate is 10-3, the average score is approximately 3.5 for ADCT and 1.2 for SAC, while it is above 4.5 in ADCT. Thus, in ADCT-MT, the damage is little noticeable. [ABSTRACT FROM AUTHOR]

This paper considers a function to improve the efficiency of the operation administration and maintenance (OAM) of the virtual path (VP) in the AIM network. A VP test method is proposed which can test the connectivity and performance at new VP establishment and locate the fault point at VP failure. The implementation of the method is discussed. The feature of proposed method is that the number of error bits, the number of lost cells, and the number of misdelivered cells can be measured by transmitting and receiving the test OAM cell in any test section of VP. In this piper, the purpose and requirements for the VP test system are described first. Then the mechanisms in the proposed system and the allocation of test functions are considered. A transmission performance measurement algorithm is proposed for the test OAM receiver so that the bit error, the cell loss, and the cell misdelivery can accurately be counted. The structure of the VP test OAM cell to realize the proposed algorithm is presented. Finally, the system parameters of the proposed method are evaluated quantitatively. [ABSTRACT FROM AUTHOR]

The protocol in the open system interconnection (OSI) basic reference model is specified as a system with a multilayer structure. The performance of the network is related closely to the network configuration and the protocol parameters. The authors have been attempting to evaluate the transmission efficiency of the using the multilayered protocol, with the transmission speed, the window size, and the transmission delay as the parameters. It is assumed in the studies that the acknowledgement is returned at the end of each window. On the other hand, it is seen that the throughput of the network in the high-speed transmission is affected greatly by the acknowledgement method. This paper notes this point and evaluates the relation between the acknowledgement method and the transmission efficiency. To achieve the desired transmission speed, the conditions for the window size, the acknowledgement method, and the protocol processing time are presented. [ABSTRACT FROM AUTHOR]

With a view to focusing the eloctromagnetic wave, an “equiangular spiral-bent slotted rectangular waveguide (SSW)” made of an axially slotted rectangular waveguide, which is one of the leaky wave antennas, was proposed and its focusing characteristics were reported. In this paper, a new diffusion-type radiator based on the operating principle fundamentally identical to that of the SSW as a focusing radiator is proposed. The radiation pattern of the offset parabolic reflector using this radiator the feed is investigated. First, its far field is treated by a wave optical approach. Using a cylindrical offset parabolic reflector as an example, the radiation pattern and the frequency scanning characteristics are studied numerically. Further, a reflector antenna was actually constructed and the measured results are compared with the analysis so that the offset parabolic antenna with a proposed diffusion-type slotted waveguide as a feed and its frequency scanning possibility are reported. [ABSTRACT FROM AUTHOR]

This paper aims at the improvement of the transmission performance of the differential detection system in the mobile radio transmission channel in a frequency selective environment. The multiple differential detection with adaptive sequence estimation (MDD-ASE) is proposed, and the performance is analyzed by a computer simulation. In MDD-ASE, not only the differential detection by one-symbol delay but also the differential detection by two- or more-symbol delays are applied. The soft decision is applied to the output of the multiple differential detection, and the symbol sequence is estimated by Viterbi algorithm (VA). The bit error rate (BER) performance is improved by the extended observation time by the multiple differential detection and the sequence estimation. The number of states in VA and the processing complexity of the adaptive algorithm increases exponentially with the extension of the observation time. Consequently, the following method is proposed: (i) the number of parameters to be estimated is reduced; and (ii) the sequence candidates stored in each path of VA are fed back. In this paper, the configuration and operation of MDD-ASE are described first and then the transmission performance of the 40 kbit/s QPSK modulation system is presented. As a result of analysis for the static and the dynamic performances of ADD-MSE using one- and two-symbol differential detection, it is shown that the improvement effect is almost the sang as in coherent detection DFE. [ABSTRACT FROM AUTHOR]

In this paper, branching configuration in a parallel two-wire transmission line is considered as the cause of the unwanted electromagnetic wave generation and the analysis and experiment ate carried out on the radiation characteristics of the discontinuity. Understanding by a simple radiation mechanism is intended. The discontinuity of the traveling-wave current on the conductor of the transmission line is considered as the radiation source. By means of the principle of pattern multiplication, the expression of the radiation field from the junction of the transmission line is derived. It is shown that the reflection and transmission coefficient of the traveling wave at the branching point are important factors to determine the radiation pattern. Two types of branching line configurations are treated. One of them is a reflectionless configuration while the other is made of identical transmission lines. The radiation characteristics due to the difference of characteristic impedance are derived. It is shown that there are electric field components radiating strongly in the traveling direction of the current of the branching line and the one radiating strongly into the intermediate direction. By means of the experiment for a T branching line, the validity of the theoretical results is confirmed. [ABSTRACT FROM AUTHOR]

This paper considers the application of the modulation level-controlled variable capacity radio channel to asynchronous transfer mode (ATM) networks and analyzes the cell loss characteristic. A system is proposed in which the transmission capacity of the overall system can be enlarged by controlling the number of modulation levels. This helps to enhance the absorption effect for the traffic variation in ATM networks. Therefore, the proposed system can reduce the cell loss probability. As a result of quantitative analysis of the system. it is shown that the cell loss improvement is by the factor of several hundreds to several thousands compared to the virtual path fixed-capacity transmission system and several to several thousands compared to the virtual path capacity control system proposed up to present. [ABSTRACT FROM AUTHOR]

One high-fidelity ring-type optical transmission network is the star-shaped ring network having a multiport accessory in its hub. The present paper describes the transmission loss budget design for the star-shaped ring network that takes into account continuously received interference signals. Conventionally, the S/X value, which is the ratio of the tram signal power to an interference signal power, has been used to evaluate the degree of interference. First, the factors responsible for determining this ratio are discussed and then a design chart is derived to correlate the S/X value with the level difference between the transmitter and the receiver for the network. Based on this design analysis, multiport optical accessors are fabricated; and measured results are presented. It is demonstrated that the star-shaped ring network with desirable performance can be realized successfully. Finally, a method to lower the level difference between the transmitter and the receiver using multiwavelengths is proposed. [ABSTRACT FROM AUTHOR]

Slotted rings have been popular medium access control protocols for local area networks (LANs) since the early proposal of Cambridge and Owell rings. This paper provides a simple approximation technique for the performance analysis of a slotted ring based on a single-buffer model in which at most one packet can be stored at each node. The technique produces approximate values of the network throughput by using an assumption which is valid for large networks and a solution of a quadratic equation whose complexity does not depend on the number of nodes in the network. It is shown by numerical examples that the present technique also gives accurate performance dam for rather small networks to the extent that the relative error of the approximate throughout values is less than 0.3 percent of exact values. Since other performance measures for the single buffer model of a slotted ring can easily be calculated from the throughput, the proposed technique is very useful for evaluating the total performance of a slotted ring network. [ABSTRACT FROM AUTHOR]

This paper describes the S-band intersatellite communication (SIC) antenna to be carried on the Engineering Test Satellite VI scheduled for launch in 1994, to undertake the first intersatellite data relay experiments in Japan. The SIC antenna is an on-board formed multibeam phased array antenna, the first of this kind in the world to be carried on a satellite. The SIC antenna is capable of simultaneous data relays to several orbiting satellites (user satellites) by means of an electrically scanned beam. With an on-board microprocessor, the location of a user satellite can be computed, and the beam is pointed toward that direction automatically. In comparison with the system used in the data relay satellite of the United States, the on-board beam-forming system has several advantages, such as the effective use of power and frequency in the case in which the number of user satellites is small, as in Japan. In this paper, the function and the configuration of an SIC antenna are described first. Next, analysis of the antenna is presented, including the effect of the phase and amplitude errors caused by temperature fluctuations. Further, as the main components, the newly developed broadband microstrip antenna, a small beam-forming network with small phase errors, and the phase shifter controller making the computation of the orbit of the user satellite are presented. Finally, the total test results of the on-board model of the SIC antenna are described. [ABSTRACT FROM AUTHOR]

A two-wire voice-band automatic gain control (AGC) with echo cancellers is studied and applied to an automatic call-transfer repeater. A four-wire circuit model of the amplifier and its stability are discussed. Fast tracking and/or stabilizing AGC using variable-rate control is proposed. Also, a singing protection control method in which the dominant path is selected depending on voice signal powers of the two speech paths is proposed and investigated. The amplifier gain of the inferior path is computed using the measured echo return loss (ERL) values of the echo cancellers. Furthermore, an automatic call-transfer repeater prototype that is based on the new AGC amplifier and its characteristics is introduced. The maximum amplifier gain of the proposed methods is about 10 dB higher than that of a conventional two-wire amplifier with a voice switch. The configuration and algorithms proposed in the paper are proven to be effective for two-wire amplifiers. [ABSTRACT FROM AUTHOR]

In the SLC (sidelobe canceler) which automatically suppresses the interference signals received by the sidelobe of the main antenna, there is a problem of suppression of the desired signal in addition to the interference signal if the desired signal power in the auxiliary antenna is larger than the receiver noise power and if the number of received interference signal is smaller than that of the auxiliary antennas. In this paper, an SLC is proposed in which the number of auxiliary antennas is adjusted automatically to be equal to that of the interference signals so that the problem of suppression of the desired signal is prevented. It is assumed here that both the desired signal and the interference signals have narrow bandwidths. In this SLC, with a view to adjusting the number of auxiliary antennas and the weights at the same time, the Gram-Schmidt SLC (GS-SLC) is used so that a sudden change of the input-output signal power ratio of the Gram-Schmidt processor is detected and the number of auxiliary antennas are made to coincide with that of the received interference signals. By way of a computer simulation, the fundamental characteristics of the present GS-SLC are evaluated. It is confirmed that the desired signal preservation property is improved in comparison with the conventional SLC. [ABSTRACT FROM AUTHOR]

In general, an optimum quantizer which gives the minimum distortion at a given bit-rate is uniquely determined when the statistical characteristics of the source signal are given. This quantizer, however, is not optimum for the human visual characteristics; and a quantizer which is designed to minimize the estimated distortion (estimated noise) reflecting the human visual characteristics is more likely to be optimum. In the optimum quantization of orthogonal transform schemes, theoretical quantizer design schemes considering only the human visual characteristics of the spatial frequency direction have so far been reported. However, there is another human visual characteristic, that is, the noise-masking effect which is the difference in the detectability of noise, depending on the local variation of a video signal (activity). For this, only the quantizers which use this effect experimentally have been reported; and they have not been studied theoretically. In this paper, it is proposed, as the first step, that the visual sensitivity to noise be expressed on two axes, i.e., spatial frequency and ‘activity.’ A three-dimensional (3-D) structure quantization cube is then proposed which is obtained by minimizing the noise estimated by the visual sensitivity of the noise at the given bit-rate and the theoretical design scheme of this optimum quantization cube is described. Finally, the effectiveness of the quantization cube designed by this theoretical scheme is compared with that of the conventional quantization schemes by a computer simulation using real picture data. [ABSTRACT FROM AUTHOR]

The TDMA scheme, a typical multiple-access scheme, can provide secure transmission; but its efficiency is poor under low traffic conditions. By contrast, the random access scheme, represented by the ALOHA scheme, has a small-delay characteristic under low traffic conditions but a stability problem under heavy traffic conditions. This paper presents a new multiple-access scheme in which each station is assigned a slot in every frame and stations are assigned to a slot at different power levels to obtain the capture effect. Therefore, the proposed scheme can adapt itself under various traffic conditions with channel status monitoring based control. Different models of capture effect are proposed, and the performance of the models is analyzed both by theory and by computer simulation. [ABSTRACT FROM AUTHOR]

This paper presents a data compression scheme which uses the statistical properties of ordered dither image by vector reputation. When a part of the dither image corresponding to n × n dithering matrix is described as a vector, it is observed that there is high correlation ratio between neighbor blocks for level information (the number of black pixels in the vector), the resolution information (the number of kinds of vectors) is a few, and their frequency distribution is very biased. Thus, if these two kinds of information on vector are coded separately by the variable length coding scheme, then high compression ratio can be attained for transmission and storage of dither image. [ABSTRACT FROM AUTHOR]

As multibeams begin to be used in satellite communication, the satellite-borne antennas have become larger. Hence, development of an antenna with a large aperture with a lightweight and high surface accuracy is being carried out. Unlike conventional small antennas, this antenna experiences a large thermal deformation due to severe environmental conditions on the geostationary orbit. In addition, a large deformation due to gravity occurs in the performance confirmation test on the ground. In the development of such a large antenna, it is indispensable to develop a method to appropriately evaluate the change of electrical performance by the deformation. In this paper, an antenna characteristic computation method is presented which can compute the radiation characteristics of the reflector surface for arbitrarily deformed shapes. The present method uses Akima's interpolation scheme for the deformation data so that data needed for computation of the radiation characteristics are obtained and highly accurate computations are realized. The analysis results of the deformation of the reflector surface of a reflector by a general-purpose structural analysis program (NASTRAN) is linked to the present computation method so that the variation of the antenna electrical performance by deformation is obtained and the results of the present method are presented. Further, it is shown that the measured antenna characteristics and the numerical results of the electrical performance by the reflector surface measurement data agree well. Hence, the present antenna characteristic computation method is extremely useful for the evaluation of the antenna characteristics. [ABSTRACT FROM AUTHOR]

This paper proposes a novel direct sequence/spread spectrum communication system for use in power line data transmission where the transmission characteristic varies largely and rapidly. In the proposed system, two similar PN sequences are used, one of which is loaded with data and the other is used as a reference PN. Waveform distortion during transmission can be cancelled out by an appropriate process utilizing two PN sequences. Data can be recovered as the sign of correlations between two PN sequences at the receiver. Results of computer simulation show considerable improvement in the data error rote over the conventional DS/SS system. [ABSTRACT FROM AUTHOR]

In the wake of the development of computer-aided facsimile equipment, office documents may be digitized, circulated on a network, and in the near future stored into files as soft copy. In this paper, we call this type of service facsimile-mail, and we discuss a multisignature method which is applied to facsimile documents. This method makes it possible to sign digital documents multiplexively and simplify the document exchange process. Document management is simplified and the reliability of the network is improved. [ABSTRACT FROM AUTHOR]

An end-to-end error recovery scheme is a promising way to obtain low end-to-end delays in packet switching networks. However, a too-short timeout interval may cause unnecessary packet retransmissions even when a packet is transmitted successfully to the receiver. On the other hand, a longer timeout interval may introduce large end-to-end delay when a packet is actually lost. Thus, it becomes important to determine an appropriate timeout period in the scheme. This paper analyzes a tandem queueing network system with blocking due to finite capacity in intermediate nodes and investigates the effect of the timeout period on the end-to-end delay performance. It is found that there exists the timeout period minimizing the mean packet transmission delay in the end-to-end error recovery scheme. The delay performance between end-to-end and link-by-link error recovery schemes also is compared and it is found that the delay performances of these schemes are influenced significantly by the node-to-node delay. [ABSTRACT FROM AUTHOR]

Recently, the printed dipole antenna has attracted attention as a two-dimensional array element which is electromagnetically coupled to an open-type feed line. This paper analyzes the characteristics of the printed dipole which is excited by an infinitely long microstrip line, by applying the method of moment to Richmond's reaction equation. If we assume that the feed line is sufficiently close to the ground plane, the dipole which is placed perpendicular to the feed line is treated as an equivalent parallel element. If the dipole forms a rotation angle with the feed line at the center of the dipole, it is regarded as an equivalent series element. Through a comparison of theoretical and experimental results for their frequency characteristics of equivalent impedances, the appropriateness of the theory has been confirmed. Basic characteristics were examined by numerical analyses for equivalent impedances of a microstripline-fed printed dipole antenna, the distribution of the electric current on the dipole, and the antenna radiation pattern. [ABSTRACT FROM AUTHOR]

This paper considers the Contention-ring (C-ring), an integrated token-passing/contention control scheme in a ring network. The C-ring is expected to combine the advantages of two control mechanisms and show an excellent performance for a wide range of traffic conditions. This paper analyzes the medium access control of the C-ring and proves its superiority to the Token-ring and CSMA/CD on the throughput-delay. Further, it is shown that the C-ring has a potential adaptability to very high-speed local networks with optical fiber links from its inherent multitoken property. [ABSTRACT FROM AUTHOR]

Over the past few years, the use of electromagnetic (EM) waves on highways has increased due to the spread of Electronic Toll Collection (ETC) systems in Intelligent Transport Systems (ITSs). Conventionally, roadside walls have been set up while considering the sound absorption of noise, but the need has developed for a structure also equipped with an EM wave absorption effect with the objective of preventing unwanted EM waves when EM waves are used. In addition, based on the properties of the EM waves used in Dedicated Short Range Communication (DSRC), the EM wave absorber used in the roadside walls should handle the circularly polarized waves that are second-order reflections due to the wall surface and have ultrawide angle characteristics. In this paper, we place an EM wave absorber that does not harm the acoustic absorption characteristics behind a commercial acoustic absorber (standard acoustic panel of the Japan Highway Public Cor- poration) and unify the acoustic absorber and the EM wave absorber in a single structure. We then study the implemen- tation of an acoustic and EM wave absorber having both functions of absorbing sound and EM waves, and wide angle characteristics for circularly polarized waves. [ABSTRACT FROM AUTHOR]

Although a reflector antenna with a single reflecting surface called a doubly curved reflector, based on a reflector shaping technology that uses geometrical optics approximation, was effective in synthesizing a fan-beam, there was ambiguity in the reflector design technique. This paper shows that an exact and unique solution in the sense of geometrical optics is obtainable as a solution of an ordinary differential equation. It then generalizes the doubly curved reflector design method, extending it to the synthesis of a curved fan-beam whose beam footprint has curvature. [ABSTRACT FROM AUTHOR]

In this paper, a cancellation technique using a reference signal which does not contain the components of the desired signal is proposed for optical synchronous M-ary FSK/CDMA. As spreading codes, the modified prime sequence codes which can increase the number of users are employed. Interference cancellation is done by using the correlation property of the modified prime sequence codes. A reference signal is constructed by using one of the modified prime sequence codes that do not have data components of the desired signal, and cancellation is performed by subtracting the reference signal from the received signal of the desired user. In the theoretical analysis, the Poisson effect in the input–output characteristic of the photodetector is considered, and the upper bound on the bit error rate (BER) is derived. The performance is compared to the optical synchronous M-ary PPM/CDMA system with an interference canceler in which a reference signal does not contain the data components of the desired signal. It is found that an optical synchronous M-ary FSK/CDMA system with an interference canceler has better BER performance than optical synchronous M-ary PPM/CDMA systems with an interference canceler under the condition of the same chip rate and number of symbols M, and achieves higher bit rate. Also, when the chip rate and bit rate are constant, it is found that optical synchronous M-ary FSK/CDMA system with an interference canceler can increase the number of simultaneous users. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(9): 20–32, 2000 [ABSTRACT FROM AUTHOR]