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The dual-frequency antenna with the same beam- width is well suited to the mobile communication base station antenna. One candidate is a corner reflector antenna whose elements are connected to a parallel feed line. However, no design equations or analysis have been published. This paper corrects this deficiency through analysis of the characteristics after integration of the two factors, spatial coupling and transmission line, for this antenna. A two dual-frequency corner reflector antenna is designed. One uses co-phase feedlines and is a wide band sector-beam antenna with a 3 dB beamwidth difference of 300 in the field pattern of horizontal plane and a return loss of less than -15 dB over a wide frequency range (from 900 MHz to 1.5 GHz). The other uses antiphase feed lines and its beamwidths can be varied by changing the corner angle while the beamwidths are coincident at two frequencies. [ABSTRACT FROM AUTHOR]

This paper proposes a flexible parallel optical data transmission system as follows. The data transmission itself is executed in parallel by utilizing the super- parallelism of the Light. In addition, the address information which is necessary for the transmission is superposed on the transmitted data. By those schemes, the capacity of the individual transmission channel as well as the number of transmission channels in the system are made variable. This paper describes first the principle of parallel optical data transmission. It is shown that the symbolic substitution (SS) is useful in the superposition and separation of the address information, which are the basic operations of the system. SS is a parallel and position-invariant Logical operation. An experimental system is constructed by the SS technique using the computer- generated Fourier hologram (CGFH). A result of experiment is shown for the single-channel parallel transmission of two-dimensional data. Thus, it is shown that the flexible transmission system, where the capacity of the individual transmission channel as well as the number of transmission channels are variable, can be realized by the proposed transmission scheme. [ABSTRACT FROM AUTHOR]

In this paper, the statistical characteristics of Middleton class A impulsive noise are investigated to obtain a receiver that is robust against impulsive radio noise. It is shown that the in-phase and quadrature phase components of class A impulsive noise are not statistically independent though they are uncorrelated. Then a new receiver design based on the dependence between these components is proposed for class A impulsive noise. Numerical results show that the proposed receiver is quasioptimum and its performance is much better than that of a conventional receiver. [ABSTRACT FROM AUTHOR]

The improvement of the signal-to-noise (SN) ratio is one of the most important issues for the high resolution earth observation system. A time delay and integration (TDI) method combining plural CCD output signals should provide the solution for acquiring high SN ratio without increasing the optical diameter. However, for an actual satellite, there are various fluctuations in the satellite attitude or jitters from other equipment, which degrade the SN improvement ratio achieved by the time delay and integration method. This paper analyzes SN improvement ratio characteristics under the above fluctuations. This paper reveals optimum integration times and the maximum SN improvement ratio and also the requirement on satellite attitude variation and jitters from other equipment. The paper also discusses the methods to obtain the maximum SN improvement ratio using correlation detection between adjacent CCD for the time delay and integration method even under the presence of the above fluctuations. [ABSTRACT FROM AUTHOR]

This paper analyzes the throughput of a transport protocol, such as the ISO transport protocol class 4 (TP4) and the transmission control protocol (TCP), in a fiber distributed data interface (FDDI) network. ft also studies the influence of the target token rotation time (TTRT), ring latency, window size, and frame length on the throughput performance in cases of both symmetric traffic and asymmetric traffic. Furthermore, the throughput is compared with that of FDDI without transport protocol in order to quantify the overhead of the transport protocol. Numerical results indicate that the influence of window size and frame length on the throughput is larger than that of TTRT. [ABSTRACT FROM AUTHOR]

A variety of multiaccess optical communication systems with common carrier have been reported recently. This paper proposes a new type of multiaccess coherent optical communication system with star configuration in which a common optical carrier from a single source is distributed by a star coupler. In this system, the carrier is phase-modulated at each user by an external modulator through a subcarrier signal and the signal is received by an optical heterodyne receiver. A feature of the system is that the distributed optical carrier and the modulated light are directional-division multiplexed. Theoretical analysis of the carrier-to-noise power ratio (CNR) of the system is carried out in this paper taking into account the effect of interference light caused by reflections, backscattering, or insufficient isolation of a circulator used in the system, followed by discussions on the allowable value of the signal-to-interference light power ratio and on the relation between transmitter power and maximum user numbers. [ABSTRACT FROM AUTHOR]

In the communication system using a constant modulus signal, a constant modulus algorithm (CMA) adaptive array antenna is effective for elimination of the frequency-selective tiding generated in multiple propagation paths. On the other hand, in the system in which CMA adaptive loops are installed for each antenna element in an array with mare than 10 elements used for mobile satellite communication, the computing time and the amount of hardware become excessive. in this paper, a beam-space CMA adaptive array antenna (BSCMA) is proposed in which a portion of the multibeam output is selected to form a CMA adaptive array. In the BSCMA, first, a multibeam is formed by means of a fast Fourier transform (FFT) and only the beams whose output power exceeds a threshold level are selected. An adaptive process is carried out with the CMA as a guiding principle only for the selected beam outputs. The BSCMA has an advantage of carrying out the capture of the desired wave and the elimination of the interference wave effectively with degrees of freedom corresponding to the number of arriving waves. The method is effective for an adaptive antenna system applied to an array antenna constructed with many antenna elements. In this paper, the configuration of the BSCMA is shown and its characteristics are investigated by the numerical simulation. [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]

In asynchronous transfer mode (ATM) networks, each user requests a call setup with the traffic descriptor which describes its own traffic characteristics. Since network resource control is carried out by this traffic descriptor, it would be necessary that the traffic generation is monitored by the network, which is the so-called usage parameter control (UPC). In this paper, three methods are evaluated analytically for implementing the UPC function: a discarding method, a tagging method, and a hybrid method. The last method is proposed anew in the paper and the comparative results for the three methods are offered from a viewpoint of performance of the cell multiplexer when the output traffic from UPC is super. [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 discusses the multipath allocation problem in the communication network and proposes a multipath allocation algorithm suited to the distributed environment. The multipath allocation problem is a problem where multiple paths arc to be allocated without a conflict. This problem has been difficult to solve in the distributed environment since relations among various routes must be considered. The algorithm proposed in this paper solves this point by realizing the asynchronous path search. In this paper, the basic characteristics of the proposed algorithm are described through the comparison between the proposed and the traditional algorithms for the case of serial computation under the centralized control. Then the proposed algorithm is applied to several kinds of distributed cooperative multiagent models, and it is demonstrated that the proposed model can easily be applied to the distributed environment. A simulation is executed actually using several workstations, and it is shown that the proposed algorithm is desirable as a solution method for the multipath allocation problem m the distributed environment. [ABSTRACT FROM AUTHOR]

Pipelined protocol processors are used in high-speed networks such as FDDI for achieving high-throughput data communications between end users. In this paper, we present a model for computing the maximum throughput that can be delivered by such processors. The parameters of the model are: input packet length, length of PDU (Protocol Data Unit) and SDU (Service Data Unit) headers, packet processing time of pipeline stages, capacity of the FIFO channels that inter-connect stages, and average number of packets assembled/segmented at a stage. As an example, the maximum throughput of an idealized pipelined processor that executes the FDDI, LLC Class I, IP, and TCP protocols is computed. Also, we show that the formulas given in [1] and [2] are particular cases of the formulas presented in this paper. In a typical application of the proposed model, some desired, or measured, throughput characteristics of a protocol processor will be given, and the parameters of the processor will be computed. [ABSTRACT FROM AUTHOR]

The Virtual Path concept has several beneficial features to construct an economical and efficient Asynchronous Transfer Mode (ATM) network. The Virtual Path capacity control technique can increase network flexibility and improve transmission efficiency through statistical sharing of facilities. This paper presents an adaptive virtual path capacity control method which maximizes transmission efficiency under the condition of limited processing load. Evaluation shows that the proposed method successfully im- proves network transmission efficiency with a slight increase in processing load compared to the fixed virtual path capacity scheme. [ABSTRACT FROM AUTHOR]

This paper evaluates the performance of the two-way message transmission system on the meteor burst channel developed and tested by the authors. First, the usual channel model is simplified and then the system is analyzed. It is shown through simulations that the errors introduced by the new channel model and by the approximated analysis method are negligible and the proposed method can be used to design and evaluate the system. The performance of the system having packets with subblocks is compared to that of one with usual packets. It is shown that, by using packets with subblocks, robustness of the system performance against changes of channel parameters as well as a shorter time needed to transmit a message can be obtained. The method of performance evaluation shown in this paper has adequate generality and is also applicable to many other meteor burst communication (MBC) systems. [ABSTRACT FROM AUTHOR]

This paper studies the system performance of a zone-structured packet radio network with mobile terminals to which the slotted ALOHA protocol is applied. Conventional performance analyses of the zone-structured packet radio network have not considered the effect of terminal mobile speed. Here, a model is developed for such a zone-structured network where a Markov model is used as the mobility model of a terminal and analytical techniques to evaluate static and dynamic performance of the system are presented. Numerical results and their intuitive interpretations are discussed to examine the effect of zone overlapping, mobile speed, etc. [ABSTRACT FROM AUTHOR]

In conjunction with a recent increase in information density, radio wave communication becomes more complex and more varied. Hence, effective use of radio wave resources is required. Under such a situation, the frequency-selective screen (FSS) with which a single antenna is capable of receiving multifrequencies at the same time has drawn attention. The FSS consists of conductors placed periodically on a dielectric substrate. In this paper, the spectral domain moment method is applied to the problem of scattering from infinitely many conductors with arbitrary shaped elements on a semiinfinite dielectric substrate. From the results, the effect of the surface resistance of the conductor and the characteristics due to the conductor shape are investigated. Various scattering characteristics by linearly and circularly polarized incidence are discussed. [ABSTRACT FROM AUTHOR]

In the multichannel frequency division multiplex (FDM) optical transmission, the intermodulation distortion generated by the nonlinearity of the LD is a problem. In this paper, it is analyzed that fin the number of transmission channel, N, and the optical modulation index per channel, m, the CSO and CTB are constant for a different value of N if the effective optical modulation index, m√N, is maintained. The results are compared with experiments. In the present analysis, two types of nonlinearity of the current-to-optical conversion characteristics are considered. One of them is the nonlinearity near the bias current of the LD and is predominant in the region of a small effective optical modulation index. Another is the nonlinearity at the threshold value of the LD and is dominant when the effective optical modulation index is large. It is shown by means of the probability density function that the CSO and CTB degrade suddenly if the effect of the nonlinearity of the threshold value appears. In the FM-FDM optical transmission. many distortions in the transmission bandwidth behave as the white noise due to frequency modulation when the carrier is frequency modulated by a video signal. Hence, the CN ratio is effectively degraded. In this paper, it is further presented that the CN ratio degraded by the distortions can be derived from the CSO and CTB by taking into consideration the frequency allocation of the FM signal. [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]

Electrostatic discharge (ESD) usually is accompanied by two phenomena: the injection of discharge current, and the radiation of electromagnetic pulses. The discharge phenomenon can cause transient electrical interference of electronic equipment and the time-domain measurement of radiated fields associated with ESD is a difficult task because of the very fast and wide-band waves involved. This paper describes measurement and analytical results of ESD pulses. ESD pulses were measured by three EMI-type antennas (a loop antenna, a biconical antenna, and a double-ridged guide antenna) in the time domain. It is shown that the electromagnetic pulses can be evaluated by the energy spectrum without using the phase reformation of antenna factors. Based on the measurement of waveforms of the known electromagnetic pulses, it is shown that the waveform can be evaluated with an accuracy of 2 to 6 dB. As a result, it was found that radiated ESD energy does not always increase in proportion to discharge voltage and that ESD pulses produced by low-voltage ESD can cause strong electromagnetic interference. [ABSTRACT FROM AUTHOR]

This paper presents a BCMP-type closed queuing network which models the error recovery defined as HDLC based protocols such as LAPB, LAPD, and LLC type II. Throughput and average end-to-end delay against the I-frame loss probability owing to bit errors are obtained by using the queuing network. With the I-frame length independence assumption, agreement between analytical and simulation results is shown to be fairly good. [ABSTRACT FROM AUTHOR]

Intensive efforts have been observed in recent years on the development of data communication technology, aiming at the effective utilization of such existing transmission tines as the in-house distribution line. The automatic consumption meter reading, for example, uses the low-voltage distribution line as the transmission channel. This paper aims at the improvement of the receiver demodulation performance m the data transmission using the low-voltage distribution line and proposes the phase-diversity reception using two phases (red and black) of the single-phase, three-wire system. In the data transmission using the low-voltage distribution line, stray signals are produced between the two phases of the single-phase, three-wire lines and two signals with different signal-to-noise (SN) ratios are received. If a simple scheme such as the addition is employed, a problem arises in that the reliability of the demodulated data is deteriorated. To cope with this problem, this paper proposes a phase-diversity reception, where time-varying phase difference is adjusted to zero using an adaptive phase shifter and the SN ratio is improved by synthesizing the two-phase received signals. The proposed scheme is implemented on a digital signal processor (DSP), and a robustness against the channel noise and the periodic attenuation is realized by the feedback (FB) control. As a result of an experimental evaluation, it is shown that the SN ratio is improved by 2.7 dB at the maximum for the stationary phase error, compared to the traditional simple addition and the addition/subtraction selection schemes. Thus, it is verified that the receiver demodulation performance of the low-voltage distribution line data transmission can be improved. [ABSTRACT FROM AUTHOR]

There are two aspects to the region segmentation coding and the model-based coding which extract and encode the structure and features from image information. They are the “technique for compression of image reformation7rdquo; and the “technique for structural description of image information.” If me image information is described structurally, not only is the highly efficient coding realized but also a new image can be constructed by a local manipulation of the original image. This paper combines the region segmentation of the image based on Munsell color space and the region merge based on the hue difference between the regions. Then a new region segmentation coding based on the result of the formentioned region segmentation is proposed. It is assumed that an object consisting of the color image corresponds to a region of almost the same hue. The hue information within the region is course-quantized based on the memory colors, and the shape information is coded using the chain code. For the value information which contains the information for the shape, shade, etc., of the object, the adaptive cosine transform coding is applied. For the chrome information, the region is approximated by a polynomial function and its coefficients are encoded. The proposed coding method is applied to several standard images which are portraits of relatively simple structures with different face sizes. The color information is transtmitted with a relatively high efficiency, occupying approximately one-fourth of all the transmitted information; and the usefulness of the region segmentation proposed in this paper is demonstrated. Compared to the traditional waveform coding, the method has the advantage that the local manipulation of the image is easier, although the total trasmitted information is slightly larger. [ABSTRACT FROM AUTHOR]

Multipath fading is a (actor degrading the communication quality in mobile communications. It has been reported that an adaptive array antenna can enable elimination of the effect of delayed signals by an appropriate control of the radiation pattern. In this paper, it is recognized that an optimum weight of the array antenna can be computed if the direction of arrival and the signal to-noise ratio of the received signal are known. By using the spatial frequency derived by the discrete Fourier transform (DFT) of the received signal which is spatially sampled by the array antenna, an algorithm is proposed in which the directions of arrival and the signal-to-noise (SN) ratio of the desired and interference waves are estimated and an optimum weight coefficient of the antenna is computed. This algorithm is different from those in the conventional adaptive digital filter algorithms such as the LMS algorithm. It requires no reference signal and can follow quickly changes in the communication channel. Further, a method is proposed to improve the estimation accuracy of the direction of arrival and the SN ratio with a limited number of elements by using the property of the DFT. To confirm the principle of the proposed algorithm, the basic characteristics are evaluated by computer simulation. [ABSTRACT FROM AUTHOR]

Traffic generated by B-ISDN services is difficult to predict because the fluctuations in normal traffic patterns are large. As a result, it is difficult to provide network equipment to avoid traffic unbalance. The advantage of using asynchronous transfer mode (ATM) in BISDN networks is that path bandwidth control facilities can be used to dampen the unbalance in traffic. This paper proposes a new algorithm, based on the hatch modification method, for controlling traffic fluctuations. The batch modification method is used to control path bandwidth from a centralized control center. The virtual path bandwidth is calculated using optimization calculations based on information from the entire net-work. Hence, it is necessary to develop an algorithm to perform the optimization calculations. The algorithm uses the worst case blocking probability and the total amount of traffic. The algorithm is verified with numerical examples that compare traffic patterns in a model net work. [ABSTRACT FROM AUTHOR]

Previously, the authors have proposed a design method of a shaped dual-reflector contoured-beam antenna with virtual multihorns with a view to applications to the broadcast satellite BS-3. In such a design, there were discontinuities on the main reflector. In this paper, a method for eliminating these step discontinuities is studied for the dual-reflectors. The current distribution on the main reflector corresponding to the desired radiation pattern is determined by optimization depending on the constraint gain of the far field. Note that the optimization method for the aperture phase distribution was known for a single smoothly shaped contoured-beam antenna. Also, in this paper, an optimization method for the amplitude distribution is proposed anew. Further, by adding a restriction to the phase difference between the adjacent elements in the optimization of the phase distribution, the step discontinuity on the reflector is eliminated. By means of this method, an antenna made of a main reflector with an aperture diameter of 2.3 m is designed at 12 GHz which is the frequency of the downlink of the broadcast satellite. Most of Hokkaido, Honshu, Shikoku, Kyushu, and Okinawa is covered by a radiation pattern with more than 40 dBi and other remote islands with more than 28 dBi. A one-half scale model is fabricated and the radiation pattern is measured at 22 GHz. The results agree well with the numerical results. Also, the sidelobe and the cross-polarization characteristics of this antenna sufficiently satisfy the technical standards in RR.AP 30. [ABSTRACT FROM AUTHOR]

With the advent of the information age. congestion of communication networks due to natural and social phenomena occurs more easily, and coping with this overload traffic is necessary. In this paper, a mathematical model for evaluating overload traffic is presented, and methods for using this model to evaluate overload traffic are shown. Since the state of a congested network varies with time, the transient behavior of the traffic needs to be analyzed. However, it is impossible to conduct the analysis by means of existing methods because of the enormous amount of computations required. Therefore, by regarding the traffic in a congested network as deterministic, an approximate solution, by means of deterministic equations, is proposed in this paper. The transient analysis of the throughput and overflow rate of networks with finite resources can be evaluated by means of this approximate solution. In accordance with the proposed model, the methods to compute the call blocking probability, which is used to evaluate the network robustness against temporary overload, and the throughput in circuit-switched networks are shown. It is possible to compute the number of resources (i.e., buffers) which is appropriate for a given blocking probability considering the robustness of the network against congestion. The maximum throughput of the network can also be evaluated with transient analysis of the throughput. [ABSTRACT FROM AUTHOR]

The multibeam transponder allows one to use a smaller ground station in satellite reception system and to make good use of the frequency hand. The redundant system is important for the higher reliability of transponder, especially as the number of the beams increases. This paper considers a redundant system for a multibeam transponder. The concept of the expected system value herein introduced takes the reliability and the transponder weight into account simultaneously. Comparing the performance of eight typical redundant configurations, the importance of the common and active redundancy is shown. [ABSTRACT FROM AUTHOR]

This paper discusses the Layered construction of the OSI second layer (data link layer) in the satellite packet communication network from the viewpoint of the system performance. The isolated-type system, where the media access control (MAC) sublayer and logical link control (LLC) sublayer are defined independently, and the combined-type system, where they are defined in a related way, are considered. The performances of those two systems are compared, using the throughput and the average response time as the evaluation criteria. The TDMA-Reservation and the slotted-ALOHA are considered as the MAC protocol. The connection-oriented type is considered as the LLC protocol. As to the TDMA-Reservation communication network, the isolated-type system is analyzed by the equilibrium point analysis. Then the performances of the isolated type and the combined type are compared by the analysis and simulation. It is shown quantitatively by comparison that the performance of the isolated type is always better than that of the combined type. As to the Slotted-ALOHA communication network, it is shown by simulation that little difference is observed in the performances of the isolated and the combined types. [ABSTRACT FROM AUTHOR]

An asynchronous transfer mode (ATM) switching network handles not only traffic of various bandwidths, but multirate bursty traffic including constant bit rate and variable bit rate traffic as well. Consequently, to simplify the design and operation of the facility, it is desirable for the ATM network to be nonblocking at the connection level. The nonblocking issue when the network must handle variable bit rate traffic is related closely to the connection admission control (CAC) method. While the non blocking feature for a linear CAC function has been studied in the past, the relation between the switching network cell-level quality and non-blocking characteristic for a specific CAC premising variable bit rate traffic has not been analyzed. This paper examines a nonlinear CAC, evaluates the cell loss probability and statistical multiplex gain when it is applied and proposes the definition for a non-blocking feature called "(ρ0, p, q) nonblocking." Next, a cell distribution-type, three-stage ATM switching network is shown that ensures (ρ0, p, q) nonblocking for traffic including multicast connections without expanding the internal link capacity either in terms of space or speed. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive predictive coding method for still images using neural networks. Using a neural network, this method realizes data compression by representing the image in a hidden layer which has a lower dimensionality (i.e., contains fewer unfits) than the input layer and then quantizing the output of each hidden layer unit. In this method, extrapolative prediction of a 4 × 4 pixel block is utilized and the prediction residual error is the target of coding. Then, to realize neural networks which possess high versatility, training of the neural networks using training vectors which are generated based on a statistical model of interpolative error signals is performed. The rate-distortion characteristics of 11 types of neural networks, having different numbers of units in the hidden layer, are calculated. The optimal relationship between the number of units in the hidden layer and the number of quantization levels corresponding to each unit are explained. Based on the local statistics within the image and the forementioned rate-distortion characteristics, the neural networks and the number of quantization levels are controlled adaptively. At the same time, by introducing a variable block-size method, high encoding efficiency and good reproduction quality are realized. Finally, it is demonstrated that the method presented herein exhibits better encoding performance than the method which performs vector quantization of the same prediction residual error. [ABSTRACT FROM AUTHOR]

It is known that the bit error rate is deteriorated if them exist echoes on the transmission line. This paper presents a theoretical analysis on influences of an echo on the bit error rate in the optical DPSK communication system. In general, there exists a floor in the bit error rate due to the phase fluctuation of the laser light, which is not reduced by increasing the received optical power. It is shown that the floor value increases with the increase of the amplitude ratio of the echo to the principal wave, as well as the increase of the delay time. It also is shown that the effect of the echo is more remarkable when the hit rate is higher and the spectral Iinewidth of the laser light is narrower. [ABSTRACT FROM AUTHOR]

Intensive research and development efforts have been made on the intelligent network (IN) to realize diversified and advanced telecommunication services and the early introduction of new services under a multi-vendor environment. Earlier research and development, however, assume the conventional telephone service and narrowband ISDN services and gave little consideration to the broadband ISDN. The study of the IN from the viewpoint of the broadband ISDN is urgent considering the systematic realization of the services (i.e., multimedia services) that are not yet sufficient as well as the increase of the demand for the development of new services. This paper proposes the call model, which provides the basis for realizing the IN architecture incorporating the broadband ISDN. First, the basic concepts are defined clearly. Then the call model is proposed which can realize the general connection control for various connection types as well as the flexible control for the multiple virtual channels in the multimedia environment. The model also facilitates the control of the interactions among related services. Finally, the service control characteristics of the proposed call model are investigated. [ABSTRACT FROM AUTHOR]

In an ATM network, calls are transmitted through several, nodes. At this time, quality control over multiple nodes is considered to be better than quality control for each node independently. In view of such considerations, this paper proposed two control methods regarding discard (loss) quality and call level delay over nodes by carrying quality information in the call. In controlling delay quality, a call delayed at a node is given a higher priority in the next node to recover the delay. Since a cell can remain in one node for a long time, the buffer length of each node is lengthened. This leads to a decrease in the discarding rate. In addition, in discard quality control, the variations in the discard quality of each call can be minimized by per- forming discard of cells inside a buffer on the basis of the discard quality information of previous nodes when the buffer is full. The effect of these control methods is illustrated by simulation. [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]

In cellular mobile communication, the same channel is shared by a number of cells. Up to now, the model has been considered where the same channel is used with a sufficient separation, so that the radiowave interference is sufficiently small for any call generated in the cell. Recently, on the other hand, a model has been proposed where the same channel is assigned independently of the specified cell separation, as long as the carrier-interference ratio is above a certain value. Although the assignment algorithm has been discussed for the traditional model, no report has been made on the detailed assignment procedure for the new model. With such a situation as the background, this paper proposes an application of Hopfield's neural net as an approach to the channel assignment in the new model and derives the energy function. Several results of computer simulation are shown where the proposed neural net is applied to the mobile communication model. It is not always true that the neural net produces the optimal solution, but it is interesting that an unexpected improvement of the channel utilization is observed in the communication traffic as far as the result of computer simulation is concerned. [ABSTRACT FROM AUTHOR]

This paper derives an estimating equation for the received power space-correlation coefficient needed for the design of a space diversity receiving system for improved transmission performance of a microwave relay system as a semiempirical equation based on the theoretical investigation, with corrections by measured data, from a three-ray model in which the received wave consists of the direct wave, reflected wave, and duct refractive wave. This equation is determined from the amplitude statistics of the three waves, the propagation conditions such as the distance and the transmitter and receiver heights, the frequency and the radio meteorological statistics. This model contains the two-ray model method intended for propagation path with a strong reflection (strong reflection link) and the Makino-Morita method which assumes Rayleigh fading for a propagation path with a weak reflection (weak reflection link). The measured results of the spatial-correlation coefficient of the received power in about 30 links measured in Japan, including both the strong and weak reflection links, are found to agree well with the estimated values based on the present equation. Hence, the effectiveness of the estimation equation proposed in this paper is confirmed. [ABSTRACT FROM AUTHOR]

This paper investigates an adaptive equalizer with career frequency offset compensation for digital mobile radio transmission over several tens kbit/s. The performance of conventional adaptive equalizers for mobile radio severely degrades for receiving signals having carrier frequency offset which is mused by local oscillator frequency offset due to misadjustment, temperature dependence, and aging. Carrier frequency offset compensation for TDMA burst signaling requires both accurate and short-time measurements. However, both requirements have a trade-off relationship and must be optimized. This paper proposes the carrier-acquisition-during-training (CAT) algorithm for transmissions allowing a training signal. First, two basic configurations and their equivalence are discussed. Next, computer simulations and real-time experiments with one-chip DSP show the effectiveness of CAT by demonstrating training convergence, optimum parameter characteristics, and average BER performance under two-path selective fading with one-symbol delay difference and independent Rayleigh components. [ABSTRACT FROM AUTHOR]

This paper reviews recent worldwide activities concerning research and development for spread spectrum communication technologies. Included are various novel proposals, remits of analysis, and experimental results concerning spreading code, synchronization, device, system construction, and applications to consumer and mobile communications. For the spreading code, however, two invited papers are presented in this special issue and hence only a brief explanation is made hole. Instead, considerable space is devoted to the recent progress toward development of CDMA public land mobile telecommunication systems in the United States. [ABSTRACT FROM AUTHOR]

This paper proposes a method to detect a fault location in a faulty paired cable consisting of branching cables and different gauge wires along a length. Calculating an input-admittance of a faulty pair cable involves consideration of cable length, cable secondary constants, branching conditions, and a fault location. Under this principle, a measured input-admittance can be indicated by fault location if cable length, cable secondary constants, and branching conditions are known. In addition, when a calculated input-admittance agrees with a measured input-admittance, the fault can be located. However, a location error appears because actual cable secondary constants are slightly different from those cable secondary constants that are calculated. This paper also describes the location errors caused by secondary constants differences. Furthermore, two improvement methods for location errors have been developed. One method applies the difference between input-admittances before and after fault. The other method refers a measured input-admittance of a fault-free cable to that of a faulty cable. As results, fault location errors in an open fault (a breakdown of wires) and an insulation degradation fault were significantly decreased. [ABSTRACT FROM AUTHOR]

Strong international effort has been made toward the realization of a B-ISDN based on ATM techniques. This paper proposes self-healing techniques for enhancing ATM network reliability. Self-healing is defined here as failed path restoration with distributed control mechanism by using cross-connects. First, the characteristics of virtual paths (VPs) are compared with those of digital paths in STM networks. It is clarified that VP benefits can be exploited for network restoration upon failure. Two high-speed self-healing algorithms that make the best use of VP characteristics are then proposed for restoring single-link failures. A technique for multiple-link failure restoration also is proposed. Finally, restoration performance is evaluated by computer simulation. It is confirmed that the proposed algorithm enables faster restoration than that possible using the existing algorithm for STM networks. [ABSTRACT FROM AUTHOR]

In the conformance test of the communication protocol, it is desired from the viewpoints of strictness and efficiency to generate automatically the test sequence, based on the formal description. Several methods have been proposed for this purpose. All of these methods are based on the two formal descriptions which can be the basis for the test-sequence generation: one is the description based on the order of the input/output events, and the other is the decription based on the finite-state machine model. This paper attempts to compare the applicability of the two description methods to the conformance test. Also, it evaluates the error-detection capability which actually generates the test sequences for the following two cases: (1) The test sequence is generated directly from the specification based on the order of events; (2) The test sequence is generated from the finite-state machine model, which is obtained from the description of (1). In the evaluation, a simulation technique is employed which uses as a testing object a finite-state machine containing random errors. Finally, this paper notes the handling of the undefined transitions contained in a large number in the actual protocol and considers the class of errors pertinent to the actual protocol, such as the redundant state errors or the replicated state errors. [ABSTRACT FROM AUTHOR]

Recent construction of corporate communication networks with the use of high-speed digital links, etc., is becoming popular. Economical and reliable networks must be designed. Few papers have been published on the design of corporate communication networks. Moreover, some need improvement. This paper proposes a new topological design algorithm for efficiently constructing economical and reliable corporate communication networks. This algorithm achieves effective network design by utilizing the correct network information. The triangle network configuration, which provides higher reliability than two-connected networks with only a small additional cost, is proposed. Moreover, this paper proposes a new idea at a lower cost (cost lower bound) that evaluates the results obtained by various heuristic algorithms. Superiority of the proposed algorithm is verified by means of this cost lower bound. [ABSTRACT FROM AUTHOR]

This paper proposes a prioritized resolvable-contention-ring scheme for high-speed optical communication networks and investigates its performance. The priority mechanism is based on the time-token control scheme. This mechanism attempts to guarantee the frame delay of time-critical traffic by controlling the frame transmission of noncritical traffic. The noncritical frame can be transmitted only if token rotation time is faster than target rotation time. This paper examines the priority mechanism in the case of two priority levels and also in the case of four priority levels. System performance is studied using a computer simulation method with a time-continuous simulator. The validity of the priority mechanism is demonstrated in a comparison with a fiber distributed data interface (FDDI) and the nonprioritized resolvable-contention ring. Efficient operation of the priority mechanism is investigated by considering the buffer overflow rate of each priority class. The proposed scheme performs effectively. Moreover, the performance of FDDI is comparatively degraded because of long token waiting time and large token capture time. [ABSTRACT FROM AUTHOR]

In this paper, characteristics of degenerate parametric amplifiers are analyzed and are expected to be useful as a generator of a squeezed state or a noiseless amplifier for an optical wave. Especially, when a degenerate parametric amplifier is used as a noiseless amplifier or a squeezed-state generator (squeezer), the depletion of the pumping light which has been neglected affects the quantum noise characteristic of the squeezed light. This effect is analyzed in this paper. Further, when the incident light does not satisfy the phase matching condition, the effect of this phase shift on the gain and quantum noise characteristics of the degenerate parametric amplifier is studied. On the other hand, when a degenerate parametric amplifier is used as a preamplifier for the receiving side of the communication system, the phase noise of the pumping light can be a cause of degradation of the communication system performance. The phase noise of the pumping light is classified as the phase shift and the phase fluctuation caused by the quantum noise and then the effects of these phase noises on the quantum noise characteristics of the squeezed light are analyzed. Further, in the BPSK optical coherent communication system, the effect of the phase noise on the bit error rate is analyzed. A quantitative evaluation is made to determine how small the phase noise of the pumping light should he in order not to degrade the error rate. [ABSTRACT FROM AUTHOR]