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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 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]

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

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]

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 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 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]

To realize a future high-speed and ultralarge-capacity optical transmission, it is indispensable to analyze the ultrahigh-speed transmission characteristics of the entire system as well as functional circuits, devices and materials comprising the system. Evaluation of such a transmission characteristic requires ultrahigh-speed optical waveform measurement method. In this paper, a new optical waveform measurement method called the sum frequency generation (SFG) optical sampling method is proposed. In this method, the SFG which is a second-order nonlinear optical effect is used for all-optically sampling the optical waveform to be measured (at the optical stage) by means of an ultrashort optical gate pulse. Hence, the bandwidth limitation of the optical receivers and the electronics can be eliminated. By means of this technique, accurate measurement without waveform distortions can be realized while high time resolution and high S/N ratios are maintained. In this paper, the theoretical performance of the present measurement technique is discussed and the measured results by the present method are presented. [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]

This paper discusses the properties of the motion- compensating prediction error signal and the appropriate coding scheme. For a high-efficiency coding of the moving picture, generally, a method combining the motion-compensating prediction and the spatial coding such as discrete cosine transform (DCT) is used. It is shown that the spatial coding used here is effective for the input picture signal. On the other hand, the motion-compensating prediction error signal has spatial properties which are considerably different from those of the input picture signal. For example, the correlation between pixels is small, especially in the vertical direction, or the magnitude of the correlation locally fluctuates greatly. Consequently, such signal transformations as the orthogonal transform and subband partition are not effect tin in the motion-compensating prediction error signal. This paper analyzes the correlation between pixels to reevaluate the traditional coding schemes and to propose the adaptive coding scheme with and without signal transformation. It is shown that the proposed scheme can prevent the deterioration of the picture quality found in the traditional schemes while retaining equal or better rate-distortion performance than that of the traditional scheme. [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]

This paper describes a method of converting a specification and description language (SDL) specification into a program by introducing SDL/OS. The TRON-specification OS is adopted as OS and C++ as a programming language to make the program portable. SDL/OS, which consists of libraries described in C++, is constructed on OS so that the program converted from SDL can run as it is, SDL/OS realizes the SDL functions easily by using the functions of TRON-specification OS. Finally, this paper reports that this method is very effective in enhancement of software productivity by applying it to software development of real communication systems. Moreover, performance degradation can be compensated to some extent by introducing function calls in the same task. [ABSTRACT FROM AUTHOR]

Multimedia backbone local area networks (LAN) have recently become key components of private networks as fiber distributed data interface (FDDI) backbone LANs. This paper discusses the architecture of loop-type high-speed multimedia backbone LANs (MBLANs) based on B-ISDN technology as the next generation LAN targeting the introduction stage of the B-ISDN age and its realization. This paper highlights problems to be solved with respect to the adoption of B-ISDN technologies, such as synchronous digital hierarchy (SDH) and asynchronous transfer mode (ATM) technology, to MBLANs and proposes some solutions. It also presents high-speed MBLANs with transmission rate of 622 Mbit/s and the basic hardware implementations of the system. [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]

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

With the advent of the radio relay system and multilevel modulation, the multicarrier system and variable capacity transmission system are proposed to realize excellent performance in the lading channel. Accordingly. ills desired to realize & highly functional MODEM which can cope with those systems in a flexible way. On the other hand, intensive studies have been made on digital signal processing in the modulation and demodulation in the field of data modem. However, these methods consider the low-rate system of 1ess than 100 Kbaud and are difficult to apply directly to the system where the transmission rate of 10 Mbaud or above is required For the foregoing masons, this paper considers the realization of the all-digital modulator which can realize the high-capacity transmission of over 10 Mbaud for the multilevel modulation system, such as 256 QAM. This paper discusses the design of the digital filter with excellent intersymbol interference. The condition for the carrier frequency for a given clock rate is presented. Then a variable multilevel modulator with a simple correction circuit is proposed which can be applied to the variable-capacity transmission system. Finally, the proposal circuit is constructed and it is confirmed that an excellent modulation performance is obtained without adjustment in various multilevel modulation systems. [ABSTRACT FROM AUTHOR]

The digital cross-connect system (DCS) employs cross-connect equipment composing the synchronized digital network. The scale of DCS is enlarged using the rearranged-type TST switches based on the nondisturbing rearrangement control algorithm. This paper considers the case where DCS is controlled using the proposed rearrangement pattern search algorithm. A control algorithm is proposed which can avoid the generation of a blocking state, thereby necessitating the rearrangement control, and can realize the nondisturbing rearrangement control when a blocking is produced. The effectiveness of the method is demonstrated by computer simulation. In this paper, knowledge in other studies such as the mechanism of block generation is summarized. Then an evaluation measure is introduced for the S switch state. A control algorithm is proposed which suppresses the generation of the blocking by selecting the S switch timeslot to maximize the evaluation measure. It was verified by the computer simulation that the generation of the rearrangement control is reduced by approximately 5 to 30 percent, depending on the switch structure, compared to the algorithm that minimizes the evaluation measure for the switch. A nondisturbing control method for the switch also is presented. [ABSTRACT FROM AUTHOR]

This paper proposes an interference cancellation method called the in-band power minimizing method (IPMM), and describes the tree of the method in satellite communication earth stations. In this method, an interfering signal arriving from an earth station antenna is combined by a cancellation circuit with an interfering signal received by an auxiliary antenna and the two interfering signals are arranged to have equal amplitudes but opposite phase. To achieve this condition, the amplitude and phase are adjusted so that the signal power of the output signal from the cancellation circuit contained in the desired signal frequency band is to be a minimum. This method is characterized by the fact that a simple circuit can be used to detect interference rapidly and accurately even at low C/N ratios. This paper also discusses the principle of IPMM and examines the remits obtained when it is applied to small earth stations. It was found that IPMM is quite effective in this application. [ABSTRACT FROM AUTHOR]

Multidimensional traffic models where calls of more than two classes of different properties share the same resource are very important as basic models for tightly coupled multiprocessor systems, etc. Thus, this type of research has long been actively performed. So far, some papers on finite-source loss models have been presented. However, neither finite-source delay models nor their approximate analyses have been investigated much. As an approximate analysis method of delay queueing model with two different classes of quasi-random input (Ml, M2/M1, M2/S//N1, N2 model), this paper proposes a method which approximates combination states of waiting calls of each call class by the ratio of numbers of waiting calls of each call class. Moreover, by comparing numerical results of tiffs approximate analysis with exact solutions and simulation values, it is shown that this approximate analysis method has very good accuracy. [ABSTRACT FROM AUTHOR]

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

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]

In the practical implementation of the coherent optical transmission system, it is important to establish the techniques for stabilizing the optical frequency con- sidering the actual environmental condition, as well as a technique for compensating for the variation of the state of polarization in the usual single-mode optical fiber cable. This paper considers the application of the polarization diversity receiver to the CPFSK heterodyne delay detection in the 2.4-Gbit/s band and discusses the construction and performance. The regenerative repeater equipment is designed in a compact form to be implemented in a commercial rack (INS cabinet rack). Using the designed equipment end the existing trunk fiber transmission route, an experiment in the actual site is conducted and the results are shown. The first part of this paper presents the construction of both the automatic frequency control (AFC) system and the automatic gain control (AGC) system suited to the polarization diversity system. The design guides are presented for the required frequency response speeds of AFC and AGC, the required frequency stability of AFC, and the response performance to the fluctuation of polarization. A high-output, high-sensitivity 2.4-Gbit/s regenerative repeater equipment (with repeater gain above 48 dB) is realized with the overall performance that the variation of optical received sensitivity against the polarization fluctuation can be suppressed to within 0.5 dB. Finally, the stable operation of the equipment is verified by the experiment at the actual site, and the practical usefulness is indicated. [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 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]

There is an urgent need to reduce the frequency occupancy bandwidth over speech channels to prevent radio resources from being exhausted. A Hilbert transformer plays the role of efficiently reducing the occupied bandwidth in such high-efficiency systems as single-side band (SSB) or RZ SSB. In this paper, it is shown that a Hilbert transformer may be implemented using the instantaneous spectrum concept and then applied in communications systems. The new Hilbert transformer described m this paper is based on the concept that the Hilbert transform is fully realized in the frequency domain by exchanging the complex real part with the complex imaginary part of the instantaneous spectrum, which is then analyzed using a short-time DFT. The Hilbert transformed output signals are then synthesized from these exchanged instantaneous spectra through a short-time IFT. The short-time DFT Hilbert transformer is shown to be superior to the standard minmax Hilbert transformer proposed by Rabiner et al. by means of a discussion of the ideal unit response and through computer simulations. It is also shown that the concept can be applied in practical communications systems due to the fact that it has the property of being free from the synchronization of a DSP processing clock. [ABSTRACT FROM AUTHOR]

Stuffing synchronization systems are now being applied actively to new fields such as digital cross-connect and SONET. In stuffing synchronization systems, however, the analog PLLs are still used for the receive destuffing circuitry. This paper describes a method of applying a complete second-order digital phase-locked loop (PLL) to a stuffing synchronization system. In the PLL used for the stuffing synchronization systems, a buffer memory consisting of an N-stage frequency divider is provided in order to suppress jitter. This paper analyzes first the effects on the DPLL resulting from the incorporation of an N-stage frequency divider based on a multilevel quantized phase comparator. The characteristics parameters of the complete second-order DPLL when the N-stage frequency divider is added arc determined. Significant low-frequency jitter is present in the narrow-band complete second-order DPLL. The phenomenon of low-frequency jitter generation is analyzed and procedures for determining the coefficient values of the complete second-order DPLL that will result in tolerable levels of low-frequency jitter are described. Finally, the DPLL parameters are evaluated theoretically and experimentally to determine the suitability of the DPLL design for stuffing synchronization [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]

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]

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

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]

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

The equation of the magnetic shielding effectiveness for a configuration made of a circular (transmitting) coil in a semi-half space on one side of a metal sheet and a magnetic sensor in the space on the other side of the sheet has been derived by Moser for the case where the axis of the coil is perpendicular to the sheet. One of the objectives of the present paper is to derive an equation for the magnetic shielding effectiveness in the case where the coil axis is parallel to the sheet. This paper shows that this effectiveness is smaller by a certain amount than the case where a magnetic dipole is placed at the center of the transmitting coil instead of the coil. The amount of reduction is a function of the ratio of the coil radius to the distance from the center of the coil to the observation point. Another objective of this paper is to determine what kind of quantities can be obtained by the measurement method by the MIL-STD-285 which is used for the measurement of the shielding effectiveness of the wall of the shielded room. In this measurement, the magnetic field shielding effectiveness is derived by measurement of the induced voltage of the receiving coil when the transmitting and receiving coils with a diameter of 12 inches are placed on both sides of the sheet at a distance of 12 inches, respectively, from the sheet in a plane perpendicular to the sheet. It is shown that the result of such a measurement gives rise to a value almost equal to (or smaller by about 0.4 dB than) the magnetic shielding effectiveness in s hypothetical ease where a magnetic dipole is pieced at the center of the transmitting coil and a magnetic sensor is placed at the center of the receiving coil. [ABSTRACT FROM AUTHOR]

This paper describes the improvement of characteristics of an offset tri-reflector antenna by introduction of reflector surface shaping, and the importance and allowance of suppression of the higher periodic components of the reflector surface distortion caused in the fabrication process. In an antenna with a good wide-angle radiation pattern, degradation of the sidelobe characteristics due to the higher-order periodical components of the surface distortion cannot be taken lightly. In this paper, the angle and the level of the sidelobe peak due to the periodic aperture phase error are expressed in simple formulas. These formulas are combined with an approximate expression of the wide-angle radiation pattern so that the allowance of the periodic reflector surface distortion is given. Next, a design and measured characteristics are described for a shaped offset tri-reflector antenna with its aperture diameter of 3600 mm to be used at frequencies of 3.6 to 6.475 GHz. Two prototypes with difference values of surface accuracy are compared. By means of measured examples, it is pointed out that suppression of higher-order periodic components of the surface distortion is important. By means of reflector shaping, a nonaxisymmetric aperture distortion is important. By means of reflector shaping, a nonaxisymmetric aperture distribution is realized so that the edge level in the horizontal cross section is made small. Further, by suppressing the higher-order periodic components of the surface distortion, an offset tri-reflector antenna with a good wide-angle pattern and a good cross-polarization characteristic was realized. [ABSTRACT FROM AUTHOR]

The integrated services digital network (ISDN), which is under construction at present, will enlarge the range of communication service by developing radio access systems, with the digital mobile communication systems as the core. The purpose of such a radio access system is to realize the communication capability, which is as flexible as that of the fixed system, while utilizing the features of the radio system. The following problems arise in the traditional access schemes, however, when multiple types of calls with various information characteristics and rates are to be handled. The immediate (circuit switching) system cannot contain efficiently the multiple type of traffic, while the waiting (packet switching) system may produce a delay with a long variation. This paper proposes a new scheme for radio channel access, aiming at a positive integration of the multiple type of traffic. In this scheme, the blank of information is compressed to construct a block (cell) with a constant length, and the physical channel is controlled to be assigned to each cell. The blank is inserted on the receiving side to ensure the time-transparency. Then, the flexibility to various types of immediate and waiting calls, as well as the efficient operation of the channels, are realized. This paper describes also the concept of the scheme and fundamental composition. The channel capacity and the channel occupancy are evaluated by a computer simulation, and it is shown that the proposed scheme has the desirable property that the statistical multiplexing effect is utilized. [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]

The transmission-type periodic branching filter presently is used as the multiplexer/demultiplexer for communication satellites. This type of filter can be applied to the submillimeter band multibeam communication satellite, in an attempt to realize large-capacity communication for the efficient use of frequencies in the future. It can also be applied to the branching filter in the optical communication, aiming similarly at the large-capacity communication, if the filter is constructed using the dielectric transmission line. To realize such an application, it is desired to improve the performance of the conventional periodic branching filter to realize a wider bandwidth and sharper roll-off of the amplitude transmission response. The conventional periodic branching filter is composed of two 90-deg hybrids, a quarter-wavelength transmission line and a resonator. This type of filter has a narrow usable relative bandwidth of approximately 6 percent, with a frequency response of third-order elliptic function type. This paper proposes a new transmission-type periodic branching filter with two resonators. It is composed of two hybrids and two resonators of different kinds. A bandwidth of approximately twice the width of the conventional filter end an approximately three-times sharper roll-off of the amplitude transmission response, with the frequency response of fifth-order elliptic function type, are obtained. This paper discusses the theoretical characteristics, design method and the result of experiment for this periodic branching filter. As a result of experimental construction, it was verified that the wide-band, low-loss property and the sharp roll-off of amplitude characteristic can be realized. [ABSTRACT FROM AUTHOR]

This paper describes the estimation of the propagation loss in an urban environment important for channel design of land mobile communication. Conventional methods for intimating the propagation loss in an urban environment gives a representative value of the propagation loss in the urban environment or the propagation loss (median value) within a 500 m ×800 m area obtained by introducing an area factor of occupied buildings. Such a method is not suitable for estimation of the propagation loss depending on the situation near the mobile station. In this paper, the relationship of the measured data of the propagation loss in the Tokyo Metropolitan area at 813 and 1433 MHz with the urban environment parameters such as the base station antenna height, distance, frequency, width of the street where the mobile station exists, direction, average building height, building height on the street side is derived by the multiple regression analysis method. A prediction formula for the propagation loss (median value in the section of about 80 m) including these parameters is derived. The parameter dependencies of the propagation loss, such as the antenna height dependence and the average building height dependence, are described. In addition, the distance dependencies of the propagation loss in this prediction formula and conventional method are compared with the measured values. The prediction formula is expressed in terms of the sum of simple functions of the foregoing parameters. Hence, the estimation of the propagation loss can be carried out easily, taking into consideration the urban environments such as the height of the buildings and width of the streets. [ABSTRACT FROM AUTHOR]

This paper discusses a framing system which uses error checking information obtained by a CRC or parity check. Theoretical analysis with a signal flow graph clarifies that the system is effective in extending the misframe interval, in reducing the reframing time, and in decreasing the quasi-reframing probability. The system is also found to increase the rehunting probability due to bit errors which occur during the reframe check process. Taking the forementioned advantages and disadvantage into consideration, this paper assesses the framing performance of the system using the ratio of blocks including burst errors due to the out-of-frame and shows that the system is effective in improving that ratio. [ABSTRACT FROM AUTHOR]

This paper proposes a digital signature scheme for a facsimile document which embeds a signature directly onto the document. The scheme modifies each run of white or black pixels with a single bit of the signature data. It is designed to be compatible with CCITT G3 facsimile standards and to protect the document from the insertion, modification, replacement, overwriting or deletion of characters. Furthermore, the total amount of data to be transmitted is about the same as that of the original facsimile document. In this paper, the authentication scheme is shown with a prototype model under a one-key encryption system. [ABSTRACT FROM AUTHOR]

With the increased use of personal computers (PCs) in communication environments have come the expectation of reliable communication protocols. This paper describes the implementation details of two very similar packet communication protocol interfaces on PCs. One is the X.25 interface for packet-switched public data networks, and the other is the X.32 interface for public-switched telephone networks. The implementation of these protocols is performed with consideration of the future introduction of OSI higher-layer protocols. This paper describes also that the addition of the assigning mechanism of level 2 address to the Rec. X.32 enables powerful personal computer communication through public-switched telephone networks. Furthermore, the results of the performance evaluation are described which show the high throughput of more than 90 percent on various speeds of the physical circuit. [ABSTRACT FROM AUTHOR]

Most of the past studies concerning the decoding performance of trellis coded modulation (TCM) in a fading channel have been based on time diversity using interleaving/deinterleaving. One problem with time diversity is that a large decoding delay is produced due to the interleaving/deinterleaving which depends on the fading interval. This paper considers TCM signals using space diversity which can drastically improve the decoding relay and analyzes the decoding characteristics in Rice fading channels. An analysis is also made of the effect of the Euclidean distance (ED) and the Hamming distance (HD) of the trellis code on the average bit error rate (BER), and it is shown that a code design considering those two distance structures is needed in a channel with severe fading. This paper considers the major application of the proposed method to be digital voice transmission in mobile communication via satellite. Consequently, a simulation is made for the second-order space diversity decoding performance for the trellis coded 8-PSK signal. The optimal trellis coding at the transmitter is discussed for BER = 10-4. [ABSTRACT FROM AUTHOR]

This paper describes double-flare type, triple-mode horns made of two sets of cascaded combinations of a circular waveguide and a flare with a mechanism to generate higher order modes. This horn is intended to be used in two frequency bands. At a lower frequency band, the horn works as a dual-mode horn, while it operates as a triple-mode horn at a higher frequency band. Desired electrical characteristics can be obtained in both frequency bands. In this paper, a design method of this triple-mode horn is described first and the condition for minimizing the cross-polarization components is presented. Next, the double-flare type triple-mode horn is described. It is shown that this condition is satisfied in two frequency bands. Various characteristics of the triple-mode horn fabricated for 12/14 GHz designed on the basis of the present design procedure are presented. Excellent electrical characteristics are measured including the level of the cross-polarization components of less than -29 dB with respect to the peak level of the co-polarization component. The measured results are similar to the designed data. [ABSTRACT FROM AUTHOR]

When the frequency sharing between the fixed satellite communication system and the radio relay system is realized, it is indispensable to evaluate the interference noise in the design of each channel. Especially, to treat the interference between the satellite station and the terrestrial radio-relay station, it is necessary to find the separation angle between the radio-relay antenna beam and the geostationary satellite orbit. This paper presents a method for evaluation of the separation angle with the atmospheric beam refraction. The beam refraction angle is given as an integration along the beam path of the infinitesimal rate of change of the elevation angle for the altitude. A simple approximate expression is derived for facilitating the derivation of the separation angle. By comparison with the rigorous theory, the approximation errors are shown to be small enough for all practical purposes. A computation method for the separation angle is described for a terrestrial radio-relay station position and an antenna beam direction from the geostationary satellite orbit. As an application, an actual radio-relay link is chosen for which the separation angle distribution and the interference noise distribution are derived. By means of the computational method presented in this paper, the interference noise from the satellite station to be terrestrial radio-relay station is now evaluated rather easily. [ABSTRACT FROM AUTHOR]

This paper discusses a simple go-back-N- ARQ scheme in which the satellite is provided not with the repeater function but also with the processing function. The satellite detects the error in the data block sent from the transmitter. It returns ACK/NACk to the transmitter and relays the correctly received date block to the receiver. The receiver detects the error in the received data block and returns ACK/NACk to the transmitter. The transmitter examines two acknowledgement signals returned from the satellite and the receiver, and transmits the data block based on the basic go-back-N ARQ protocol. This paper analyzes the scheme in which the hardware complexity of the satellite is minimized. It is shown that the throughput can be increased and the average transmission delay can be decreased. [ABSTRACT FROM AUTHOR]

Methods for evaluating the cross-polarization power ration (XPR) in mobile communication include the one using a crossed dipole, the one using a dipole antenna and a turnstile antenna, and that using a dipole antenna and a loop antenna. However, measurement errors in these methods have not been investigated. In this paper, the measurement error characteristics of various XPR measurement methods are analyzed theoretically. By finding the factors causing degradation of measurement accuracy, this paper proposes a method with more accuracy and clarifies its measurement error characteristics. it is found that the measurement error depends on the XPR and the measurement accuracy id degraded significantly because the measuring antenna does not have isotropic characteristic and the antenna for horizontal polarization has a vertical polarization pattern. To improve this deficiency, a method is proposed in which a cylindrical slot antenna is used for the horizontal polarization because the sensitivity of this antenna to the vertical polarization can be made sufficiently low. it is pointed out that the measurement error with this antenna can be improved significantly. [ABSTRACT FROM AUTHOR]