摘要:

AbstractWith the introduction of communication services into business activities, such as telemarketing, customer requirements for these services are becoming more varied. Since communication service has become competitive, quick provision of services has become important.This paper proposes a hierarchical service control scheme aimed at achieving service specification independence and the software architecture of an experimental intelligent network service system based on this new scheme. In the proposed new scheme, elementary functional parts are prepared beforehand and a service is realized using interpreter control based on the information about an execution order of functional parts.To localize modifications in software when a new service is introduced, functional parts are arranged in a hierarchical manner. This experimental system can change complicated service specifications in a few minutes. Processing volume is about half of that for an existing system in which service specification is described by a programming language and service associated data are managed by a common data management program.

ISSN:8756-6621    

DOI:10.1002/ecja.4410740401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper proposes a queueing network model for the layered communication protocol and its approximate analysis method. The performance of the layered communication protocol is evaluated by using the proposed model and analysis.First, the queueing network model is constructed for the connection‐oriented and connectionless data transmissions between peer layers. In each queueing network model, the transmission delay in the lower layer protocol is represented by an infinite‐servor queue.The performance model for the layered communication protocol is constructed by piling up each model. Then an approximate analysis is presented for each queueing network model. Based on the relation to be satisfied by the packet transmission delay in each layer and the throughput between adjacent layers, an approximate analysis of the whole model can be executed iteratively.In numerical examples, the validity of the approximate analysis for the model is shown. The effects of window size, the time‐out period, and receiver buffer size on the transmission delay are disc

ISSN:8756-6621    

DOI:10.1002/ecja.4410740402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper considers the CRV collision detection method which detects the signal collision in the star configured optical local area network by detecting CRV, using the dipulse code and the partial response (1, ‐1) circuit. The result of theoretical investigation of the performance improvement also is presented.First, the reflection‐type partial response (1, ‐1) circuit using a delay line is considered, and the transmission characteristics are formulated for the case where the delay line has a loss. Based on the result of formulation, a method to prevent the increase of the CRV rate due to the loss of the delay line without signal collision is considered.The methods which are shown to be effective are the method to set the driving source impedance for the delay line at approximately 1.08 times the characteristic impedance of the delay line, and the method to employ a first‐order high‐pass filter with the 3‐dB cut‐off frequency at approximately 0.046 times the bit‐rate frequencyfo.Then, as a method to increase the CRV rate due to the signal collision, a method is considered in which two CRV detectors are used with the decision levels at Δ‐and Δ+, respectively. It is shown to be effective to lower the decision level as far as possible.Next, the use of two CRV detectors with the phase of the driving clock signal differing by π is considered, and it is shown that the end of signal collision can be detected in the CRV collision detection method by forming the logical su

ISSN:8756-6621    

DOI:10.1002/ecja.4410740403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe transmission rate of several Gbit/s is required at present for the optical fiber baseband transmission system. From such a viewpoint, a clear design principle must be established for the transmission circuit, which operates at the Gbit/s band. This paper describes especially the result of studies on the design and experimental construction of the clamping circuit, which is indispensable in the capacitor‐coupled optical receiver. The elements to be employed in the clamping circuit for several Gbit/s transmission are different for the conventional transmission system of several hundred Mbit/s. The distortion of the transmitted waveform is enhanced in the Gbit/s band. Consequently, the operation of the clamping circuit is different.From such a viewpoint, the behavior of the clamping circuit in the Gbit/s band is clarified by the analysis. An experimental circuit is constructed using the Schottky‐barrier GaAs diode and the depression‐type GaAs MESFET, and the operation is verified. As a result, it is shown that the characteristics of the experimental circuit agree well with the result of calculation, and the proposed method is useful in practice as the circuit design for the case with a large waveform disto

ISSN:8756-6621    

DOI:10.1002/ecja.4410740404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractIn voice packet communication, a fluctuation is produced in the delay time in the network. This makes the packet, which is originally continuous, discontinuous at the receiver, and results in an interruption. The interruption deteriorates the voice quality. Then it is necessary that a delay should be provided at the side of the receiver to absorb the interruption. If the delay for absorbing the fluctuation is too small, the delay cannot sufficiently be absorbed; and if it is too large, the total delay is increased. In either case, the quality of the voice or speech is deteriorated.From such a viewpoint, this paper discusses the absorption of the delay fluctuation of the voice packet. To set the delay for absorbing the fluctuation, the quality of the voice containing interruptions must be evaluated.First, an objective evaluation measure is presented which is well aligned to the subjective evaluation of the deterioration of the voice quality with interruption. A control method to ensure the voice quality above a certain level is presented, which examines the objective evaluation measure for the varying traffic in the network. The method adjusts adaptively the delay for absorbing the delay fluctuation so that the voice quality is kept above a certain reference value.

ISSN:8756-6621    

DOI:10.1002/ecja.4410740405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe call‐wise control of a communication network, such as dynamic routing, is a very complex problem, although the extent of difficulty depends on the control target. Especially, the optimization of a communication network in a multiservice environment contains the difficulty of the choice of the state variables. The analytical method is limited in handling such a problem.This paper discusses the application of the fuzzy system by extending the range of search for the optimal solution for the communication network control from the analytic single expression to the description by the combination of several rules. The usefulness of the idea is demonstrated by a simulation. Then aiming at the full utilization of the descriptive power of the fuzzy system, the modularization of the control system corresponding to network installations, as well as the hierarchical structure corresponding to the data abstract level, is proposed. Further, this paper considers the revenue maximization control of the communication network as an example, and the usefulness of the hierarchical fuzzy system is demonstrated through a simulation. By applying the proposed method, it is made possible to cope with a range of problems not previously handled by the analytical metho

ISSN:8756-6621    

DOI:10.1002/ecja.4410740406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractTo improve the efficiency of a small‐sized antenna, a normal mode helical antenna (NMHA) is promising with a high radiation resistance. However, its efficiency is subject to degradation due to a nearby human body or radio equipment. In this paper, we replaced the human body, etc., by a conductive plate as a basic problem to analyze the influence of the human body and calculated the impedance when NMHA is in proximity of a conductive plate. In our calculation method, the influence of the conductive plate was replaced by an electric image of NMHA. We obtained the current distribution of a two‐element NMHA array which was placed in parallel by the improved circuit theory method which is similar to the moment method. As a result, we found that the real part of the mutual impedance between the array was positive, negative or zero depending on the value of the structural parameters of the antenna. The radiation resistance with a nearby conductive plate was the real part of subtracting the mutual impedance from the input impedance of a NMHA in a free space. In the shapes for zero or negative the real part of mutual impedance, the radiation resistance was equal to or greater than that of the unit antenna so that the conductive plate could be utilized effectively. We showed that the NMHA is a combined model of a dipole antenna and a loop antenna. For shapes with zero mutual impedances, we found that the far radiated field components of the dipole and those of the loop antenna were equal to the structural parameters which were almost equal to 2π2a2=pλ (a: helical radius, andp: p

ISSN:8756-6621    

DOI:10.1002/ecja.4410740407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractWhen various broadcasting radio waves in the 12‐GHz band from a geostationary satellite such as a broadcasting satellite are received in an urban area by a mobile receiver, transmission and reception systems such as a temporal diversity system often are designed. In such instances, it is necessary to evaluate quantitatively the mobile receiving characteristics such as the areal visibility on an urban street. When driving on an urban street, one finds that the waves from satellites frequently are disturbed by buildings. The degree of disturbance depends on the direction of the street, the density, height and width of the building.This paper describes first characteristics of measured satellite areal visibility on a road using an airscape photographed at a time when the apparent locations of the satellite and the sun coincide. The histogram of the visibility length is modeled by a log normal distribution. Second, from these distributions and the measurement and analysis of the actual velocity characteristics of automobiles in the Tokyo metropolitan area, the histogram of the visibility duration time is estimated. Third, an estimation method of the satellite areal visibility on a road is proposed in which the statistical data are published by a governmental agency on the building distributions and on the road. The results obtained by these measurement and estimations can provide quantitatively the mobile receiving characteristics of satellite broadcasting at 12 GHz so that they can be effective guidelines in the design of various transmission and reception system

ISSN:8756-6621    

DOI:10.1002/ecja.4410740408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractStandards for electromagnetic protection taking into account human health have been established in a number of countries. Most of the present standards are expressed in terms of the intensities of electric and magnetic fields or the power density of the irradiating electromagnetic field. Usually, for conversion among these quantities, the relationship in the electromagnetic field at a distance far away (far field, plane wave) is used. However, near the electromagnetic source where the electromagnetic wave is the strongest, the relationship among the forementioned quantities varies depending on the location of the observation point or the type of the source. Therefore, there are recommendations to reconsider the standard values.The purpose of this paper is to provide fundamental references for modeling the electromagnetic sources in various electromagnetic equipment to reconsider the protection standard of the near field, and to develop the electromagnetic shielding theory in the near field. In this paper, the distance characteristics and the spatial distribution of the electromagnetic wave impedance characterizing the nature of the electromagnetic wave are studied near the elementary radiating elements such as the electric dipole, magnetic dipole, half‐wave dipole antenna, small current loop and small helical antenn

ISSN:8756-6621    

DOI:10.1002/ecja.4410740409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper analyzes the problem of excitation of an electromagnetic wave inside a rectangular tunnel by means of the waveguide modes. As the boundary condition, the surface impedance approximation will be used. It is assumed that the separable solution can be adopted. For the excitation by a waveguide, the Wiener‐Hopf solution of the two‐dimensional problem is assumed to be applied. Although the results obtained are approximate, future applications are expected since an analytical expression is provided. For instance, the solution may be applied to the problem of electromagnetic wave propagation in a three‐dimensional tunnel with branches and bends. In the experiment, a microwave simulation is carried out with a model of the tunnel made of concrete. It is found that the computed results and the measured results agree rather well for the electric field intensity distribution inside the t

ISSN:8756-6621    

DOI:10.1002/ecja.4410740410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY