摘要:

AbstractIt is known as generally impossible to generate automatically the test cases for arbitrary LOTOS expression containing data parameters. A subclass of LOTOS, called P‐LOTOS, is defined. In P‐LOTOS, the data type is restricted to be integer and Boolean and the operation on the integer is restricted to be the addition/subtraction and comparison.This paper presents an algorithm for automatic generation of the test cases for this class of LOTOS descriptions. Algorithms also are presented solving the detection problems for the deadlocks, the unexecutable edges, and the nondeterministic branches. The proposed algorithm is applied to a simplified OSI session protocol, and the result is reported in this pa

ISSN:8756-6621    

DOI:10.1002/ecja.4410770301

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

年代:1994

数据来源: WILEY

摘要:

AbstractVarious communications services are provided over asynchronous transfer mode (ATM) networks, and traffic produced by these various services has various characteristics. Thus, in attempting to utilize circuits effectively by statistical multiplexing effects as in ATM networks, band management control reserving bands necessary to ensure communications quality in terms of cell loss probability, etc., is necessary when a call occurs. In addition, since communications quality required by various services differ, band management considering priority processing is effective. In addition, since a number of switching machines exist between transmission and reception nodes and a number of channels exist in links between each ATM switching machine, control to select one of these channels at the time of call setup is important. It is necessary even in this case to sufficiently consider traffic characteristics of calls for each service.In this paper, channel selection methods for such multichannel links are studied. For this purpose, the multiplicity of traffic establishable for a set of channels is obtained analytically following a step‐modeling technique and the efficiencies of various channel selection methods for a number of channels are studied. The characteristics and efficiency of each method are clarified by analyses and simulation using channel utilization rate and call loss rate as efficiency parameters for designing the efficiency of channel selection system

ISSN:8756-6621    

DOI:10.1002/ecja.4410770302

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn this paper, functional requirements for the MPEG 2 coding method are presented and, as an implementation method of these requirements, a hierarchical video coding scheme is proposed. In the proposed coding method, the prediction efficiency is increased by introducing spatial prediction in addition to temporal prediction as used in the MPEG 1 coding method. The hierarchical scheme is also characterized by the following features. (1) The input format is an output device‐independent noninterlaced video; (2) the coder has a hierarchical structure that permits the resolution level to be selected by the user; (3) by means of a small number of operations and a wide compensation area, the coder gives a motion‐detection method which detects motion vectors of each layer and a coding method of motion vectors; and (4) the proposed coding system introduces the use of down/up sampling processes with no phase distortion. Furthermore, the coding data description method is realized as an extension of that used by MPEG 1 and thus retains the compatibility. Simulation experiments show that this coding method satisfies the functional requirements without any obvious decrease in coding efficie

ISSN:8756-6621    

DOI:10.1002/ecja.4410770303

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

年代:1994

数据来源: WILEY

摘要:

AbstractWith the development of communications service for high performance and for wider bandpass widths, a single‐mode optical fiber has been started to be utilized in subscriber loops in addition to connection loops. An optical fiber cable has an advantage of huge transmission capacity, as compared to a conventional metal cable and, therefore, any breakdown in a cable may cause significant impact on the society. In this sense, a test capability of optical cables without causing any service interruption is needed.In this paper, a system using the optical time domain reflectometer (OTDR) which can perform such testing is discussed. The optical filter characteristics such as cutoff loss, transmission loss, and bandpass width are discussed. A prototype of the system consisting of optical filter parts has been made in the present study. The influence of the OTDR test light on transmission signal and that of the transmission signal on the OTDR waveform are examined. No degradation of the transmission quality was found. Furthermore, no disturbance in the OTDR waveform was observed. Therefore, it is concluded that a test without disturbing the transmission output signal can be performed by using the present metho

ISSN:8756-6621    

DOI:10.1002/ecja.4410770304

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

年代:1994

数据来源: WILEY

摘要:

AbstractAs a method of compensating for the voltage drop on the dc side of ferroresonant dc stabilized power supplies, a magnetic‐only controlled power supply was developed. When a dc magnetic field is applied in the direction of diameter of a saturable ring core, using the saturation flux density, that is, resonant voltage change, by dc load current feedback to an electromagnet positioned in the diametric direction, the resonant voltage is altered and output voltage stabilization is achieved.By increasing the operation frequency of the power supply, miniaturization is achieved and simultaneously, as a feedback control method, is expressed in a block diagram. An investigation was made on the power supply design method and the response to various disturbances. As a result, design criteria were established to make the steady‐state output voltage error zero. The transient response simulation was verified to explain well the experimental res

ISSN:8756-6621    

DOI:10.1002/ecja.4410770305

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

年代:1994

数据来源: WILEY

摘要:

AbstractTo provide audiovisual communication such as television telephone and television conference economically and efficiently, high efficiency coding, satellite communication and asynchronous transfer mode (ATM) are considered for introduction to the communication network. However, these technologies may degrade communication quality since they increase the signal propagation delay time. The effect of the propagation delay on the communication quality has been studied frequently for voice communication by telephone, but there have been few studies on audiovisual communication. Further, the effect on the delay quality by the addition of video to the voice has not sufficiently been understood.

ISSN:8756-6621    

DOI:10.1002/ecja.4410770306

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe requirements of today's communication networks are changing rapidly with the introduction of highcapacity transmission links and the increased amount of data traffic, thus fast restoration from failures is of increasing importance. To meet this requirement, self‐healing algorithms, which are distributed algorithms based on autonomous control at each node, are discussed.The conventional self‐healing algorithms called single‐search self‐healing algorithms have the following problems: (1) the self‐healing process for bidirectional path failure has not been investigated; and (2) a large search area is affected by restoration messages.To solve these problems, this paper proposes and evaluates the restoration characteristics of a new self‐healing algorithm called the “double‐search self‐healing algorithm.” The results indicate that the proposed algorithm can restore foiled bidirectional paths faster and find alternate paths more effectively man conventional self‐healing algorithms. To evaluate the restoration characteristics, an SDH network model based on existing telephone network data in Japa

ISSN:8756-6621    

DOI:10.1002/ecja.4410770307

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn the two‐way beyond line‐of‐sight communication using meteor burst, several station pairs can operate on the same frequency band. To date, however, no quantitative studies have been carried out to determine how many station pairs can use a given frequency band.In this paper, the characteristics are analyzed quantitatively in the case wherenstation pairs commonly use the same frequency band. As the simplest system, a meteor burst system with full‐duplex station pairs is considered. The throughput, optimum number of station pairs, and channel utilization are analyzed.First, an ideal case is studied in which neither the overhead by the header nor the loss of division into blocks is considered. Next, the case with a header and then the case with constant block size are considered. In each case, the relationship of the number of the station pairs to the throughput and channel utilization is derived. Some numerical results for practical models are presented. It is shown that such a configuration is useful for improving the utilization of frequen

ISSN:8756-6621    

DOI:10.1002/ecja.4410770308

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

年代:1994

数据来源: WILEY

摘要:

AbstractA transmission system suitable for a small Hi‐Vision wireless camera is proposed and a small transmitter and receiver for the 42‐GHz band is developed. In the present system, no signal processing is performed on the camera output which is directly frequency modulated. Orthogonal circular polarizations are co‐used for transmission.By means of this system, miniaturization and weight reduction of the equipment (with a transmitter of 5 kg) are attained. At the same time, the transmission bandwidth is reduced to 80 MHz. Also, as the key 42‐GHz devices for realization of the present equipment, a direct FM modulator (modulation sensitivity of 20 MHz/ V), an HEMT power amplifier, an orthogonal circular polarization feed system (with a cross‐polarization discrimination ratio of more than 23 dB), a low‐noise down‐converter (with a noise figure of less than 5 dB) and a simple IF cross‐polarization interference equalizer are developed.The antenna for the transmitter automatically adjusts its direction by means of the signal returned from the receiver at 10 GHz. The present equipment has a transmission distance of about 250 m with a transmitter output of 25 mW and the signal‐to‐noise (SN) ratio is 48 dB (Y signal). Also, the equipment can be unified with the Hi‐Vision two‐thirds inch small CCD camera developed in our laboratory and can be operated for close to on

ISSN:8756-6621    

DOI:10.1002/ecja.4410770309

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

年代:1994

数据来源: WILEY