摘要:

AbstractAsynchronous transfer mode (ATM) networks are nonhierarchical networks that can reduce network cost and simplify network operation, administration, maintenance, and provisioning. During the period in which ATM and existing synchronous digital hierarchy (SDH) networks coexist, it is necessary to convey SDH signals using ATM technologies. First, the SDH signal transport units, the VC or TU/AU level, are considered and the best choice is found to be TU/AU. Next, algorithms for handling lost and misdelivered cells using the sequence number SN and its protection SNP are presented. Finally, SDH signal phase information transport methods are discussed.

ISSN:8756-6621    

DOI:10.1002/ecja.4410770601

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

年代:1994

数据来源: WILEY

摘要:

AbstractSince the discovery of semiconductor‐optical fiber, the development of optical communication has been significant. In particular, a baseband modulation frequency in high‐speed communication has been increased up to the order of 10 GHz at the research level and of 1 GHz at the practical level. A factor which is the obstacle for further improvement is the bandpass width limitation for a transmitted signal caused by the spread of an oscillation spectrum of LD and also the wavelength dispersion of an optical fiber. For long‐distance and high‐speed transmission, it is important to determine accurately the spread of the LD spectrum for designing an optical transmission system.The objective of the present study is to clarify the condition required for a high‐resolution optical spectrum analysis system, which is essential for understanding the spectrum‐spread and chirping of the LD laser at a time of high‐speed modulation. A comparison of various measurement systems is made. A method of combining the diffraction grating system and the Fabry‐Perot etalon system is proposed, and the optimization of the system is discussed in detail.The present paper describes for the first time the optimization of the tandem configuration of a diffraction grating and Fabry‐Perot etalon systems. Based on those discussions, a prototype system has been constructed with which a maximum wavelength sweeping width of 200 MHz/div and resolution of 100 MHz

ISSN:8756-6621    

DOI:10.1002/ecja.4410770602

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis 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 ranging time rate and the average visible number of satellites in various operating environments also is inves

ISSN:8756-6621    

DOI:10.1002/ecja.4410770603

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe sudden deterioration in transmission quality due to rain or snow attenuations is a problem in VSAT communications using the 14/12‐GHz band‐link, and a system that can cope with such a problem has been developed and studied.This paper proposes a method for improving the bit error rate (BER) of an overall system for satellite channels showing a decreased carrier‐to‐noise (CNR) by using a terrestrial channel of low error rates in addition to satellite channels and by coding both channels simultaneously. The effectiveness of the proposed scheme has been clarified by deriving the theoretical upper bounds of the BER and evaluating its performance by computer simulations for the case of multidimensional coding based on QPSK

ISSN:8756-6621    

DOI:10.1002/ecja.4410770604

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe multibeam antenna for the 22‐GHz band satellite broadcasting has been studied. The aim of this study is to meet future satellite broadcasting demands and advanced services such as high definition television (HDTV), digital broadcasting, and regional satellite broadcasting. The breadboard model of the 22‐GHz band multibeam antenna has been developed.Here, a new type of primary feed and a pattern synthesis method are proposed to achieve high gain and low sidelobe antenna performance which is required for the 22‐GHz band satellite broadcasting. The feasibility of the proposed antenna system and the design method have been verified numerically and experimen

ISSN:8756-6621    

DOI:10.1002/ecja.4410770605

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn the buried‐object search technique using a pulsed radar, the estimation method for the buried‐pipe location and the underground propagation velocity of the electromagnetic wave by means of a synthetic aperture method has been studied. In general, the electromagnetic wave attenuates as it propagates in the underground and the amplitude of the received signal often becomes extremely small. Therefore, it has been difficult in the signal processing using the amplitude value to recognize several buried objects at different depths by an identical discrimination standard.To resolve this difficulty, a new zero‐crossed synthetic aperture method is developed. In the underground cross‐sectional image, the waves reflected from a buried pipe form a hyperbolic pattern dependent on the underground propagation velocity of the electromagnetic wave. By evaluating only the edge of this hyperbolic pattern, the underground propagation velocity of the electromagnetic wave and the location of the buried object are estimated.First, to extract the edge, the amplitude value at the time when the observed signal has a “0” amplitude is replaced with “1” if the phase of the original waveform changes from minus to plus whereas with “‐1” if it changes from plus to minus. The amplitude at other time points is replaced with “0.” Subsequently, a synthetic aperture process (addition process) is carried out. Since the absolute value of the amplitude is 1 or 0, it is not necessary to consider the effect of the attenuation of the amplitude due to propagation of the electromagnetic wave as a discrimination reference in the estimation of the location of the buried pipe after the addition process. The location of the buried pipe c

ISSN:8756-6621    

DOI:10.1002/ecja.4410770606

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

年代:1994

数据来源: WILEY

摘要:

AbstractFin electromagnetic wave absorbers are proposed in which the sintered ferrite plates are placed in the direction perpendicular to the electric field of the incident electromagnetic field. By numerical calculations, it is shown that this structure has a broadband reflection suppressing characteristic. The characteristics of the absorbers in terms of the structural parameters of the absorber and ferrite permeability are shown, and it is found that the optimum structure of the absorber for a broadband operation depends on the permeability of the ferrite. Further, by means of the model experiment, the broadband characteristics of the proposed absorber are demonstrated.

ISSN:8756-6621    

DOI:10.1002/ecja.4410770607

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

年代:1994

数据来源: WILEY

摘要:

AbstractWith a view to increasing the bandwidth of ferrite electromagnetic wave absorbers, the reflection characteristics were studied for an absorber made of sintered ferrite loaded with rubber ferrite via an appropriate dielectric layer.First, by means of calculations, it is shown that this structure has a bandwidth wider than that for the sintered ferrite single‐layer absorber. Also, the bandwidth of the absorber increases as the permittivity of the dielectric material inserted in between is lower. By loading an appropriately thick rubber ferrite plate via an air layer on a sintered ferrite plate, an absorber can be constructed for which the reflection is less than ‐20 dB over the frequency range from 30 to 1830 MHz. By loading another air/rubber ferrite pair, an even further increase of the bandwidth is possible. For an existing ferrite single‐layer absorber, it is effective for increase of the bandwidth to load the air/rubber ferrite by attaching a sheet resistance on the ferrite surface.Finally, by an experiment, it is shown that a broader bandwidth can be obtained than the ferrite single‐layer absorber by loading a rubber ferrite via a low‐permittiv

ISSN:8756-6621    

DOI:10.1002/ecja.4410770608

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

年代:1994

数据来源: WILEY

摘要:

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

ISSN:8756-6621    

DOI:10.1002/ecja.4410770609

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

年代:1994

数据来源: WILEY

摘要:

AbstractTo understand the radiation and scattering phenomena of electromagnetic waves visually, streamlines of the electromagnetic energy flux density are drawn. This paper attempts to show the scattering phenomena of circularly polarized waves in the presence of an infinitely long perfectly conducting circular cylinder by graphical presentation of the streamlines. This is based on the Poynting vector and circularly polarized electromagnetic energy flux densities proposed recently.From the viewpoint of circularly polarized electromagnetic energy flux density, the conversion of a circularly polarized field to a cross‐polarized field on the cylindrical surface is drawn specifically. Even though the structure of the scatterer is two‐dimensional, the streamlines of the electromagnetic energy flux density is threedimensional. This phenomenon originates from the nature of toroidal fields of the Poynting vector and the cross Poynting vec

ISSN:8756-6621    

DOI:10.1002/ecja.4410770610

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

年代:1994

数据来源: WILEY