摘要:

AbstractSlotted rings have been popular medium access control protocols for local area networks (LANs) since the early proposal of Cambridge and Owell rings. This paper provides a simple approximation technique for the performance analysis of a slotted ring based on a single‐buffer model in which at most one packet can be stored at each node. The technique produces approximate values of the network throughput by using an assumption which is valid for large networks and a solution of a quadratic equation whose complexity does not depend on the number of nodes in the network. It is shown by numerical examples that the present technique also gives accurate performance data for rather small networks to the extent that the relative error of the approximate throughput values is less than 0.3 percent of exact values. Since other performance measures for the single buffer model of a slotted ring can easily be calculated from the throughput, the proposed technique is very useful for evaluating the total performance of a slotted ring networ

ISSN:8756-6621    

DOI:10.1002/ecja.4410770501

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

年代:1994

数据来源: WILEY

摘要:

AbstractPresently, integrated network management systems are being developed based on the open systems interconnection (OSI) management standards to manage information networks under the multivendor environment in an integrated manner. In this paper, an optimal scope‐patterns decision method for efficient OSI management operation is proposed. The scope patterns are common management information service (CMIS) operational range specifications based on the containment relationship between managed objects. The motivation for this study is to improve human interfaces for network management systems by providing a translating function for operator‐specified operational ranges based on various kinds of relationships into CMIS scope patterns. The proposed method provides the ability to translate automatically operator‐specified operational ranges based on any kind of relationship into possible CMIS scope‐pattern candidates and the ability to define optimal scope patterns for minimizing invoked operations by solving an integer programming problem using a fast computing approximate algorithm. Thus, network management operators can achieve user‐friendly human‐machine interaction and efficient managemen

ISSN:8756-6621    

DOI:10.1002/ecja.4410770502

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn recent years, eliminating adjacent channel interference (ACI) for effective utilization of frequency resources has been considered important in digital radio communications. As an effective method for eliminating interference, adaptive equalizers have been utilized and limitations associated with their linear form processing have also been clarified.In this study, as equalizers showing better interfering wave‐eliminating characteristics of adaptive linear equalizers (ALEs), an adaptive nonlinear equalizer (ANLE) containing the conventional nonlinear ALE and a nonlinear canceller, which eliminates ACI by nonlinear processing, in its body are proposed and their efficiencies are verified by computer simulations.First, the optimal number of taps of the proposed ANLE was determined by computer simulations and the characteristics obtained with an optimal number of taps have been compared with those of the conventional method. The results showed that the proposed ANLE can effectively eliminate the interfering wave component whose spectrum has become overlapped with a desired wave and thus gives better interfering wave‐eliminating characteristics than the ALE and the nonlinear cancel

ISSN:8756-6621    

DOI:10.1002/ecja.4410770503

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

年代:1994

数据来源: WILEY

摘要:

AbstractOne high‐fidelity ring‐type optical transmission network is the star‐shaped ring network having a multi‐port accessory in its hub. The present paper describes the transmission loss budget design for the star‐shaped ring network that takes into account continuously received interference signals. Conventionally, theS/Xvalue, which is the ratio of the main signal power to an interference signal power, has been used to evaluate the degree of interference.First, the factors responsible for determining this ratio are discussed and then a design chart is derived to correlate theS/Xvalue with the level difference between the transmitter and the receiver for the network. Based on this design analysis, multiport optical accessors are fabricated; and measured results are presented. It is demonstrated that the star‐shaped ring network with, desirable performance can be realized successfully. Finally, a method to lower the level difference between the transmitter and the receiver using multiwavelengths

ISSN:8756-6621    

DOI:10.1002/ecja.4410770504

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

年代:1994

数据来源: WILEY

摘要:

AbstractAs a cause of generation of unwanted electromagnetic radiation, the bend of a surface wave transmission line is investigated. The transmission and radiation characteristics at the bend are studied analytically and experimentally. First, by applying the traveling wave mode method, it is shown that the transmission characteristics of the surface wave transmission line can easily be obtained. The change of the equivalent voltage near the bend is observed.Next, the discontinuity of the traveling wave current is considered as a radiating source and the radiation field from the bend in a surface wave transmission line is derived by means of the principle of pattern multiplication. It is found that there exist an electric field component which strongly radiates into the traveling directions of the current in a bent transmission line and the component which radiates into the intermediate direction. It is found that the power is radiated strongly into the intermediate direction. Further, by experiments which agree well with the theoretical results, the validity of the method is presented.

ISSN:8756-6621    

DOI:10.1002/ecja.4410770505

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

年代:1994

数据来源: WILEY

摘要:

AbstractWith a view to focusing the electromagnetic wave, an “equiangular spiral‐bent slotted rectangular waveguide (SSW)” made of an axially slotted rectangular waveguide, which is one of the leaky wave antennas, was proposed and its focusing characteristics were reported. In this paper, a new diffusion‐type radiator based on the operating principle fundamentally identical to that of the SSW as a focusing radiator is proposed. The radiation pattern of the offset parabolic reflector using this radiator as the feed is investigated. First, its far field is treated by a wave optical approach. Using a cylindrical offset parabolic reflector as an example, the radiation pattern and the frequency scanning characteristics are studied numerically. Further, a reflector antenna was actually constructed and the measured results are compared with the analysis so that the offset parabolic antenna with a proposed diffusion‐type slotted waveguide as a feed and its frequency scanning possibility are

ISSN:8756-6621    

DOI:10.1002/ecja.4410770506

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe increase in communications facilities is accompanied by a rapid increase in the number of groundings required. However, it is difficult to achieve the required ground resistance values in areas of high grounding resistance such as volcanic ash, sandy or rocky soils, so that there is a strong need for the use of ground resistance reducing materials. This article proposes a method of reducing ground resistance using water‐absorbent polymers. The use of water‐absorbent polymer materials is expected to provide approximately twice the resistance reducing effect as currently used materials. When selecting such materials for placement in the soil, it is necessary to consider susceptibility to decomposition by microorganisms as well as temperature characteristics. One type of water‐absorbent polymer, anhydrous maleic acid polymers, is found to satisfy both requirements. In addition, the use of such polymers as ground resistance reducing materials requires approximately 1/160 the quantity of currently used bentonite mixtures and causes approximately 1/10 to corrosion of the copper used in grounding electrodes, demonstrating that water‐absorbent polymers are a highly useful method of reducing grounding res

ISSN:8756-6621    

DOI:10.1002/ecja.4410770507

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper aims at improvement of the interbeam connectivity of the multibeam satellite for fixed satellite communications under frequency division multiple access (FDMA) operation and proposes the subchannel switched FDMA (SS/FDMA) system, which is realized by installing the filter matrix on‐board the satellite. In the proposed system, each transponder is used to realize multiple interbeam connections and the interbeam connectivity is improved greatly compared to the traditional system. A satellite network among multiple beams can be constructed efficiently.A method is shown in this paper to determine the transmission parameters which maximize the system capacity of the multibeam satellite network and minimize the average transmission equivalent isotopically radiated power (e.i.r.p.) for one carrier. Example calculations are shown for the power‐limited and band‐limited systems. In the band‐limited system, the number of subchannels and the ratio of band widths of the subchannels are important parameters.From such a viewpoint, a method is shown which determines the number of subchannels when the bandwidth ratio of the subchannels is specified. An example calculation is shown taking into account uniform and nonuniform traffic distribution p

ISSN:8756-6621    

DOI:10.1002/ecja.4410770508

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

年代:1994

数据来源: WILEY

摘要:

AbstractIt is important to know the scattering properties of objects buried underground so that the techniques of imaging the buried objects by electromagnetic waves may be established.This paper analyzes numerically the transient scattering characteristics by the finite difference time domain (FDTD) method where an infinitely long perfect conductor of arbitrary cross section is buried in the ground and an infinitely long current source is located above the ground surface parallel to the object. The calculation error resulting from the approximation of the scattering object by square mesh is decreased by introducing the field interpolation which satisfies the boundary conditions of the scattering surface.The spatial distribution of the electromagnetic field at each step of the calculation is shown. Moreover, the propagation characteristics of the wave near the ground surface and the scattering characteristics of various objects are studied and the presence of two types of waves, i.e., direct and lateral, is confirmed between the source and ground and between the object and ground.

ISSN:8756-6621    

DOI:10.1002/ecja.4410770509

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper aims at the improvement of the transmission performance of the differential detection system in the mobile radio transmission channel in a frequency selective environment. The multiple differential detection with adaptive sequence estimation (MDD‐ASE) is proposed, and the performance is analyzed by a computer simulation. In MDD‐ASE, not only the differential detection by one‐symbol delay but also the differential detection by two‐ or more‐symbol delays are applied. The soft decision is applied to the output of the multiple differential detection, and the symbol sequence is estimated by Viterbi algorithm (VA).The bit error rate (BER) performance is improved by the extended observation time by the multiple differential detection and the sequence estimation. The number of states in VA and the processing complexity of the adaptive algorithm increases exponentially with the extension of the observation time. Consequently, the following method is proposed: (i) the number of parameters to be estimated is reduced; and (ii) the sequence candidates stored in each path of VA are fed back.In this paper, the configuration and operation of MDD‐ASE are described first and then the transmission performance of the 40 kbit/s QPSK modulation system is presented. As a result of analysis for the static and the dynamic performances of ADD‐MSE using one‐ and two‐symbol differential detection, it is shown that the improvement effect is almost the same as in coher

ISSN:8756-6621    

DOI:10.1002/ecja.4410770510

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

年代:1994

数据来源: WILEY