摘要:

AbstractTo study overload characteristics of a telephone network, a simple and useful method using fluid approximation is presented. Taking a two‐stage telephone network as an example, it is shown that the circuit trunk part is congested under an overall overload and the outgoing register part is congested under a focused overload. Since under overload conditions the number of calls in a telephone network is large enough that the law of large numbers is applicable, the traffic flow can be regarded as a deterministic continuous process. Specifically, a fluid approximation can be applied. The calculation time of this method is much less than that of the simulation method. Accordingly, the overload characteristics of a telephone network, which have been analyzed mainly through simulation, can now be analyzed by simple numerical calculation. This fluid model can be applied to the overload analysis of not only telephone networks, but also other communication network

ISSN:8756-6621    

DOI:10.1002/ecja.4410721201

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

年代:1989

数据来源: WILEY

摘要:

AbstractModified MR (MMR) coding is the coding method for G4 facsimile. It has a better compression performance than the MR (modified read) code, which is a coding scheme for G3 facsimile. Consequently, the facsimile using the MMR code is expected to realize a high‐speed transmission. In the facsimile using MMR code, a high‐speed printing is also required to achieve such a highspeed transmission. From such a viewpoint this paper discusses the high‐speed thermal printing, suited to the facsimile over the telephone network using the MMR code. A high‐speed transmission by the black ratio control is considered, where the printing speed is varied according to the number of black pixels in the line. Detailed parameters are presented for the black ratio control which can realize almost the same printing speed as the transmission speed. Next, as the means toward a practical system, a high‐speed document feed technique is considered, together with its realization, where the document feed is performed smoothly following the change of the printing speed. It is shown by computer simulation that the loss of the printing time due to this mechanism is at most 10 percent for the usual document. Finally, to reduce the number of feed stops in a page, a high‐speed document feed is proposed where the maximum feed speed is limited according to the number of buffered coded bits. It is verified by computer simulation that a high‐speed and smooth document feed can be realized without a stop for the u

ISSN:8756-6621    

DOI:10.1002/ecja.4410721202

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe integrated service digital network aims at providing communication service by various kinds of media, such as speech, data and image, by a single communication network, realizing higher‐level convenience and economy compared with the communication networks for individual services. In its design and management, the traffic problem must be solved for the sharing of a system by heterogeneous traffic. This paper discusses especially the measurement accuracy for the carried traffic when the channel is shared by heterogeneous traffic, which is important in the management of traffic statistics. To discuss the measurement accuracy of the carried traffic, the autocovariance function which represents the correlation between measured values with the time difference of the scanning period must be determined. As a fundamental model, the strict solution is derived for the autocovariance function of the simultaneous connections in the loss system with two kinds of inputs. Using the result, the relation between the variance of the measured values and the scanning period is determined, and the determination of the optimal scanning period is discussed. Since the calculation of the strict solution becomes difficult with the increase of the number of channels, a practical approximation expression is proposed for the autocovariance functio

ISSN:8756-6621    

DOI:10.1002/ecja.4410721203

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

年代:1989

数据来源: WILEY

摘要:

AbstractWhen the sampling points of an image are divided into two complementary subsampling points, an image with low resolution is restored from one set of subsampling points, and the image with full resolution can be restored using both sets of subsampling points. In such a complementary subsampling system, either of the two restored images contains aliasing distortion. This paper discusses the restoration of subsampled values, in which the high‐frequency components are lost due to the prefiltering. A method is presented in which the subsampled value is restored by utilizing the other complementary subsampled values, which preserves the highfrequency components as the aliased components. The condition for the restoration by the proposed method is described. Based on the derived properties, a new complementary subsampling system is proposed. This new system can restore without distortion both the image with low resolution and the image with high resolution simultaneously. The usefulness of the method is verified by experiment. The method is useful in the realization of the HDTV system, which contains a high compatibility to the present TV syste

ISSN:8756-6621    

DOI:10.1002/ecja.4410721204

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe three‐wire transmission lines consisting of square‐wave‐formed line conductors has a structure in which any two of the three line conductors iterate narrow and wide sections at a specified interval along the longitudinal direction. Among those sections, the narrow section has the following problem. If line conductors deviate even a little from their normal positions due to the inaccuracies in the manufacturing process, relatively large unbalances will be produced in the mutual impedances and admittances between them. This leads to the crosstalk between the positive and negative phase sequence components of the signal and consequently to the detection error in the position of the vehicle. We considered the case where the manufacturing inaccuracies distribute at random or uniformly along the longitudinal direction. A quantitative analysis is made for the problem arriving at a guide for the manufacturing accuracy of the transmission line, which is required to ensure the desired accuracy of position detection. It is desirable in the narrow section that the two conductors maintain a distance above a certain value. It is also desirable that the radius of the line conductor be as small as possible, as long as the transmission loss of the line is within the tolerable value. Compared with the transmission line consisting of helically wound conductors, which we have already reported, there will still be a more strict requirement on the manufacturing accuracy on the transmission line consisting of square‐wave‐formed c

ISSN:8756-6621    

DOI:10.1002/ecja.4410721205

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe electromagnetic field generated in a concave boundary by a magnetic line current source placed on a semicylindrical conducting concave boundary is analyzed by means of three representations. The effectiveness and physical interpretation of these representations are discussed. If the product of the wave number and the radius is sufficiently large, the conventional representation by the geometric optical rays and the integral‐type interference wave cannot be applied well. The representation by means of a combination of the geometric optical rays, lower‐order whispering gallery modes and the error‐correcting term has simple calculations and good accuracy. The mutual relationship between the geometric optical rays and the modes is found and the propagation characteristics within the boundary layer characteristic to the concave boundary are addr

ISSN:8756-6621    

DOI:10.1002/ecja.4410721206

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

年代:1989

数据来源: WILEY

摘要:

AbstractPolarization diplexing is possible by means of a grid plate and hence a frequency reuse antenna can be realized. Usually, the characteristics of a grid plate can be evaluated by an analysis based on an equivalent circuit. However, for a practical grid with a support mechanism made of dielectric or honeycomb structures, the reflection level of the unwanted polarization at the time for transmission of the desired wave is larger than the value for the metal grid only and hence the results are different from those by the equivalent circuit analysis. In this paper, the characteristics of the grid with a dielectric support layer are analyzed by means of full‐wave analysis so that the relationship between the thickness of the dielectric support layer and the reflection level of the unwanted polarization is detected. Next, a method is proposed for suppression of this unwanted polarization in a grid with a dielectric support layer. The validity was confirmed by theoretical analysis and experiments. Further, the design method and the numerical results are presented for a low‐loss polarization diplexing grid used in a frequency reuse antenna. It is pointed out that there exists an optimum parameter that minimizes the insertion loss in the operating bandwi

ISSN:8756-6621    

DOI:10.1002/ecja.4410721207

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

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper investigates theoretically and experimentally the electromagnetic wave propagation in a two‐dimensional tunnel with a modified cross‐junction in connection with radio communications in tunnels, underground, urban areas with high‐rise buildings and others. Modal expansions and Fourier transform are used as an analytical method, and the surface impedance model is employed as a boundary condition on the tunnel walls. The results presented here can be applied to special tunnels such as the T‐type, modified T‐type, L‐type and step‐type. Experiments based on a microwave simulation are performed by using tunnels composed of concrete slabs. It is found that, concerning electric field intensity, experimental and theoretical resul

ISSN:8756-6621    

DOI:10.1002/ecja.4410721208

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe full‐wave analysis method is described for computing the electromagnetic field on the ground when a beam‐shaped wave is incident from above the ionosphere. By means of this method, the directional error was evaluated in various VLF direction finders which measure the exit point of the natural wave at the lower portion of the ionosphere, under the assumption that the downgoing wave is radiated from a duct. In this method, the directional errors due to multiple reflection, polarization, beam wave of the arriving radio wave and the type of ionospheric models can be found systematically so that a simulation result most resembling the practical situation is provided. The main results are as follows: (1) When the transmission cone is within the trapping cone, the NPF method using orthogonal loop antennas and vertical antennas can indicate an almost correct direction within a radius of about 100 km from the maximum point of the radiowave strength on the ground. The error increases at a distance of more than 150 km. On the other hand, the Poynting method indicates almost correct directions even at a distance of more than 200 km regardless of the polarization. The goniometer method has almost the same accuracy as the Poynting method; (2) if the overlapping of the transmission cone and the trapping cone is smaller, the error is increased in the south direction in all three methods; and (3) no significant frequency dependence is observed in the directional er

ISSN:8756-6621    

DOI:10.1002/ecja.4410721209

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

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper proposes a switching system for the broadband integrated service digital network (B‐ISDN). The proposed system uses self‐routing and a multistage switching configuration. Asynchronously arriving information blocks are switched one by one at high speed. This configuration suppresses cell collision that can occur in asynchronous transmission. This paper describes the system configuration, a technique for designing the system's basic parameters, and system effectiven

ISSN:8756-6621    

DOI:10.1002/ecja.4410721210

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

年代:1989

数据来源: WILEY