摘要:

AbstractLANs are used to achieve mutual communication among microcomputers and workstations and their wiring flexibility with terminals is becoming a necessity. However, the wiring flexibility of a bus‐type twisted pair LAN is low because of limited tap connection.Although the equalization of a transmission line is necessary to improve wiring flexibility, a long sequence of training signals (more than a kilo bit long) must be sent before data transmission. Therefore, the transmission efficiency becomes significantly low in the case of a short data transmission such as in an LAN, and hence the application of conventional equalization techniques becomes difficult. Thus, wiring system technology to improve wiring flexibility becomes important in a private network system.This paper proposes an asynchronous correlation receiver which improves wiring flexibility for a bus‐type twisted pair LAN by allowing taps. Hence, a received waveform is decoded by pattern matching between the received waveform and the reference waveforms. The reference waveforms are stored in a memory in a prior training period using the multiple sampling method.Several experiments are carried out and their results revealed that the training time can be shortened (e.g., to 19 bits), the required clock accuracy is well realized by an ordinary crystal oscillator, and the transmission error rate can be made less than 10−6under the worst transmission condition for a bus‐t

ISSN:8756-6621    

DOI:10.1002/ecja.4410740201

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

年代:1991

数据来源: WILEY

摘要:

AbstractRigorous study of optical communication processes has become interesting since around 1970. Especially, quantum information theory has been developed in both mathematics and engineering. In this paper, by controlling the energy associated with a quantum input state, we obtain an optimal solution (optimal state, optical modulation, etc.) giving the minimum value to the error probability in the attenuation optical communication process. For instance, we find some relations between the energy constraint of the input state and the optimal error probabilities in each modulation.

ISSN:8756-6621    

DOI:10.1002/ecja.4410740202

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe scale for evaluating the picture quality of coded pictures objectively becomes very important because some high‐efficiency coding techniques (e.g., DCT and VQ) are applied to the practical stage. An objective picture quality scale (PQS) has been proposed which approximates well the mean opinion score (MOS) by analyzing the perceptual properties of image distortions and using multiple regression analysis (MRA) to construct a linear combination of the essential factors of distortions extracted from the fundamental distortions by principal component analysis (PCA).In this paper, a new objective picture quality scale (PQS) is obtained by three‐layered neural networks feeding the coded error images to the input layer and giving the mean opinion scores as a target. No knowledge of visual perception is given to neural networks.After learning that the mean opinion score of open test images (out of learning) is approximated well by neural networks, it is shown that neural networks (or NN) estimate MOS well with two hidden units and that the estimate performance is improved with an increase in the number of learning images. A very interesting fact is clarified, i.e., NN learned the same functions as visual perceptions. An objective picture quality scale, with considerable precision in estimating test images without professional knowledge about perceptual properties, can be obtained by using this new objective picture quality scale PQS

ISSN:8756-6621    

DOI:10.1002/ecja.4410740203

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe block demodulation method recently has received considerable attention because of its high data transmission efficiency and superior performance. However, the conventional block demodulators do not consider the distortions of amplitude and phase in a transmission channel. As a result, the conventional block demodulators cannot compensate such distortions.In this paper, a new block demodulator with an automatic equalizer is proposed. A two‐dimensional block equalizer is used in the proposed demodulator. The overall performance is improved greatly by the repeated estimation method of combined automatic equalization and carrier estimation. In addition, the number of taps in the equalizer is changed for further improvement.The computer simulation result indicates that the mean‐square error by the proposed demodulator is about 1/100 compared with that of the conventional one when SNR = 30

ISSN:8756-6621    

DOI:10.1002/ecja.4410740204

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

年代:1991

数据来源: WILEY

摘要:

AbstractAs the local area network (LAN) becomes popular, LAN systems which cover wider areas and which resolve traffic concentration in the system are going to be needed. This paper analyzes a system which consists of a token ring LAN as the main network to which some CSMA/CD‐LANs are connected with bridges. Such a system is called the “compound LAN system” in this paper. The optimum condition of this system due to the performance evaluation of the compound LAN system is shown by comparison with the throughput of each LAN. The results of analysis are confirmed by computer simulations. Moreover, the optimized scheme condition is confirmed by using the power function evaluation for the s

ISSN:8756-6621    

DOI:10.1002/ecja.4410740205

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

年代:1991

数据来源: WILEY

摘要:

AbstractImprovement of the radiation characteristics by the “nonaxisymmetrical aperture field distribution” is described. The aperture distributions in the horizontal and vertical planes are designed to be a low‐sidelobe type and a high‐efficiency type, respectively. As a measure of the degree of nonaxisymmetry, the ratio of the edge levels in the vertical and horizontal planes is introduced. The dependences of the degrees of improvement of the aperture efficiency and the wide angle radiation pattern upon the edge level ratio were studied and the amount of improvement was presented quantitatively.For example, the wide angle radiation level was reduced by about 15 dB by nonaxisymmetric aperture distribution with the aperture efficiency kept constant. On the other hand, if the wide angle levels were kept constant, the aperture efficiency was improved by about 0.4 dB with nonaxisymmetric distribution. In the case of an offset antenna, sidelobe levels in the wide‐angle region were increased from the numerical results with the aperture field method by the effect of the edge diffraction.The increase is shown to be less than 3 dB in the case of an offset angle of 60°. Moreover, the wide‐angle directivity can be improved in a certain region centered on the plane in which the attempt was made to achieve a low sidelobe level by means of a nonaxlsymmetric distribution. Possibilities and examples of widening or reducing this region and furthermore shifting it to the surface other than the horizontal one we

ISSN:8756-6621    

DOI:10.1002/ecja.4410740206

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn a multipath fading channel, the arrival time delay difference of multipath signals gives rise to an asymmetric transfer function of the channel, thereby causing cross‐channel‐interference (CCI) between in‐phase and quadrature channel components of a transmitted signal. This paper proposes the use of CCI for detecting multipath signals and roughly estimating multipath delay spread in a digital mobile communication environment.First, the relation between CCI and multipath signal delay time is analyzed under the assumption of static two‐ to three‐ray multipath signals, taking BPSK and QPSK as examples.Next, taking BPSK as an example, the existence of a close relation between CCI and delay time difference or between CCI and delay spread under quasi‐static and Rayleigh fading multipath signal conditions is shown by theoretical analysis and computer simulation. The correspondence between CCI and bit error rate (BER) performance also is studied by computer simulation, and good agreement is found.Finally, the relations obtained were confirmed by laboratory measurements. Accordingly, multipath signal can be detected from CCI. Moreover, rough estimation of delay spread and variation characteristic of BER can be obtained from CCI. Thus, CCI can be used as an effective piece of information for evaluating transmission quality in digital mobile co

ISSN:8756-6621    

DOI:10.1002/ecja.4410740207

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe authors have developed the tracking control system of astronomical objects in the Nobeyama millimeter array. A system was studied which can accomplish sufficient tracking accuracy for an interferometer, such as delay tracking, phase tracking, and fine delay correction. It was found that the location error of an astronomical object can be made less than 1 percent of the maximum spatial resolution on a synthesized map and the radio intensity degradation less than 0.1 percent if the phase tracking is executed at an interval of about 10 s and the fine delay correction at 1 ‐ 2 s. Further, from the actual observation results, it was confirmed that this system has realized an extremely high tracking accurac

ISSN:8756-6621    

DOI:10.1002/ecja.4410740208

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn a radio communication system using a frequency in the UHF and higher band, the fading due to change of the refractive index profile of the air is a significant problem which must be predicted. In this paper, an analysis using the geometrical optics theory is attempted to determine the propagation characteristics in a nonuniform air in which the refractive index varies in both height and range due to a small‐scale nonuniform air mass occurring in the propagation path.After the refractive index of atmosphere is modified by the Earth‐flattening approximation, the Euler‐Lagrange differential equation is solved directly by numerical means so that the ray path is determined. In regard to low‐layer propagation with transmission and reception heights of less than several hundred meters, an air model was conceived in which a surface duct occurred in a part of the propagation path.The relation of the location and size of the duct along the propagation path to the maximum arrival distance (line‐of‐sight) of the direct ray, divergence and convergence of the direct ray and the reflected ray and the arrival angle at the receiving point was studied in detail. It was found that the maximum arrival distance of the direct ray increases significantly depending on the location of the surface duct if it is small in size, the effect of the ray flux is greater on the convergence of the reflected ray than the divergence of the direct ray, and no significant change in arrival angle is seen at the receiving point for both the direct ray and the re

ISSN:8756-6621    

DOI:10.1002/ecja.4410740209

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn the rectenna array used for rectification of the microwaves received on the ground in the solar power satellite system, it is required that the rectenna elements have a high dc power conversion efficiency and that the element spacing is optimized so that the arriving microwave power is received efficiently and the number of elements can be reduced. In this paper, a microwave rectifier is fabricated in an integrated form with a microstrip line on a teflon substrate. A circular microstrip patch antenna is used. A high rectification efficiency, 66.7 percent is obtained at a microwave input of 750 mW and 75.7 percent for input of 500 mW.With this rectenna element, a 7 × 7 lattice array is formed and the variation of the receiving efficiency (the ratio of the power converted to dc to the input microwave power) is measured by varying the element spacing. On the other hand, the receiving efficiency is calculated for a given element spacing of this rectenna array from the circuit equation of the antenna system by deriving the mutual coupling between the elements. The relationship between the element spacing of a finite array and the receiving efficiency is obtained both experimentally and theoretically. This computation method is extended to the case with many elements so that the change of the receiving efficiency is investigated

ISSN:8756-6621    

DOI:10.1002/ecja.4410740210

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

年代:1991

数据来源: WILEY