摘要:

AbstractIn designing a highly reliable nonhierarchical communication network, it will be more practical if not only the required number of disjoint routes is ensured, but also the cost is minimized. Under certain assumptions, the communication network cost can be evaluated by a simple matrix calculation. The branch cost and its associated switching node cost are evaluated by the sum of the fixed cost and the traffic proportional cost. It is assumed that the traffic is carried through a minimum cost route in a normal state and, based on this assumption, the traffic offered to each branch is calculated. Then the communication network cost for given nodes, branches, and traffic matrix, is obtained by matrix calculation. Moreover, the approximate formula, which has already been proposed, is used to calculate the number of disjoint routes. Therefore, the minimization of the network cost under the constraints of the number of disjoint routes can be done by matrix operation. Since the matrix calculation is especially suitable for a supercomputer, relatively large‐scale networks can be designed systematically by the proposed design metho

ISSN:8756-6621    

DOI:10.1002/ecja.4410720701

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn recent years, block demodulation systems have been proposed which store blocks of phase‐shift keying (PSK) signal and derive data by batch processing. In such systems the traditional method of realtime demodulation is not considered and block processing is applied after quasicoherent demodulation. Training signals required for traditional methods are not at all needed for this system. Therefore, the data transmission efficiency becomes very high. However, conventional block demodulators have a serious disadvantage–they cannot demodulate the signal without external timing information. This paper proposes a new timing extraction circuit not contained in a conventional block demodulator, which improves greatly practical applicability. Also, a method is proposed for accurate carrier estimation. According to computer simulation results, the permissible noise limit becomes 4 to 5 dB lower in comparison to the conventional met

ISSN:8756-6621    

DOI:10.1002/ecja.4410720702

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe optical directional coupler is one of the key devices for an optical time domain reflectometer (OTDR). In this paper, an optical directional coupler employing an acoustooptical deflector was used to investigate the backscattered light from a multimode fiber. First, the fundamental characteristics of an acoustooptical deflector, diffraction efficiency, and rise time were evaluated. For this evaluation, the theoretical value of the diffraction efficiency was obtained by the ray tracing method. The length and height of the transducer in an acoustooptical deflector were optimized. The relationship between the rise time of the acoustooptical deflector and the focusing distance of a lens in the collimator was also obtained. Using the results, an optical directional coupler was designed and fabricated. Finally, the optical directional coupler was built in an OTDR and excellent performance was confirmed.

ISSN:8756-6621    

DOI:10.1002/ecja.4410720703

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe problems in measurement of the beacon wave XPD are pointed out when the satellite is tracked automatically by the step tracking method in the CS‐2 operation test station. Since the antenna is driven on a trial‐and‐error basis in the step tracking system so that the beacon receiving level always increases, measured values of the beacon receiving level and the XPD vary during the tracking operation. If the tracking operation is performed periodically at a constant time interval to avoid these unwanted variations, the pointing error of the ground station antenna to the satellite during this interval causes degradation of the antenna gain and the XPD. In this paper, the antenna pattern of the ground station antenna is measured. In addition, the characteristics of the location variation of the satellite on the elevation and azimuth angles are determined. The reduction of the maximum beacon receiving level and the XPD degradation are computed which are likely to occur if the tracking interval is 10 ‐ 210 min. It is pointed out that the satellite tracking must be done at least once every 50 – 90 min to perform the on‐propagation‐path XPD measurement in the satellite channel with an estimated accuracy o

ISSN:8756-6621    

DOI:10.1002/ecja.4410720704

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

年代:1989

数据来源: WILEY

摘要:

AbstractTo find the unwanted reflection characteristics of a Fresnel region wave from a building and a wall, it is necessary to know the direction of the reflection source. This paper proposes an algorithm which estimates successively the direction of arrival of the reflected wave in the Fresnel region, based on the study of the characteristics and the shape of the spatial series in that region. This algorithm is realized by a combination of the maximum entropy method in which a spectrum can be estimated at a high resolution with a few data and an error correction by the Newton‐Raphson method for solution of a nonlinear equation. To confirm the validity, a computer simulation and experimental results are shown. In the computer simulation results, the reflection direction was estimated with an error of 0.1° ‐ 2.9° from 40 measured data for an aperture of 5 wavelengths. In the experiment, the reflection direction was estimated with an error of less than 0.5°. From these results, it is found that this algorithm can be applied for direction finding of the reflected wave under an actual electromagnetic envir

ISSN:8756-6621    

DOI:10.1002/ecja.4410720705

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

年代:1989

数据来源: WILEY

摘要:

AbstractRecently, extensive efforts have been expended in research and development of patch antennas which are small in size, lightweight and not very thick. In these antennas, the effect of the near field on the far field characteristics cannot be ignored. The former is affected in turn not only by the antenna element but also by the shape of the structure on which the antenna is installed. This near field has a complex field distribution which is dependent on the three‐dimensional structure and the medium conditions of the system. A systematic analysis in which the three‐dimensional structure and the medium conditions of the system are given rigorous consideration is indispensable. In this paper, a rectangular patch which is a basic form of the patch antenna is analyzed by the Bergeron method in terms of the three‐dimensional time response of the near field. Based on the aperture distribution of the electric field thus obtained, the far field is computed by Fourier transform. A method is proposed for efficiently deriving the far field in the Bergeron method. By comparison with analytical solutions, the validity of the fundamental treatment is verified. Further, by taking advantage of vector analysis, the electric field near the patch is expressed in a vector form for both the linear and circular polarizations. The spatial and temporal evolution of the field and the change from the near field to the far field are exhibited. Also, by means of the representation of the Poynting vector, the energy flow important for understanding the radiation characteristics of the antenna is depicted. The fundamental characteristics of the patch system are thus obt

ISSN:8756-6621    

DOI:10.1002/ecja.4410720706

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

年代:1989

数据来源: WILEY

摘要:

AbstractThere is a need for large deployable antennas with diameters larger than 10 m for space‐VLBI satellites and mobile communication satellites. Several deployment mechanisms have been proposed, each of which uses determined lines and points on a smooth prototype reflector surface. The basic structure is to use the reflector surfaces which are located between them as meshes or films.This paper examines types of mechanical errors of a deployable antenna and its relation with the radiation characteristics. Its effects on the radiation characteristics are shown numerically. As a result, it is shown that the gain reduction is less than 0.18 dB by subdividing the reflector surfaces by equilateral triangles whose side is about one‐eighth the radius for a 2‐GHz band tension‐truss type antenna of 15 m diameter. With a penalty of an additional 0.1 dB, the number of approximating triangles can be reduced by about 30 percent by subdividing the outer portion of the reflector twice as roughly as the interior portion. However, it is important to add phase offsets.It is shown that grating lobes appear in the sidelobe characteristics due to the periodic errors. The relationship between mechanical error and the effective error of the reflector surface is also cl

ISSN:8756-6621    

DOI:10.1002/ecja.4410720707

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

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper is a detailed theoretical study of the basic radiation characteristics of a cutoff‐waveguide aperture antenna excited by a post when it is used as a hyperthermia applicator for heating tumors located deep inside the human body. The effect of the wave reflected from the body on the radiation characteristics is considered by an approximate evaluation of the reflected wave from a semi‐infinite lossy medium with electrical constants equivalent to those of a muscle placed in front of the antenna aperture. In the analysis, an equivalent problem is considered in which the aperture is closed by a conductor and unknown magnetic current sources are placed on both sides of this conductor. The integral equation derived from the continuity condition of the tangential magnetic field components at the aperture is solved by Galerkin's method. Extensive numerical data are presented for the relationship of the radiation power and the input impedance to the location of the lossy medium and the dimensions of various parts of the waveguide applicator. It is found that although the radiation power is generally larger if the distance between the lossy medium and the aperture is smaller, for a certain distance the radiation power can be smaller than the case without a lossy medium. It is also found that if the location of the excitation post is distanced somewhat from the aperture, the imaginary part of the input impedance is not affected by the location of the lossy med

ISSN:8756-6621    

DOI:10.1002/ecja.4410720708

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

年代:1989

数据来源: WILEY

摘要:

AbstractWith the open use of the communication activities and the diversified applications of services with various functions, a tendency to utilize the communication network in various ways and for various purposes is observed. There is an increasing need to realize network management based on the prediction technique for the communication activities of the user. This paper proposes a modeling for the choice behavior of communication services by applying the disaggregate behavioral model used in the field of urban engineering as a means of estimating commuter demand. The possibility of application to the communication network management is demonstrated. First, the decision‐making factors to be considered in the model are classified and then the general construction procedure for the model is presented. The qualitative and subjective decision‐making factors are represented numerically using the cardinal scaling based on paired comparisons, and are then used as factors of the model. Assuming a communication service providing 28 kinds of information data concerned with daily life activities, a model construction experiment was made. An examination is made based on actual survey data regarding user intention. It is shown that an excellent performance is obtained in the prediction of service choice, learning based on accumulated data, and the evaluation of service functions. Based on the realized performance, the application of the model to the management and operation of the communication network is discus

ISSN:8756-6621    

DOI:10.1002/ecja.4410720709

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn the TAT (time‐axis transform) picture bandwidth compression system the pixels are selectively utilized. Because of its high reproducibility of the details of a picture, an application is expected to the bandwidth compression of HDTV (high‐definition TV) and other pictures of high quality. In the one‐dimensional (1–D) TAT system, the pixels are reduced and interpolated along the horizontal direction. This paper reports on the two‐dimensional (2–D) TAT system which reduces and interpolates the pixels not only in the horizontal direction but also in the vertical direction. Using this system, a system for the color TV signal with 7–MHz bandwidth was constructed, which compresses the bandwidth to one‐half in real‐time. Compared with the 1–D system, the number of modes is reduced from 3 to 2, and the size of the block is increased from 8 to 16 pixels. Then the mode information is reduced to approximately one‐third the 1–D system. On the other hand, a faithful picture is obtained with little degradation of resolution both in moving and still pictures. Sometimes a flicker is observed due to the time‐variation of the mode in the reconstructed picture, which can be suppressed by the new mode decision

ISSN:8756-6621    

DOI:10.1002/ecja.4410720710

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

年代:1989

数据来源: WILEY