摘要:

AbstractAlthough orthogonal transform coding exhibits superior coding efficiency at low rates, it shows a decreased picture quality of reproduced images as a result of noises unique to transform coding, such as mosquito noise and block distortion.This paper proposes a new transform coding scheme, which has a high coding efficiency and significantly reduced noises. It is based on applications of the concepts of region‐oriented coding, to orthogonal transform coding, and has been attracting attention in recent years. The proposed scheme expresses all the regions by quadrilateral blocks to reduce the number of bits required for coding a region shape. Block segmentations are realized with stability and certainty by repeatedly transforming the shapes of the blocks with the square block as the initial shape.The approximating accuracy of an image is improved by the mean values of the blocks by using a smoothing filter. In addition, KL‐transform coding derived from a correlation function model of images is applied to the luminance elements of each block, and bit allocation is optimized on the basis of this model; and the coding efficiency is improved by using an adaptive control method. Simulation results confirm that this method realizes a coding efficiency which surpasses that of the conventional orthogonal transform coding based on square blocks, and gives visually good reproduced ima

ISSN:8756-6621    

DOI:10.1002/ecja.4410770801

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper describes a hitless path switching technique that utilizes fully the benefits of an ATM. First, hitless path protection switching in ATM networks is discussed. It is shown that for the path configuration of working and preestablished protection paths, the best switching method switches on the transmitting side. Then the proposed switching algorithm is described, along with several examples of its application to mesh and ring networks.A cell interval compression method suitable for hitless path switching is proposed that empties and disconnects the transmission delay difference absorption buffer. Finally, an approximate formula is proposed that directly determines the multinode queuing delay. This delay is needed to calculate the capacity of the delay difference absorption buffer. The accuracy of the formula is confirmed by simulations.

ISSN:8756-6621    

DOI:10.1002/ecja.4410770802

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

年代:1994

数据来源: WILEY

摘要:

AbstractA large‐scale switching system composed of distributed modules requires a system testing architecture that automatically tests for verification of call connections normality and determines the fault position when a system fault occurs.This paper proposes a system testing architecture for high‐speed testing of the entire system and wide‐area tests in the system. In the proposed, the distributed modular switching system is divided into upper and lower level modules. The upper level has a system testing function for executing tests of the lower level in parallel. The lower level is provided with various kinds of test equipment and test execution control functions. Similarly, test control functions and test execution control functions, respectively, are provided to the upper and the lower function units composing the module.Compared to the existing sequential test control architecture, the test execution time for verification of the system operation normality of the entire switching system is reduced to 1/[(number of modules) × (number of function units composing a module)]. Testing started by maintenance personnel and diagnosis automatically executed by the switching system itself in the case of a fault can share the test agent for controlling the testing. Then, not only the fault position analysis but also the verification of call connection normality can be realized through the originating and terminating connection t

ISSN:8756-6621    

DOI:10.1002/ecja.4410770803

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

年代:1994

数据来源: WILEY

摘要:

AbstractWhen the coherent detection technique is employed in optical time domain reflectometry (OTDR) (C‐OTDR), enhancing the dynamic range is expected to be an effective means of improving the minimum detectable signal level to that of shot noise. In C‐OTDR, however, there are fluctuations in the OTDR trace, and the problem is the degradation of the resolution of the loss measurements. The main reasons for such amplitude fluctuations are: (1) scattering light‐power jags due to the interference between Rayleigh backscattered lights; (2) variations of the heterodyne detection efficiency due to rotations of Rayleigh backscattering polarization; and (3) variations of the detection efficiency due to phase fluctuations of Rayleigh backscattering light.In this paper, such fluctuations are evaluated stochastically, and the techniques for their reduction are proposed. With regard to cause (1), the amplitude fluctuations can be reduced by integration over the frequency of light, while with regard to cause (2), the improvement can be achieved by polarization diversity detection or integration over the polarization. In case (3), phase diversity detection or phase integration is effective in reducing the amplitude fluctuations. Experimental investigations with regard to cause (1) are conducted in detail, and it is shown that the amplitude fluctuations can be reduced by about 3 to 7 times as a result of integration in the frequency domain compared to those without such integr

ISSN:8756-6621    

DOI:10.1002/ecja.4410770804

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper aims at solving the problem of channel quality deterioration due to the reducedD/UandC/Nby the rain attenuation. A method is proposed to improve the control accuracy in the transmission power control method. In the proposed method, the feedback‐loop control is applied to control the traffic earth station, and the set‐back closed‐loop control is applied to the control of the reference earth station. The site diversity is employed in the reference earth station, and the reference of the transmission power control is determined independently of the TDMA synchronization reference.It is verified as a result of computer simulation and RF set‐back experiment for the proposed method that the control error for the reference earth station in Ku and Ka bands is within ±2.5 dB, and the control error for the traffic earth station is within ±2.0 dB, which is an excellent performance. The proposed method is applied to the actual system, and an excellent performance is obtained in the control through a

ISSN:8756-6621    

DOI:10.1002/ecja.4410770805

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

年代:1994

数据来源: WILEY

摘要:

AbstractWith the increase in the need for versatility in satellite communication, improvements in satellite launching technology and development of small satellites with higher capabilities, there is tremendous research activity in satellite communications using nongeostationary satellites. However, most of these satellites are meant for the polar regions and the application to general communication between widely scattered areas or the marine and airborne in which traditional communication systems are difficult to use.This paper shows first the possibility of a low‐orbital satellite system for an area such as Japan where population density is high and where a geostationary satellite or a terrestrial communication system may easily be employed, and the performance of such a system is investigated.Next, we investigate the Doppler shift in the low orbit. It is shown that complete correction on the transmitting station is not possible, which is different from a long elliptical‐orbit satellite. Moreover, phase‐locked loop (PLL) and block demodulation techniques are considered for carrier recovery in the presence of Doppler shift. A comparative study of the Doppler shift on the spectral efficiencies of multiple access techniques is performed, and the superiority of CDMA over FDMA is

ISSN:8756-6621    

DOI:10.1002/ecja.4410770806

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

年代:1994

数据来源: WILEY

摘要:

AbstractDevelopment of a laser diode (LD) transmitter that has such characteristics as high power, fast frequency response, and good beam profile is essential to a realization of broadband optical intersatellite communications. Both an LD collimator to achieve a good wavefront quality and an LD driver to achieve a fast frequency response are designed for use with an LD operated at a wavelength of 0.83 μm.Also developed is an LD transmitter using an LD collimator and an LD driver. The objective of the LD collimator design was an acceptable degree wavefront aberration with a minimum number of lenses, by applying aspheric lens technology. As a result, a three‐lens configuration for the collimator was obtained. As for the LD driver, two high‐speed LD‐driver GaAs‐ICs are fitted in parallel. Their outputs are combined and fed to an LD. The parallel‐feed configuration enabled a fast frequency response at a high current.For fabrication results, a circularly collimated output beam 5 mm in diameter, with an output power of 60 mW, a transmission rate of 2.5 Gbit/s, and a wavefront aberration of λ/16 was obtained. The result satisfies the system requirements for optical intersatellite link between satellites in low earth orbits.This paper presents an LD transmitter design and data on its test samples, followed by discussions of further i

ISSN:8756-6621    

DOI:10.1002/ecja.4410770807

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

年代:1994

数据来源: WILEY

摘要:

AbstractAn increase in the size of on‐board antenna reflectors is a key technology in providing economical services by miniaturized portable equipment in future mobile satellite communication systems. In practice, a mesh antenna can be used as the on‐board antenna. However, since the reflector surface of this antenna is supported by the cable and the mesh, and its size is larger, the surface is subject to larger thermal deformation in orbit than is the solid antenna reflector. Conventional compensation methods such as passive thermal control or rotation of the antenna reflector cannot maintain the required antenna performances. Various methods have been reported to compensate for the deterioration of antenna performance by thermal deformation.This paper describes a static shape control system for a 10‐m diameter antenna which actively compensates for the deformation by using a shape‐measuring sensor and shape‐compensation actuator. The configuration of the sensor and the experimental results by a functional model are described to confirm the design validity. The shape‐compensation method by the actuator was confirmed to be useful in achieving a required surfa

ISSN:8756-6621    

DOI:10.1002/ecja.4410770808

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper describes a concept and key technologies for a modular mesh deployable antenna. A modular concent is suggested. The advantage of the modular concept and the influence of alignment errors on the surface accuracy are estimated quantitatively. The antenna reflector consists of a mesh surface, a cable network, and deployable truss modules. The cable network comprises three kinds of cables–surface, tie, and back cables. Adjustment of tie cable lengths improves the surface accuracy. Synchronous deployment truss structures are considered as a supporting structure. Their design method, bread board models, and deployment analysis are explaine

ISSN:8756-6621    

DOI:10.1002/ecja.4410770809

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper proposes a new system [1] in which the frequency channel of the wide‐area cordless telephone is reused doubly by the frequency channel employed in the urban cellular mobile telephone with a weak power. A condition is imposed whereby the two systems can operate with equal telephone qualities when cochannel interferences exist between two systems.The radius of the microcell and the weak power are analyzed and completed. According to the analysis, the theoretical limit of the spectrum efficiency of the new system is doubled compared to the system where the frequency bands of the two systems are placed independently in adjacent bands (AB) [2, 3]. To realize the cooperation between the wide‐area cordless telephone and the urban cellular mobile telephone on the equally coexistent condition, an autonomous spectrum distributed management system is proposed in principle [3]which can maintain in a simple way the cochannel interference shar

ISSN:8756-6621    

DOI:10.1002/ecja.4410770810

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

年代:1994

数据来源: WILEY