摘要:

AbstractThe progressive coding scheme (PCS) has been proposed as the coding scheme for the binary image with the progressive build‐up function. However, a problem in PCS is that a simple subsampling is employed in the resolution conversion, and the image quality is not sufficiently high in the intermediate stage.This paper proposes a progressive coding scheme using block reduction (PCSB) as a new coding method for the binary image with progressive build‐up function, with emphasis on the image quality. It is shown first by a subjective evaluation experiment that the progressive build‐up display has a better image quality in the intermediate stage than in the conventional scheme. Then the result of examining the coding efficiency is described in detail.By a simulation experiment using CCITT test documents Nos. 1 through 8, it is shown that the coding efficiency is improved by approximately 17 percent at the final stage, compared to the MMR scheme. It is shown also that dither image can be encoded with a high efficiency. Finally, it is shown that the proposed scheme can be applied to the highly efficient image storage at the image database center, as well as to efficient transmission to the receiver terminals with various perform

ISSN:8756-6621    

DOI:10.1002/ecja.4410740801

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

年代:1991

数据来源: WILEY

摘要:

AbstractWith the increased use of personal computers (PCs) in communication environments have come the expectation of reliable communication protocols. This paper describes the implementation details of two very similar packet communication protocol interfaces on PCs. One is the X.25 interface for packet‐switched public data networks, and the other is the X.32 interface for public‐switched telephone networks. The implementation of these protocols is performed with consideration of the future introductions of OSI higher‐layer protocols.This paper describes also that the addition of the assigning mechanism of level 2 address to the Rec. X.32 enables powerful personal computer communication through public‐switched telephone networks. Furthermore, the results of the performance evaluation are described which show the high throughput of more than 90 percent on various speeds of the physical

ISSN:8756-6621    

DOI:10.1002/ecja.4410740802

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper proposes a digital signature scheme for a facsimile document which embeds a signature directly onto the document. The scheme modifies each run of white or black pixels with a single bit of the signature data. It is designed to be compatible with CCITT G3 facsimile standards and to protect the document from the insertion, modification, replacement, overwriting or deletion of characters. Furthermore, the total amount of data to be transmitted is about the same as that of the original facsimile document. In this paper, an authentication scheme is shown with a prototype model under a one‐key encryption syste

ISSN:8756-6621    

DOI:10.1002/ecja.4410740803

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper discusses a framing system which uses error checking information obtained by a CRC or parity check. Theoretical analysis with a signal flow graph clarifies that the system is effective in extending the misframe interval, in reducing the refraining time, and in decreasing the quasi‐reframing probability. The system is also found to increase the rehunting probability due to bit errors which occur during the reframe check process.Taking the forementioned advantages and disadvantage into consideration, this paper assesses the framing performance of the system using the ratio of blocks including burst errors due to the out‐of‐frame and shows that the system is effective in improving that

ISSN:8756-6621    

DOI:10.1002/ecja.4410740804

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe double‐stage phase‐diversity (DSPD) scheme we have proposed features a phase‐diversity‐type optical homodyne detection followed by a phase‐diversity‐type electrical frequency up‐conversion, giving a heterodyne‐like intermediate frequency (IF) signal. It has the advantages of both heterodyning and homodyning. In this paper, we first calculate the sensitivity penalty due to the optical circuit (hybrid) imbalance in a DSPD receiver. It is shown that the penalty is as small as that in a conventional phase‐diversity receiver and that the optical circuit requirement is not severe.The DSPD experiment with an adjustable imbalance is then performed to confirm the theory; experimental results are in good agreement with the theory. Finally, the possibility of compensation of the optical imbalance at the electronic stage of the

ISSN:8756-6621    

DOI:10.1002/ecja.4410740805

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn response to the need for construction of new customer lines, usually the construction takes place at the joints where in‐service lines are accommodated. It is very difficult to select and establish connection to a specific line without touching other in‐service lines, thereby imposing additional curvatures upon them. Therefore, the losses are increased because of fiber bending; and, in such construction works, there is the fear that the transmission‐loss variations exceed the tolerable threshold.To eliminate such fears, experiments on optical fiber handling are carried out and the factors which influence the transmission losses and the magnitude of such variations are clarified. Further, it is shown that by proper choice of the mode field diameter and the cut‐off wavelength, it is possible to limit the variations of the transmission losses. The guidelines in the design of optical receivers which can tolerate these variations also ar

ISSN:8756-6621    

DOI:10.1002/ecja.4410740806

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

年代:1991

数据来源: WILEY

摘要:

AbstractFrequency diversity usually is employed in microwave radio systems, where protection channels with different frequencies are prepared and the transmitting data signal is switched to the protection channel to secure the channel reliability when the channel quality is deteriorated by the fading. In multicarrier radio systems, there can be various channel switching configurations, since the protection channel is composed of more than one primary carriers.This paper discusses the effects of the frequency diversity in various switching schemes in the multicarrier radio system. As the model for the theoretical analysis for the microwave fading, the three‐ray multipath fading model is assumed which is close to the actual transmission path. The frequency correlation coefficient and the joint probability for the received power distribution in different radio channels also are derived by a simulation calculation.The effects of the frequency diversity of various switching schemes in the multicarrier system are evaluated. The validity of the presented result is verified by the simultaneous measurement of more than one channel with different frequencies in the actual over‐water transmission path by the measurements of the frequency correlation coefficient and the joint probability distribution for the received po

ISSN:8756-6621    

DOI:10.1002/ecja.4410740807

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn this paper, propagation delay measurements were carried out in Tokyo (metropolitan urban area) where high rises and other buildings are concentrated on a plane and in Kofu (urban area adjacent to mountains) surrounded by tall mountains. The delay characteristics such as delay spread and wave numbers were found.The principal results obtained in these areas are as follows.(1) In a metropolitan urban area, i.e., Tokyo, (a) the average delay spread in a high‐density residential district is less than about 1 μs and the delay profile consists of a group of direct waves arriving directly from the base station; and (b) the average delay spread in a location with high‐rise buildings is also less than 1 μs and the average number of arriving waves is about five with the delay profile consisting of a direct wave group and a reflected wave group from reflecting object.(2) In an urban area adjacent to mountains, i.e., Kofu, the average delay spread is less than about 2 μs and the average number of arriving waves is four. The delay profile consists of a direct wave group and a reflected wave group. The level of the reflected wave group decreases exponentially with the delay time in the case of reflection from buildings, while the level is almost constant within a certain range of delay time and is of a spread shape (rectangular) in the case of reflection from mountains.From these measured results, a simple propagation model consisting of a direct wave group and a reflected wave group is proposed. It is shown that the distance dependence of the delay spread has a peak between the base station and a reflecting

ISSN:8756-6621    

DOI:10.1002/ecja.4410740808

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe unavailable time percentage and the SES (severely errored seconds) occurrence rate within available time was investigated according to CCITT definition using Ku band low elevation angles satellite system data obtained mainly at the Yamaguchi station. As a result, the CCITT unavailable time percentage was found to agree with the cumulative signal attenuation time percentage as determined by the traditional statistical treatment. This agreement held even in the case of low elevation angles.Further, the ratio of SES occurrence rate within CCITT available time to the conventional cumulative signal attenuation time percentage was found to be much larger than in the case of high elevation angles, and to have a high correlation with tropospheric scintillation. An experimental formula was developed for this ratio as an index of the degree to which tropospheric scintillation affects overall signal deterioration. Using this formula a formula was developed to predict the SES occurrence rate within CCITT available time from the index and the traditional cumulative signal attenuation time percentage. Also, it was confirmed that there was good agreement between the predicted value and the experimental value.

ISSN:8756-6621    

DOI:10.1002/ecja.4410740809

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

年代:1991

数据来源: WILEY

摘要:

AbstractAntenna diversity reception can significantly alleviate fading with a relatively simple configuration. Hence, this technique will be indispensable in future portable radio systems. In the antenna diversity system installed in a portable transceiver, degradation of the diversity effect due to artificial variation of the radiation pattern (polarization characteristics) is expected. To design an effective diversity branch which reduces degradation by such variations, it is necessary to carry out an analysis of characteristics of the diversity branch in which the arrivals of both the co‐polarization and cross polarization are taken into account.This paper presents a theoretical analysis method for the antenna diversity correlation characteristics which takes into account the statistical incident wave distributions of both the co‐polarization and cross polarization. In addition, a theoretical study is carried out on the correlation between the cross dipole antenna branches, constituting a polarization diversity antenna. The theoretical analysis reveals that the correlation characteristics of the diversity branches depend strongly not only on the antenna directivity but also on the incident wave characteristics and that the correlation between the diversity branches becomes almost zero regardless of the antenna pattern variation and the incident wave characteristics if the cross‐polarization power ratio (XPR) is ‐1.5 dB. Further, the validity of the present analysis is confirmed through 900‐MHz band experiments in a metropol

ISSN:8756-6621    

DOI:10.1002/ecja.4410740810

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

年代:1991

数据来源: WILEY