摘要:

AbstractFor efficient processing of various types of traffic in LAN's, the introduction of a priority mechanism is considered to be effective. This paper considers nonpersistent CSMA/CD systems with a new priority mechanism, and derives the throughput and the average response time for each priority class by using the imbedded Markov chain method. The priority structure is achieved by assigning higher exponential retransmission rates to higher priority classes. As for the basis of priority assignment, we analyze two mathematical models: one is terminal‐based and the other is message‐based. Because the models allow feedback of packets, we can apply our results to error‐prone CSMA/CD systems, also. Numerical results show that the simple priority mechanism works effectively, and clarify the differences between the terminal‐based system and the message‐bas

ISSN:8756-6621    

DOI:10.1002/ecja.4410720901

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

年代:1989

数据来源: WILEY

摘要:

AbstractMany ARQ error control schemes have been proposed in data transmission, including go‐back‐N and selective‐repeat schemes. In those schemes, most of the parameters affecting performance, such as the number of continuously transmitted data blocks and the data block length, are fixed. Consequently, the performance may be greatly degraded when there is a time‐variation in the bit‐error rate or when the bit‐error rate is difficult to estimate. This paper proposes a control scheme wherein the number of continuously transmitted data blocks and the data block length are adapted dynamically to the bit‐error rate. The throughput of the proposed scheme is analyzed for go‐back‐N and selective‐repeat schemes using the half‐duplex channel. The evaluations for the go‐back‐N and the selective‐repeat schemes are obtained as special cases of the result of analysis. The effects of various parameters on performance are discussed and the performances of various schemes are compared. The results show that the proposed scheme based on the adaptive control has a performance which is very close to the scheme with a fixed number of continuously transmitted data blocks and fixed data block length, where those parameters are se

ISSN:8756-6621    

DOI:10.1002/ecja.4410720902

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn digital transmission through a metallic subscriber line, burst bit errors are produced due to impulsive noise and other causes. It is important to investigate the actual properties of those bit errors. This paper presents the result of long‐term measurements using various kinds of cores concerning the bit error gap length in the time‐compression multiplex directional control transmission system. It is shown that the bit error rate can be characterized by three gap length ranges. A model is proposed which can represent accurately the features of those distribution patterns of gap length through a simple formulation. The model is compared with the actual characteristics, and the usefulness of the model is demonstrated. As an application of the model, several evaluation measures for the transmission quality (such as bit error rate and errored seconds) are discussed, and it is shown that a more detailed quality specification than in the past (the evaluation in a short‐term observation for 100 ms, for example) can be realized, based on the estimated distrib

ISSN:8756-6621    

DOI:10.1002/ecja.4410720903

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

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper proposes a high‐efficiency coding algorithm realization of a 64 kbit/s video coding equipment. A prototype equipment constructed shows a high quality performance for video conferencing and videophones. For high efficiency coding for video conferencing a coding algorithm combined with motion‐compensated interframe prediction and the orthogonal transform coding or vector quantization is usually employed. It is known theoretically that the latter has an excellent characteristic which approaches the rate‐distortion bound. However, another coding system is desired which not only has a high coding efficiency, but a small‐scale hardware and easy control of information generation. This paper proposes an adaptive tree‐search vector quantization in which the size of a code book can be varied according to the local property of an image. The improvement of the coding efficiency due to this idea is demonstrated by a computer simulation compared with a conventional system with a fixed size code book. A 64 kbit/s video‐coding system having the resolution of 384 (horizontal) × 240 (vertical) pixels per frame was constructed. Using the coding system with the proposed algorithm, a temporal resolution of 5 to 7.5 frames/s was obtained, confirming the satisfactory results for practical applications such as video conferencing and

ISSN:8756-6621    

DOI:10.1002/ecja.4410720904

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

年代:1989

数据来源: WILEY

摘要:

AbstractOne kind of digital PLL (DPLL), i.e., nonuniform sampling DPLLs, can control the sampling intervals. As a result, they can be used for timing extraction circuits and carrier extraction circuits in PCM and PSK systems, etc. The present authors have already proposed a new nonuniform sampling DPLL, the multisampling digital tanlock loop (MSDTL), which can handle more than two samples in each time period of the input sinusoid. The MSDTL can satisfy the sampling theorem because of the multisampling scheme. Therefore, a system with the MSDTL can easily utilize higher digital signal processing technologies. However, the performances of the MSDTL have not been reported yet. This paper presents detailed analyses of the MSDTL and shows its superior performances. In addition, the range (phase detection characteristic) extended MSDTL (RE‐MSDTL) is propose

ISSN:8756-6621    

DOI:10.1002/ecja.4410720905

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

年代:1989

数据来源: WILEY

摘要:

AbstractAlthough optical fiber communication systems have recently been utilized in many fields, most of these have been realized by using a light source‐detector pair. Therefore, two fibers have been needed for bidirectional communication. Alternately, for small‐scale systems such as communication between personal computers and measuring systems, for which not too high a speed is required, a single‐fiber half‐duplex optical communication can be realized by using an LED as source and detector. However, the LED as source stores many excess charge carriers, and the LED as detector has a large depletion capacitance. Therefore, the transceiver must be constructed to minimize these effects for possible high‐speed communication.This paper proposes a transceiver applied to a multivibrator, which has both functions of switching between transmitting‐ and receiving‐mode and modulating the data to FSK signal. The characteristics of trial system including the methods of data‐input and demodulation are investigated. Although the transmitting speed by the proposed method depends on the LED characteristics, we have established a transmitting speed of about 200 k‐bit/s in unidirection by

ISSN:8756-6621    

DOI:10.1002/ecja.4410720906

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn high‐efficient motion picture coding such as systems to compress moving image information below several 100 kbit/s, some visible spatial and temporal distortions are unavoidable. The spatial distortion is perceived by humans as a spatial degradation or noise on the image. On the other hand, the temporal distortion, which is caused by frame dropping, occurs as unnaturalness of motions in the processed image sequence. Here, spatial and temporal distortions are in a trade‐off relationship. Finding the visually best point from this trade‐off is a key feature of good codecs. This paper describes a newly developed coding control algorithm aimed at keeping spatial and temporal distortions in a good balance. In the algorithm, the trade‐off relationship is calculated first from generated information amount vs. the SNR characteristics of the current input frame. Next, an optimal distribution is determined from the viewpoint of human perception. Finally, a coding parameter set is chosen for realizing the distribution and reproduces visually good images. This paper shows the principal of the coding control algorithm and describes an application of the algorithm to an MC‐DCT coding system and simulatio

ISSN:8756-6621    

DOI:10.1002/ecja.4410720907

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

年代:1989

数据来源: WILEY

摘要:

AbstractIt is important to clarify error sequence characteristics in digital land mobile radio channels with memory for accurate performance evaluation of error control schemes such as error correction coding. This research deals with the theoretical analysis of error sequence characteristics in digital land mobile radio channels with very slow Rayleigh fading. First, the digital channel model is studied on the basis of the error generation mechanism in digital land mobile radio channels and the analytical model is simplified, assuming that the envelope fading effect is dominant and fading rate is very small. The quasi‐static approximation method is applied to simplify analysis. Numerical expressions of gap probability and joint gap probability, which are important in making the mathematical model of error process, are derived for binary PSK under the Rayleigh fading environment. The calculated result from the anlytical model and the experimental measured result from the laboratory experiment are shown to agree wellwhen the effect of fading variation is smal

ISSN:8756-6621    

DOI:10.1002/ecja.4410720908

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

年代:1989

数据来源: WILEY

摘要:

AbstractBecause of its all‐weather capability and high resolution, the synthetic aperture radar (SAR) is very effective for remote sensing of the ocean. However, for a moving target such as ocean waves, they affect the SAR images as a phase distortion. This paper considers the orbital motion of the ocean waves. By modeling the waves with an ensemble of the moving points, the SAR image is computed. Previously, the discussions were limited to the case of snapshot observation of the slowly moving ocean waves with a rather long wavelength by a high‐speed SAR such as that on a satellite for simplicity of the model. In this paper, this restriction is removed and the estimate and study of the SAR image become possible including a low‐speed SAR such as the one on an aircraft and waves with a short wavelength. As a result, it is pointed out that the phase velocity of the ocean waves cannot be neglected in a low‐speed SAR so that the wavelength of the SAR image is expanded or compressed and that the SAR image is strongly dependent on the ocean waves and the SAR par

ISSN:8756-6621    

DOI:10.1002/ecja.4410720909

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

年代:1989

数据来源: WILEY

摘要:

AbstractRecently, interest has been increasing greatly in the various services and possibilities offered by the new communication media. At the same time, the demand for higher‐speed communication also has increased. Therefore, flexible systems based on ATM (asynchronous transfer mode) have received particular attention because they can meet these demands by transmitting various types of information in a unified form. In this case, the transmission method can utilize effectively the variable rate characteristics of the information sources. Thus, the understanding of basic characteristics of the coded information sources becomes important. This paper investigates the basic characteristics of the variable rate video coding from this viewpoint. The interframe coding method is considered and the burst characteristics of the information as well as the improvement due to variable rate coding are analyzed, using simulation methods. The results relating to video conference scenes show that the peak rate is about three times as much as the average rate and the quality improvement expressed in minimum SNR is about 5 to 10 d

ISSN:8756-6621    

DOI:10.1002/ecja.4410720910

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

年代:1989

数据来源: WILEY