摘要:

AbstractIn sampled‐value transmission such as TAT where pixel values are transmitted, the transmission characteristics must be equalized so that the transmission distortion caused by the interference between sampled values is reduced below the detectable limit or tolerable limit. This paper considers the situation where the image signal bandwidth compressed by subsampling is to be transmitted by baseband or VSB transmission.The analysis and computer simulation for the transmission distortion are presented. The relation of the maximum transmission distortion to the deviation of the frequency characteristics or the deviation of resampling timing of the transmission system is examined quantitatively. The detectable limit and the tolerable limit of the distortion, for the case where the distortion spreads by the interpolation, are determined by subjective experiment. Their relation to the compression ratio and interpolation scheme is examined.The following properties were obtained. The maximum distortions are nearly the same for the transmitted and interpolated pixels, independently of the bandwidth compression ratio and the scheme of compression. The detectable limit and the tolerable limit become smaller with the extent of compression, imposing more severe requirements on the transmission characteristics. The effect of the interpolation scheme is smal

ISSN:8756-6621    

DOI:10.1002/ecja.4410730601

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn the applications of still picture coding such as image data base, the progressive coding is effective in reducing the retrieval time and the transmission cost. For the block coding based on the discrete‐cosine transform (DCT), a study has been made on the progressive and successive transmission from dc to higher‐order ac components. In this scheme, the major cause of the picture quality degradation is the block distortion produced at the initial stage.This paper proposes two methods to reduce the block distortion where the lower‐order ac coefficients are determined from the dc coefficients transmitted at the first stage and applied the inverse‐DCT. The first method is to determine the lower‐order ac coefficients so that pixel values are smoothly connected at some points on the block boundary. The second method is based on the application of the interpolation filter utilizing the property of DCT. Furthermore, it is shown that by transmitting the difference between the DCT coefficients to be transmitted and the coefficients generated by the proposed method, the coding efficiency can be improved by 5 to

ISSN:8756-6621    

DOI:10.1002/ecja.4410730602

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

年代:1990

数据来源: WILEY

摘要:

AbstractAdaptive ARQ (automatic repeat request) is an error‐control scheme in data transmission in which the number of successively transmitted data blocks and the data block length are adjusted according to the bit error rate. This scheme performs better in half‐duplex transmission than the conventional selective repeat (SR) and go‐back‐N (GBN) schemes when the bit error rate is either not known or varies with time.This paper proposes a control procedure for the full‐duplex adaptive ARQ scheme. In this procedure an observation period is defined and the data block length is adjusted dynamically according to the success of the data block transmission in the observation period. The throughput of this scheme is analyzed. The proposed scheme is compared with nine conventional schemes, including SR and GBN, in terms of performance. The results indicate that the performance of the adaptive ARQ scheme is very close to that of the fixed data block scheme in which the optimal data block length is selected statically. It is also shown that the performance of the adaptive ARQ scheme does not degrade as rapidly as in other schemes when the bit error rate

ISSN:8756-6621    

DOI:10.1002/ecja.4410730603

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe performances (throughput and transmission delay) of the Go‐back‐N ARQ scheme are affected greatly by the bit error rate of the link and the round‐trip propagation delay. This paper discusses the transmission delay of the tandem Go‐back‐N scheme, in which the round‐trip propagation delay can substantially be reduced. First, the generating function for the transmission delay distribution is derived, and then the result is applied to derive the average transmission delay. As a result, it is shown clearly that the performance of the tandem Go‐back‐N ARQ scheme is better than that of the standard Go‐

ISSN:8756-6621    

DOI:10.1002/ecja.4410730604

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper considers the block demodulation method with carrier phase synchronization without preamble, and presents a proposal and evaluation for the new carrier phase synchronization method based on the sequential regression estimator. The block demodulation has a feature in that the traditional way of real‐time demodulation is not adhered to, and the preamble is not required. This improves greatly the throughput especially in a short packet communication.The traditional system is based on the least‐square scheme, noting that the cumulative carrier phase variation between data symbols is represented in a linear form. It has a problem in that the linearity is lost due to noise in deriving the cumulative value for the phase variation, which may greatly deteriorate the demodulation performance.The sequential regression estimator proposed in this paper is based essentially on the least‐square principle. However, the cumulative value is not determined for each time as in the traditional method but the estimation is updated based on the difference between the observed value and the value estimated from the data up to the previous sample. Consequently, the problem in the traditional system essentially is eliminated.Because of this elaboration, the computation in the proposed system is very small compared with traditional systems. It is seen as a result of simulation that the tolerable noise margin for 80 percent synchronizing probability, which has been used as the evaluation criterion, is improved by 11 dB for BPSK.In the satellite packet communications network such as VSAT (very small aperture terminal), the throughput is improved remarkably. Applying the proposed principle to the design of the present link, the time‐ratio, where the burst synchronization error is 1 percent or less in the Ku band, is 0.03 percent. In VSAT, a random access scheme is employed. Considering the burst collision probability of the access, it follows that the burst synchronization error probability of 1 percent does not affect the overall performance, and the proposal in this paper can be considered as sufficiently pr

ISSN:8756-6621    

DOI:10.1002/ecja.4410730605

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn the analog transmission of high‐definition television signal using satellites, the transmission must be performed within a limited band. For this purpose, an adaptive subsampling system is proposed and is used in the highly efficient transmission of the high‐definition television signal. One of the important problems in the adaptive subsampling for improving the picture quality is to partition the picture into as many subsampling modes as possible in an efficient way.This paper proposes an adaptive subsampling system with four different subsampling modes. The four modes are composed of three modes for the moving part and one mode for the still part. Discussions are made on the partitioning of three modes in the moving part, and the partitioning between moving and still parts. In the mode partitioning in the moving part, a method (histogram method) is proposed where the distortion over the whole picture is reduced, based on the histogram derived from the distortion for each subsampling block to determine the subsampling mode partitioning.The proposed method is compared with the traditional method by computer simulation, and it is verified that the SN ratio is improved by the proposed method. As to the partitioning between moving and still parts, a control method for the motion detection threshold is proposed, which seeks a balance between the distortions of still and moving parts. The performance of the control method is verified by a computer simulation for the picture data containing a scene change. Finally, the usefulness of the proposed method is verified by a simulation using motion pictu

ISSN:8756-6621    

DOI:10.1002/ecja.4410730606

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe convolutional coding combined with continuous phase modulation (CPM) has been shown as a good tradeoff between coding and bandwidth. This paper proposes the coded CPM with the nonuniform signal constellation and the multi‐h scheme to achieve further coding gains over the conventional uniform mapping single‐h coded CPM. Using the minimum Euclidean distance, the number of merge events up to a certain depth in the state trellis and the average bandwidth as estimated criteria, the performance of the non‐uniform multi‐h coded CPM is analyzed. It is found that the nonuniform multi‐h coded CPM achieves larger Euclidean distance and diminishes the number of merge events without expanding the

ISSN:8756-6621    

DOI:10.1002/ecja.4410730607

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper proposes a method to diagnose and restore automatically hang‐ups at the nodes connected into networks of ring topology and afterward reports the place where the hang‐ups occurred to an arbitrary equipment. Various measures have been taken to prevent hang‐ups from occurring at the nodes. These hang‐ups affect the network seriously when they occur, and it is important to determine and restore them immediately.The following method is introduced. Each node sends a mutual checking packet at regular intervals, and each node itself determines whether or not its hang‐up occurs from the result of receiving this packet and restores it. After restoration is completed, the node reports to the equipment connected with an arbitrary node the place where hangups occurred. This method has the following features:1It can be applied generally to networks of ring topology;2little hardware is needed;3diagnosing, restoration and reporting are done at each node. A special‐purpose control system

ISSN:8756-6621    

DOI:10.1002/ecja.4410730608

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

年代:1990

数据来源: WILEY

摘要:

AbstractUntil now, four different types of first‐order digital phase‐locked loop (DPLL) for tracking of clock signal have been reported which are distinguished mainly by a difference in the control circuit. The performance of these digital loops is determined by rms phase error and transient response which are obtained in the reporter's own way established on a basis of Markov theory. However, performance comparison has not yet been made.In this paper, first, it is proved that phase error sequences of four digital loops are all classified into semi‐Markov sequences (SMS) if time jitter in each cycle of the input signal is an independent random variable with a certain distribution function.Second, under the condition that time jitter is an independent random variable with Gaussian distribution, the rms phase error and power density spectrum of the phase error sequence are computed for typical values of input variance according to formulas derived for SMS.Finally, using this curve and equivalent first‐order linear PLL, the rms phase error, loop noise bandwidth and phase amplification factor are obtained; and based on these results, the performance of four digital loops is di

ISSN:8756-6621    

DOI:10.1002/ecja.4410730609

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

年代:1990

数据来源: WILEY

摘要:

AbstractSatellite communication has the following problems. The propagation delay is larger than in the terrestrial channel. When the carrier frequency exceeds 10 GHz, the bit‐error rate tends to increase due to the effect of rain and snow, which degrades the transmission efficiency. To cope with such problems, a highly efficient error control protocol has been proposed to prevent the degradation of the transmission efficiency.This paper describes a new large‐capacity, highly efficient retransmission scheme for satellite communication (extended SREJ scheme), which was devised considering the compatibility to the terrestrial network. The method is based on the SREJ (selective reject) scheme, which is specified in the HDLC (high‐level data link control) protocol, employed widely in terrestrial data transmission. To evaluate quantitatively REJ, SREJ and extended SREJ schemes, a satellite communication control equipment was developed.The result of the data transmission experiment is described in detail, indicating that the extended SREJ scheme is efficient. Then, through the discussion of practical usefulness, it is shown that the extended SREJ scheme has no problem from the viewpoint of the number of buffers in transmitting and receiving stations. Furthermore, to realize the efficient processing as far as possible, even if the bit‐error rate is higher than 1.0 × 10−4, the extended SREJ/REJ scheme is discussed by combining the proposed scheme with the

ISSN:8756-6621    

DOI:10.1002/ecja.4410730610

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

年代:1990

数据来源: WILEY