摘要:

AbstractDiscrete coding transform (DCT) coding is a highly efficient coding method for still images with continuous intensity. It has a feature that a drastic image compression can be realized. Among the coding methods considered by JPEG for international standardization, it is adopted as the most basic baseline system which is a cooperative organization of CCITT and ISO. However, the method is an irreversible coding.When the coding/decoding is applied iteratively to the image once coded and decoded, the image deterioration progresses due to the accumulation of the error. The major causes of the error accumulation are the quantization of the transform coefficient after DCT and the rounding off of the value when the intensity is converted to the integer value in the decoding.This paper shows theoretically the following property. When the quantization stepQsatisfies a certain condition and if the image after coding/decoding stays within the range that can be represented by the same number of bits as the original image, no further image deterioration takes place in the following sense. When the decoded image is encoded again using the same quantization table, the result is the same as the previous value. When the image after coding/decoding is outside the range that can be represented by the number of bits of the original image, the value must be restricted.Thus, it is not necessarily true that the DCT transform coefficient of the image after encoding the image is the same as in the previous image. However, it is seen by the result of simulation that even in such a case, the process converges by a finite number of iterative codings, with only a slight deterioration of the signal‐to‐noise (SN) ra

ISSN:8756-6621    

DOI:10.1002/ecja.4410760601

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper discusses the layered construction of the OSI second layer (data link layer) in the satellite packet communication network from the viewpoint of the system performance. The isolated‐type system, where the media access control (MAC) sublayer and logical link control (LLC) sublayer are defined independently, and the combined‐type system, where they are defined in a related way, are considered. The performances of those two systems are compared, using the throughput and the average response time as the evaluation criteria.The TDMA‐Reservation and the slotted‐ALOHA are considered as the MAC protocol. The connection‐oriented type is considered as the LLC protocol. As to the TDMA‐Reservation communication network, the isolated‐type system is analyzed by the equilibrium point analysis. Then the performances of the isolated type and the combined type are compared by the analysis and simulation.It is shown quantitatively by comparison that the performance of the isolated type is always better than that of the combined type. As to the slotted‐ALOHA communication network, it is shown by simulation that little difference is observed in the performances of the isolated and the

ISSN:8756-6621    

DOI:10.1002/ecja.4410760602

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

年代:1993

数据来源: WILEY

摘要:

AbstractHybrid forward error correction/automatic‐repeat request (FEC/ARQ) systems achieve greater throughput than ARQ systems by combining forward error correction with automatic‐repeat requests. A type‐II hybrid FEC/ARQ system is capable of adapting error‐correction capacity according to varying channel conditions. Although a high throughput can be achieved in such systems by using conventional convolutional or rate compatible punctured convolutional (RCPC) codes, when the channel signal‐to‐noise ratio (SNR)Es/N0is low, resulting throughput efficiency and mean block delay performances are unsatisfactory.In this paper, selective repeat type‐II hybrid FEC/ARQ systems using concatenated codes are proposed to improve the throughput efficiency and mean block delay performances on channels with low SNRs. Systems using concatenated Reed‐Solomon outer codes and either rate one‐half convolutional or rate compatible convolutional (RCPC) inner codes are evaluated. The throughput efficiency and mean packet waiting and block delay times of these two types of concatenated coding systems are evaluated. A theoretical analysis and computer simulation of throughput efficiency of the proposed systems show increased performance for a wide range ofEs/N0over previous systems that use either stand‐alone rate one‐half convolutional or RCPC codes. It is also shown that the transmitter mean packet queueing delay and mean block delay times are reduced. In particular, by computer simulation, it is shown that when the traffic density is high, mean block delay times are greatly reduced by the us

ISSN:8756-6621    

DOI:10.1002/ecja.4410760603

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn this paper, a new optical matrix switch using Er‐doped fiber amplifiers is reported. The Er‐doped fiber amplifier acts as an optical gate, depending on the presence or absence of the pump light. The pump light may be a pulsed light whose repetition period is shorter than the fluorescence lifetime. Here the pump light contains interconnection information as a code, and an optical matrix switch where the pump light is distributed through an optical decoder to multiple optical gates is proposed. As a result, an optical matrix switch where the interconnections may be changed by changing the code became possible.In experiments, first, a basic optical gate characteristics were investigated. Using a 20‐mW pump light, the isolation for ON/OFF was 35 dB in the optical gate. In optical gates pumped by pulsed light, it was clarified that there was no influence on the signal light when the repetition rate of the pump light is above 5 kHz. Next, from the above conditions, a 1 × 2 optical switch using an acousto‐optical deflector for the optical decoder was constructed and the switching operation controlled by a coded pump light was demonstrated. The extensibility of matrix size was also investigated; and, by a combination of the proposed switch configuration and Clos‐network construction, it was found that a realization of a 225 × 225 optical matrix switch w

ISSN:8756-6621    

DOI:10.1002/ecja.4410760604

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

年代:1993

数据来源: WILEY

摘要:

AbstractSubsampling is used widely in a bandwidth compression of video signals because it simply decreases the sampling rate with less artifacts. The compression efficiency and a final picture quality of a video compression based on a subsampling normally are improved by applying a motion adaptive technique. Such a technique switches processing between the static picture area and moving picture area depending on the movement. This switching is controlled as the result of detecting the moving picture area, a technique called “moving area detection.”In moving area detection used by a frame‐offset subsampling system such as a MUSE decoder, the frame difference cannot be obtained because the sampled value is omitted by subsampling, thereby causing erroneous detection or detection failure.In this paper, the improvement of the moving area detection method used in a MUSE decoder, which is the analog transmission system for Hi‐Vision signals, is described as an example of moving area detection of a subsampling system. The improvement of moving area detection is confirmed by an LSI MUSE decoder. The frequency characteristics of a moving area detection circuit also are discussed. Consequently, the frequency characteristics of moving area detection necessary for a MUSE decoder are o

ISSN:8756-6621    

DOI:10.1002/ecja.4410760605

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

年代:1993

数据来源: WILEY

摘要:

AbstractHigh‐speed transmission technology is accomplishing dramatic reforms due to the application of optical fiber amplifiers.This paper reviews the high‐speed and long‐span repeater transmission which has become possible because of the application of wide‐band and low‐noise optical fiber amplifiers. Also, the device structure together with several other topics and their significance are

ISSN:8756-6621    

DOI:10.1002/ecja.4410760606

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

年代:1993

数据来源: WILEY

摘要:

AbstractIt has been demonstrated that the receiving sensitivity in the direct detection scheme is significantly improved by using an optical preamplifier. The bandwidth of an optical filter plays an important role in the characteristics of such an optical preamplifier. Therefore, in this paper, a method to optimize the optical filter bandwidth by taking into account the wavelength tolerance is presented. First, the noise figure is found to increase due to the relative increase of the ASE power compared to the signal optical power on detuning, if we consider the tolerance of the wavelength and the spectrum of the filter. Second, the increase in the noise figure is expressed in terms of the equivalent noise bandwidth of the ASE‐ASE beat noise and is compared with the experimental result obtained for the various detuning values. The optimized bandwidth which keeps the preamplifier noise level low even for the maximum detuning is determined. For example, for a Lorentzian‐type optical filter spectrum, the full‐width at half‐maximum (FWHM) is 3.46 times larger as compared to that at the maximum detuning. Also, a preliminary study on the intersymbol interference due to the detuning in a 2.4 Gbit/s intensity modulation‐direct detection system was conducted; it was found that the intersymbol interference can be neglected for a Lorentzian‐type filter spectrum wit

ISSN:8756-6621    

DOI:10.1002/ecja.4410760607

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe diplexing bandwidth of a cylindrical‐cavity directional filter is restricted of coupling of the coupling hole, which is installed in order to excite a circular polarization on the common walls of the input and output rectangular waveguides and in the adjacent cylindrical cavity.This paper proposes a method of increasing the coupling of circular polarization by means of an iris‐loaded cross‐coupling hole (consisting of an iris mounted on the crossed‐coupling hole of a rectangular waveguide). The results of analysis of the magnetic field distribution and the magnetic field intensity in a rectangular waveguide loaded with an iris are described.It shown that the iris‐loaded cross‐coupling hole is effective in exciting a circular polarization and increasing coupling. The results of a trial fabrication of a directional filter using this type of coupling hole are presented. In the case of a three‐stage maximally flat K band filter, a passband relative bandwidth of 2.7 percent was obtained. This bandwidth is three times as great as in conventional filters. Hence, the range of application of the cylindrical cavity directional filter has

ISSN:8756-6621    

DOI:10.1002/ecja.4410760608

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

年代:1993

数据来源: WILEY

摘要:

AbstractWhen a circularly polarized phased array is used for communication, it is required to maintain a high gain and suppress the cross polarization over the beam scanning region and over the frequency region. However, in the traditional phase‐setting method in which only the feed line length and the array factor are taken into consideration, the desired radiation characteristics cannot be obtained because the elemental electric field in the array environment is fluctuated by the effect of the mutual coupling between the elements and the scattered wave from the structures.In this paper, a method is presented for improving the gain and suppressing the cross‐polarization level by controlling the excitation phase with the phase shifters inherent to the phased array under these complex electromagnetic environments. The main idea of the present method is in the measurement of the correct and cross‐polarization components for each element antenna and in the derivation of the optimum excitation phases based on the minimization algorithm of the output power. An experiment is carried out in which the proposed method is compared with the phase‐setting method where only the feed line length and the array factor are taken into account. Thus, the effectiveness of the proposed method is demon

ISSN:8756-6621    

DOI:10.1002/ecja.4410760609

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

年代:1993

数据来源: WILEY

摘要:

AbstractFor an airborne collision avoidance system, it is necessary to measure the directions of other aircraft in the vicinity with high accuracy. As one of the methods for such a purpose, a method was studied in which a small circular array and Butler matrix are combined. In such a case, the mutual coupling between the elements increases. However, by adjusting the phases appropriately, it is found possible to maintain a phase relationship in the same way as in the case without mutual coupling. Also, an angular measurement method was proposed in which the outputs of the Butler matrix are combined at the output stage. It was found that the accuracy is close to the one obtained in the maximum likelihood estimator while the circuit is simple.

ISSN:8756-6621    

DOI:10.1002/ecja.4410760610

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

年代:1993

数据来源: WILEY