摘要:

AbstractTo realize a future high‐speed and ultralarge‐capacity optical transmission, it is indispensable to analyze the ultrahigh‐speed transmission characteristics of the entire system as well as functional circuits, devices and materials comprising the system. Evaluation of such a transmission characteristic requires ultrahigh‐speed optical waveform measurement method.In this paper, a new optical waveform measurement method called the sum frequency generation (SFG) optical sampling method is proposed. In this method, the SFG which is a second‐order nonlinear optical effect is used for all‐optically sampling the optical waveform to be measured (at the optical stage) by means of an ultrashort optical gate pulse. Hence, the bandwidth limitation of the optical receivers and the electronics can be eliminated.By means of this technique, accurate measurement without waveform distortions can be realized while high time resolution and high S/N ratios are maintained. In this paper, the theoretical performance of the present measurement technique is discussed and the measured results by the present method ar

ISSN:8756-6621    

DOI:10.1002/ecja.4410761001

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper analyzes the performance of a number of MAC protocols in high‐speed ring‐type networks and determines the suitable region for each protocol. The authors previously have evaluated the slotted rings, register‐insertion rings and register‐insertion‐type slotted rings, and begin with the analysis of the token ring in this report. To compare the results of the various analyses, the models of each MAC protocol are constructed under the same set of conditions and evaluated with the same method (EPA). Since the nodes of each model are assumed to have buffers to finite capacity, the discussion of buffer overflow is made possible. The results obtained from analysis matched closely with simulation results verifying the accuracy of the analysis. The MAC protocols also are analyzed under high‐speed network conditions, and a comparison of the results reveals the most suitable protocols for various environments keeping in mind the issue of buff

ISSN:8756-6621    

DOI:10.1002/ecja.4410761002

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

年代:1993

数据来源: WILEY

摘要:

AbstractAs a low bit‐rate speech coding method to realize a satisfactory quality of reconstructed speech, this paper proposes a 4.8 kbit/s pitch‐controlled multipulse coding method, which adaptively controls the speech pitch prediction interval and represents the multipulse positions for the excitation signals with a small number of bits. As a method to control the pitch adaptively, an algorithm is derived and proposed where the pitch prediction interval is adjusted adaptively for each frame so that the pulse position is determined to minimize the perceptual error power representing subjectively important difference.In addition to the forementioned method, another method also is proposed to improve the speech quality, where the pitch‐controlled multipulse coding is proposed to control adaptively the coefficients of the synthesis filter. An algorithm is proposed for the adaptive control of the coefficients of the synthesis filter, to calculate anew the optimal filter coefficients for excitation pulses derived from the adaptive control of the pitch.A simulation is executed for the two methods, and the following results are obtained as an evaluation of SNRseg. It is 7.5 dB in the conventional MPC algorithm, 8.6 dB in the proposed pitch‐controlled MPC algorithm, and 9.8 dB in the pitch‐controlled MPC algorithm including the adaptive control of the synthesis filter coefficients. In other words, the improvement in the latter two is 1.1 and 2.3 dB, respectively. The performance is satisfactory also from the viewpoint of the cepstral distance. The improvement in the reconstructed speech quality also is verified for the proposed methods by the subjective e

ISSN:8756-6621    

DOI:10.1002/ecja.4410761003

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper discusses a new signal processing method which helps improve the quality of moving area images in the MUSE system. The essential point of this method is the application of an interfield signal processing technique to moving areas. Moving images are used to conduct computer simulation tests on the method and this has proved efficient. In addition, the method offers good compatibility with conventional MUSE encoders and decoders.

ISSN:8756-6621    

DOI:10.1002/ecja.4410761004

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper presents a BCMP‐type closed queuing network which models the error recovery defined as HDLC based protocols such as LAPB, LAPD, and LLC type II. Throughput and average end‐to‐end delay against the I‐frame loss probability owing to bit errors are obtained by using the queuing network. With the I‐frame length independence assumption, agreement between analytical and simulation results is shown to be fa

ISSN:8756-6621    

DOI:10.1002/ecja.4410761005

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

年代:1993

数据来源: WILEY

摘要:

AbstractRecently, in parallel with the advancement of lightwave technology, there has been a considerable amount of research and development work in the system engineering aspects of optical communication, including important basic research. Various types of modulation have now been applied in real optical communication systems. In this paper we introduce a scale that can be used to measure the efficiency of optical modulation in terms of the quantum entropy. With the aid of this scale, we then discuss the efficiency of information transmission in various types of optical pulse modulation (PAM, PPM, PWM) for particular photon number states of the input system and for an optical channel with noise.

ISSN:8756-6621    

DOI:10.1002/ecja.4410761006

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe FM multiplex broadcasting is one of the broadcasting configurations for providing a new service, where digital signals are multiplexed by utilizing the empty spectrum of the baseband signal in the FM stereo broadcasting. The fixed reception FM multiplex broadcasting system, where reception is done by setting up an antenna has already been developed and used in practice, and its broadcasting has been started. On the other hand, it would be desirable to develop a mobile reception FM multiplex broadcasting system with a certain amount of transmission capacity, where the broadcast can be received by a car or portable radio, for an application to the traffic information transmission. As to the digital transmission to moving objects, interferences such as fading and multiple paths are known to be present and the technical difficulty is increased with the increase of the bit rate. Furthermore, there are difficulties in the FM multiplex broadcasting such as the cross‐talk from the sound signal, due to the nature of the multiplex signal. Only a very low bit‐rate system of about 1 kbit/s has been developed such as RDS (Radio Data System) [1] in Europe for practical applications to the mobile reception. This study aims at the development of a mobile reception FM multiplex broadcasting system with a higher bit rate. An FM multiplex transmission simulator is constructed first, and the transmission characteristics inherent to the FM multiplexing are analyzed. A digital modulation method suited to these transmission characteristics is presented. By laboratory and field transmission tests, the effectiveness of the proposed digital modulation scheme is demonstra

ISSN:8756-6621    

DOI:10.1002/ecja.4410761007

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

年代:1993

数据来源: WILEY

摘要:

AbstractDiversity technology is an effective means to improve the transmission quality in mobile communications. Hence, some portable telephones are equipped with diversity antennas. However no detailed analysis has been carried out. The reason for the low correlation coefficient of such antennas in experiments has not been clarified quantitatively.In this paper, the diversity antenna is assumed to be made of two half‐wave dipole antennas placed in parallel on a small transceiver with a rectangular shape, and its correlation coefficient and efficiency characteristics are analyzed by the method of moments using wire grid models. It is found that the correlation coefficient of 0.23 and the efficiency including the mismatch loss is −2.7 dB even for an antenna element spacing of 0.1 wavelength. Thus a sufficient diversity effect can be obtained on a small transceiver. Specifically, the reason for the low correlation coefficient is studied by separating the mutual coupling between the antenna elements and the effect of the metal body. The relationship between the incoming wave profile and the correlation coefficient is presented. It is shown that the correlation coefficient never exceeds 0.6 in an ordinary operating condition and that the correlation coefficient can be made almost 0 if the load impedance of the parasitic antenna element is chosen appropriat

ISSN:8756-6621    

DOI:10.1002/ecja.4410761008

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

年代:1993

数据来源: WILEY

摘要:

AbstractTo understand the propagation structure of the microcells with a tall and medium‐height antenna in an urban area, the fundamental propagation parameters are found and the structural model of the propagation loss was constructed. The fundamental propagation parameters were obtained based on the multivariable analysis of the propagation data at 800 MHz measured in the Tokyo Metropolitan area. These parameters are the distance between the transmitter and receiver, the average building height between the transmitter and receiver, and the base‐station height which have high correlation and regression coefficients with the propagation loss.The relationship of parameters obtained from the model is (20 ‐ α) log(h) for the base‐station height characteristics and (α ‐ 20) log (H) for the building height characteristics if the distance characteristics are α log (d). The relationships of coefficients of the conventional estimation equation and the regression equation obtained by the measured data almost agreed with those of the model so that the validity of the model w

ISSN:8756-6621    

DOI:10.1002/ecja.4410761009

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

年代:1993

数据来源: WILEY

摘要:

AbstractElectrostatic discharge (ESD) usually is accompanied by two phenomena: the injection of discharge current, and the radiation of electromagnetic pulses. The discharge phenomenon can cause transient electrical interference of electronic equipment and the time‐domain measurement of radiated fields associated with ESD is a difficult task because of the very fast and wide‐band waves involved.This paper describes measurement and analytical results of ESD pulses. ESD pulses were measured by three EMI‐type antennas (a loop antenna, a biconical antenna, and a double‐ridged guide antenna) in the time domain. It is shown that the electromagnetic pulses can be evaluated by the energy spectrum without using the phase information of antenna factors.Based on the measurement of waveforms of the known electromagnetic pulses, it is shown that the waveform can be evaluated with an accuracy of 2 to 6 dB. As a result, it was found that radiated ESD energy does not always increase in proportion to discharge voltage and that ESD pulses produced by low‐voltage ESD can cause strong electromagnetic int

ISSN:8756-6621    

DOI:10.1002/ecja.4410761010

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

年代:1993

数据来源: WILEY