摘要:

AbstractPassive double‐star networks (PDS) in which optical branches are used to connect local offices and subscribers have been intensively studied. If optical time domain reflectometry (OTDR) is used to test optical cables, the return wave will be a complex superposition of many reflected waves from many optical branches. Therefore, the determination of fault locations by conventional analytical methods is difficult. To detect fault locations more accurately, a new method using pattern matching of the reflected waveforms obtained by OTDR with the waveforms calculated by a computer is proposed. The scattering matrix and an algorithm for calculating the waveform are described and the principle used in detecting the fault location is discussed. A theoretical equation for the error due to noise in the optical circuit is formulated and is used to derive an equation relating the measurement error to the location of the fault, the number of branches, the bandpass frequency, and the pulsewidth. An experimental optical cable (about 3 km long) with four branches was fabricated and used in tests of the accuracy of fault location with a pulsewidth of 1 μms. The error was found to be less than 12

ISSN:8756-6621    

DOI:10.1002/ecja.4410770701

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn asynchronous transfer mode (ATM) networks, each user requests a call setup with the traffic descriptor which describes its own traffic characteristics. Since network resource control is carried out by this traffic descriptor, it would be necessary that the traffic generation is monitored by the network, which is the so‐called usage parameter control (UPC).In this paper, three methods are evaluated analytically for implementing the UPC function: a discarding method, a tagging method, and a hybrid method. The last method is proposed anew in the paper and the comparative results for the three methods are offered from a viewpoint of performance of the cell multiplexer when the output traffic from UPC is superpose

ISSN:8756-6621    

DOI:10.1002/ecja.4410770702

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

年代:1994

数据来源: WILEY

摘要:

AbstractA multimedia communication network is expected to treat various kinds of information, e.g., voice, image, and data which have different demands of grade of service. Furthermore, in new high‐speed networks, end‐to‐end delay distributions or packet‐loss probabilities rather than average delays become more important performance measures.This paper presents a new heuristic design algorithm for packet switching communication networks in which the end‐to‐end delay distribution and packet‐loss probabilities are adopted as design constraints. It is shown that, while the total cost is increased slightly when compared with the former approach, end‐to‐end delays and packet‐loss probabilities between every two end‐nodes can satisfy predefined c

ISSN:8756-6621    

DOI:10.1002/ecja.4410770703

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe Laguerre density and its distribution function which represent the noise in communication systems with an optical amplifier are evaluated by the Cornish expansion and it is found that the result is sufficiently useful for practical applications.The variable transition, skewness, excess, and mode are used as figures of the difference between the Laguerre and Gaussian functions. Then the error rate and decision level on the optimum and quasi‐optimum conditions of a digital on‐off keying (OOK) communication system are analyzed. Assuming the noise to be Gaussian, the error rate is overestimated by about one order. This result agreed with one reported elsewh

ISSN:8756-6621    

DOI:10.1002/ecja.4410770704

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe transmission delay and throughput performances of a hybrid Go‐Back‐N automatic repeat request (ARQ) scheme are analyzed. In the hybrid scheme, multiple alternate transmissions of the copy and parity block of each data block are repeated continuously by transmitter. The receiver detects or corrects errors in a received block by using Wang and Lin's error control algorithm. It is shown that we can obtain the optimum total number of continuous transmissions of copies and parity blocks, which minimizes the average delay time and maximizes the through

ISSN:8756-6621    

DOI:10.1002/ecja.4410770705

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn the two‐dimensional radar image reconstruction using diffraction tomography, missing data become a significant problem if the observation direction and the scan range are restricted. A method is proposed in which these missing data are interpolated in the wavenumber domain. As an object image, a collection of the point targets is assumed. By means of a method which minimizes repetitively the square residual of the observed values and the reconstructed image in the wavenumber space, it is shown by simulation that a good image reconstruction is possible even if the missing rate is as high as 50 percent.As a method to provide the initial value for the repetitive method, an interpolation method using the autocorrelation function is proposed. It is shown that this scheme works well in a stable manner even for a high missing rate and a poor SN ratio. Further, an objective discrimination criterion is proposed for estimation of the number of targets. It is shown that the true target can easily be discriminated if the SN is good and that a stable estimation is still possible even if the SN is poor and the extraction of a weak image is difficul

ISSN:8756-6621    

DOI:10.1002/ecja.4410770706

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

年代:1994

数据来源: WILEY

摘要:

AbstractOnboard resource sharing (ORS) is a method wherein, for increasing effective isotropically radiated power, surplus satellite resources (radiated power or time slots in TDMA) are used to maintain communications quality in areas affected by rain attenuation. This paper analyzes simultaneous occurrence rates of rain over a wide area using Automated Meteorological Data Acquisition System (AMeDAS) data (1 hr rain rate data at approximately 1300 locations in Japan provided by the Japan Meteorological Agency).An ORS system is proposed using AMeDAS data as dynamic information for controlling satellite transmission power. Then a control simulation is performed by using actual reception intensities of satellite signals and rain rate information derived from AMeDAS data at corresponding times. The effect of the proposed ORS system is demonstrated in compensating for rain attenuation.From these results it was confirmed that the forementioned compensation provides a saving of about one‐third compared to the case where unavailable time is not compensate

ISSN:8756-6621    

DOI:10.1002/ecja.4410770707

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

年代:1994

数据来源: WILEY

摘要:

AbstractSystem models and evaluation parameters are proposed for comparing the efficiency of transmitting power utilization of various kinds of PSK transmission systems and bandlimiting and spectrum‐shaping schemes by the peak output power of the transmitting amplifier and the signal‐to‐noise ratio (SNR) at the decision instant. Applying this method to the transmitter‐side Nyquist shaping model and the Butterworth reference equalization model, the characteristics of the BPSK, QPSK, and offset and π/4 shifted QPSK for power amplification before and after filtering are calculated and d

ISSN:8756-6621    

DOI:10.1002/ecja.4410770708

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

年代:1994

数据来源: WILEY

摘要:

AbstractBy extending the electromagnetic field representation on a cylindrical concave boundary with a constant radius of curvature, two types of representations are proposed for analysis of high‐frequency electromagnetic field on a concave boundary in which the radius of curvature depends on the location. They are: (1) a combination of the ray‐tracing method and the adiabatic whispering gallery (WG) mode; and (2) a combination of the ray‐tracing and the modified integral‐type interference waves. The limitations of the application of these field representations also are presented.Especially, the adiabatic WG mode is obtained by an approximate analysis of a parabolic equation in a curvilinear coordinate system under the condition that the radius of curvature changes slowly. A transformation equation is obtained from the lower‐order WG modal solution on a cylindrical concave boundary to the adiabatic WG mode.The foregoing transformation which is similar to the one proposed in the problem of diffraction of a creeping wave on a convex boundary is applied to an integral‐type interference wave and subsequently a modified integral‐type interference wave is derived which can be applied to the case where the radius of curvature changes as an adiabatic approximation. Further, a ray‐tracing algorithm is proposed for determination of the geometrical rays arriving at an arbitrary observation point within a concave surface and its usefulne

ISSN:8756-6621    

DOI:10.1002/ecja.4410770709

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe versatile and affluent adaptive array antenna (adaptive array) is studied as a linear dynamical system. Also, the concept of the equivalent steering signal is introduced by expanding the concept of the steering signal of a maximum signal‐to‐noise ratio (MSN) array. The adaptive array is considered as a system which is expressed by two equations, i.e., the state equation and the output equation, and its model is proposed. As the input signal to this method, the equivalent steering signal is defined. Based on the correlation coefficient between the equivalent steering signal and the array input signal, the characteristics of adaptive arrays are analyzed.From this viewpoint, a simple, clear and systematic investigation method for adaptive antennas is proposed for several characteristics of adaptive arrays for which the analysis is cumbersome and the physical meaning is not clear in the conventional methods. Further, it is illustrated that the equivalent steering signal is related closely to thea prioriinformation of the desired signal which is important in the adaptive array. The importance of thea prioriinformation in the adaptive array is emphasi

ISSN:8756-6621    

DOI:10.1002/ecja.4410770710

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

年代:1994

数据来源: WILEY