摘要:

AbstractThis paper proposes a system of realtime bandwidth management and call admission control in an ATM network, which guarantees communications quality with high reliability and control simplicity. In this call admission control system, the allocated bandwidth for each bursty class is determined by theX‐percent value of the superposed bursty traffic distribution in each bursty class. Whether a requesting call is accepted or rejected is judged by the total allocated bandwidth of all bursty classes.Since the communications quality of each class can be approximately estimated from theX‐percent value of the superposed bursty traffic distribution and this probabilityX, a method of determining the allocated bandwidth satisfying quality specification is presented by formulating the probability event that each peak state is superposed.Bandwidth management, where bursty classes are introduced in order to realize optimal and simple control in accordance with the traffic burstiness and a method of call admission control are also presented. Although throughput performance is too deteriorated to realize the safety‐side bandwidth management, computer simulation confirms that the statistical multiplexing effect can be expected by using the proposed m

ISSN:8756-6621    

DOI:10.1002/ecja.4410740901

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn this paper, a link capacity assignment algorithm for a packet switched communication network is presented. This algorithm, called max‐delay‐link algorithm, prevents sharp performance degradation in a network even in case of link failures. An optimal link capacity assignment can be obtained with respect to link cost minimization, subject to the constraint that the average packet network transmission delay does not exceed a predetermined value.Robust networks against failures can be designed by assigning large capacities to links where overflow traffic and packet delay are expected to increase in case of a failure. Several numerical examples also are shown to examine the effectiveness of the algorithm in comparison with the conventional capacity assignment algorithm where link failures are not taken into acco

ISSN:8756-6621    

DOI:10.1002/ecja.4410740902

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper discusses a signal transmission method based on the existing digital hierarchical transmission system that transmits signals as defined in the network node interface (NNI) of the new CCITT synchronous digital hierarchy (SDH). The method transmits the information corresponding to two virtual containers (VC‐3s) with the capacity of 28 of 1.5 Mbit/s over existing transmission systems using the fourth digital level, which is the basic unit of operation in the existing network. The fourth digital level signal in Japan has a bandwidth of 97.728 Mbit/s as specified in Rec. G.702. If two VC‐3s are to be contained according to the basic SDH philosophy of NNI, the required transmission capacity is 103.68 Mbit/s. The method that allows two VC‐3s to be transmitted at 97.728 Mbit/s should be considered.It is shown first that the use of the pointer introduced in SDH is adequate. A pointer scheme with a fourmultiframe structure is proposed, aiming at efficient information transmission. The characteristics of the fourmultiframe‐type pointer are then discussed, and the assignment of the overhead required in the transfer of maintenance/operation information is considered. Based on those discussions, the frame structure for the 97.728 Mbit/s signal is derived, which is the fourth level of the existing digital hi

ISSN:8756-6621    

DOI:10.1002/ecja.4410740903

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

年代:1991

数据来源: WILEY

摘要:

AbstractATM (asynchronous transfer mode) system transfers and switches the information from various media such as voice, data, and video in a unified way. Since media with severe requirements for high‐speed transfer or real‐time processing must be handled, there is no flow control function during communication. As a result, a certain bandwidth must be assigned to each call to ensure service quality.This paper considers first the case where the same bandwidth is shared by several classes with different service requirements. The “flexible processing” system is proposed as a priority processing method where the qualities of other classes are not deteriorated even if there arises an unexpected traffic flow of a particular class. For bandwidth assignment to each call in the same class, the “volume declaration” method is proposed, wherein the user declares the maximum information content (= volume) that can be transferred in the specified time, in addition to the maximum information transfer rate. It is shown that the service quality of the call can be insured by this method.Then we examine the case in which physically distributed bandwidths are utilized by more than one service quality class, and it is shown that the results of past studies on the multirate circuit switching can be applied, by assuming the forementioned volume declara

ISSN:8756-6621    

DOI:10.1002/ecja.4410740904

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper considers CMA adaptive array for the high‐speed TDMA transmission system using GMSK, which is the most ordinary constant‐envelope modulation system in the digital mobile land communication. A computer simulation is executed for the case where a four‐element adaptive array is applied to cope with the selective fading. CMA is employed as the array control algorithm, which is suited to the compensation of the constant‐envelope modulated signal. Assuming a model with two arriving waves, the convergence and the BER performances of CMA are evaluated. It is shown that the BER is improved greatly up to the limit that no more error can be reduced, compared to the case without an adaptive array. It is seen also that the error rate is improved better when the delay difference between the two arriving waves is large. Thus, the proposed method is shown to be an effective technique to cope with selective

ISSN:8756-6621    

DOI:10.1002/ecja.4410740905

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

年代:1991

数据来源: WILEY

摘要:

AbstractPerformance of a DSP demodulator for FM broadcasting receiver is examined by computer simulation and system parameters suitable for obtaining demodulated signal quality (SNR) are clarified. The DSP demodulator is preceded by anm‐digit linear A‐D converter operating at the IF stage of the receiver. A relation between required values ofn, the register length of the processor, andmis investigated under the condition that a demodulated signal SNR of 60 dB and 55 dB for monophonic and stereophonic signals, respectively, is ensured. Moreover, only a slight increment ofC/Ni (Cis input carrier power;Niis thermal noise power at the receiver input) is necessary to recover degradation due to quantization noise and mathematical rounding‐off errors. Simulation results show that demodulation can be performed with a margin by using parametersn= 16 withm= 7 and 10 under the condition ofC/Ni= 23.5 dB and 40.5 dB for monophonic and stereophonic signals, respectively. However, an ideal analog receiver requiresC/Niof 23.2 and 40.0 dB to obtain the previously mentioned demodulated

ISSN:8756-6621    

DOI:10.1002/ecja.4410740906

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

年代:1991

数据来源: WILEY

摘要:

AbstractTo develop a radiation pattern synthesis technique for array antennas, the relationship between the ripple depth of the radiation pattern and the flatness of the array excitation amplitude distribution is clarified analytically. The roots of the representation equation of the radiation pattern are shifted radially from Schelkunoff's unit circle so that the ripple depth is changed. The ripple depth of the radiation pattern and the flatness of the excitation amplitude distribution are expressed by approximate equations in terms of the amount of the shift of the root. If the amount of the shift of the root is eliminated from these two equations, the relationship between the ripple depth and the flatness of the excitation amplitude distribution can be derived.Approximate equations indicate that the relationship between the two is almost independent of the sidelobe level and is determined mainly by the number of elements. As a numerical example, an asymmetrically shaped pattern is generated for a 20‐element array antenna with an element spacing of 0.5 wavelengths. The approximate equations and the rigorously calculated results are compared for error evaluation. It is confirmed that the approximate equations yield accurate evaluations if the ripple depth is more than 4 dB. Flatter excitation amplitude distributions reduce the influence of fabrication error and the mutual coupling of the elements and thereby improve the accuracy of the excitation coefficients. Useful design data also are obtaine

ISSN:8756-6621    

DOI:10.1002/ecja.4410740907

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe space diversity technique is used widely to improve propagation impairment on line‐of‐sight microwave links. Although prediction methods for the space diversity improvement in received power were proposed by Makino and Morita, Vigants, Boithias and Battesti, and Boithias, Battesti, and Rooryck, the predicted results were quite different among all these methods.To investigate this point, a data bank was constructed. This data bank consists of 27 data from Japan, the United States, Italy, France, FRG, Sweden, and Finland. Some theoretical investigations also were conducted.Based on the investigations, it was clarified that the cause of the difference in predicted results was a regional dependence of the long‐term variation in the short‐term average of the received power. This regional dependence is included effectively in the Rayleigh fading occurrence factor. A unified prediction method, which was derived by a multiple linear regression and included the Rayleigh fading occurrence factor as a new parameter, was proposed. Based on the testing by the data bank, the proposed method was proved to be more accurate than the existing

ISSN:8756-6621    

DOI:10.1002/ecja.4410740908

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn time‐harmonic electromagnetic fields, the Poynting vector, the cross product of electric field with the complex conjugate of the magnetic field, is well known as an energy flux density vector. Here, a new type of vector is proposed in which the cross products of electric and magnetic fields with their corresponding complex conjugates are taken, and its relationship with the Poynting vector is established as a pair of Max‐wellian‐type equations. Moreover, the usefulness of this vector is demonstrated by the examples of optical theorem, reciprocity theorem and decomposition of radiated power into circularly polarized fields, where it supplements the Poynting vector. This vector, like the Poynting vector, can also be considered as the energy flux density vector of the electromagnetic

ISSN:8756-6621    

DOI:10.1002/ecja.4410740909

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe airborne antenna may be considered to be small since it is mounted on a conductor which is large compared to the wavelength and its radiation pattern has to include the diffracted fields from the conductor. Moreover, thick dielectric coating on the body, which is used as insulating material, causes a serious distortion of the radiation pattern; and this is confirmed through measurements that the effect is quite large.This paper proposes a method of analysis where the effect of dielectric material on the radiation pattern is estimated analytically using a simple plane conductor model. Analysis is based on the excitation of the surface wave which propagates inside the dielectric sheet and making assumptions about the radiation mechanism, its diffracted field is calculated by the uniform theory of diffraction (UTD) method. The availability of this method of analysis was confirmed by comparing the measured results of this model with the calculated values. From the measured and analytical results, it was confirmed that a large effect is produced in the axially back direction of the rocket due to dielectric coating on the body.

ISSN:8756-6621    

DOI:10.1002/ecja.4410740910

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

年代:1991

数据来源: WILEY