摘要:

AbstractThis paper considers a slotted ALOHA network which consists of a central base station and many mobile terminals. In classical performance analyses of random access networks, a channel between the station and a terminal is assumed to be always in a good state. However, this is not the case in mobile radio networks since the channel suffers from many factors such as fading, shadowing, and so on. Moreover, the channel condition changes with the terminal location.In this paper, a simple channel model is used to consider the effects of time‐varying channels in a random access network. The channel model assumed in this paper has three states: shadowing, good, and bad. The transitions between the channel states are described by a Markov chain. The dynamic performance of a slotted ALOHA network over such time‐varying channels is evaluated by means of the equilibrium point analysis. Then the influence of the time‐varying channel on the throughput performance of a slotted ALOHA network is st

ISSN:8756-6621    

DOI:10.1002/ecja.4410761101

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper evaluates a leaky‐bucket‐type control method as a means of policing control of input traffic in ATM networks. In an ATM network, a user reports parameters specifying traffic characteristics to each traffic source at the time of making a request for a call connection and the network determines whether or not to accept the call on the basis of these parameters. In addition, after the call reception, input traffic after a call connection must be controlled such that the cell arrivals from the traffic source conform with the reported parameters. In this paper, as a method of controlling input traffic, the mean arrival rate and burstiness of input traffic are evaluated quantitatively using the leaky‐bucket method and problems associated with introduction of such an input control system to an ATM network are disc

ISSN:8756-6621    

DOI:10.1002/ecja.4410761102

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe in‐house information communication network using local area network (LAN) is required to cope flexibly with the expansion/modification of the system and to avoid the system‐down in the generation of a fault by detaching the fault domain.This paper considers the star‐ring LAN with the ring spurs and a dual ring. It proposes also the structure and control of the wiring concentrator of ring LAN with the dedicated automatic reconfiguration control by the ring spur bypass and the ring wrapback. Since the ring contains both the ordinary terminals and WC, the reconfiguration‐dedicated medium access control (MAC) frame is introduced anew and can be sent only by wiring concentration (WC), making unnecessary the specification modification of the MAC layer of the terminal.The WC which handles the localization and detachment of the fault point is determined by this mechanism. The test ring is automatically expanded from the local ring in WC to the ring containing the ring spur and the ring containing the dual ring successively by testing the conductivity.Using WC, a ring LAN system with the automatic ring degeneration/expansion function can be realized, while providing the terminal with the function of connection/detachment/shift on LAN (hot‐pluggability). The time required for reconfiguration by the proposed reconfiguration control is evaluated by summing up the times for the major control steps and by experimental ex

ISSN:8756-6621    

DOI:10.1002/ecja.4410761103

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

年代:1993

数据来源: WILEY

摘要:

AbstractA two‐wire voice‐band automatic gain control (AGC) with echo cancellers is studied and applied to an automatic call‐transfer repeater. A four‐wire circuit model of the amplifier and its stability are discussed. Fast tracking and/or stabilizing AGC using variable‐rate control is proposed. Also, a singing protection control method in which the dominant path is selected depending on voice signal powers of the two speech paths is proposed and investigated. The amplifier gain of the inferior path is computed using the measured echo return loss (ERL) values of the echo cancellers. Furthermore, an automatic call‐transfer repeater prototype that is based on the new AGC amplifier and its characteristics is introduced.The maximum amplifier gain of the proposed methods is about 10 dB higher than that of a conventional two‐wire amplifier with a voice switch. The configuration and algorithms proposed in the paper are proven to be effective for two‐

ISSN:8756-6621    

DOI:10.1002/ecja.4410761104

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe TDMA scheme, a typical multiple‐access scheme, can provide secure transmission; but its efficiency is poor under low traffic conditions. By contrast, the random access scheme, represented by the ALOHA scheme, has a small‐delay characteristic under low traffic conditions but a stability problem under heavy traffic conditions.This paper presents a new multiple‐access scheme in which each station is assigned a slot in every frame and stations are assigned to a slot at different power levels to obtain the capture effect. Therefore, the proposed scheme can adapt itself under various traffic conditions with channel status monitoring based control. Different models of capture effect are proposed, and the performance of the models is analyzed both by theory and by computer simul

ISSN:8756-6621    

DOI:10.1002/ecja.4410761105

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn general, an optimum quantizer which gives the minimum distortion at a given bit‐rate is uniquely determined when the statistical characteristics of the source signal are given. This quantizer, however, is not optimum for the human visual characteristics; and a quantizer which is designed to minimize the estimated distortion (estimated noise) reflecting the human visual characteristics is more likely to be optimum. In the optimum quantization of orthogonal transform schemes, theoretical quantizer design schemes considering only the human visual characteristics of the spatial frequency direction have so far been reported. However, there is another human visual characteristic, that is, the noise‐masking effect which is the difference in the detectability of noise, depending on the local variation of a video signal (activity). For this, only the quantizers which use this effect experimentally have been reported; and they have not been studied theoretically.In this paper, it is proposed, as the first step, that the visual sensitivity to noise be expressed on two axes, i.e., spatial frequency and “activity.” A three‐dimensional (3‐D) structure quantization cube is then proposed which is obtained by minimizing the noise estimated by the visual sensitivity of the noise at the given bit‐rate and the theoretical design scheme of this optimum quantization cube is described. Finally, the effectiveness of the quantization cube designed by this theoretical scheme is compared with that of the conventional quantization schemes by a computer simulation using real

ISSN:8756-6621    

DOI:10.1002/ecja.4410761106

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

年代:1993

数据来源: WILEY

摘要:

AbstractNonregenerative repeating systems on digital microwave radio have the advantage of network flexibility and low‐cost transmission. This paper describes a means of compensating self‐interference passing adjacent channels (S‐IPAC), which degrades the transmission performance. This interference is specific to nonregenerative repeating systems. A transversal equalizer with multitaps is discussed as a countermeasure against S‐IPAC. Bit error rates (BER) and signatures are presented theoretically and experimentally as a parameter of hop

ISSN:8756-6621    

DOI:10.1002/ecja.4410761107

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper considers the diversity reception system where the combining coefficients are controlled by the least‐squares method. The CNR characteristics in the presence of the interference wave are derived, and the signal transmission characteristics are analyzed.First, the optimal coefficients are determined by the MMSE criterion. The expression for the optimal CNR is derived in two ways, i.e., from the macroscopic and the microscopic viewpoints. It is shown that the two results agree and the variables are related through the Pythagorean theorem. Then CNR is represented by the projection matrix which is specified by the correlation matrix for the noise and the interference wave. The signal combining/interference canceling characteristics are examined.Next, the eigenvector expansion for the correlation matrix is applied and the representation for CNR under fading condition is derived, using the statistical properties of the eigenvalue, the probability density function and the probability distribution function for CNR are derived in two ways. Then the expression for the average BER is derived for CBPSK and DBPSK. The extension of the idea to the nonlinear interference canceler and the application to the cellular mobile communication also are discusse

ISSN:8756-6621    

DOI:10.1002/ecja.4410761108

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes an adaptive array antenna using a signal processing system which is implemented by a systolic array processor (SAP), SAP‐AA. Computer simulations show the behavior of the SAP‐AA against multipath fading. The SAP realizes a parallel pipelined processing by regularly placing many SAP cells with identical functions and structures so that it achieves the high throughput rate in the data processing. Also, the SAP has many desirable features for very large‐scale integration (VLSI) system design and enables miniaturization, weight reduction, and mass production of the processing equipment.In this paper, first, the SAP‐AA is described which realizes the least squares (LS) algorithm based on the QR decomposition for the input data matrix using the Givens rotations. In addition, the fundamental performances of the SAP‐AA are studied including both the transient response and the steady‐state behavior in multipath signal environments. To date, there has been no report which treats the multipath signal suppression performance of the SAP‐AA. Finally, it is concluded from the discussion that the SAP‐AA is effective for unwanted signal suppression in a multipath sig

ISSN:8756-6621    

DOI:10.1002/ecja.4410761109

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn the SLC (sidelobe canceler) which automatically suppresses the interference signals received by the side‐lobe of the main antenna, there is a problem of suppression of the desired signal in addition to the interference signal if the desired signal power in the auxiliary antenna is larger than the receiver noise power and if the number of received interference signal is smaller than that of the auxiliary antennas.In this paper, an SLC is proposed in which the number of auxiliary antennas is adjusted automatically to be equal to that of the interference signals so that the problem of suppression of the desired signal is prevented. It is assumed here that both the desired signal and the interference signals have narrow band widths.In this SLC, with a view to adjusting the number of auxiliary antennas and the weights at the same time, the Gram‐Schmidt SLC (GS‐SLC) is used so that a sudden change of the input‐output signal power ratio of the Gram‐Schmidt processor is detected and the number of auxiliary antennas are made to coincide with that of the received interference signals. By way of a computer simulation, the fundamental characteristics of the present GS‐SLC are evaluated. It is confirmed that the desired signal preservation property is improved in comparison with the conve

ISSN:8756-6621    

DOI:10.1002/ecja.4410761110

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

年代:1993

数据来源: WILEY