摘要:

AbstractIn the pulse compression radar, it is necessary to suppress the time sidelobes which can cause a false alarm so that reliability of target detection is improved. For the pulse compression system to be adaptable for radar management which is considered to be important in recent years, it is indispensable that the radar waveforms be controlled flexibly by means of pulse compression. A method to this end can be provided by the pulse compression system using several random binary sequences with maximum entropy. However, since a coded sequence generated with a probabilistic manner is used in this method, both the time sidelobes and the mismatch loss tend to increase. Therefore, it is necessary to reduce both of them. From the forementioned viewpoint, in the case that the number of stages of the pulse compression filter is set equal to the code length, a method for deriving the filter coefficients realizing the minimum value of the peak time sidelobe level is analyzed as an optimization problem in the nonlinear programming. The pulse compression characteristics obtained by this method are described.

ISSN:8756-6621    

DOI:10.1002/ecja.4410720101

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

年代:1989

数据来源: WILEY

摘要:

AbstractRecently, many conducting plastic shielding materials have been retailed in connection with environmental electromagnetic problems. This paper proposes a method of measuring the shielding effectiveness using a spherical cell as a means of evaluating shielding effectiveness. The shielding effectiveness against electric and magnetic fields can be evaluated by the proposed method. The measured values provide quantitative information for practical shielding because the cell forms a practical shield housing of circuits or parts. It is easy to handle theoretically since we use a spherical shape. Favorable agreement is obtained between the results of theoretical analysis and values of experimental measurements. Gradual decreases of the shielding effectiveness occurred in the high‐frequency region against the electric fields and in the low‐frequency region against the magnetic fields for a material with low electrical conductivity. Sudden large decreases of the shielding effectiveness against the electric and the magnetic fields due to resonant effects were observed when the diameter of the sphere becomes close to the wavelength based on numerical calculations. It was found that in designing shielding housings, careful attention must be given to their dimensi

ISSN:8756-6621    

DOI:10.1002/ecja.4410720102

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe network interconnection technique is one of the keys for expansion of a local area network. This paper gives a performance evaluation of the multiring local area network system which consists of several token ring networks interconnected by using this technique. The result shows that this network system is better than the single‐ring network system, which is an ordinary token ring network, at heavy load operation. This paper also gives a performance comparison among three network interconnection topologies, “MESH connection,” “RING connection,” and “BUS connection,” and the optimum regions for these network interconnection topologies

ISSN:8756-6621    

DOI:10.1002/ecja.4410720103

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

年代:1989

数据来源: WILEY

摘要:

AbstractOne of the features of satellite communications is broadcasting ability (multiple address communication). Since a satellite has lengthy transmission delay, transmission errors at each link accumulate and the number of retransmissions increases, resulting in decrease in throughput efficiency if a one‐to‐one transmission control procedure (such as HDLC) is applied to a multiple address communication. This research proposes a multiple address communication system via a satellite link. In this system, information sequence is divided intoNblocks based on the Chinese Remainder Theorem and theNblocks are sent with the SREJ (selective reject) procedure. At a receiving station the original information sequence can be restored with at leastK(N)received frames. Therefore, the number of frames re‐sent from a transmitting station decreases and a decrease in throughput efficiency is prevented. The transmission characteristics of the proposed system are examined under the assumption that an ideal SREJ procedure is used. As a result, it is revealed that the proposed multiple address communication system can achieve higher throughput efficiency than the iterations of individual one‐to‐one comm

ISSN:8756-6621    

DOI:10.1002/ecja.4410720104

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

年代:1989

数据来源: WILEY

摘要:

AbstractMultipacket transmission can achieve higher transmission efficiency because many packets are inserted into a frame and per‐packet overhead is small. However, in practice, too many packets cannot be inserted into a frame and too long a frame has higher probability of error. Therefore, the number of packets in a frame must be restricted. This paper analyzes the continuous‐service‐type multipacket transmission with restriction on the number of packets in a frame. Also, the distribution for the number of transmission waiting packets is derived along with the number of packets in buffer,z‐transform of the distribution for the number of packets in a frame, transmission efficiency, average queue length, and average packet delay time. From numerical examples, we examine the influence of the restriction on these performance m

ISSN:8756-6621    

DOI:10.1002/ecja.4410720105

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

年代:1989

数据来源: WILEY

摘要:

AbstractWhen different kinds of local area networks are interconnected, a gateway holds the key to better performance of the interconnected network. Since gateways are lia‐able to overflow easily because of their comparatively long processing time, it is necessary to estimate their appropriate buffer size with regard to the input traffic. This paper considers a local area network working under CSMA/CD protocol. First, we analyze the output process of messages which constitutes a part of arrival process at a gateway, by solving an embedded Markov chain. Second, two stochastic models of the gateway are formulated by queueing theory and loss probability of messages is evaluated in regard to its buffer size. Numerical results show some interesting features of the output and arrival processe

ISSN:8756-6621    

DOI:10.1002/ecja.4410720106

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

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper investigates the effects of noise‐induced transmission errors on the performance of compression coding methods for still pictures. The following four coding methods are considered: (1) adaptive cosine transform coding; (2) DPCM coding; (3) adaptive block coding; and (4) vector quantization coding. First, the relations among the bit error rate, signal‐to‐noise ratio (SNR), and code lengths by these coding methods are compared in the case of transmission without error control. Adaptive cosine transform coding and adaptive block coding require control information for adaptivity; therefore, they are investigated with and without transmission errors in the coding control information. Further, transmission with error control is studied for sending control information. Considering the error control methods, both automatic repeat request and forward error correction are considered. In these cases SNR deterioration by transmission noise beyond error correction capability and the amount of additional data required for error detection/correction or retransmission are examined. BCH codes are used for error detection and corre

ISSN:8756-6621    

DOI:10.1002/ecja.4410720107

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn the digital radio system using dual polarizations, an interference canceller is needed that cancels excessive interference. In this paper, a fully digital cross‐polarization interference canceller is proposed in which digital signal processing (DSP) technology and LSI technology are applied. By means of DSP technology, the cancellation characteristics are determined mainly by the quantization accuracy and the number of taps. The only degradation factor is the rounding‐off error of the operations. High accuracy and large cancellation effects are expected. Also, an application of an advanced control algorithm is possible. Flexible applications are possible for any symbol rate. In this paper, the estimation method for the fully digital cross‐polarization interference canceller is presented. Based on this method, the relationships among the cancellation characteristics, the input signal quantization accuracy, tap coefficient quantization accuracy, and number of taps are analyzed theoretically for the case where the method is applied to the 256 QAM system. Next, the configuration of the canceller is presented. From the results of the experiments using the symbol rate of 12.5 MBaud and 256 QAM signals, good agreement with the theoretical prediction is obtained and, hence, the validity of the present estimation method is demonstrated. It is demonstrated that a high‐performance cross‐polarization interference canceller is realized which can be applied to a multilevel modulation system for a high‐speed region, such as

ISSN:8756-6621    

DOI:10.1002/ecja.4410720108

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

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper considers the polling system with the single message buffer at the station. Most of the past studies on the polling system have been concerned primarily with the mean delay and the mean throughput. To analyze the multihop system which appears in the interconnection of information networks, however, the interdeparture process in the system must be analyzed. This is because the output process in each system is related closely to the input process in other systems. From such a viewpoint, this paper analyzes the interdeparture process in the polling system with the single message buffer at the station, and presents the Laplace‐Stieltjes transform of the interdeparture time distribution. Using the obtained result, numerical examples are presented, indicating some interesting results concerning the coefficient of variation of the interdeparture time distributio

ISSN:8756-6621    

DOI:10.1002/ecja.4410720109

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe packet‐switched network design problem can be formulated as a capacity and flow assignment problem (CFAP). The CFAP of an elementary network consisting of one tandem switch (TS) andnlocal switches (LSs) has been analyzed, and economical configurations shown in previous papers. This paper extends the study to include cases in which there are constraints on circuit discreteness. A large‐scale network usually employs a hierarchical structure with elementary networks used as structural units. In addition, the most economical structure of an elementary network in a hierarchical network is ascertained.The first assumption is that circuit speed is restricted to a predetermined discrete number (multiple of unit speed), and either one or no circuit can be installed per link. When the elementary network represents the entire small‐scaled network, economical regions of star, mesh and combined star/mesh are complicated. This is because effective traffic packing to a discrete capacity circuit sometimes yields more economical network configurations. When the elementary network is a structural unit in a large‐scale network, star occupies most of the economical region because a tandem circuit is always installed for carrying external traffic. The second assumption is that circuit speed is fixed. If a number of circuits can take real numbers, combined star/mesh is always the minimum cost topology in which internal traffic is assigned to the direct circuit, and external traffic through a tandem switch is assigned to the tandem circuit. When the number of circuits is a natural number, it is more economical in some cases to assign some part of the traffic to a tandem circuit because of the integrity of the number of c

ISSN:8756-6621    

DOI:10.1002/ecja.4410720110

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

年代:1989

数据来源: WILEY