bluuebunny/crossref_metadata_2025_split huggingface dataset:
Propagation characteristics of tweek atmospherics below anisotropic and inhomogeneous ionosphere models
Authors: Baba Kiyohide , Ohta Kenji , Hayakawa Masashi 
Published: July 2007

AbstractTweek atmospherics have been used to estimate the physical quantities of the ionosphere and to understand the propagation mechanism of the waveguide modes due to the propagation characteristics. As the ionosphere, several realistic models which are anisotropic and inhomogeneous are used.From the theory of the waveguide mode of ionosphere and the ground surface, the propagation characteristics of the tweek atmospheric are evaluated theoretically. The results of the cutoff frequency and the polarization characteristics are compared with the measured data. The cutoff frequency of the first mode of the tweek atmospherics has been found to be very close to the measured value by means of the computation of the phase velocity and the attenuation constant on the actual waveguide in which the electron density profile by Reagan was used.The polarization of the 0th mode is extremely close to the linear polarization regardless of the electron density profile and agrees well with the measurement. The measured result of the polarization of the first mode is almost completely left‐handed circular at the cutoff frequency. This experimental evidence can be explained by the electron density profile by Reagan. However, it is found that the frequency dependence of the polarization at frequencies higher than the cutoff is substantially different from the measured data. Significant dependence of the polarization characteristics on the electron density profile and the earth's magnetic field suggests that the model of the ionosphere and the propagation characteristics of the waveguide mode can be estimated from the detailed measurement of the polarization.
Use of a human‐body simulator for analysis of MRI antennas
Authors: Ochi Hisaaki , Yamamoto Etsuji , Sawaya Kunio , Adachi Saburo 
Published: July 2007

AbstractOptimization of an antenna for magnetic resonance imaging (MRI) requires an accurate analysis of antennas loaded by a human body. We have developed a computer code for obtaining the current distribution on the antenna loaded by a human model with an arbitrary geometry and material properties by incorporating the impedance method into the Richmond method. Numerical results for the input impedance are compared with measured impedances confirning the validity of the proposed method. Furthermore, sensitivity. distributions of antennas loaded by a human model are calculated.
Evaluating the performance of a message transmission system on meteor burst channel
Authors: Fukuda Akira , Yamashima Hiroyuki , Mukumoto Kaiji 
Published: July 2007

AbstractThis paper evaluates the performance of the two‐way message transmission system on the meteor burst channel developed and tested by the authors. First, the usual channel model is simplified and then the system is analyzed. It is shown through simulations that the errors introduced by the new channel model and by the approximated analysis method are negligible and the proposed method can be used to design and evaluate the system.The performance of the system having packets with subblocks is compared to that of one with usual packets. It is shown that, by using packets with subblocks, robustness of the system performance against changes of channel parameters as well as a shorter time needed to transmit a message can be obtained. The method of performance evaluation shown in this paper has adequate generality and is also applicable to many other meteor burst communication (MBC) systems.
Prediction of the number of coherent signals for mobile communication systems using autoregressive modeling
Authors: Minamisono Kenichi , Shiokawa Takayasu 
Published: July 2007

AbstractOne effective technique for reducing multipath fading in mobile communications is introduction of directional diversity with the help of adaptive arrays. This technique requires direction of arrival (DOA) estimation of coherent signals and relative time delay estimation. Eigenvector analysis or maximum likelihood localization is an efficient technique to estimate DOA. However, for coherent signals, spatial smoothing preprocessing is required and information about the number of signals is needed.This paper proposes to use spatial autoregressive modeling and final prediction error (FPE) to estimate the number of coherent signals. Since FPE drastically decreases with p when the length of prediction filter p is less than the number of coherent signals k and FPE converges to a constant value determined by C/N when p is greater than k, the number of coherent signals can be estimated. Moreover, by appropriately defining the FPE threshold, the number of dominant coherent signals can be estimated under the C/N concept. Numerical experiment indicates that this technique can estimate the number of signals and DOA with sufficient accuracy. Further, by appropriately defining the FPE threshold, the number of dominant coherent signals can be estimated.
Testing method for in‐service line of optical subscriber loops with optical time domain reflectometer
Authors: Takasugi Hidetoshi , Suzuki Hideki , Tomita Nobuo , Chida Ryouichi , Oguchi Taisuke 
Published: July 2007

AbstractWith the development of communications service for high performance and for wider bandpass widths, a single‐mode optical fiber has been started to be utilized in subscriber loops in addition to connection loops. An optical fiber cable has an advantage of huge transmission capacity, as compared to a conventional metal cable and, therefore, any breakdown in a cable may cause significant impact on the society. In this sense, a test capability of optical cables without causing any service interruption is needed.In this paper, a system using the optical time domain reflectometer (OTDR) which can perform such testing is discussed. The optical filter characteristics such as cutoff loss, transmission loss, and bandpass width are discussed. A prototype of the system consisting of optical filter parts has been made in the present study. The influence of the OTDR test light on transmission signal and that of the transmission signal on the OTDR waveform are examined. No degradation of the transmission quality was found. Furthermore, no disturbance in the OTDR waveform was observed. Therefore, it is concluded that a test without disturbing the transmission output signal can be performed by using the present method.
A small 42‐ghz transmitter and receiver for a wireless HDTV (hi‐vision) camera
Authors: Mizuno Haruhiko , Mitsumoto Hideo , Nakakita Hisao , Yazawa Norihiko 
Published: July 2007

AbstractA transmission system suitable for a small Hi‐Vision wireless camera is proposed and a small transmitter and receiver for the 42‐GHz band is developed. In the present system, no signal processing is performed on the camera output which is directly frequency modulated. Orthogonal circular polarizations are co‐used for transmission.By means of this system, miniaturization and weight reduction of the equipment (with a transmitter of 5 kg) are attained. At the same time, the transmission bandwidth is reduced to 80 MHz. Also, as the key 42‐GHz devices for realization of the present equipment, a direct FM modulator (modulation sensitivity of 20 MHz/ V), an HEMT power amplifier, an orthogonal circular polarization feed system (with a cross‐polarization discrimination ratio of more than 23 dB), a low‐noise down‐converter (with a noise figure of less than 5 dB) and a simple IF cross‐polarization interference equalizer are developed.The antenna for the transmitter automatically adjusts its direction by means of the signal returned from the receiver at 10 GHz. The present equipment has a transmission distance of about 250 m with a transmitter output of 25 mW and the signal‐to‐noise (SN) ratio is 48 dB (Y signal). Also, the equipment can be unified with the Hi‐Vision two‐thirds inch small CCD camera developed in our laboratory and can be operated for close to one hour with one battery.
Multipath allocation algorithm for the distributed computer environment
Authors: Minato Kenji , Okumura Yasuyuki , Kishimoto Ryozo 
Published: July 2007

AbstractThis paper discusses the multipath allocation problem in the communication network and proposes a multipath allocation algorithm suited to the distributed environment. The multipath allocation problem is a problem where multiple paths are to be allocated without a conflict. This problem has been difficult to solve in the distributed environment since relations among various routes must be considered. The algorithm proposed in this paper solves this point by realizing the asynchronous path search.In this paper, the basic characteristics of the proposed algorithm are described through the comparison between the proposed and the traditional algorithms for the case of serial computation under the centralized control. Then the proposed algorithm is applied to several kinds of distributed cooperative multiagent models, and it is demonstrated that the proposed model can easily be applied to the distributed environment. A simulation is executed actually using several workstations, and it is shown that the proposed algorithm is desirable as a solution method for the multipath allocation problem in the distributed environment.
Satellite communication applications to B‐ISDN
Authors: Kawai Makoto , Nakaya Kenji , Hojo Hiroshi , Okada Kazuyasu 
Published: July 2007

AbstractThe terrestrial communication network is making progress from the analog public network based mostly on telephone traffic to the N‐ISDN. The development to BISDN also is considered, aiming at an integrated network which can provide large‐scale file transfer, high‐speed data communication such as the communication between high‐speed LAN, and dynamic image communication such as TV and HDTV. This paper proposes the application of the multibeamSatellite communication to such B‐ISDN, and presents such technical subjects as the satellite communication. First, the purpose of application of the satellite communication to B‐ISDN is described. The requirement in the application to B‐ISDN is presented. Then, aiming at the fulfillment of the requirement, the technical subjects and evolution are shown for the configuration of the communication system, the channel control system, the synchronization control system, OAM system, and the interface to the terrestrial network.
Radiation from the multibranching point of a transmission line
Authors: Nakamura Takashi , Ozawa Akiyoshi , Yokokawa Senji 
Published: July 2007

AbstractIn this paper, branching configuration in a parallel two‐wire transmission line is considered as the cause of the unwanted electromagnetic wave generation and the analysis and experiment are carried out on the radiation characteristics of the discontinuity. Understanding by a simple radiation mechanism is intended. The discontinuity of the traveling‐wave current on the conductor of the transmission line is considered as the radiation source.By means of the principle of pattern multiplication, the expression of the radiation field from the junction of the transmission line is derived. It is shown that the reflection and transmission coefficient of the traveling wave at the branching point are important factors to determine the radiation pattern. Two types of branching line configurations are treated. One of them is a reflectionless configuration while the other is made of identical transmission lines. The radiation characteristics due to the difference of characteristic impedance are derived. It is shown that there are electric field components radiating strongly in the traveling direction of the current of the branching line and the one radiating strongly into the intermediate direction. By means of the experiment for a T branching line, the validity of the theoretical results is confirmed.
Cornish's expansion analysis of characteristics of a communication system with an optical amplifier
Authors: Mieda Hiroyuki , Yoshino Takayuki , Hirano Nobuo 
Published: July 2007

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 elsewhere.
Consideration of effects of handover during data communications and error reduction
Authors: Uchiyama Hiroki , Miyachi Tatsuo , Kasuga Masao 
Published: July 2007

AbstractEfficient handover during both mobile telephone and portable telephone communication is a technology essential in implementing ideal mobile communications. However, there exists the possibility of a transmission data slip during the process of circuit switching, which has become a problem in communication using terminal machines such as data modems and FAX machines connected to mobile telephones and portable telephones.In this paper, a transmission data slip accompanying route changes inside digital exchanges in a handover during telephone communications is assumed; it is shown on the basis of this assumption that a lag in synchronism occurs in the receiver terminal equipment.Then a sync lag of the receiver terminal modem during handover has been confirmed by tests using actual analog cellular phones and a transmission data slip has been shown on the basis of the results of the tests. In this paper, a synchronism control method minimising the sync lag has been studied. The efficacy of this method has been confirmed as a result of applying the method to a mobile telephone FAX modem.
The barrel switch: An ATM switch architecture for high‐speed switching
Authors: Shobatake Yasuro 
Published: July 2007

AbstractThis paper proposes a new asynchronous transfer mode (ATM) switch architecture called a “barrel switch.” The barrel switch is constructed from n/2 × n identical element switches which are placed out around a cylinder and connected to each other.The features of this proposed switch are as follows.1. This switch has an architecture suitable for high‐speed (2.4 Gbps and more) cell switching.2. It is a multistage self‐routing and nonblocking switch.3. Copy connections can be realized with this switch.4. The building‐block method is applicable to switch implementation, which ensures a full scalability.Cell loss rate and delay characteristics of this switch also are discussed using computer simulation results. Simulation results under random traffic prove that a 64 × 64 barrel switch has adequate cell loss rate and mean delay characteristics to an actual ATM switching system.
Communication and radio determination system using two geostationary satellites
Authors: Morikawa Eihisa , Kimura Kazuhiro , Wakana Hiromitsu , Miura Ryu , Ohmori Shingo , Matsumoto Yasushi , Wakao Masayoshi 
Published: July 2007

AbstractWith the recent development of satellite communication and the diversified demands for communication, there has been increasing demand to utilize the position of the mobile object as the information. This idea is proposed and has been developed in various countries of the world as the radio determination satellite system (RDSS).This paper outlines the hybrid communication/ positioning system using two geostationary satellites. The system has been developed by the Communication Research Laboratory in collaboration with the R & D Center for Radio System, together with the result of basic experiments.Two kinds of experimental systems with different modulation/demodulation methods are constructed. One is the method based on the offset QPSK (called SCPC), and the other is based on the spread‐spectrum (called SS). The former transmits the narrowband signal for distance measurement, in addition to the communication signal. Consequently, this method can easily be introduced into the SCPC satellite communication system presently used in practice, although the accuracy of the positioning is slightly deteriorated. Compared to the former, the latter has the advantage that a highly accurate positioning can be realized since a high‐speed positioning signal is employed using a wide transmission bandwidth. However, the system configuration becomes complex. A field experiment is conducted for each system using the Engineering Test Satellite V (ETS‐V) and the Inmarsat satellite. The positioning accuracy of 2 to 8 km for low altitude and 1 to 2 km for middle altitude is obtained in SCPC. The position accuracy of 400 to 600 m is obtained near Japan by SS.
SAW filter matrix for SS/FDMA system
Authors: Shinonaga Hideyuki , Ito Yasuhiko 
Published: July 2007

AbstractThe configuration and function of a surface acoustic wave (SAW) filter matrix used on board a satellite to implement a subchannel switched FDMA (SS/FDMA) system is described. The function and configuration of the SAW filter matrix (SFM) are described. Conditions imposed on the amplitude and phase of two adjacent subchannels to provide a broad channel by combining the outputs of the subchannels are investigated. Electrical and transmission characteristics of an SAW filter matrix used in four‐beam SS/FDMA system with a subchannel‐combining function are presented, demonstrating its technical feasibility.When implementing an SFM, it is important that the devices used for a satellite‐based SS/FDMA router are sufficiently reliable for the design life of the satellite. A methodology is shown that gives a redundant configuration with the lightest mass and that achieves the targeted reliability. Example calculations for a four‐beam SS/FDMA router are given.
Time‐domain analysis of yagi‐uda antennas using the FD‐TD method
Authors: Kashiwa Tatsuya , Tanaka Shuichi , Fukai Ichiro 
Published: July 2007

AbstractThe fundamental importance of the Yagi‐Uda antenna is its structural simplicity and its director and reflector actions. To fully comprehend the working principle of this antenna, it is important to be able to visualize the radiation mechanism directly in the time domain. In this paper, transient analysis of the Yagi‐Uda antenna is performed using the FD‐TD method. First, the input impedances and directivities obtained by this method are compared with the moment method, good agreement was found between the two methods, and the validity of this method was demonstrated. Next, the quasi‐impulse responses of the antenna are calculated. The field pattern obtained by this method was visualized in the time domain. The radiation from the antenna edge is shown in the early time responses, and dispersion of the pulse shape with the passage of time is shown in late time responses. Moreover, the difference of characteristics due to the length of parasitic elements is shown by time‐domain observation.
Generalized product codes and their performance
Authors: Hatamori Toshifumi , Kasahara Masao 
Published: July 2007

AbstractProduct codes show improved correcting capability by a comparatively simple method of combining codes and are also effective in correcting bursty errors. In this study, product codes using several kinds of single‐error correcting and double‐error detecting (SEC‐DED) codes, different by rows, are proposed. A method of probabilistically correcting bursty errors by using SEC‐DED codes different by rows and utilizing the differences in these error‐correcting characteristics is proposed. In addition, a decoding method that can correct random errors of the type that could not be corrected by the conventional product codes for this code is proposed.
Frequency‐offset compensation for MPSK differential detection by using double differential encoding
Authors: Ishikawa Hiroyasu , Kobayashi Hideo 
Published: July 2007

AbstractAlthough differential detection methods having superior fading resistance and, in general are effective in digital land mobile communications systems, phase shifts due to frequency offsets become a major factor that deteriorates the error rate in these differential detection methods. Although various frequency‐offset compensating methods have been studied and developed, the maximum amount of frequency offset that can be compensated is limited due to the ambiguity of the phase, which has become a problem in estimating the phase shift due to a frequency offset.In this paper, a method for compensating frequency offset by double differential encoding of transmission data sequences, which allows a resolution of the forementioned problem even when a large frequency offset occurs, is proposed and the error rate performance in the application of a /4‐shift QPSK scheme is evaluated by computer simulation. As a result, it is shown that the proposed method has superior compensating performance on land mobile communications channels.
An application of chirp to spread‐ALOHA system
Authors: Enomoto Masaru , Takahata Fumio 
Published: July 2007

AbstractThis paper proposes a spread‐ALOHA system using chirp. the system is composed of the modulator containing the chirp filter and the demodulator containing the chirp matched filter, the quasi‐coherent detector and the block demodulator. In the proposed system, the data transmission is realized by using the chirp signal with phase information corresponding to binary data and then, using the chirp effect, the frequency component of the transmitted signal is spread continuously. In addition, since the respective bits composing a packet are compressed in time by the correlation processing using the chirp matched filter, the multiplexed packets are separated in individual packets based on the timing difference among the received packets.The carrier synchronization, which is required in the demodulation process, is achieved by quasi‐coherent detection and the block demodulation. the frequency and the phase offset occurring in the quasi‐coherent detection are corrected by a method of highly accurate frequency detection based on the fast‐Fourier transform in the block demodulator. Furthermore, assuming various conditions, quantitative evaluations are made on the bit‐error rate performance by means of computer simulation. It is verified that a high interference immunity is realized by the frequency spread using chirp, and frequency offset generated in the quasi‐coherent detection is well estimated and corrected.
Design algorithm for packet‐switching networks with different classes of packets‐capacity, priority, and flow assignment under endto‐end packet delay constraint
Authors: Sugano Masashi , Takashina Hiromitsu , Yokohira Tokumi , Okamoto Takuji 
Published: July 2007

AbstractThis paper proposes a design algorithm for packet‐switching networks with different classes of packets under end‐to‐end packet delay constraint and a design algorithm for fault‐tolerant networks. the former is a heuristic capacity, priority, and flow assignment algorithm which locally minimizes the network cost while satisfying a constraint that the average transmission delay of each class of packets between two arbitrary nodes never exceed a value predetermined for the class.This algorithm is composed of three subalgorithms and the cost minimization is pursued by iterating these algorithms as long as the constraint is satisfied. the latter is a design algorithm for a fault‐tolerant network which satisfies the foregoing constraint even if an arbitrary single link fails. With this algorithm, an assignment with relatively large cost but satisfying the constraint is obtained first. Then a procedure of reducing the capacity of a link whose effect on cost reduction is great but whose effect on path delay increase is not so great is iterated to reduce the network cost as long as the constraint is satisfied.