bluuebunny/crossref_metadata_2025 huggingface dataset:
Notes on capability of demultiplexing coded packets on a collision channel
Authors: Inaba Hiroyuki , Kasahara Masao
Published: July 2007

Packet exchange methods have come to play a central role as exchange methods in various networks. Especially, the random access method has been attracting attention since networks can be constructed comparatively easily by this method without having to establish special control offices. However, a collision of packets is inevitable with the random access method, which becomes a major factor in decreasing network efficiency. In past access methods, collided packets, in general, are retransmitted.

In this paper, a method of considering a collision of packets as collision error, correcting this error, and demultiplexing (isolating) into original packets is proposed. In this method, demultiplexing (isolating) collided packets as well as detecting and correcting the transmission path error occurring simultaneously is possible. In addition, the method has a characteristic of superior compatibility with conventional systems. In addition, it has been clarified that the performance is improved greatly when the proposed method is applied to a random access network, by taking the ALOHA system as an example.
Design and performance of optical fiber identification system for optical fiber transfer splicing system
Authors: Shimizu Masatoshi , Kobayashi Hideo , Chijiwa Youichi , Takashima Seiji
Published: July 2007

Both the expansion of optical networks and their maintenance techniques are becoming increasingly important During optical fiber cable transfer work, while securing user's services, it is very important to develop optical cable transfer splicing systems for efficient cable transfer which raises the possibility of low‐cost maintenance.

In this paper, the realizable configuration of the optical fiber identification equipment used in the optical cable transfer splicing system is investigated. The structures of the two identification systems of local injection/local detection and end‐face injection/local detection is proposed and the required functions together with the design guidelines of these two systems are clarified. Further, the design method and characteristics of the local injection and local detection equipments together with evaluation method of the transfer connection losses are presented.

Finally, it is shown that the allowable distances of the local injection/local detection and end‐face injection/local detection systems are 11 km and 29 km, respectively.
Propagation characteristics of very low latitude whistlers by ray tracing
Authors: Ohta Kenji , Tomomatsu Tooru , Takahashi Osamu , Hayakawa Masashi
Published: July 2007

Simultaneous measurement made in South China in January 1988 has already indicated that the nighttime whistlers observed at very low latitudes (geomagnetic latitudes, 10° to 14°) are attributed to field‐aligned propagation. On the other hand, a few researchers have suggested, based on the ray‐tracing computations, that nighttime whistlers at very low latitudes are due to nonducted propagation.

To solve the discrepancy between the authors' experimental results and the previous ray‐tracing studies, extensive two‐dimensional ray‐tracing calculations have been made for the nonducted propagation of whistlers in the inner plasmasphere in a wide frequency range (1 to 10 kHz). The conditions for nonducted whistlers to penetrate through the ionosphere onto the ground have been discussed to clarify the difference from the experimental results reported here.
Multislotted ALOHA scheme for high‐efficiency transmission of variable‐length packets
Authors: Kawazoe Katsuhiko , Kazama Hiroshi , Kato Shuzou , Masamura Tatsurou
Published: July 2007

The paper proposes the multislotted ALOHA (MS‐ALOHA) as a new random access scheme which can improve the throughput in variable‐length packet signal transmission. This scheme is to improve the throughput in the variable‐length packet signal transmission by controlling the transmission timing according to the packet‐signal length.

The throughput performance of the proposed scheme for the variable‐length packet transmission is formulated for the infinite station model and the finite station model. The proposed scheme is compared to the traditional slotted ALOHA with the single transmission timing by computer simulation. It is shown that the throughput of the proposed scheme is larger independently of the signal length and the performance is stable against the variation of the signal‐length distribution.

When the signal length is distributed uniformly, the maximum throughput is improved by approximately 20 percent compared to the traditional scheme. The application of the retransmission slot‐control scheme to the proposed scheme is considered. Here, the transmission slot for the retransmission packet is assigned to each transmitting station. As a result of analysis by computer simulation, it is shown that a higher throughput is obtained than the ALOHA scheme with the selective rejection retransmission protocol.
Adaptive array antenna based on estimation of arrival angles using DFT on spatial domain
Authors: Yim Choonsik , Kohno Ryuji , Imai Hideki
Published: July 2007

Multipath fading is a factor degrading the communication quality in mobile communications. It has been reported that an adaptive array antenna can enable elimination of the effect of delayed signals by an appropriate control of the radiation pattern. In this paper, it is recognized that an optimum weight of the array antenna can be computed if the direction of arrival and the signal‐to‐noise ratio of the received signal are known. By using the spatial frequency derived by the discrete Fourier transform (DFT) of the received signal which is spatially sampled by the array antenna, an algorithm is proposed in which the directions of arrival and the signal‐to‐noise (SN) ratio of the desired and interference waves are estimated and an optimum weight coefficient of the antenna is computed. This algorithm is different from those in the conventional adaptive digital filter algorithms such as the LMS algorithm. It requires no reference signal and can follow quickly changes in the communication channel. Further, a method is proposed to improve the estimation accuracy of the direction of arrival and the SN ratio with a limited number of elements by using the property of the DFT. To confirm the principle of the proposed algorithm, the basic characteristics are evaluated by computer simulation.
Methods for constructing a management information base (mib) in transmission network operations
Authors: Yoda Ikuo , Fujii Nobuo
Published: July 2007

Methods of realizing a management information base (MIB) under a CMIS/CMIP environment using RDBMs for realizing a transmissions network operations system using the OSI management techniques are presented. A method of constructing an MIB by an attribute unit table with respect to the restrictions of CMIP without a specific object class in the operations process is proposed. Corresponding to management information that has become complicated with the times, this method proposes a mechanism of global searching independent of management object definitions by deriving a general procedure required for attribute operations within an agent system to make the CMIS processing codes as independent management object definitions and storing the forementioned procedure in an MIB. In addition, this construction method was evaluated by using an MIB constructed experimentally and the realizability of the proposed method of construction of MIBs and the performance of the experimental MIB evaluated by the experiment are presented. This MIB construction method is applicable to high‐level agent systems that are complicated and of large scale.
Analysis of switching converters with switched snubber
Authors: Noguchi Seiichi , Sakamoto Hiroshi , Harada Koosuke
Published: July 2007

It is considered that the key to miniaturization of switching power supplies is in high frequency. With respect to the high frequency of switching power supplies, the losses and surge during switching are frequent problems. In switched snubber circuits constructed from parallel connection of a switching element and condenser, it is reported that there is essentially no loss and the surge suppression effects are excellent.

In this paper, with respect to converters incorporating switched snubber circuits, general state equations taking into account low‐frequency characteristics are determined by the state averaging method. As a consequence, while taking into account parasitic inductances such as the leakage inductance of transformers and floating inductance of wiring, a unified analysis was made of buck type, boost type, and buck‐boost type. Moreover, the general state equations taking into account the parasitic elements of the smoothing condenser were determined by transformation into simple equivalent circuits. The suitability of the analysis was verified by using a flyback converter. The fact that the parasitic inductance in the circuit increases the output impedance is verified quantitatively.
Conditions for a rotationally symmetric aperture mapping in dual reflector antennas—a new category of reflector systems allowing double‐offset configuration
Authors: Nomoto Shinichi , Mizuguchi Yoshihiko
Published: July 2007

The aperture mapping in general dual reflector antennas including the shaped‐reflector type is studied based on the geometrical optics. The condition for a rotationally symmetric aperture mapping is derived. As a result, it is found that there exists a curved surface system which is completely different from the rotational quadratic surfaces for realizing a rotationally symmetric aperture mapping. This new surface system category has higher degrees of freedom in design than the conventional rotated quadratic surfaces (Cassegrainian/Gregorian). It is possible to realize a rotationally symmetric aperture mapping even in a double‐offset reflector arrangement in which no symmetric plane exists.
Phase‐diversity receiver using two pairs of three wires for data transmission over a low‐voltage distribution line
Authors: Hashimoto Naoki , Arai Toshio , Ozawas Yoshitaka , Kohno Ryuji , Imai Hideki
Published: July 2007

Intensive efforts have been observed in recent years on the development of data communication technology, aiming at the effective utilization of such existing transmission lines as the in‐house distribution line. The automatic consumption meter reading, for example, uses the low‐voltage distribution line as the transmission channel.

This paper aims at the improvement of the receiver demodulation performance in the data transmission using the low‐voltage distribution line and proposes the phase‐diversity reception using two phases (red and black) of the single‐phase, three‐wire system. In the data transmission using the low‐voltage distribution line, stray signals are produced between the two phases of the single‐phase, three‐wire lines and two signals with different signal‐to‐noise (SN) ratios are received. If a simple scheme such as the addition is employed, a problem arises in that the reliability of the demodulated data is deteriorated.

To cope with this problem, this paper proposes a phase‐diversity reception, where the time‐varying phase difference is adjusted to zero using an adaptive phase shifter and the SN ratio is improved by synthesizing the two‐phase received signals. The proposed scheme is implemented on a digital signal processor (DSP), and a robustness against the channel noise and the periodic attenuation is realized by the feedback (FB) control.

As a result of an experimental evaluation, it is shown that the SN ratio is improved by 2.7 dB at the maximum for the stationary phase error, compared to the traditional simple addition and the addition/subtraction selection schemes. Thus, it is verified that the receiver demodulation performance of the low‐voltage distribution line data transmission can be improved.
On efficiency of optical modulations for optical channel with noise
Authors: Watanabe Noboru
Published: July 2007

Recently, in parallel with the advancement of lightwave technology, there has been a considerable amount of research and development work in the system engineering aspects of optical communication, including important basic research. Various types of modulation have now been applied in real optical communication systems. In this paper we introduce a scale that can be used to measure the efficiency of optical modulation in terms of the quantum entropy. With the aid of this scale, we then discuss the efficiency of information transmission in various types of optical pulse modulation (PAM, PPM, PWM) for particular photon number states of the input system and for an optical channel with noise.
Digital modulation scheme for FM multiplex broadcasting with mobile reception
Authors: Kuroda Toru , Saito Tomohiro , Takada Masayuki , Yamadas Osamu
Published: July 2007

The FM multiplex broadcasting is one of the broadcasting configurations for providing a new service, where digital signals are multiplexed by utilizing the empty spectrum of the baseband signal in the FM stereo broadcasting. The fixed reception FM multiplex broadcasting system, where reception is done by setting up an antenna has already been developed and used in practice, and its broadcasting has been started. On the other hand, it would be desirable to develop a mobile reception FM multiplex broadcasting system with a certain amount of transmission capacity, where the broadcast can be received by a car or portable radio, for an application to the traffic information transmission. As to the digital transmission to moving objects, interferences such as fading and multiple paths are known to be present and the technical difficulty is increased with the increase of the bit rate. Furthermore, there are difficulties in the FM multiplex broadcasting such as the cross‐talk from the sound signal, due to the nature of the multiplex signal. Only a very low bit‐rate system of about 1 kbit/s has been developed such as RDS (Radio Data System) [1] in Europe for practical applications to the mobile reception. This study aims at the development of a mobile reception FM multiplex broadcasting system with a higher bit rate. An FM multiplex transmission simulator is constructed first, and the transmission characteristics inherent to the FM multiplexing are analyzed. A digital modulation method suited to these transmission characteristics is presented. By laboratory and field transmission tests, the effectiveness of the proposed digital modulation scheme is demonstrated.
Evaluation of input traffic control in atm networks
Authors: Sakamoto Nobuo , Ohba Yoshihiro , Murata Masayuki , Miyahara Hideo
Published: July 2007

This 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 discussed.
Cell delay variation smoothing methods for atm‐based sdh signal transport system
Authors: Uematsu Hitoshi , Ueda Hiromi
Published: July 2007

If the synchronous digital hierarchy (SDH) signal is converted into asynchronous transfer mode (ATM) cells to be transmitted through the ATM transport network, the efficiency of the operation/management/maintenance of the network will be improved in addition to maintaining the economy and reliability of the network. This is one of the advantages of the ATM transport network.

This paper considers the system where SDH signal is transported by ATM technique. The delay variation produced in the ATM transport network is evaluated. Then the buffer readout control and the required buffer capacity are discussed. The order of processing between the delay variation smoothing function and other required functions in the proposed system is analyzed.
Analysis of a magnetic resonance imaging antenna inside an RF shield
Authors: Ochi Hisaaki , Yamamoto Etsuji , Sawaya Kunio , Adachi Saburo
Published: July 2007

Optimization of an antenna for magnetic resonance imaging (MRI) requires an accurate analysis of antennas located inside a conducting cylindrical RF shield. A Galerkin‐moment method analysis which can be used for an arbitrary‐shaped shield is used. The surface current on a conducting plane is expanded by means of surface patch segments based on Richmond's method. Numerical results are compared with measured input impedance, which confirms the validity of the proposed method. Furthermore, a relation between the dimension of shield and the sensitivity of the antenna is discussed theoretically.
Scattering from a periodic array of arbitrary shaped elements on a semiinfinite substrate
Authors: Kominami Masanobu , Wakabayashi Hideaki , Sawa Shinnosuke , Nakashima Hiroshi
Published: July 2007

In conjunction with a recent increase in information density, radio wave communication becomes more complex and more varied. Hence, effective use of radio wave resources is required. Under such a situation, the frequency‐selective screen (FSS) with which a single antenna is capable of receiving multifrequencies at the same time has drawn attention. The FSS consists of conductors placed periodically on a dielectric substrate.

In this paper, the spectral domain moment method is applied to the problem of scattering from infinitely many conductors with arbitrary shaped elements on a semiinfinite dielectric substrate. From the results, the effect of the surface resistance of the conductor and the characteristics due to the conductor shape are investigated. Various scattering characteristics by linearly and circularly polarized incidences are discussed.
An analysis of atm cell loss probability based on virtual queueing system
Authors: Sato Shohei
Published: July 2007

Numerous methods have been employed to analyze the traffic characteristics of an asynchronous transfer mode (ATM) communication system when multiplexed bursty traffic is applied to a single server. Some of the well‐known methods include solving a state equation numerically, approximating the arrival process by Markov modulated Poisson process (MMPP), and a fluid‐flow approximation method.

This paper proposes a new approximating analysis technique employing fluid‐flow approximation that requires very small computational quantity. It also focuses on a queue where constant bit‐rate cell traffic and multiplexed N‐independent bursty cell traffic are applied to a finite buffer single server.

The characteristics of cell generation during a cell‐overload period and a cell‐underload period are studied to derive a virtual queueing system. If the burst length and the burst interval of the original queue are distributed exponentially, it will be shown that this virtual queue is a GI/GI/1 queue.

Finally, a method of calculating the cell loss probability by approximating this virtual queue is presented and it is shown that the results agree with the results of simulations and existing theories.
Adaptive antennas using a kalman filter
Authors: Wang Jinkuan , Takano Tadashi
Published: July 2007

This paper proposes an application of a Kalman filter for an adaptive array antenna. This method has an advantage in that the control gain can automatically be adaptable to the variation of the arriving signal and the convergence speed is high. The convergence condition to optimum weight coefficients is analyzed in the case where a Kalman filter is used for the control of the weight coefficients. By means of a simulation for a four‐element array antenna, it is confirmed that the directivity control error is small and the convergence is swift. The effect of the initial value of the unknown weight coefficient vector W(0) and the initial value P(0) of the estimated error covariance matrix on the convergence characteristics is studied. By means of the simulation, the range of allowable values is indicated. If W(0) and P(0) are chosen appropriately, the maximum error for the directivity control can be restricted to less than 1.5 degrees.
Unique word detection using quantized soft‐decision data
Authors: Sasai Hiroyuki , Takeyabu Masato , Minomo Ken , Takahata Fumio , Ogikubo Junichi
Published: July 2007

The efficacy of applying quantized soft decision data to unique word (UW) detection, which plays an important role in frame synchronization in digital radio transmission systems, is discussed considering hardware implementation. This UW detection method represents the received signal vector using representative points within a multidimensional space and measures the Euclidean distance from the vector point corresponding to the UW pattern.

Probability calculations are employed for obtaining theoretically UW detection characteristics such as missed detection and false detection, assuming that white Gaussian noise is added to the signal during transmission. These various characteristics are then compared quantitatively with the characteristics obtained by the conventional UW detection method using hard decision data. In addition, the UW detection characteristics obtained experimentally using hardware are presented. As a result of the quantitative evaluations, it has been clarified that the application of soft decision data is effective in reducing the UW length required for objectives of the UW detection performance associated with frame synchronization characteristics.
Design of optical connectors with ID modules
Authors: Ohtsuki Fumio , Yamashita Katsuya , Yamamoto Yoshikazu
Published: July 2007

To improve the present conventional management system for further expansion of line facilities, a new system which has an automated, real‐time updating capability of system data has been proposed. The design principle and the result of SC2‐ (in‐house single wire) and MT‐type (outside, single∼multiwires) optical connectors with ID modules, which are the key components for this proposed system are presented in this paper. For the design of those connectors, the requirement for the ID module memory device is clarified and a serial‐type electrically‐erasable programmable ROM (EEPROM) is demonstrated to be the most suitable as a memory element.

For further designing an integrated structure with connectors to avoid the degradation of the operationality, the packaging is discussed. As a result, the SIP‐type ID modules are located at one side of a connector. To minimize the contact‐loss fluctuation, the design for the structural and mechanical characteristics is discussed where a lateral force or electrode insertion force required to attain a desirable electrical resistance is evaluated. A prototype connector has been fabricated, which exhibits a contact loss change of ‐0.01 dB (SC2) and +0.02 dB (MT) and also a dynamic loss fluctuation level of less than 0.1 dB at the time of a connector insertion. Further, a contact resistance of less than 4 mμ (target: less than 40 mω), the package density of 1.5 to 1.8, and the connector loading time of 1.0 to 1.08 were obtained, which are comparable to the conventional case.
A future traffic‐dimensioning method: A nonparametric approach for cell loss‐rate evaluation
Authors: Saito Hiroshi
Published: July 2007

This paper advocates the nonparametric approach and shows its application to asynchronous transfer mode (ATM) network dimensioning. The conventional dimensioning procedure, which is used in conventional dedicated and low‐speed networks, can cause the following problems in ATM networks and intelligent networks:

(1) The need for a complicated arrival process model to describe high burstiness. As a result, elaborate modeling is necessary for each new service, which reduces flexibility in introducing new services.

(2) The need for traffic measurement of higher moments of interarrival times. However, traffic measurement mechanisms cannot meet this requirement.

(3) It is impossible to verify the arrival process model. The nonparametric approach dispenses with parametric modeling of arrival processes and derives performance measures directly from traffic measurement, thereby resolving the forementioned problems. This approach can be applied when the peak and average cell rates in ATM networks are known and provides an accurate measure of the cell loss rate.
Hierarchical video coding scheme with scalability and compatibility
Authors: Hanamura Tsuyoshi , Sekiguchi Shun‐Ichi , Kameyama Wataru , Tominaga Hideyoshi
Published: July 2007

In this paper, functional requirements for the MPEG 2 coding method are presented and, as an implementation method of these requirements, a hierarchical video coding scheme is proposed. In the proposed coding method, the prediction efficiency is increased by introducing spatial prediction in addition to temporal prediction as used in the MPEG 1 coding method. The hierarchical scheme is also characterized by the following features. (1) The input format is an output device‐independent noninterlaced video; (2) the coder has a hierarchical structure that permits the resolution level to be selected by the user; (3) by means of a small number of operations and a wide compensation area, the coder gives a motion‐detection method which detects motion vectors of each layer and a coding method of motion vectors; and (4) the proposed coding system introduces the use of down/up sampling processes with no phase distortion. Furthermore, the coding data description method is realized as an extension of that used by MPEG 1 and thus retains the compatibility. Simulation experiments show that this coding method satisfies the functional requirements without any obvious decrease in coding efficiency.
Adaptive virtual path capacity control in multimedia ATM networks
Authors: Watanabe Yutaka , Hadama Hisaya
Published: July 2007

The Virtual Path concept has several beneficial features to construct an economical and efficient Asynchronous Transfer Mode (ATM) network. The Virtual Path capacity control technique can increase network flexibility and improve transmission efficiency through statistical sharing of facilities.

This paper presents an adaptive virtual path capacity control method which maximizes transmission efficiency under the condition of limited processing load. Evaluation shows that the proposed method successfully improves network transmission efficiency with a slight increase in processing load compared to the fixed virtual path capacity scheme.
Throughput analysis of pipelined protocol processors
Authors: Cardona Mario , Tsuji Shigeo , Satake Tadashi
Published: July 2007

Pipelined protocol processors are used in high‐speed networks such as FDDI for achieving high‐throughput data communications between end users. In this paper, we present a model for computing the maximum throughput that can be delivered by such processors.

The parameters of the model are: input packet length, length of PDU (Protocol Data Unit) and SDU (Service Data Unit) headers, packet processing time of pipeline stages, capacity of the FIFO channels that interconnect stages, and average number of packets assembled/segmented at a stage.

As an example, the maximum throughput of an idealized pipelined processor that executes the FDDI, LLC Class I, IP, and TCP protocols is computed. Also, we show that the formulas given in [1] and [2] are particular cases of the formulas presented in this paper.

In a typical application of the proposed model, some desired, or measured, throughput characteristics of a protocol processor will be given, and the parameters of the processor will be computed.
Performance analysis of a slotted ring LAN by a single‐buffer model
Authors: Yamazaki Genji , Kobayashi Noboru , Takagi Hideaki , Wolff Ronald W.
Published: July 2007

Slotted rings have been popular medium access control protocols for local area networks (LANs) since the early proposal of Cambridge and Owell rings. This paper provides a simple approximation technique for the performance analysis of a slotted ring based on a single‐buffer model in which at most one packet can be stored at each node. The technique produces approximate values of the network throughput by using an assumption which is valid for large networks and a solution of a quadratic equation whose complexity does not depend on the number of nodes in the network. It is shown by numerical examples that the present technique also gives accurate performance data for rather small networks to the extent that the relative error of the approximate throughput values is less than 0.3 percent of exact values. Since other performance measures for the single buffer model of a slotted ring can easily be calculated from the throughput, the proposed technique is very useful for evaluating the total performance of a slotted ring network.
FDTD analysis of two‐dimensional transient scattering of cylindrical wave via buried conducting objects
Authors: He Yiwei , Uno Toru , Adachi Saburo
Published: July 2007

It is important to know the scattering properties of objects buried underground so that the techniques of imaging the buried objects by electromagnetic waves may be established.

This paper analyzes numerically the transient scattering characteristics by the finite difference time domain (FDTD) method where an infinitely long perfect conductor of arbitrary cross section is buried in the ground and an infinitely long current source is located above the ground surface parallel to the object. The calculation error resulting from the approximation of the scattering object by square mesh is decreased by introducing the field interpolation which satisfies the boundary conditions of the scattering surface.

The spatial distribution of the electromagnetic field at each step of the calculation is shown. Moreover, the propagation characteristics of the wave near the ground surface and the scattering characteristics of various objects are studied and the presence of two types of waves, i.e., direct and lateral, is confirmed between the source and ground and between the object and ground.
Optical spectrum measurement system with very high resolution
Authors: Nagaki Yoshiro , Ooka Takao , Sonobe Youji , Kikugawa Tomoyuki
Published: July 2007

Since the discovery of semiconductor‐optical fiber, the development of optical communication has been significant. In particular, a baseband modulation frequency in high‐speed communication has been increased up to the order of 10 GHz at the research level and of 1 GHz at the practical level. A factor which is the obstacle for further improvement is the bandpass width limitation for a transmitted signal caused by the spread of an oscillation spectrum of LD and also the wavelength dispersion of an optical fiber. For long‐distance and high‐speed transmission, it is important to determine accurately the spread of the LD spectrum for designing an optical transmission system.

The objective of the present study is to clarify the condition required for a high‐resolution optical spectrum analysis system, which is essential for understanding the spectrum‐spread and chirping of the LD laser at a time of high‐speed modulation. A comparison of various measurement systems is made. A method of combining the diffraction grating system and the Fabry‐Perot etalon system is proposed, and the optimization of the system is discussed in detail.

The present paper describes for the first time the optimization of the tandem configuration of a diffraction grating and Fabry‐Perot etalon systems. Based on those discussions, a prototype system has been constructed with which a maximum wavelength sweeping width of 200 MHz/div and resolution of 100 MHz were demonstrated.
Development of a breadboard model for the 22‐ghz band satellite broadcasting multibeam antenna
Authors: Shoki Hiroki , Kawabata Kazuaki , Nakatsuka Hirotaka , Tokunaga Kyoko , Orikasa Teruaki , Tsuzuku Aiichiro , Fukuchi Hajime , Ohmori Shingo
Published: July 2007

The multibeam antenna for the 22‐GHz band satellite broadcasting has been studied. The aim of this study is to meet future satellite broadcasting demands and advanced services such as high definition television (HDTV), digital broadcasting, and regional satellite broadcasting. The breadboard model of the 22‐GHz band multibeam antenna has been developed.

Here, a new type of primary feed and a pattern synthesis method are proposed to achieve high gain and low sidelobe antenna performance which is required for the 22‐GHz band satellite broadcasting. The feasibility of the proposed antenna system and the design method have been verified numerically and experimentally.
Effect of compensation for rain attenuation on earth‐satellite links by onboard resource sharing using AMeDAS data
Authors: Matsudo Takashi , Karasawa Yoshio , Shiokawa Takayasu
Published: July 2007

Onboard 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 compensated.
System testing architecture for a distributed switching system
Authors: Imagawa Hitoshi , Sakakibara Hajime
Published: July 2007

A large‐scale switching system composed of distributed modules requires a system testing architecture that automatically tests for verification of call connections normality and determines the fault position when a system fault occurs.

This paper proposes a system testing architecture for high‐speed testing of the entire system and wide‐area tests in the system. In the proposed, the distributed modular switching system is divided into upper and lower level modules. The upper level has a system testing function for executing tests of the lower level in parallel. The lower level is provided with various kinds of test equipment and test execution control functions. Similarly, test control functions and test execution control functions, respectively, are provided to the upper and the lower function units composing the module.

Compared to the existing sequential test control architecture, the test execution time for verification of the system operation normality of the entire switching system is reduced to 1/[(number of modules) × (number of function units composing a module)]. Testing started by maintenance personnel and diagnosis automatically executed by the switching system itself in the case of a fault can share the test agent for controlling the testing. Then, not only the fault position analysis but also the verification of call connection normality can be realized through the originating and terminating connection testing.
Stochastic amplitude fluctuation in coherent optimal time domain reflectometry and its reduction technique
Authors: Izumita Hisashi , Koyamada Yahei , Furukawa Shin‐Ichi , Sankawa Izumi
Published: July 2007

When the coherent detection technique is employed in optical time domain reflectometry (OTDR) (C‐OTDR), enhancing the dynamic range is expected to be an effective means of improving the minimum detectable signal level to that of shot noise. In C‐OTDR, however, there are fluctuations in the OTDR trace, and the problem is the degradation of the resolution of the loss measurements. The main reasons for such amplitude fluctuations are: (1) scattering light‐power jags due to the interference between Rayleigh backscattered lights; (2) variations of the heterodyne detection efficiency due to rotations of Rayleigh backscattering polarization; and (3) variations of the detection efficiency due to phase fluctuations of Rayleigh backscattering light.

In this paper, such fluctuations are evaluated stochastically, and the techniques for their reduction are proposed. With regard to cause (1), the amplitude fluctuations can be reduced by integration over the frequency of light, while with regard to cause (2), the improvement can be achieved by polarization diversity detection or integration over the polarization. In case (3), phase diversity detection or phase integration is effective in reducing the amplitude fluctuations. Experimental investigations with regard to cause (1) are conducted in detail, and it is shown that the amplitude fluctuations can be reduced by about 3 to 7 times as a result of integration in the frequency domain compared to those without such integration.
A laser diode transmitter for optical intersatellite communications
Authors: Nohara Mitsuo , Inagaki Keizo , Fujise Masayuki
Published: July 2007

Development of a laser diode (LD) transmitter that has such characteristics as high power, fast frequency response, and good beam profile is essential to a realization of broadband optical intersatellite communications. Both an LD collimator to achieve a good wavefront quality and an LD driver to achieve a fast frequency response are designed for use with an LD operated at a wavelength of 0.83 μm.

Also developed is an LD transmitter using an LD collimator and an LD driver. The objective of the LD collimator design was an acceptable degree wavefront aberration with a minimum number of lenses, by applying aspheric lens technology. As a result, a three‐lens configuration for the collimator was obtained. As for the LD driver, two high‐speed LD‐driver GaAs‐ICs are fitted in parallel. Their outputs are combined and fed to an LD. The parallel‐feed configuration enabled a fast frequency response at a high current.

For fabrication results, a circularly collimated output beam 5 mm in diameter, with an output power of 60 mW, a transmission rate of 2.5 Gbit/s, and a wavefront aberration of λ/16 was obtained. The result satisfies the system requirements for optical intersatellite link between satellites in low earth orbits.

This paper presents an LD transmitter design and data on its test samples, followed by discussions of further improvements.
On‐board large mesh antenna reflector with high surface accuracy
Authors: Ueba Masazumi , Tanaka Hiroshi , Kawakami Yoichi , Ohtomo Isao
Published: July 2007

An increase in the size of on‐board antenna reflectors is a key technology in providing economical services by miniaturized portable equipment in future mobile satellite communication systems. In practice, a mesh antenna can be used as the on‐board antenna. However, since the reflector surface of this antenna is supported by the cable and the mesh, and its size is larger, the surface is subject to larger thermal deformation in orbit than is the solid antenna reflector. Conventional compensation methods such as passive thermal control or rotation of the antenna reflector cannot maintain the required antenna performances. Various methods have been reported to compensate for the deterioration of antenna performance by thermal deformation.

This paper describes a static shape control system for a 10‐m diameter antenna which actively compensates for the deformation by using a shape‐measuring sensor and shape‐compensation actuator. The configuration of the sensor and the experimental results by a functional model are described to confirm the design validity. The shape‐compensation method by the actuator was confirmed to be useful in achieving a required surface accuracy.
Use of concentrators to obtain an asymmetric broadcast ATM switching network
Authors: Tanaka Yoshiaki , Tsuchiya Hirofumi
Published: July 2007

As the broadband integrated services digital network (B‐ISDN) become more available for home use, it is expected that the demand for broadcast services, e.g., video distribution from a center to end terminals, will increase. Thus, in the local switching system, the number of output subscriber lines is much larger than the number of input trunk lines. Therefore, an asymmetric broadcast ATM switching network is needed for this service. However, most of the switching networks already proposed are symmetric.

In this paper, an asymmetric switching network is realized by partitioning the output and by using existing symmetric switching networks. Furthermore, the size of symmetric switching networks which are used as parts is reduced by placing concentrators in the front. This decreases the total amount of hardware. Since excessive concentration invites cell loss, the relation between the hardware‐reduction effect and the cell‐loss characteristic also is studied.
A multicast hybrid ARQ scheme with stored error recovery
Authors: Sakakibara Katsumi , Kasahara Masao
Published: July 2007

A multicast error control scheme which takes advantage of both MDS codes and GMD decoding is proposed and analyzed. The proposed scheme is characterized as follows:

1. The sender does not retransmit data frames. The frames to be retransmitted consist of the redundant symbols obtained by encoding the previously transmitted data frames.

2. Each receiver stores erroneous frames not greater than the prearranged number and decodes them all of a lump using the retransmitted frames of the fixed number.

Numerical results show that the proposed scheme yields higher throughput not only for the case where the bit error rate is very large but also for the case where the number of VSATs is very large.
Interference cancelling characteristics of DFE transversal‐combining diversity in mobile radio environment–comparisons with metric‐combining schemes
Authors: Yoshino Hitoshi , Suzuki Hiroshi
Published: July 2007

This paper considers the decision feedback transversal‐combining (TC) diversity reception system in the digital mobile communication, and describes experimentally the interference cancelling characteristics of decision feedback equalizer‐type (DFE) TC diversity reception through laboratory tests. Three kinds of interference signals are considered: the intersymbol interference (ISI), the cochannel interference (CCI), and the adjacent channel interference (ACI). The exponentially weighted RLS, which executes the least‐square method in realtime, is employed in the adaptive control of the combining coefficients.

It is shown first that the method for equalization and diversity combining can be classified into the TC and the metric combining (MC), among which TC has the linear interference cancelling effect. By 40 kbit/s quadri‐phase‐shift keying (QPSK) transmission experiments under Rayleigh fading condition, the following properties of TC are shown compared to MC: (1) In ISI, dominant condition in double path model, the average BER performance for average Eb/N0 values over 20 dB; (2) For CCI, dominant condition BER performance of TC is better than that of MC by 5 dB in average CIR at average BER of 10−2.
Method of Estimating Deterioration of Lead‐Acid Batteries Using Pulse Discharge and Charge Characteristics
Authors: Ogata Tsutomu , Takano Kazuo , Kohno Masaru , Yoshida Kazuki
Published: July 2007

Lead‐acid batteries have been used as emergency back‐up power supplies for communication systems. These batteries usually are charged and provide power to communication systems when a power blackout occurs. If the communication system is out of order during the blackout, the problems can be enormous. Therefore, NTT has been serious about the maintenance of the lead‐acid batteries.

Since it takes longer than 20 hours to check the capacity of a battery, some other convenient battery evaluation method must be established. In this paper, the degradation mechanism of the lead‐acid battery was studied and it was concluded that the degradation of the internal resistance is related strongly to the capacity degradation. By measuring the internal resistance, the charge/discharge characteristics were evaluated for a short period of time.

It was confirmed also that the internal resistance measured by measuring the charge/discharge characteristic for a period shorter than 500 ps is related strongly to the battery capacity. Using the forementioned relationship, the battery degradation was determined.
Facsimile image high‐speed coding and decoding processor
Authors: Horie Hitoshi , Ozaki Tohru , Shirai Hideyuki , Iizuka Yasuo
Published: July 2007

This paper describes a very high‐speed coding and decoding processor Image Pipeline Codec (ImPC, MN86063), which can be applied to bi‐level image, focusing on the architectural design and performance evaluations. An application example for a facsimile apparatus also is presented.

The ImPC integrates basic functions required for an advanced facsimile such as two‐channel encoding and decoding, resolution conversion, and direct memory access (DMA) transfer functions. The ImPC includes the redundancy reduction coding algorithms modified Huffman (MH), modified READ (MR), modified MR (MMR), and an original coding scheme. A line of 4096 alternating black and white pixels can be encoded or decoded in 0.84 ms with 100‐ns cycle time. A typical A4 size office document is processed in 0.17 s. The ImPC chip is fabricated using 1.2 μ CMOS technology, integrating approximately 480,000 transistors on a 98‐mm2 die.
An optimum weak optical signal receiver for intensity modulation/direct detection optical communication systems
Authors: Tsukamoto Katsutoshi , Morinaga Norihiko
Published: July 2007

This paper presents a detailed study of a binary optical direct detection optimum receiver for the use of optical space communication systems, where a long‐distance transmission makes optical received signals extremely week. At such a low‐power operation of the receiver, the quantum discreteness structure of the shot noise process is evident in the optical detector output.

A statistical model for optical detection output is derived, considering this quantum discreteness, thermal noise at the receiver circuit system, dark current at optical detector, and random photomultiplication. Moreover, the optical detection system is considered as an ideal integration system, and optical detection output is expressed by using a time‐dependent sample value vector.

A logarithmic likelihood function derived from this sample value vector on the basis of maximum likelihood testing is studied, and the optimum receiver structure for weak optical signals is clarified. That is, it is shown that, even under the existence of thermal noise and random photomultiplication, primary photon count plays an essential role in signal detection similar to that in the shot noise limited case and the primary photocount estimator‐maximum likelihood detection receiver is derived theoretically. Then the error rate performance is analyzed theoretically and compared with that of a conventional direct detection receiver. As a result, it is shown that by introducing a wide‐band optical detection system, a significant improvement in error rate performance is observed over conventional receivers.