bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of EDB code in optical fiber communication systems
Authors: Ohishi Tomofumi , Takahara Mikio
Published: July 2007

Optical fiber is generally believed to have a wide band but the step type or some of the graded‐type fibers have a narrow band and hence a narrow‐band code is necessary for high bit rate transmission or a long repeater interval. In the system with signal‐dependent noise, such as the optical fiber communication system, the optimum code levels of a multilevel code are spaced unequally when the average light power is prescribed. In this paper three types of codes — the duobinary code typical of a narrow‐band transmission code, the extended duobinary code with three unequally spaced decision levels, and the conventional binary code — are compared with respect to the maximum transmission distance. Also, the difference of maximum transmission distances of duobinary code and binary code is calculated with the fiber bandwidth as a parameter and the range in which the duobinary code and extended duobinary code are advantageous over the binary code is clarified. As an example, when the oscillation wavelength=0.85 μm, the fiber bandwidth=100 MHz · km, length‐dependent parameter of fiber=0.7, BER=10−9 and bit rate=200 Mbps, maximum transmission distances of duobinary code are about 1.8 times and about 2 times that of the binary code, respectively.
On routability for channel routing problem
Authors: Shimamoto Takashi , Sakamoto Akio , Ushida Akio
Published: July 2007

The routing requirement in the channel routing problem for automatic wire routing in the interior of LSI is realizable if the constraint graph contains no cycle. Otherwise, the trunks for several appropriate nets must be divided into pieces. In this paper we modify a routing requirement with cyclic conflicts into one without them by dividing trunks into two parts. First we define a directed bipartite graph G to represent the routing requirement. A set of vertices in a strongly connected component in G is called a crowded set. It is shown that a routing requirement is realizable if there exists no crowded set in G. On the other hand, in the presence of a crowded set we define a method of dividing a net n contained in the crowded set into two subnets n' and n'' at some terminal position. If n' and n'' are not contained in any crowded set in the graph modified by division, we say that the division is effective. We then present a necessary and sufficient condition for the existence of effective division. Further, a semi‐effective division is defined to deal with the case where there is no effective division and then the routability for the channel routing problem is discussed.
A design technique for adaptive filter using lattice elements as adaptation modules
Authors: Kumazawa Itsuo , Iijima Taizo
Published: July 2007

A lattice filter has several advantageous properties for adaptive applications. The gradual increase of the degree of estimation by the regular repetition of the adaptation module is particularly advantageous for hardware realization. In this paper, this adaptation module is called a lattice element and a method is proposed for the design of adaptive filters using such lattice elements. The efficiency of this method is demonstrated by the derivation of orthogonalizing and biorthogonalizing filters. The operation of these filters is tested by computer simulation and some problems arising at higher‐order filters are pointed out.
Analysis of electromagnetic wave scattered from cylinders buried in the ground
Authors: Tajima Katsusuke , Iiguchis Shin‐Ichi
Published: July 2007

The phenomena of scattering from an object buried in the ground have been analyzed in the case where the frequency is a few kHz. In such cases the displacement current is negligibly small and the scattering object is sufficiently smaller than the wavelength. On the other hand, recently a ground radar using an RF signal of several hundred MHz has been studied. At such high frequencies the scattering body to be detected is located at a relatively shallow depth and has a size of the order of wave‐lengths because the attenuation is significant. For low‐frequency applications Green's function for the structure with a ground surface does not cause numerical problems. For high‐frequency cases the computation time increases significantly. The integrand for Green's function varies substantially depending on the relative locations of the source, scattering object and observation point. In the present paper the computation time is reduced significantly by deformation of the integration path. When both the source and the observation point are close to the ground surface, the maximum value of the scattered wave computed with consideration of the effect of the ground surface is about (1 + R) times that with this effect neglected if R is the reflection coefficient of the ground to air. The effect of higher‐order scattering is found to be small.
Sets of cyclically orthogonal multilevel sequences derived from monomial phase
Authors: Tanada Yoshihiro
Published: July 2007

This paper derives a set of cyclically orthogonal sequences taking real multilevel values and having different waveforms, aiming at the application to the spread‐spectrum multiplex communication. The real cyclic orthogonal sequence is represented by the cosine function with the phase which is an odd function, and the cross‐correlation functions among sequences with the same or different lengths are discussed. By defining the convolution between sequences of the same length, a set of sequences with different waveforms and the same length can be derived. As examples of the set of sequences, the sets with length being prime number or compound number lengths are considered, which are obtained by forming convolutions of sequences with phases being monomial with odd power. Their properties are discussed. In the set of N sequences with the prime number length N, each of (N ‐ 1) sequence takes odd multilevels between 3 and N, and the cross‐correlation function between sequences is 1/√N times the sequence value. By forming the product of such sequences with different prime number lengths, a set of sequences with compound number lengths can be generated, which is a good compromise between the number of multilevels and the absolute maximum value of the cross‐correlation function. N ‐ 1 sequences of prime number lengths generated by the third‐order monomial takes 3 to N multilevels and their cross‐correlation function does not exceed 2/√N in the absolute value.
In‐house wireless optical digital SSMA
Authors: Yamauchi Yukiji , Sato Masashi , Namekawas Toshihiko
Published: July 2007

With the recent development of the office automation, portable in‐house terminals for data communication have attracted attention. For this purpose, wireless transmission by optical link is considered promising, since it does not require the installation of signal lines. The past discussions and experiments, however, considered only the one‐to‐one or one‐to‐many communications, but many‐to‐many, i.e., multiple connections were not considered. This paper aims at the application of the spread‐spectrum system to the wireless optical communication link to realize the multiple connections, and derives the basic theoretical expressions for the receiver characteristics. More precisely, the modulation scheme is selected taking the restriction into consideration, which is inherent to the inhouse wireless optical link. Then, the receiver error rate and the multiple connection characteristics of the proposed modulation scheme have been theoretically derived, providing the basis for the system design. Finally, a qualitative discussion is made on the construction and operation of the synchronous system for the proposed modulation scheme.
Performance analysis of a buffered CSMA/CD system
Authors: Tasaka Shuji , Ishikawa Hiroshi
Published: July 2007

Most of the performance analyses of CSMA/CD systems have assumed that each user has a buffer space for only one packet. Using the technique of equilibrium point analysis, this paper analyzes the dynamic behavior of a slotted nonpersistent CSMA/CD system with a finite number of users, each of whom has a finite buffer space for more than one packet. Two schemes of packet transmission are studied: (1) once a user captures the channel, he continuously transmits all of the packets which have been stored in his buffer by the instant of the capture (gating type); and (2)he transmits at most one packet at a time (limiting type). First the gating type is analyzed, and its throughput, its average packet delay and its system stability are evaluated. An approximate probability distribution for the number of packets in the buffer space of a user is derived. On the basis of these analytic results, we study how to select both the buffer size and the rescheduling probability of packets which guarantee the system stability, keep the probability of buffer overflow sufficiently small and at the same time minimize the average packet delay. The two schemes are compared and it is shown that the gating scheme out performs the limiting scheme in terms of average packet delay and the average and variance for the number of packets in a buffer.
Arrangement of sources in the charge simulation method and singularities of solutions of the helmholtz equation. Scattering by a perfectly conducting cylinder of electromagnetic waves radiated from a line source
Authors: Komiyama Akira
Published: July 2007

In the charge simulation method, the scattered wave is represented by a linear combination of electromagnetic waves radiated from fictitious sources which are arranged inside the scattering body. The singularities of the scattered wave are the true sources from which the scattered wave is radiated. Therefore, the arrangement of fictitious sources will be affected by the location of singularities of the exact solution.

This paper treats the scattering by a perfectly conducting cylinder of electromagnetic waves radiated from a line source. Singularities of the exact solution are located by a simple method, making use of the comformal mapping. An arrangement of sources taking the location of singularities into consideration is proposed.

Numerical calculations of the residual error of the boundary condition are performed for an elliptic cylinder. The results show the effectiveness of the source arrangement. Calculations of the electric field distribution and scattering pattern are done by making use of the arrangement for an elliptic cylinder and a square cylinder. The fundamental properties of the line source scattering are clarified.
Radiation characteristics of reflector antenna with radome at 10∼30 GHz in rainy conditions
Authors: Kondou Manabu , Fukuda Shigeru , Kagoshima Kenichi
Published: July 2007

The increase in radome loss, sidelobe levels, and cross‐polarization level in the rain plays an important role in determining antenna characteristics. These effects have been investigated at 10 GHz ∼ 30 GHz with a reflector antenna having a planar radome, and a new method has been propsoed for deriving the radome loss in which a water‐shedding property of the radome is taken into account. Raindrops on the radome form water streams that flow down onto the surface thereby increasing the loss of the vertical polarization wave. It is also found that the cross‐polarization level generated by a wet radome is less than −40 dB. The sidelobe level is not increased and the paraxial radiation pattern is not changed by a wet radome but it is lowered as a whole. In the present theory, the contact angle of a raindrop surface with a radome surface determines the condition of the wet radome surface and this angle was predicted theoretically by using measured radome loss.
A method for reducing the number of product terms in a symbolic reliability expression
Authors: Higashiyama Youichi , Ariyoshi Hiromu
Published: July 2007

Among methods for deriving a symbolic reliability expression between two specified vertices (s, t) in a network, a treeexpansion method proposed herein generates an expression in summation form with fewer product terms and computes it very fast. The tree‐expansion method has a fundamental operation to enumerate s – t paths {μ1, μ2, …, μm} and generates a rooted tree (reference tree) from subpaths of paths μj (J = 1, 2, …, i – 1) having their initial and terminal vertices on a path μi and then derives a symbolic reliability expression directly from its subtree (implicant tree). This method has a disadvantage in that the number of product terms depends heavily on the order of path generation since the reference tree must be generated according to the order of paths obtained by a depth‐first search. In this paper for each vertex in a network we define its weight as the number of edges in a shortest path from the vertex to t. We show that if we generate paths by a depth‐first search to prefer those edges with terminal vertices having small weights and apply the tree‐expansion method according to the generation order, then we can reduce the number of product terms (this is called the modified tree‐expansion method). Also, we show by computer experiments that the modified tree‐expansion method can reduce the number of product terms and its running time.
Mullis–Roberts–type approximation for continuous–time linear systems
Authors: Nagaoka Hiroshi
Published: July 2007

As lower‐order approximation methods for discrete‐time linear systems, Mullis and Roberts have proposed two methods: the so‐called modified least‐square approximation (MLSA), and the interpolatory approximation (IA). The characteristics of the two methods were investigated considering their relationships. In this paper, a lower‐order approximation method for continuous‐time linear systems is presented in a form corresponding to MLSA, with its property, algorithm and state‐space representation discussed in correspondence with the discrete‐time case. The approximation can also be regarded as corresponding to IA, and thus the proposed method is called the continuous‐time Mullis‐Roberts‐type approximation (CMRA). The latter half of this paper presents a formulation for the limiting case (as sampling time ← 0) from a lower‐order approximation method for discrete‐time systems to one for continuous‐time systems. Thus it is shown that CMRA is obtained as a common limit of MLSA and LA, thereby providing a physical interpretation to the formal correspondence between CMRA and MLSA/IA.
Analysis for loss system with finite sources which require several channels simultaneously
Authors: Miyake Kou
Published: July 2007

This paper analyzes a loss system with finite sources. The idle period of a source forms a renewal process and each customer requires several channels simultaneously. The service time of customers which require the same number of channels exhibit a general independent identical distribution. This is a general traffic model for a subscriber concentration stage in a high‐speed wide‐band communication network. The distributions of the numbers of customers in the system at arbitrary and customer arrival epochs are derived using the supplementary variable technique, where the backward recurrence‐time of call idle period and holding time are chosen as supplementary variables. It is shown that these distributions are determined only by the mean service time and the mean idle period of a source, irrespective of their distributions (robustness). Finally, some traffic characteristics, such as loss probability and circuit occupancy, are evaluated numerically for two‐traffic models and unbalanced input traffic models.
Grounded immittance simulation using single operational amplifier with a finite gain‐bandwidth product
Authors: Ishida Masaru , Ebisutani Keisuke , Fukui Yutaka , Kasai Tamotsu
Published: July 2007

Many papers on the active‐RC immittance simulation using operational amplifiers with a finite open‐loop gain have been published. This structure is not suitable for high frequency operation. It has been shown that the active‐R immittance simulator utilizing a finite gain‐bandwidth product give the reliable high frequency performance. However, in the active‐R form, magnification in value of simulated elements has not been considered to date.

In this paper, a grounded immittance simulator composed of a single operational amplifier and thirteen passive circuit elements is presented. In order to analyze the driving‐point admittance using the computer, the circuit configuration is simplified such that eight passive elements out of thirteen are removed from the general circuit. Analytical results show that the various immittances can be realized. In particular, we deal with the increase in value of the simulated inductance and the circuit for generating a negative conductance. Furthermore, the effects of the second pole of an operational amplifier on the driving‐point admittance are also discussed. From experimental results, it is seen that both circuits work well in the high frequency range.
A method of measuring shielding effectiveness for conducting materials using a spherical cell
Authors: Hasebe Nozomu , Kobayashi Kazuhiko
Published: July 2007

Recently, 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 dimensions.
Polarization characteristics in UHF‐band mobile radio propagation
Authors: Kaji Masatake
Published: July 2007

A propagation study has been conducted for horizontal and vertical polarization inside buildings in residential areas and in business districts with tall buildings. The following findings have been obtained: (i) when half‐wave dipole antennas are used both for transmission and reception, the received power is stronger for transmission and reception in the vertical polarization than for transmission and reception in the horizontal polarization. This phenomenon is due to the difference of the directivity of the dipole antenna; (ii) the cross polarization discrimination (XPD), defined as the ratio of the in‐phase polarization component voltage to that of the orthogonal polarization, correlates with the loss increase from the free space propagation. As the latter is increased, the XPD degrades more; (iii) the XPD degrades more as the propagation distance increases. This is because the attenuation constant of the in‐phase polarization component is larger than that of the orthogonal polarization component; (iv) the XPD of the wave propagation outside is determined by the ratio of the RG wave guided along a road to the BD wave diffracted by the top edge of a building. It degrades more as the BD wave component is increased; and (v) for a distance of less than about 1 km line‐of‐sight, the difference in attenuation by the polarization is negligible.
Detection of objects buried in snow using multifrequency holography
Authors: Sakamoto Yuji , Tajiri Katuhiro , Sawai Takaya , Aoki Yoshinao
Published: July 2007

Several approaches are being considered for use in the visualization of the interior of snow and ice which are invisible to visible light. The authors have studied this subject with the objective of developing a radar system that detects an object buried in snow. Good transparency of the microwave in snow and the high resolving power of long wavelength holography are used for snow radar. A multifrequency holography has been used for further enhancing the resolving power. Using the snow radar system developed herein, we carried out experiments for detecting three‐dimensional information of objects buried in snow. The relationship of the three‐dimensional positions and the shapes are detected successfully for metal cylinders and mannequins. Also, it is proved that the system is effective for detection of nonmetal objects, such as meat.
Analysis of a DC current detector in a highly accurate DC‐DC converter
Authors: Yamamoto Katsuhiko
Published: July 2007

This paper describes the analysis and design method for a new biased rectifier amplifier (BRAM). The BRAM is driven by a high‐frequency square wave, employs a new self‐biased circuit configuration, and simulates dc detection characteristics using equivalent circuits. Design parameters of the core and operating frequency are studied to obtain a high conversion ratio of 2750. Applying the BRAM to a dc current detector gives a highly accurate, constant current dc‐dc converter.
TV interference from foreign transmitters and the polarization characteristics of Es‐propagation wave
Authors: Watari Shin‐Ichi
Published: July 2007

The ionospheric sporadic‐E (Es) layer has a high electron concentration and is capable of reflecting VHF radiowaves. It shows up mainly in summer in an unpredictable manner. The problem of TV interference by Es propagation waves has become increasingly severe with the increase in TV and FM stations between neighboring countries. Measurements have been made of the polarization characteristics of Es propagation waves in an attempt to find possible techniques to counteract this interference. In the summer of 1985, 1986, and 1987, observations were made of several VHF waves from known transmitting stations using log‐periodic antennas placed horizontally and vertically, and the ratios of horizontally and vertically polarized signals were measured. The results show that Es propagation waves have the same strength between two received signals, independent of propagation direction. Horizontally polarized signals are used in transmitting stations, showing that the polarization is rotated during Es propagation.
Traffic evaluation of channel‐reservation methods to improve the imbalance among internal blocking probabilities on a T‐S‐T network
Authors: Masuda Etsuo
Published: July 2007

Channel reservation methods RSC, RBC, and RIC are proposed and studied. These methods handle a mixture of single‐ and multislot calls and improve the imbalance among the internal blocking probabilities of the calls on a T‐S‐T network. They also restrict the connection of lower bit‐rate calls based on the scope of channels (RSC), the number of the channels already being used by the same class of lower bit‐rate calls (RBC), or the number of pairs of primary and secondary T‐switches having the minimum idle channels that are required to connect either class of higher bit‐rate calls (RIC). Simulation results show that these three methods are nearly equal in improving imbalance, and RIC is most desirable because of its robustness in handling a variation of possible traffic mixes.
Performance comparison of two CSMA/CD systems with prioritized retransmission
Authors: Matsumoto Yutaka , Takahashi Yutaka , Hasegawa Toshiharu
Published: July 2007

For efficient processing of various types of traffic in LAN's, the introduction of a priority mechanism is considered to be effective. This paper considers nonpersistent CSMA/CD systems with a new priority mechanism, and derives the throughput and the average response time for each priority class by using the imbedded Markov chain method. The priority structure is achieved by assigning higher exponential retransmission rates to higher priority classes. As for the basis of priority assignment, we analyze two mathematical models: one is terminal‐based and the other is message‐based. Because the models allow feedback of packets, we can apply our results to error‐prone CSMA/CD systems, also. Numerical results show that the simple priority mechanism works effectively, and clarify the differences between the terminal‐based system and the message‐based system.
Number of subscribers and system cost in mobile communication systems
Authors: Ogawa Keisuke , Sakamoto Masayuki
Published: July 2007

The rapid growth in mobile communication services has created the serious problem of how to accommodate the expanding demand in metropolitan areas. Also, a large problem is how to provide services at a reasonably low cost for a small number of subscribers in less populated areas.

This paper considers both subscriber capacities and system costs per subscriber in large‐demand areas, and numbers of subscribers and system costs per subscriber in small‐demand areas. The following results are obtained.

There exists an optimum zone radius to minimize the system cost per subscriber, and the optimum radius is smaller in large‐demand areas than in small‐demand areas.

Service quality degradation probability allotments are studied under the condition that the sum of degradation probabilities due to thermal noise and interference is constant. From the viewpoints of both subscriber capacity and system cost per subscriber, it is desirable to assign most of the probability to interference in large‐demand areas and, on the other hand, to thermal noise in small‐demand areas.
A new network configuration with local and global channels for packet radio networks
Authors: Mutsuura Kouichi , Okada Hiromi
Published: July 2007

A new configuration for packet radio networks, called local/global (LG) network configuration, is proposed, aiming at total throughput improvement. By using two kinds of channels (local channel and global channel) and geographically partitioning the total area, the spatial reuse of channel capacity is realized. The performance of this LG configuration is analyzed for a fixed radio network by introducing the delay ratio γ between local and global channels. s‐ALOHA protocol is used under heavy overload. By the performance analysis and numerical results, it is concluded that the improvement of the total throughput is attained for a typical network configuration without greatly increasing the mean delay. Also, various schemes for determining the allocation ratio of channel capacity to the local and global channels are presented and studied to apply this LG configuration effectively.
Beam‐scanning characteristics of offset reflector antennas with polarization grids
Authors: Chikara Sakae , Ando Makoto
Published: July 2007

When a multibeam antenna uses a reflector antenna, the effect of blocking for a large feeder system cannot be neglected. An offset type becomes advantageous for such a case. However, the cross‐polarized waves increase due to asymmetry of the reflector. We considered an antenna in which a grid plate is inserted between the primary radiator and the reflector. We can suppress the components of cross‐polarized waves by choosing the position of the grid plate and by designing strip patterns. In this paper, we performed a full‐wave analysis for such an antenna. We clarified the cross‐polarization suppression effects of grids during beam scanning. It provides guidance in designing a multibeam antenna. We showed a design method using geometric optics for strip patterns according to scanning directions. We confirmed the effectiveness of this design method.
High‐frequency long‐range propagation phenomena in semicylindrical conducting concave boundary
Authors: Ishihara Toyohiko , Shirai Kazuhiro , Goto Keiji , Toda Kohji
Published: July 2007

The electromagnetic field generated in a concave boundary by a magnetic line current source placed on a semicylindrical conducting concave boundary is analyzed by means of three representations. The effectiveness and physical interpretation of these representations are discussed. If the product of the wave number and the radius is sufficiently large, the conventional representation by the geometric optical rays and the integral‐type interference wave cannot be applied well. The representation by means of a combination of the geometric optical rays, lower‐order whispering gallery modes and the error‐correcting term has simple calculations and good accuracy. The mutual relationship between the geometric optical rays and the modes is found and the propagation characteristics within the boundary layer characteristic to the concave boundary are addressed.
An evaluation of systematic errors in VLF direction findings via full‐wave analysis
Authors: Nagano Isamu , Mambo Masayoshi
Published: July 2007

The full‐wave analysis method is described for computing the electromagnetic field on the ground when a beam‐shaped wave is incident from above the ionosphere. By means of this method, the directional error was evaluated in various VLF direction finders which measure the exit point of the natural wave at the lower portion of the ionosphere, under the assumption that the downgoing wave is radiated from a duct. In this method, the directional errors due to multiple reflection, polarization, beam wave of the arriving radio wave and the type of ionospheric models can be found systematically so that a simulation result most resembling the practical situation is provided. The main results are as follows: (1) When the transmission cone is within the trapping cone, the NPF method using orthogonal loop antennas and vertical antennas can indicate an almost correct direction within a radius of about 100 km from the maximum point of the radiowave strength on the ground. The error increases at a distance of more than 150 km. On the other hand, the Poynting method indicates almost correct directions even at a distance of more than 200 km regardless of the polarization. The goniometer method has almost the same accuracy as the Poynting method; (2) if the overlapping of the transmission cone and the trapping cone is smaller, the error is increased in the south direction in all three methods; and (3) no significant frequency dependence is observed in the directional error.
Highly contoured beam antennas for 21 ghz‐band ldr hub stations
Authors: Nomoto Shinichi , Watanabe Fumio
Published: July 2007

With a view to applications of the 21‐GHz LDR (local distribution radio) system to point‐to‐multipoint systems, a hub station antenna was developed which produces an improved cosecant square beam in the vertical plane and the fan beam in the horizontal plane. The antenna is made of an offset‐shaped reflector fed by a corrugated conical horn with a rotationally symmetric beam. As a shaped reflector synthesis, an efficient and accurate method is proposed, which is a combination of the geometrical optics method and the physical optics method. To produce the high gain part of the shaped beam (beam nose), the method of a doubly curved reflector is extended so that the main part of the reflector surface is obtained in the geometrical optic process. Next, to form the low gain part (beam skirt), the physical optics shaped reflector design method is applied to an upper portion of the reflector. By defining the boundary shape of the reflector on the cone with a horn as the vertex and the flare angle from the horn axis constant, the control of the illumination level over the entire reflector edge is low and uniform regardless of the polarization, thereby improving the sidelobe characteristics. The measured radiation characteristics of the test antenna are extremely good so that the validity and effectiveness of the present antenna design are proven. The measured values include the simulated experimental results in the case where rain drops are attached to the radome.
Spherical array antenna using digital beamforming techniques for mobile satellite communications
Authors: Chujo Wataru , Kashiki Kanshiro
Published: July 2007

Problems arise in providing excitation phases and amplitudes to individual antenna elements for wide‐angle scanning by applying spherical array antennas for mobile satellite communications for ships, automobiles, and aircraft. These antennas do not have many antenna elements. Thus, emphasis is on obtaining the maximum gain rather than realizing the characteristics of low sidelobe levels.

This paper considers the application of spherical arrays for antennas of mobile satellite communications. An adoption of a control method is assumed which regulates the phases and amplitudes freely and accurately for individual antenna elements for the beamforming circuits of digital beamforming antennas. A beamforming method is examined for spherical arrays.

First, a selection of necessary antenna elements is proposed utilizing the received signals and an adjustment of their phases and amplitudes. This method is applied to a 16‐element spherical array which had circular micro‐strip antennas. Their radiation characteristics are calculated. As a result, it was clarified that the maximum directive gain could be obtained almost without being influenced by the properties of individual antenna elements.

Next, circuits are designed for the reception of binary PSK signals of constant envelope modulated waves. Carrier recovery circuits are established for individual antenna elements for spherical arrays, and a method is used to detect their phases and amplitudes. The method shows the effectiveness in obtaining the amount of gain reduction due to the detected phase and amplitude errors.
Abstraction and control of transport network resources for intelligent networks
Authors: Esaki Shuji , Omiya Tomoki , Shigematsus Naoki
Published: July 2007

The intelligent network (IN) is expected to play an important role in rapidly and efficiently introducing new telecommunication services. This, paper discusses the abstraction and control methods for constructing a service control environment in the intelligent network which does not depend on specific service. By using this method, a real network configuration is abstracted into several patterns, considering the control points required by each service specification and each pattern can be described as a combination of functional virtualized resources.

It is made possible to handle the diversified service specifications in a unified way which is independent of detailed conditions of the transport network. It is made possible also to ensure the service independency of the control interface specifying the interface by control of each virtualized resources. Moreover, a model for the call control is proposed and the function assignment in introducing IN into existing network is discussed.
Analysis of common‐channel signaling network congestion in the presence of considering various kinds of delay
Authors: Ohta Masataka
Published: July 2007

Common channel signaling networks play an important role in providing advanced switching services. With the increase in the degree of the reliability of such switching services on common channel signaling networks, the common channel signaling networks are easily congested, and controlling congestion on these networks has become increasingly important. On the other hand, the network scale has been increasing with the development of the information society. With the increase in the network scale, signal transmission delay and control signal delay have increased, giving adverse effects on congestion control. In this article, the congestion control on common channel signaling networks recommended by CCITT has been analyzed considering the above‐said transmission delay and control signal delay. As a result of this analysis, the above‐said adverse effects could be evaluated quantitatively. A rigorous solution of this model could not be obtained. Thus, a method of analysis by fluid approximation is proposed. In addition, this approximating analytical method is shown to have sufficient practical accuracy in comparison with simulation results. By this analytical method, the rates of blocking of congested resources (signal links, circuits), mean delays, etc., can be easily obtained. As a result of the analysis, it is shown that these delays greatly influence the efficiency of congestion control. Especially, it is shown that the call loss rate shows a great effect; and control parameters must be determined considering these delays in order to satisfy certain standard values by congestion control.
FD‐TD analysis of power loss distribution in a human body model heated by a waveguide applicator
Authors: Araki Noriyuki , Morita Nagayoshi
Published: July 2007

Three‐dimensional power loss distributions generated inside the human body by the electromagnetic irradiation from a waveguide‐type applicator are analyzed using the finite‐difference time‐domain (FD‐TD) method. To execute the three‐dimensional FD‐TD analysis with a small amount of computation, only a limited small muscular region representing a part of the human body near the waveguide aperture is employed in the analysis region. In this case, the external boundaries of the analysis region are located in the human body which is composed mostly of lossy media. Thus, the conventional absorbing boundary conditions often are not applied effectively.

In this paper, new absorbing boundary conditions are proposed so that the FD‐TD analysis can be executed as accurately as possible even if the external boundaries of the analysis region are located in lossy media. The waveguide‐type applicator, with which the human body is heated, is assumed to be filled with water and the radiated electromagnetic wave is assumed to be excited by the electric current on a post. To represent the electric current source on the post, the following two types of formulation method also are presented: 1) a method representing the electric current as the electric field source; and 2) the magnetic field source. Both methods are proved numerically to be valid.
Direction‐finding measurements of magnetospheric vlf chorus emissions and analysis of their generation and propagation mechanism
Authors: Hattori Katsumi , Hayakawa Masashi
Published: July 2007

Chorus is one of the most important VLF/ELF emissions in the magnetosphere, but several points are still unsolved concerning their generation and propagation mechanisms.

In this paper, the near‐equatorial direction‐finding measurements made on board a satellite are studied first and it is confirmed that the rising tone chorus (frequency of the chorus increases with time) is generated at θ (the angle between the wave normal and earth's magnetic field) ˜ 0° by the cyclotron resonance interaction with the energetic electrons.

These results support the previous theory of Helliwell. Moreover, the direction‐finding measurements of the rising tone chorus are carried out aboard the GEOS 1 satellite in the off‐equatorial regions. Their generation and propagation mechanism are studied with the help of three‐dimensional ray‐tracing computations and these results are compared with the corresponding results of OGO 5 direction‐finding measurements by Burton et al.

As a result, the observations by OGO 5 indicate that after the generation of chorus at the equator with wave‐normal direction θ0 ˜ 0°, it reaches the satellite in ducted propagation along the magnetic field line, whereas the results of GEOS 1 suggest that the waves are generated in a wider region near the equator with comparatively smaller θ0 (30° ˜ 40°, at the most 50°) and that the subsequent propagation is nonducted in the magnetosphere.

Finally, the direction finding measurements and the ray‐tracing computation are suggested to be very important in the study of generation and propagation of various emissions generated in the magnetosphere.
Prediction of mobile radio delay spread from frequency correlations
Authors: Member Shinichi Ichitsubo , Fujii Teruya
Published: July 2007

A simple method is studied for estimating the delay spread needed for understanding the transmission quality of land mobile communication by means of a narrow frequency band. There exists a certain relationship between the delay spread and the receiving level correlations of multiple waves. There is a method for estimating the delay spread by measuring the receiving level correlation of multiple waves in a relatively narrow frequency band based on the forementioned relationship. However, since the previous method is based on the relationship between the delay spread and the receiving level in the case where the delay profile is of an exponential function, there is an error in the delay spread estimated if a profile is other than the one with an exponential function.

In this paper, this error is obtained first quantitatively. Next, a new estimation method which can reduce the error is proposed. Specifically, a profile selecting‐type estimation method is proposed in which a delay profile function considered optimum is selected from the measured receiving level correlation function and the delay spread function is found based on such a delay profile function. In addition to carrying out a computer simulation of the error evaluation of the proposed method, the estimation accuracy is confirmed from the measured data of the delay spread and the receiving level in an actual propagation path. As a result, the estimation error of the average delay spread in a 50‐m section is reduced to 40 percent in the proposed method which is an improvement of about 10 percent over the previous method.
Analysis on statistical multiplexing characteristics of atm cells with voice and video inputs
Authors: Komine Takahiro , Yamada Hiroshi
Published: July 2007

In ATM networks, it is necessary to control the quality of service because a large number of traffic classes with different statistical characteristics and required quality of service is handled uniformly in these networks.

This paper evaluates the characteristics of the statistical multiplexing gain among the heterogeneous cell streams from voice and video media. It is considered that the information of picture elements that change between adjacent video frames are packetized and then transmitted into ATM networks. Therefore, when one scene finishes, all the information for the new scene appears as a sudden burst at the first frame of the next scene. This is an important characteristic of video traffic which is called scene change here.

By considering scene change, the superposed arrival process is modeled on the heterogeneous cell stream from voice and video media using the phase‐type Markov renewal process. By analyzing the queueing model with this process, the characteristics of the statistical multiplexing gain are obtained. In particular, by using numerical computation, the effect of scene change on the statistical multiplexing gain is evaluated.
A feeding technique for broadbanding and dual‐banding microstrip antenna
Authors: Sakaguchi Koichi , Hasebe Nozomu
Published: July 2007

A method for broadbanding and dual banding of the microstrip antennas (MSA) is proposed and discussed. The effect of errors at the time of fabrication of the MSA also is studied. The method described in this paper combines a transformer made of a distributed circuit with the MSA. The design consists of three steps. Since the radiating element and the transformer are separated completely by the ground plane in the present method, the technique can be applied to an MSA with an arbitrary shape without applying any fabrication on the radiating element. Broadbanding can be accomplished rather easily, and the dual‐banding can be accomplished with a slight modification in the design. The prototype stub‐loaded MSA demonstrated with a bandwidth of 1.3 percent with a VSWR ≤ 2 can be increased to 3.4 percent (2.6 times). For the dual‐banding, the separation rate of two frequencies with respect to the fundamental resonant frequency can be controlled by about 2 to 5 percent.
Time spread modulation system for digital land mobile radio communication
Authors: Sasaoka Hideichi , Kato Eiji
Published: July 2007

This paper proposes an improvement of the time‐spread modulation/demodulation system in land mobile radio communications. The following elaborations are employed in the proposed system. The quadrature modulation with fading compensation is employed to improve the spectral efficiency. The interleaving is employed to enhance the time‐spreading effect. The maximum‐likelihood estimation is employed to improve the error rate.

To demonstrate the usefulness of the proposed method, the bit‐error rate is examined by computer simulation. It is seen as a result for the four‐symbol time‐spread that Eb/N0 is approximately 12 dB and 18 dB for the bit‐error rate (BER) of 10‐2 and 10‐3, respectively. The foregoing performance is better compared to the theoretical performance for the absolute phase coherent detection QSK, with Eb/N0 being better by 2.5 dB for BER = 10‐2. It is seen also that the performance is improved by increasing the number of time‐spread symbols to 6 and 8. The proposed system also is compared to the case of the Reed‐Solomon code applied to the multivalued QAM modulation system. The difference of performances is discussed from the theoretical viewpoint.
Selective repeat type‐II hybrid fec/arq systems using concatenated codes
Authors: Miyagi Masayoshi , Niinomi Tadafusa , Sasase Iwao , Mori Shinsaku
Published: July 2007

Hybrid forward error correction/automatic‐repeat request (FEC/ARQ) systems achieve greater throughput than ARQ systems by combining forward error correction with automatic‐repeat requests. A type‐II hybrid FEC/ARQ system is capable of adapting error‐correction capacity according to varying channel conditions. Although a high throughput can be achieved in such systems by using conventional convolutional or rate compatible punctured convolutional (RCPC) codes, when the channel signal‐to‐noise ratio (SNR) Es/N0 is low, resulting throughput efficiency and mean block delay performances are unsatisfactory.

In this paper, selective repeat type‐II hybrid FEC/ARQ systems using concatenated codes are proposed to improve the throughput efficiency and mean block delay performances on channels with low SNRs. Systems using concatenated Reed‐Solomon outer codes and either rate one‐half convolutional or rate compatible convolutional (RCPC) inner codes are evaluated. The throughput efficiency and mean packet waiting and block delay times of these two types of concatenated coding systems are evaluated. A theoretical analysis and computer simulation of throughput efficiency of the proposed systems show increased performance for a wide range of Es/N0 over previous systems that use either stand‐alone rate one‐half convolutional or RCPC codes. It is also shown that the transmitter mean packet queueing delay and mean block delay times are reduced. In particular, by computer simulation, it is shown that when the traffic density is high, mean block delay times are greatly reduced by the use of RCPC inner codes.
High‐speed optical transmission systems using optical fiber amplifiers
Authors: Hagimoto Kazuo , Aoyama Koh‐Ichi
Published: July 2007

High‐speed transmission technology is accomplishing dramatic reforms due to the application of optical fiber amplifiers.

This paper reviews the high‐speed and long‐span repeater transmission which has become possible because of the application of wide‐band and low‐noise optical fiber amplifiers. Also, the device structure together with several other topics and their significance are discussed.
Redundant systems for multibeam transponder
Authors: Kondo Kimio
Published: July 2007

The multibeam transponder allows one to use a smaller ground station in satellite reception system and to make good use of the frequency band. The redundant system is important for the higher reliability of transponder, especially as the number of the beams increases.

This paper considers a redundant system for a multibeam transponder. The concept of the expected system value herein introduced takes the reliability and the transponder weight into account simultaneously. Comparing the performance of eight typical redundant configurations, the importance of the common and active redundancy is shown.