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This paper considers multiple beamforming in the transmitter and receiver in MIMO channels and discusses the weight control procedure. The first half of the paper describes the transmitter and receiver weight conditions for realizing large capacity, for the cases with and without interference signals from other users. The second half proposes a weight control method which can realize high capacity in a real environment. In the proposed system, the control signal is exchanged between the transmitter and the receiver and the transmitter and receiver weights are determined. Using the proposed method, a satisfactory transmission weight can be determined even if the transmitter does not know the propagation information. As a result of simulation, we see that the proposed method is less affected by the propagation path and can assure stable throughput. We also find that the proposed method can achieve high throughput even if a control error occurs. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(6): 55–70, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20145 [ABSTRACT FROM AUTHOR]

In this paper, a typical mobile communication environment is assumed and the eigenvalue distributions of the correlation matrix of a MIMO channel with the spatial correlation of the multipath taken into account are studied by simulation. Based on this study, a simple method is proposed for accurately deriving the probability distribu- tion of the largest eigenvalue of the correlation matrix. The proposed approximation equation is compared with simu- lation results and good agreement is obtained. In order to understand the information transmission capability of MIMO in a multipath fading environment with spatial correlation, the proposed equation is used for studying the effect of the spatial correlation on channel capacity. Finally, the digital transmission characteristics (relationship be- tween the BER and the CNR) with correlation taken into account are obtained. [ABSTRACT FROM AUTHOR]

In radio wave propagation and wireless communication fields, it is known that rainfall attenuation (or rainfall intensity) in an area with small reception power or time ratio under a fading environment can be well approximated by a Gamma distribution (Nakagami-m distribution). To investigate the selection diversity method, a joint probability function that takes correlation into consideration for multiple random variables must be used to quantitatively evaluate its results. In this paper, the authors derive an exact representation according to an infinite series for a general multivariate (M-dimensional) Gamma distribution function with correlation. In addition, besides investigating the numerical behavior of the exact representation, they obtain an extremely effective approximate representation for practical use. That approximation, which is a revision of the probability distribution with no correlation according to the determinant of a matrix having the square roots of the correlation coefficients as its elements, not only is easy to handle, but also provides an excellent physical interpretation. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(8): 1–12, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10224 [ABSTRACT FROM AUTHOR]

As a remedy to multipath fading in land mobile communication, adaptive antenna arrays combined with equalizers have been proposed. For hardware realization and adaptive algorithm development in order to alleviate fading by temporal and spatial processing, it is necessary to clarify the spatiotemporal characteristics of the propagation channel such as the delay time and direction of arrival of multipath waves. In a microcell using a low antenna-height base station, the spatiotemporal propagation characteristics are measured for line-of-sight and non-line-of-sight propagation at 3.35 GHz. Characteristics of these channels have been presented. With regard to non-line-of-sight propagation, the measured spatiotemporal characteristics are modeled and the angular spread and the delay spread of the arriving waves are quantitatively evaluated. Also, when the transmission characteristics of fading prevention techniques by spatiotemporal processing are evaluated by computer simulation, an example of the delay-azimuth profiles that is usable as a reference for setting the conditions for fading is presented. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(7): 11–21, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10032 [ABSTRACT FROM AUTHOR]

This paper considers the propagation model in which the amplitude of the direct wave is kept constant and that of the indirect wave exhibits Rayleigh fluctuations in the line-of-sight and non-line-of-sight channels. The instantaneous received signal level distribution is examined by computer simulation and a fading simululator, with the equivalent received bandwidth (product of received bandwidth 2Δf and maximum path length difference ΔLmax) as the propagation parameter. It is seen that the equivalent received bandwidth is suited as a parameter to represent the instantaneous received signal level distribution. The instantaneous received signal level distributions derived by the computer simulation and the fading simulator agree well. Conventional narrow-band transmission corresponds to the case in which 2ΔfΔLmax is less than 10 MHz-m. Then, the fading depth is determined by the power ratio a between the direct wave and the indirect wave. Wide-band transmission corresponds to the case in which 2ΔfΔLmax is larger than 10-MHz-m. Then, the fading depth is determined by a and 2ΔfΔLmax, becoming less when those quantities are increased. When 2ΔfΔLmax is very large, the fading depth also depends on the number of arriving waves. These properties are derived theoretically and are verified by the simulation and the fading simulator. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(2): 94–105, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1157 [ABSTRACT FROM AUTHOR]

For design of optimum microcells on a university campus, it is necessary to determine the propagation characteristics within a propagation environment represented by a relatively large open space scattered with large buildings and many trees. In this paper, for the radiated waves from seven PHS base sites at 1.9 GHz experimentally installed on the campus of Hokkaido University from 1993 to 1994, a median received signal level measurement method is proposed that can be applied in unpaved garden areas (with glass and pebbles) as well as in areas with woods, vegetation, and hilly terrain, and its effectiveness is discussed. Next, for quantitative evaluations of the increase of the propagation loss due to trees in the propagation paths on the campus, a propagation model is proposed that consists of the loss layer model and the geometrical optics two-ray model. In the loss layer model, the loss due to trees is replaced with a loss per unit length of the propagation path. The estimated median received signal level and the measured value are compared to determine the effectiveness of the model. The increase of the propagation loss on the campus due to trees can be estimated if the loss per unit length of the tree layer by the present loss layer model is chosen to be about 0.1 dB/m for the base site antenna installed on the rooftop of the building and 0.07 to 0.09 dB/m for the antenna installed on the roof of the public phone box. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(8): 49–61, 2001 [ABSTRACT FROM AUTHOR]

The measured results and the results of analysis by the ray tracing method in a real tunnel are compared. The propagation characteristics considering the radiation pattern of an antenna placed inside the tunnel are estimated. By comparison of the measured and analyzed results, the effectiveness and validity of the ray tracing method are shown. The propagation loss and fading in the tunnel are discussed. Further, the propagation characteristic is estimated by considering the radiation pattern of the base station antenna for the tunnel booster system. The analysis demonstrates that the dual radiation pattern is effective for the base station antenna. The variation of the covered area when the radiation pattern is varied is studied. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(4): 1–10, 2001 [ABSTRACT FROM AUTHOR]

There is no clear design guide for fixed wireless links for instrumentation in office buildings. In fact, there are no quantitative data for the propagation and fading characteristics to be utilized in link design. This article intends to provide a design guide for intermittent communication links for instrumentation in office buildings. The approach is as follows. The case where only instantaneous variation with time exists is considered. The receiver power level required to satisfy the specified transmission quality is determined. The variation of the central value depending on the site is represented as a function of the distance between the transmitter and the receiver. By superposing the variation of the central value of the site on the specified distance and variation of the instantaneous value, the zone periphery outage probability is derived, based on the case where the required transmission quality is not maintained. Then, a design guide based on the communication distance is proposed so that the outage probability is kept below the specified value. The communication completion rate is measured quantitatively by a long-term check of communication incompletion cases. The propagation characteristics of electromagnetic waves are measured for the 400-MHz band in an actual office environment. It is shown by experiments that the variation of the received power level follows the Rayleigh distribution and the distance attenuation follows an exponential function, as in a waveguide. Design of a link is attempted for an air-conditioner wireless telecontrol system, using the proposed communication distance estimation based on coefficients determined by experiment. The communicable distance is estimated as 21 m on the same floor with a seven-fold code redundant selective SD antenna. It is estimated that the required transmission quality cannot be realized in communication to adjacent floors. The communicable distance is estimated as up to 14 on in the same floor by the selective SD antenna, when the seven-fold extended code is not used. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(8): 42–52, 2000 [ABSTRACT FROM AUTHOR]

A method of estimating the refractive index distribution is suggested from the height gain profile of the received electric field strength which is generated due to the inverted atmosphere as a surface-based duct or an elevated duct. First, an initial value of the refractive index distribution is given by applying the height gain profile at one spot to the wave equation. Next, the height gain profile at another spot is derived from both the received electric field and this refractive index by the split-step method, and the refractive index distribution is modified by comparing it with the height gain profile measured at the spot. The bilinear model and 2n power N profile model are adopted as the atmospheric models to evaluate the method of estimating this refractive index, and numerical examples of the refractive index distribution to be derived from the altitude distribution of the received electric field with each model are presented, and are considered simultaneously. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(7): 40–49, 2000 [ABSTRACT FROM AUTHOR]

The problem of electromagnetic wave propagation in a two-dimensional tunnel with an arbitrary bending angle is numerically analyzed by the FVTD method. The FVTD representations for the electromagnetic field in a lossy medium and the PML absorbing boundary condition are formulated and a procedure for the numerical analysis of the two-dimensional tunnel is provided. Next, as specific numerical examples, the electromagnetic propagation characteristics near the bend of tunnels with bending angles of 30°, 45°, and 60° are computed. It is confirmed that the results agree well with those of the model experiment using microwaves. Detailed numerical calculations are performed for the case in which the width of the tunnel is much larger than the wavelength. In this way, the propagation characteristics are predicted for an electromagnetic wave in the mobile communication frequency band, used inside a tunnel. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(9): 1–9, 1999 [ABSTRACT FROM AUTHOR]

Recently, the downsizing of portable radio equipment has been progressing, and wristwatch portable radio equipment is now available. The antenna for such equipment is highly affected by the human body, but a slot antenna can positively utilize the body effect. This paper proposes a small slot antenna installed in the band of a wristwatch-type pager. The radiation characteristics were measured and calculated for cylindrical and flat shapes. The peak gain was –13 dBd for a cylindrical slot antenna (peak gain for a flat slot was –22 dBd). The effect of curvature of the cylindrical antenna element was also studied. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(9): 30–38, 1999 [ABSTRACT FROM AUTHOR]

In parabolic antennas with a defocused primary radiator, performance degradation, such as gain degradation and increased sidelobe levels, arises due to aberration in the aperture. In this paper, the aberration produced in the aperture is determined by beam mode expansion, and it is shown that various aberrations can be represented by simple expressions by considering the dominant beam mode. Using the derived expression for the aberrations, a formula for the beam deflection characteristics is derived for the co-polarization component by the aperture distribution method. A simple expression is derived for the gain degradation under the condition that F/D is large and the edge level is low. The result obtained by the proposed method is compared by numerical examples to that of the strict current distribution method, and the validity of the proposed method is demonstrated. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(9): 39–50, 1999 [ABSTRACT FROM AUTHOR]

In a low-antenna-height line-of-sight (LOS) microcell, the delay spread characteristic strongly depends on the road shape, the location of the transmitting and receiving points, and so on. To analyze this propagation mechanism, it is necessary to deal with location-specific properties. This paper describes analyzed results for the multipath delay mechanism in a rectilinear street with intersections where both transmitting and receiving stations exist. Special focus is placed on reflection at LOS building walls and on diffraction at building corners at street intersections, and their effect as a factor creating multipath delay is investigated numerically. We show that waves created by their reflection and/or diffraction are significant multipath delays making a major contribution to delay spread in microcells. This paper also presents a comparison between the calculated and measured delay spread, and discusses the effectiveness of the propagation mechanism described. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(4): 56–70, 1999 [ABSTRACT FROM AUTHOR]

One of the typical error control schemes used in data transmission systems is the selective-repeat ARQ. Previously, the transmission delay for this scheme has been analyzed mostly for an independent error channel. In practice, however, the state of the channel varies with time so that error generation is not independent. This paper considers a non-independent error channel and analyzes transmission delay performance for a selective-repeat ARQ scheme. An error model is used in which the change of the channel state is represented as a 2-state Markov chain. A strict analysis is applied using a discrete-time queuing system and the transmission delay distribution for the frame is derived. When the round-trip propagation delay or the frame queue length is increased, however, a large amount of computation is required in order to obtain the numerical result due to enlargement of the state space. In order to simplify the numerical calculation we give an approximate analysis for the case where the propagation delay or the frame queue length is increased. The average transmission delay is discussed based on numerical examples. As a result, we show that the average transmission delay performance is significantly improved when the decay factor of the Markov chain approaches zero from positive values. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(6): 31–41, 1998 [ABSTRACT FROM AUTHOR]

In magnetosphere propagation of very low latitude whistlers occurring at geomagnetic latitudes around 10 degrees, both duct propagation and nonduct propagation are conjectured as propagation mechanisms. The conjecture for nonduct propagation is based on the fact that the enhancement factor that is needed in duct propagation reaches several hundred percent at very low latitudes and thus duct propagation is hardly conceivable. The conjecture for the duct propagation is mostly based on observation of echo train whistlers, which must be generated by reverberating propagation along the same path. From this perspective, the possibility of echo train whistler generation by nonduct propagation is investigated using three-dimensional ray tracing based on the night electron density model and the IGRF magnetic field model for very low latitudes. We show that echo train whistlers can be generated by considering not only vertical emission but also conical emission angle within a 3° emission angle to the ionosphere. It is also shown that nonduct propagation can be transmitted downward through the ionosphere over a wide frequency range and that the point of downward transmission through the ionosphere depends less on the frequency. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(6): 42–50, 1998 [ABSTRACT FROM AUTHOR]

The fundamental characteristics of signals reflected from objects buried in the ground were measured with a CW radar system. In this measurement system, the reflected signals from buried objects are detected synchronously so that the measurement of amplitude and phase of the reflected signals is possible. From the results of measurement, it was found that the reflected power from buried objects is almost proportional to the minus fourth power of the equivalent distance and that the phase variation agrees almost with the result anticipated from Snell's law under a plane wave approximation. From these observations, it is found that the measurement of the reflected signals from buried objects is possible with a CW radar system, and that underground remote sensing also is possible. [ABSTRACT FROM AUTHOR]

This paper theoretically analyzes the effect of an inverted atmospheric layer, nonuniform in the lateral direction, on wave propagation by means of the coupled mode theory. A grounded duct, an inverted atmospheric model, was employed in which a 2n power N profile (height) is located under standard atmosphere and the lowest layer with a linear profile. In terms of distance, the depth of the lowest layer is assumed to vary slowly with distance. The nonuniform atmosphere varying continuously in the distance is replaced by a staircase approximation. Numerical examples are given for the coupling coefficient of the neighboring atmospheres. The coupled mode becomes maximum immediately before the trapping mode and the mode conversion is more conspicuous for a larger n. The spatial distributions of the propagation characteristics are shown in the nonuniform duct made of uniform, nonuniform, and uniform sections in the distance direction. It was found that the variation of the received electric field changes significantly according to the change in duct height in the distance direction and that the effect of the order n is extremely significant. [ABSTRACT FROM AUTHOR]

To obtain a matching over a wide frequency range, pyramid-type and wedge-type matching layers are used in front of the multilayered wave absorbers. In this paper, a transmission mode approximation is proposed in which the period of the wedges and the incident polarization direction are taken into account in the calculation of the characteristics of a wedge-type wave absorber. The degree of difference of the equivalent permittivity derived by the propagation mode approximation from the one by the conventional method (corresponding to the low-frequency limit) is presented by numerical calculations. It is also shown that there is a difference from the wave absorber characteristics derived by the conventional method even at a wavelength longer than the wedge period. The tendency of the reflection to increase at the higher frequency side is visually explained by replacing it with the taper shape. [ABSTRACT FROM AUTHOR]

To resolve the problem of electromagnetic interference generated at the actual configuration of electronic equipment by a radiated interference wave, it is desirable to establish a technique to estimate the radiated interference of electronic equipment. This paper discusses a method for estimating the radiated interference in actual configuration from the measured radiated interference at the test site of the electronic equipment. In the proposed estimation method, a simulated source of the electronic equipment is used for deriving the deviation (conversion coefficient) of the wave propagation characteristics of the test site and the actual configuration. By means of this conversion coefficient, the radiated interference in actual configuration is estimated from the radiated interference at the test site. An estimation method is shown in the case where a spherical dipole antenna is used as a simulation source of the electronic equipment. When the effectiveness of the estimation method was verified experimentally with actual electronic equipment, it was found that the radiated interference in the actual configuration can be estimated with accuracy of 4 to 5 dB at the frequencies of 30 to 300 MHz. [ABSTRACT FROM AUTHOR]

In the area of mobile communications, there has been increasing demand and development for new technologies and services such as digitalization and personalization. With this as background, this paper studies the use of adaptive antenna technology for mobile communication. In the area of mobile communications, the adaptive antenna technology has been studied with a view to reducing the fading for reception by the mobile station. In the case of microcells and indoor communication for which an expanded use is anticipated, arrivals of multiple waves tram various directions are expected even for the base station so that the application of the adaptive antennas to the base stations is effective. In the case of high-speed data transmission such as wireless local wireless networks (LAN), further reduction of fading and interference is required. Also, the frequency sharing among different radio services is an area in which the adaptive antenna is useful. Introductions of dynamic control of the systems are expected for mobile communications in time, space, and frequency domains. The adaptive antenna is effective for control in space. The dynamic zone configuration will he a new application area in which, depending on the distributions of the users, the zone shape is varied. [ABSTRACT FROM AUTHOR]

To understand the propagation structure of the microcells with a tall and medium-height antenna in an urban area, the fundamental propagation parameters are found and the structural model of the propagation loss was constructed. The fundamental propagation parameters were obtained based on the multivariable analysis of the propagation data at 800 MHz measured m the Tokyo Metropolitan area. These parameters are the distance between the transmitter and receiver, the average building height between the transmitter and receiver, and the base-station height which have high correlation and regression coefficients with the propagation loss. The relationship of parameters obtained from the model is (20 - α) log(h) for the base-station height characteristics and (α - 20) log (H) for the building height characteristics if the distance characteristics are α log (d). The relationships of coefficients of the conventional estimation equation and the regression equation obtained by the measured data almost agreed with those of the model so that the validity of the model was confirmed. [ABSTRACT FROM AUTHOR]

A case exists in which cancellation of interference is not possible with an interference canceler which cancels the interference wave from ground radio stations mixing into the ground station for the satellite communication. It is found experimentally that this is caused by the difference in the frequency characteristics of the input signals to the two antennas by the multipath effects. Further, a method is proposed to discriminate whether the arriving interferences can be cancelled. Its effectiveness is confirmed experimentally. Whether or riot the interferences can be cancelled can be determined by the amount of variation of the received electric field intensity of the interferences. If there is a signal with a constant-shaped spectrum, the distortion of the shape can be used for discrimination. As a result, the condition and limit of applications of the interference canceler are found. [ABSTRACT FROM AUTHOR]

This paper describes the results of the radio propagation experiment between an aircraft or a ship and a ground earth station by means of the Engineering Test Satellite V (ETS-V) as a part of the navigation experiment program which is aimed at developing the technology for utilizing a satellite for navigation assistance by a ship and for control of an aircraft of the ocean. First, the antenna on a moving vehicle is summarized. Next, the experimental results with each moving vehicle are described with regard to the magnitude and the periodicity of the received signal level. The results were analyzed and the cause of the level variation was found in some cases. The magnitude of the variation of the signal level (fading range) was about 6 dB at the maximum for the elevation angle of the satellite from 45° to less than 10° in the case of the experiment with an aircraft. In the case of a ship, the magnitude increased with a decreasing satellite elevation angle. In the case of a one-element antenna with a gain of 6 dBi, the magnitude of variation was more than 10 dB at an elevation angle of 10°. The periodicity of the variation was investigated by deriving the frequency components by means of the Fourier transform. In most cases for an aircraft, no remarkable frequency characteristic was observed and the spectrum was flat at the frequency range of less than 25 Hz. On the other hand, in the case of a ship, the components less than 1 Hz are predominant at a low satellite elevation angle. Hence, it is clear that the nature of the reflection is different in the aircraft and the ship. For the latter, the reflection from the ocean surface is predominant. [ABSTRACT FROM AUTHOR]

This paper derives an estimating equation for the received power space-correlation coefficient needed for the design of a space diversity receiving system for improved transmission performance of a microwave relay system as a semiempirical equation based on the theoretical investigation, with corrections by measured data, from a three-ray model in which the received wave consists of the direct wave, reflected wave, and duct refractive wave. This equation is determined from the amplitude statistics of the three waves, the propagation conditions such as the distance and the transmitter and receiver heights, the frequency and the radio meteorological statistics. This model contains the two-ray model method intended for propagation path with a strong reflection (strong reflection link) and the Makino-Morita method which assumes Rayleigh fading for a propagation path with a weak reflection (weak reflection link). The measured results of the spatial-correlation coefficient of the received power in about 30 links measured in Japan, including both the strong and weak reflection links, are found to agree well with the estimated values based on the present equation. Hence, the effectiveness of the estimation equation proposed in this paper is confirmed. [ABSTRACT FROM AUTHOR]

This paper describes the estimation of the propagation loss in an urban environment important for channel design of land mobile communication. Conventional methods for intimating the propagation loss in an urban environment gives a representative value of the propagation loss in the urban environment or the propagation loss (median value) within a 500 m ×800 m area obtained by introducing an area factor of occupied buildings. Such a method is not suitable for estimation of the propagation loss depending on the situation near the mobile station. In this paper, the relationship of the measured data of the propagation loss in the Tokyo Metropolitan area at 813 and 1433 MHz with the urban environment parameters such as the base station antenna height, distance, frequency, width of the street where the mobile station exists, direction, average building height, building height on the street side is derived by the multiple regression analysis method. A prediction formula for the propagation loss (median value in the section of about 80 m) including these parameters is derived. The parameter dependencies of the propagation loss, such as the antenna height dependence and the average building height dependence, are described. In addition, the distance dependencies of the propagation loss in this prediction formula and conventional method are compared with the measured values. The prediction formula is expressed in terms of the sum of simple functions of the foregoing parameters. Hence, the estimation of the propagation loss can be carried out easily, taking into consideration the urban environments such as the height of the buildings and width of the streets. [ABSTRACT FROM AUTHOR]

In this paper, propagation delay measurements were carried out in Tokyo (metropolitan urban area) where high rises and other buildings are concentrated on a plane and in Kofu (urban area adjacent to mountains) surrounded by tall mountains. The delay characteristics such as delay spread and wave numbers were found. The principal results obtained in these areas are as follows: (1) In a metropolitan urban area, i.e., Tokyo, (a) the average delay spread in a high-density residential district is less than about 1 µs and the delay profile consists of a group of direct waves arriving directly from the base station; and (b) the average delay spread in a location with high-rise buildings is also less than 1 µs and the average number of arriving waves is about five with the delay profile consisting of a direct wave group and a reflected wave group from reflecting object. (2) In an urban area adjacent to mountains, i.e., Kofu, the average delay spread is less than about 2 µs and the average number of arriving waves is four. The delay profile consists of a direct wave group and a reflected wave group. The level of the reflected wave group decreases exponentially with the delay time in the case of reflection from buildings, while the level is almost constant within a certain range of delay time and is of a spread shape (rectangular) in the case of reflection from mountains. From these measured results, a simple propagation model consisting of a direct wave group and a reflected wave group is proposed. It is shown that the distance dependence of the delay spread has a peak between the base station and a reflecting object. [ABSTRACT FROM AUTHOR]

A method of formulation based on the boundary element method is provided for the electromagnetic field in a two-dimensional impedance tunnel with partition walls excited by the fundamental mode. The impedance boundary condition used often for the analysis of the electromagnetic scattering problem from a lossy dielectric and of the wave propagation in a tunnel is based on the characteristic impedance for an infinitely thick medium. Since there is no provision on the transmitted wave behind the dielectric plate, this boundary condition cannot be applied directly if the dielectric plate used is thinner than the skin depth. This paper derives first a new boundary condition in which the values of the electro-magnetic field in the region opposite to the wall surface are considered. in the case of a plane wave (TE wave) incidence on an infinitely wide than dielectric plate, the computed values by the boundary element method with the new boundary condition are compared with the rigorous solutions. It is found that the results agree with each other for both the reflection and transmission coefficients so that the impedance boundary condition introduced here can be used as the boundary condition for a thin dielectric plate. Further, assuming a tunnel with a thin partition wall, we carried out a micro-wave simulation experiment with a Bakelite plate so that the validity and usefulness of the present method are confirmed. [ABSTRACT FROM AUTHOR]

In mobile satellite communications with a wide service area, the largest problems in composing the system are the Rician fading, where the direct wave component and the random time-varying scattered wave component interfere with each other, as well as the low received power due to the propagation for a long distance. This paper considers diversity as a means to overcome these problems. The four-phase DPSK system is considered, and a theoretical analysis is made on the error rate improvement by the post-detection combining diversity. The characteristic functions of two orthogonal delayed detection outputs of the branches are used in the derivation of the error rate. Three communication systems of satellite/aircraft, satellite/land mobile and satellite/ship are considered as the models. Theoretical expressions are derived to evaluate the improvements. The error rate is also evaluated for the selective diversity. The result is compared with the case of combining diversity, together with the discussion for the difference between the two schemes. [ABSTRACT FROM AUTHOR]

Satellite communication has the following problems. The propagation delay is larger than in the terrestrial channel. When the carrier frequency exceeds 10 GHz, the bit-error rate tends to increase due to the effect of rain and snow, which degrades the transmission efficiency. To cope with such problems, a highly efficient error control protocol has been proposed to prevent the degradation of the transmission efficiency. This paper describes a new large- capacity, highly efficient retransmission scheme for satellite communication (extended SREJ scheme), which was devised considering the compatibility to the terrestrial network. The method is based on the SREJ (selective reject) scheme, which is specified in the HDLC (high-level data link control) protocol, employed widely in terrestrial data transmission. To evaluate quantitatively REJ, SREJ and extended SREJ schemes, a satellite communication control equipment was developed. The result of the data transmission experiment is described in detail, indicating that the extended SREJ scheme is efficient. Then, through the discussion of practical usefulness, it is shown that the extended SREJ scheme has no problem from the viewpoint of the number of buffers in transmitting and receiving stations. Further- more, to realize the efficient processing as far as possible, even if the bit-error rate is higher than 1.0 × 10-4, the extended SREJ/REJ scheme is discussed by combining the proposed scheme with the REJ scheme. [ABSTRACT FROM AUTHOR]

The performances (throughput and transmission delay) of the Co-back-N ARQ scheme are affected greatly by the bit error rate of the link and the round-trip propagation delay. This paper discusses the transmission delay of the tandem Co-back-N scheme, in which the round-trip propagation delay can substantially be reduced. First, the generating function for the transmission delay distribution is derived, and then the result is applied to derive the average transmission delay. As a result, it is shown clearly that the performance of the tandem Co-back-N ARQ scheme is better than that of the standard Co-back-N ARQ scheme. [ABSTRACT FROM AUTHOR]

As a model for the electromagnetic wave propagation in a tunnel-shaped structure with branches and bends such as an under- ground shopping center and a street lined with buildings, a two-dimensional tunnel with modified multi cross junctions is studied both theoretically and experimentally for wave propagation. The basis of the theoretical analysis is to neglect the higher- order multiple scattering effect and to consider the field as the cascaded connection of the results of the modified single-cross junction. As the boundary condition of the tunnel wall, the surface impedance approximation is employed. The present results can be applied to special tunnels made of cascaded connection of the modified cross, step and 1. In the experiment, a microwave simulation is carried out for a tunnel model made of concrete. It is found that the numerical results of the electric field intensity in the tunnel agree well with the experimental results. [ABSTRACT FROM AUTHOR]

This paper investigates theoretically and experimentally the electromagnetic wave propagation in a two-dimensional tunnel with a modified cross-junction in connection with radio communications in tunnels, underground, urban areas with high-rise buildings and others. Modal expansions and Fourier transform are used as an analytical method, and the surface impedance model is employed as a boundary condition on the tunnel walls. The results presented here can be applied to special tunnels such as the T-type, modified T-type, L-type and step-type. Experiments based on a microwave simulation are performed by using tunnels composed of concrete slabs. It is found that, concerning electric field intensity, experimental and theoretical results agree well. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of delay propagation in the mutually synchronized network using completely digital PLL. A difference equation is derived with the rise- time differences among nodes as the variables. The dynamical properties of the mutually synchronized network including the propagation delay, the steady-state and the jitter characteristic are derived. As a result, the following properties are demonstrated. When the delay is less than half of the steady-state period, the dynamical property and the jitter of the network are the same as those of the network, without delay. However, when it is larger than the half-period, the dynamical property and the Jitter of the network are affected by the delay. It is also shown that the Jitter suppression of the N-node mutually synchronized network is approximately proportional to the number of nodes N. [ABSTRACT FROM AUTHOR]

A propagation study has been conducted for horizontal and vertical polarization inside buildings in residential areas and in business districts with tail 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 wav 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. [ABSTRACT FROM AUTHOR]

This paper proposes a prediction method for cross-polarization discrimination (XPD) during multipath fading on line-of-sight propagation paths that encounter strong surface-reflected waves. This prediction method is required for the design of radio relay systems. First, the so-called C parameter has been used widely to predict XPD but without any clear physical explanation. It is equivalent to the mean-squared value of the cross polar component of received power during deep fading, when the fade depth is 10 dB or larger, if the cross-polar component is normalized to the co-polar component of the received power during normal (i.e., nonfading) conditions. A two-ray interference and direct-wave depression (i.e., mean-value depression) model was developed. This model predicts the value of the C parameter by using such propagation path conditions as the separation angle between the direct and reflected waves and antenna directivity pattern. Finally, this prediction method was found to be fairly accurate by comparison of predicted values with XPD data, obtained from propagation paths with strongly reflected waves. [ABSTRACT FROM AUTHOR]

The Mode-Matching Method has been known as an accurate and reliable method for numerical analysis not only on the diffraction problem in the electromagnetic field, but also on the elastic waveguide and the optical thin-film waveguide. This method is applied for the rigorous analysis of an elliptically-cored optical fiber with large ellipticity whose accurate analysis in the wide range of frequency including the cutoff has so far been difficult. Moreover, a very high degree of accuracy of five figures is achieved for the normalized propagation constant. Both the dispersion relation and the field distribution in the hybrid modes are clarified and it is also confirmed that the hybrid mode analysis is not always necessary in the case analysis is not always necessary in the case of larger ellipticity. The properties of the high-order mode cutoff and the polarization preservation whose rigorous discussion has not been always sufficient, are analyzed more accurately. The results compared with the results obtained by other methods, and more exact design data for the single mode, polarization-preserved optical fiber with elliptical core are presented. Through these analyses, it is also confirmed that the Mode-Matching Method is still a useful and reliable method for rigorous analysis of the rod-type dielectric waveguide with arbitrarily shaped cross section. [ABSTRACT FROM AUTHOR]

This paper presents an analysis method for the maximum throughput of the window controlled data link under the effect of the propagation delays. The data link is divided into two submodels, and each stochastic process is analyzed independently and the results are integrated. The Calculation by this method is simpler than that by the direct analysis, and highly, accurate evaluation can be made for comparatively general frame length distribution. It is shown that this approach provides very good approximation, especially for the throughput efficiency ranging from 0.7 to 1.0. The region satisfying certain thoughtput value is derived and effective way of selecting the value of window size is presented. [ABSTRACT FROM AUTHOR]