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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]

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]

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]

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]

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]

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]