A propagation model for urban microcellular systems at the UHF band

This paper presents a new propagation model for urban environments, which takes into account propagation over buildings and inside streets. The formulation for multiple diffraction loss over rooftops results from a combination of the Vogler (1982) and Xia and Bertoni (1992) models, which enables its application to profiles of buildings with nonuniform heights and spacings, keeping the calculation time low. A ray-tracing tool based on the image method and on the uniform theory of diffraction (UTD) has been developed to estimate the attenuation inside streets; loss introduced by vegetation is also accounted for. The results obtained with the application of the model to two areas of Lisbon show the importance of rays conducted by transversal streets and diffracted by vertical edges when predicting the signal near crossroads. Average values of 3.5 dB, -0.07 dB, and 2.6 dB were obtained for the mean absolute and relative errors and for the standard deviation error, respectively     

The effect of terrain on radio propagation in urban microcells

A model based on the geometrical theory of diffraction is proposed for predicting radio propagation in urban microcells in the presence of undulating terrain. Comparisons with data show that the model is appropriate for predicting shadowing by terrain, but the effect of terrain fluctuations which do not obscure the line of sight is smaller than the model predicts. It is also shown that the presence of buildings lining the streets, while causing considerable variations over short distances, has only a small effect on the large-scale trend of the average signal     

Prediction of cellular characteristics for various urbanenvironments

The propagation channel for UHF/X-band waves in the city is modeled for two typical cases in the urban scene: (a) by regularly distributed rows of buildings placed on a flat terrain; and (b) by an array of randomly distributed buildings placed on rough terrain. The law of distribution of buildings in both cases is assumed to be Poisson. The loss characteristics in such urban propagation channels, as well as the co-channel interference parameter, the carrier-to-interference ratio (C/I), are investigated. In case (a), the three-dimensional multi-slit waveguide model is used for LOS conditions, and the two-dimensional multi-diffraction model is used for NLOS conditions. In case (b), the statistical parametric model of wave propagation is used, including single and multiple scattering effects, diffraction from buildings' roofs, the actual built-up relief, and various positions of receiver and transmitter antennas on rough terrain. The full algorithm for predicting propagation and cellular characteristics to increase the accuracy of radio and cellular maps is presented     

A prediction model for multipath propagation of pulse signals at VHF and UHF over irregular terrain

A prediction model is presented that permits calculation of the probability of occurrence of distinct multipath propagation of pulse signals at VHF and UHF over irregular terrain. The model applies to terrain characterized by an irregular distribution of obstacles such as hills, buildings, trees, etc., so as to make it impractical to calculate the effect of multipath propagation by diffraction or bistatic-reflection theory. Statistical data on wave propagation over irregular terrain form the basis for the empirical model developed. Generally, the model predicts that 1) for constant transmitter-receiver separation, the amplitudes of the received echoes decrease with increasing echo delay, and 2) for constant echo delay, the occurrence of echo pulses increases as the transmitter-receiver distance increases. The results obtained from the model for rural, hilly terrain, and for a built-up metropolitan area are compared with available measured data.     

Signal Power Distribution in the Azimuth, Elevation and Time Delay Domains in Urban Environments for Various Elevations of Base Station Antenna

We investigate signal power distribution in the azimuth-of-arrival, elevation-of-arrival and time-of-arrival domains for various positions of the base station antenna located below the rooftop as well as at rooftop level. This article is based on a multiparametric stochastic model we introduced in 2004, as combination of a statistical part, describing an array of buildings randomly distributed at the terrain, and a waveguide model, describing a grid of straight streets with buildings along them. Joint signal power distributions in azimuth-time delay and elevation-azimuth planes are obtained and compared to high-resolution 3-D measurements carried out in downtown Helsinki. A good agreement between theoretical predictions and the measurements is obtained basically, and also regarding the wave-guiding effect and antenna height dependencies. A satisfactory physical explanation, which accounts for the character of the specific building topography, the height and tilt of the antennas, is found. Finally, we present a numerical experiment of changing the base station antenna height, its directivity, and tilt. By this we show that the proposed stochastic approach allows to predict and control a-priori main parameters of smart antenna based only on knowledge of specific features of built-up terrain.     

A microcellular communications propagation model based on theuniform theory of diffraction and multiple image theory

Presents a comprehensive uniform theory of diffraction (UTD) propagation model for a city street grid, using the multiple image concept and the generalized Fermat's principle to describe the multiple reflections and diffractions. The model is a quasi 3D one in the sense that the building walls are assumed to be much higher than the transmitter height so that the diffractions from the rooftops can be neglected. The model includes all possible specular wall and ground reflections and corner diffractions in the main street, side streets, and parallel streets of a microcell. This enables the signal propagation through all the possible paths to be tracked to the receiver at various line-of-sight (LOS) or out-of-sight (OOS) positions. Previous papers on such propagation models have included only a limited number of specular reflections and diffractions or they are restricted to a rectilinear grid where all the building walls on each side of the street are coplanar. Our model includes contributions to the received signal from all possible propagation paths, including ground and wall reflections from diffracted and specularly reflected signals both in the LOS and OOS regions. Within the scope of the UTD model, the accuracy of our model is limited mainly by the assumptions of characterizing the building walls as “smoothed-out” flat surfaces with average relative permittivity ϵ_r and conductivity σ. Our theoretical results of the signal path loss along the streets are compared with measurements which have been reported for city streets in Tokyo and New York City     

A theory for propagation path-loss characteristics in a city-streetgrid

Presents a new propagation model for micro-cellular communications in an urban scene in which the buildings and streets form a rectangular grid. The model is a quasi-three-dimensional one in the sense that the building walls are assumed to be much higher than the transmitter height so that the diffractions from the rooftops can be neglected. It is based on the uniform theory of diffraction (UTD) and takes into account multiple reflections between wall-to-wall, wall-to-ground and ground-to-wall, as well as the diffraction from corners of buildings and also subsequent reflections from such diffracted signals. These multiple reflections and diffraction result in an extremely complex problem of tracking the wave or ray propagation. The authors use the concept of multiple images and the generalized Fermat's principle to facilitate the location of each point of reflection in a wall or ground or a point of diffraction at an edge, and to determine which of the multiply scattered rays will reach the receiver at a line-of-sight (LOS) or out-of-sight (OOS) position. The signal path loss along the LOS street, OOS side streets, as well as a street which runs parallel to the LOS street, are calculated and the general features and trends of the propagation characteristics are highlighted. Calculations are also done to study the profile of the signal distribution across a street width at various points in a OOS street     

Prediction of mobile radio wave propagation over buildings ofirregular heights and spacings

Two models of mobile radio wave propagation over buildings are presented. The first, the flat edge model, provides a simple yet accurate representation when buildings are assumed to be of constant height and spacing. The second model combines the first with a rapid new method of calculating multiple edge diffraction to allow deterministic predictions with arbitrary buildings and spacings. This allows predictions to be made with real building data, and the effect of building variations on location variability of the received signal to be assessed. Both models are compared with measurements made in suburban areas in the 900 and 1800 MHz bands and excellent agreement is obtained     

Application of the fast far-field approximation to the computationof UHF pathloss over irregular terrain

The availability of fast numerical methods has rendered the integral-equation approach suitable for practical application to radio planning and site optimization for UHF mobile radio systems. In this paper, we describe a conceptually simple scheme for the efficient computation of UHF radial propagation loss over irregular terrain, which is based on the fast far-field approximation. The method is substantially faster than conventional integral-equation (IE) solution techniques. The technique is improved by incorporating the Green's function perturbation method and we outline a way in which the formulation can be made more exact. Computational issues such as terrain profile truncation and the effect of small-scale roughness are addressed. The method has been applied to gently undulating terrain and compared to published experimental results in the 900-MHz band. It has also been successfully applied to more hilly terrain and to surfaces with buildings added     

Proposal of method for estimating received signal characteristicsin mobile communication environments

A method for estimating the received signal characteristics (MERS) is developed. The MERS aims at estimating the received power and the fading spectrum at the mobile in mobile communication environments. In MERS, these characteristics are estimated on the basis of both an angular probability density distribution (APD) of wave arrival and a radiation pattern. The APD can also be estimated under arbitrary environmental conditions in the MERS. For the estimation of the APD of wave arrival, a novel propagation model is proposed in this paper. The model consists of an environment model that represents the statistical features of the configuration of buildings along streets and a path model that represents geometrical propagation paths from a transmitting point to a receiving point on the streets. The estimated results of the received signal characteristics are compared with the measured ones. It is proved that the received power and the fading spectrum can be closely estimated     

Path Loss Predictions in Urban Areas with Irregular Terrain Topography

A method based on the parabolic wave equation is used to predict path loss in a two dimensional urban setting where buildings sprawl over irregular terrain. Propagation is assumed to take place in the vertical plane joining the transmitting and receiving antennas. A coordinate transformation is used to account for the irregular terrain features. The vertical walls of the buildings are assumed to be absorbing while the rooftops are taken to be flat and reflective. Ground and rooftops are allowed to have different constitutive parameters. Both horizontal and vertical polarizations are considered. Comparison is shown with various other methodologies to demonstrate the ability and accuracy of the present method to accommodate various situations.     

Spectral properties of signal fading and Doppler spectra distribution in urban mobile communication links

In this work, we continue the analysis of a probabilistic approach and the corresponding stochastic multi‐parametric model of wave propagation, in built‐up areas with randomly distributed buildings. We have concentrated on the spectral properties of signal strength spatial variations and on Doppler spread spectrum distribution of signal power. The analysis is based on a unified stochastic approach of radio wave propagation above the built‐up terrain with applications to mobile communications. We analyze the signal power spectrum of spatial frequencies and the signal power distribution in the Doppler domain for moving vehicles, taking into account a Doppler shift proportional to the vehicle antenna speed relative to the base station. The comparison between the theoretical prediction and experimental data was motivated by the proposed stochastic model and other existing statistical models to verify the signal power distribution in the Doppler domain for various urban environments and terminal heights with respect to building rooftops. New effects of terrain features on signal spectrum are obtained, examined and compared with existing models. Copyright © 2006 John Wiley & Sons, Ltd.     

Mobile radio propagation in British cities at frequencies in the VHF and UHF bands

Measurements of the received signal envelope magnitude have been made in three British cities at frequencies of 85.875, 167.2, and 441.025 MHz. In all cases unmodulated carrier waves were radiated from aerials atop tall buildings or prominent terrain features and detected using a vehicle-mounted receiver. These measurements have provided the basis for an analysis of the factors affecting the transmission loss in urban/suburban areas which, in turn, has enabled a propagation prediction model to be constructed. Close agreement between measured and predicted path losses has been found for the various terrain situations investigated. The statistical prediction errors produced by the proposed model for the three British cities analyzed are shown to be similar in magnitude to those obtained using an extrapolation of the Okumura method. Because the proposed model is much less complex and procedurally simpler, it is recommended for use, in the first instance, in British cities.     

A method of moments model for VHF propagation

Predictions of a numerical model for site specific very high frequency (VHF) propagation over irregular terrain are compared to experimental data and to other propagation models. The numerical model is based on an iterative version of the method of moments (MOM) known as the banded matrix flat surface iterative approach (BMFSIA) for either perfectly conducting or penetrable surfaces rough in one direction only. Due to the large size of the numerical problem (65000 to 130000 unknowns), a parallel implementation of the method is presented and applied in the simulations. Comparisons with measurement data show good agreement overall and also illustrate the sensitivity of the model to input terrain profiles. Comparisons with other propagation models show good agreement also in cases where these models are expected to be valid and further clarify the limitations of the approximations made in these methods     

Physical optics and field-strength predictions for wireless systems

Physical optics, or Fresnel-Kirchhoff theory, is often used for studies of particular problems in terrestrial radio-wave propagation. With efficient techniques of numerical integration, it can also be used effectively for routine predictions and for designing terrestrial wireless systems. A computer program of this type has been in use for several years. It is most useful in situations in which the base station (BS) antenna is above local clutter, and over areas large enough that ground cover can be characterized with categories such as "open," "forest," "dense residential," etc., rather than individual buildings. The main calculation is a marching algorithm that simulates diffraction over all the variations in terrain height along radials from the BS. A secondary calculation estimates the additional attenuation due to buildings and trees close to the mobile antenna. This part of the calculation is based on several parameters characterizing the local environment of the mobile antenna. Calculations are slow compared to many traditional methods, but are fast enough for routine use on a PC     

基于双向有限差分抛物方程法的海洋环境电波传播研究

采用双向抛物方程（two-way parabolic equation，2WPE）法来预测复杂海洋环境中的电波传播特性，用双向有限差分（two-way finite-difference，2WFD）法求解2WPE，考虑了海岛等不规则地形引起的电波后向传播和大气波导的影响，并在前向和后向电波传播预测中引入一种改进的分形海面模型来模拟起伏波动的实际海面边界，且能模拟海面的大尺度浪涌特性和毛细波细微结构特性.在典型的数值算例中，我们将采用改进分形模型处理海面边界时计算得到的双向电波传播因子和采用Miller-Brown模型处理海面边界时计算得到的双向电波传播因子进行对比和分析，数值分析结果表明，在相同风速条件下，采用改进分形模型处理海面边界时计算得到的双向电波传播因子波动更剧烈，能更准确地反映出实际起伏波动海面对电磁波传播的影响.     

UTD propagation model in an urban street scene for microcellularcommunications

A three-dimensional propagation model for microcellular communications in an urban street scene is presented. The model is based on the uniform theory of diffraction (UTD) and takes into account multiple wall-to-wall, wall-to-ground, and ground-to-wall reflections, the diffraction from corners of buildings, and subsequent reflections from such diffracted signals. The ray geometry is made extremely complex by the presence of ground reflections and the many combinations of sequences of reflections or diffractions from walls, edges, and ground. At each reflection or diffraction point, the local ray-fixed coordinate system or edge-fixed coordinate system is used together with appropriate dyadic reflection or diffraction coefficient matrices. The theoretical results for the signal path loss along the streets are compared with measurements done in New York and Tokyo for various values of the propagation parameters. Agreement with these measurements indicates that the UTD formulation is a good model for such urban communication applications