A novel propagation modeling for microcellular communications inurban environments

A novel method for microcellular communications to predict propagation characteristics is presented in this paper. It takes into account multiple reflections among walls, ground, vehicles, as well as the transmission/reflection due to groups of trees. Although these are three-dimensional (3-D) problems, we can combine two-dimensional (2-D) ray tracing and simple 3-D geometric considerations to solve them in a very efficient way. We have investigated the propagation loss versus size, number, and locations of vehicles and groups of trees on a safe island. Our results show that the radio wave propagation exhibits severe fast fading, attenuation, and blockage due to reflection, transmission, and shadowing, respectively     

A UTD propagation model in urban microcellular environments

This paper presents a three-dimensional (3-D) propagation model for path-loss prediction in a typical urban site, based on geometrical optics (GO) and uniform theory of diffraction (UTD). The model takes into account numerous rays that undergo reflections from the ground and wall surfaces and diffraction from the corners or rooftops of buildings. The exact location of the reflection and diffraction points is essential in order to calculate the polarization components of the reflected and diffracted fields and their trajectories. This is accomplished by local ray-fixed coordinate systems in combination with appropriate dyadic reflection and diffraction coefficients. Finally, a vector addition of the received fields is carried out to obtain the total received field strength and, subsequently, the path loss along a predetermined route. The model computes the contributions of various categories of rays, as selected, in a flexible manner. Several results-path loss versus distance and power-delay profile-are given, and comparisons with measured data are presented     

Millimetric wavelengths radiowave propagation for line-of-sightindoor microcellular mobile communications

Discusses millimeter waves for indoor microcellular communications. The results of propagation experiments conducted at 60.4 GHz (the oxygen absorption band) and 38.25 GHz to determine multipath characteristics in a number of indoor microcell channels employing omnidirectional antennas are presented. Cumulative distribution functions for received signal envelope, as well as corresponding power spectra are given. In addition, a comparison between the fading statistics measured at 60.4 GHz and 38.25 GHz under similar conditions is made. The change in multipath characteristics due to the presence of different building materials is also illustrated. A ray model is developed to represent indoor microcell propagation by considering a direct ray plus rays which have undergone single and double reflections from the walls. Specular floor-reflected and ceiling-reflected rays are included when the antennas radiation pattern does not preclude them. Using this simple model, the signal variations and the amplitude of reflected rays with respect to the line of sight (LOS) ray as functions of mobile receiver position are predicted and used to assist in interpreting experimental results. Theoretical results are found to be in good agreement with measured ones, with the model also being used to predict structure-induced root mean square (rms) delay spread along receiver routes in an indoor microcell environment. This parameter is a measure of multipath conditions in a mobile radio channel and is inversely proportional to the maximum usable data signalling rate of a channel     

城市微蜂窝的快捷精确传播预测方法

基于路测数据和统计模式,提出了针对城市微蜂窝的模式修正场强传播损耗预测方法.依据路测数据的分布和蒙特卡罗模拟的结果,将预测区域划分为若干个子区域,运用基于最小均方误差的自适应算法,从路测数据中提取每个子区域的传播损耗参数,经线性方程计算子区域内场强分布,得出整个区域的场强二维覆盖.实验结果表明,所给方法具有传统确定性模式和统计模式各自的优点,其预测精度接近确定性模式,而计算时间与统计模式相当,具有高的工程应用价值.     

小区覆盖预测中一种有效的射线跟踪技术

射线跟踪法是近年来常用于城市微小区和室内环境无线电波传播信道特性预测的方法,但其在具体实现方面仍有许多问题需要进一步的研究。本文将计算机图形学中的八叉树方法用于射线跟踪法,得到了一种提高射线跟踪效率的方法。     

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     

Transient propagation in anisotropic laminated composites

A detailed analysis of the transient response of an electromagnetic pulse (EMP) and a Gaussian pulse in anisotropic laminated composites is presented. To this end, both the equivalent transmission line circuit (ETLC) model and the finite-difference-time-domain (FDTD) method are adopted in the time-domain analysis. Numerical results are presented for graphite/epoxy laminates, based on a model which treats each lamina as a homogeneous and anisotropic sheet. The factors that influence the transient response of anisotropic laminated composites, such as laminate thickness, fiber orientation, and the angle, frequency contents, and polarization of the incident wave, are also investigated     

A microcellular ray-tracing propagation model and evaluation of itsnarrow-band and wide-band predictions

Due to the site specific nature of microcellular operational environments, propagation models are required to take into account the exact position, orientation and electrical properties of individual buildings, and hence, ray-tracing techniques have emerged as the dominant methods to predict propagation in such environments. A novel hybrid three-dimensional (3-D) ray-tracing algorithm which can evaluate scenarios incorporating many thousands of objects by utilising the concept of “illumination zones,” is presented. In order to evaluate the accuracy of the presented model, comparisons of narrow-band and wide-band predictions with measurements are performed for a variety of scenarios. First, power comparisons show that very accurate predictions can be achieved (RMS errors less than 3.7 dB). Then, wide-band analysis shows that since the RMS delay spread for systems with finite bandwidth is a function of the multipath phase, only average measured and predicted RMS delay spread values can be compared and as a result, limited averaging can produce large RMS errors. With sufficient averaging the achieved wide-band accuracy in terms of the predicted RMS delay spread, is adequate for most planning purposes     

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     

Deterministic channel modeling and performance simulation of microcellular wide-band communication systems

To evaluate the performance of future microcellular IMT-2000 modems, simple physical models are required, so that a number of system characteristics, such as the signal bandwidth, the antenna beamwidth, or the base station height can be accounted for at a limited computational cost. This paper describes a deterministic three-dimensional electromagnetic model, which allows simulation of the radiowave propagation for microcellular wide-band communication systems in urban areas. The model is based on a UTD ray-tracing tool and makes use of an improved mirror method. Simulated power-delay profiles are plotted against measured power-delay profiles recorded at 1.87 GHz in a street of Louvain-la-Neuve, Belgium, by means of an 80-MHz channel sounder. Despite several discrepancies, a satisfying matching is found considering three orders of reflection and single diffraction. Predictions of rms delay-spread accounting for the sounder limited bandwidth are presented. Finally, simulated and measured channels are also compared through the resulting performance of a typical IMT-2000 service in the presence of multiple access interference.     

A deterministic propagation model for the microcellular environment using multiple two-dimensional planes

A simplified, computationally efficient radio-wave propagation model is proposed for the microcellular environment to calculate the path loss characteristics of the line-of-sight (LOS) and out-of-sight (OOS) paths in rural and urban environments. This method is based on ray-tracing through combined multiple two-dimensional (2D) planes and the use of a proposed non-reaching ray technique based on the uniform theory of diffraction and Fermat's principle. This paper is a generalization of the use of 2D plane models in the mobile environment. Rather than putting effort into predicting the environment, which is the usual practice, we lay emphasis on the way the ray could be traced towards the mobile in a predictive sense which would lead to reduced complexity of ray-tracing execution time without any serious loss of accuracy. We have utilized the predictive nature of reflections and diffractions to model the propagation paths in terms of multiple 2D planes. It is understood that while the rays follow only reflections, be it from buildings or ground, they will traverse in a well defined plane for a given receiver's position. The same is true for diffraction also. Multiple image theory is used to simplify the ray paths for computation. Rural and urban environments are considered as streets of LOS and OOS paths. Path loss characteristics are determined as a function of polarization, base station antenna height and the diffracted field component. Validation of the theoretical curves is achieved by the experimental results to confirm the efficiency of the proposed model.     

Closed-form expressions for the prediction of microcellular mobile radio propagation in urban environments

The paper derives two closed-form expressions for predicting microcellular mobile radio signal levels in urban street-grid environments. The results demonstrate that the two expressions are faster and more accurate than existing models and methods. Benefiting from physical optics and the conservation of energy, the two expressions are alternatives to available techniques such as ray tracing. The dielectric property (i.e., permittivity) of street buildings and other obstacles is essential to the ray tracing technique. However, there are no established, widely accepted techniques for selecting the permittivity in urban mobile environments, which varies in a wide range. Establishing a natural link between the received power after a street corner to the width of the street and the angle of incidence, our expressions show the possibility of making fast and accurate propagation predictions without having to use the permittivity.     

Effect of cochannel interference on handover in microcellular mobile radio

The effect of cochannel interference on a fast handover algorithm for microcellular mobile radio systems is described. The presence of cochannel interference had only a marginal effect on the handover point when the microcell base stations were spaced by 300 m. Increasing the mobile speed increased the effective cell length.<>     

Fast two-dimensional diffraction modeling for site-specificpropagation prediction in urban microcellular environments

This paper presents fast two-dimensional (2-D) diffraction modeling in the horizontal plane for site-specific propagation prediction in urban microcellular environments. The modeling makes three contributions which are: (1) the introduction and use of an extended formulation for multiple building forward diffraction; (2) a novel equivalent source simplification for parallel street multiple diffraction; and (3) the inclusion of reflections from curved surfaces of street building corners. Comparison with measurements and simulation of published results validate the 2-D modeling that significantly reduces the computation time and overcomes the limitation and difficulty of existing techniques for multiple diffraction     

并行射线跟踪算法及其在城市电波预测的应用

射线跟踪算法的计算量较大,耗时较长.针对这一问题提出并研究了对等模式和主从模式两类并行射线跟踪算法,结合MPI并行运算函数库,在局域网计算机簇中,实现了城市复杂微蜂窝环境的电波预测.结果表明,并行算法在精度相同的情况下,大大缩减了计算机运行时间.而且,主从模式在异类网络中具有更好的并行加速增益和负载均衡.     

Comparisons of a computer-based propagation prediction tool withexperimental data collected in urban microcellular environments

Engineers designing and installing outdoor and indoor wireless communications systems need effective and practical tools to help them determine base station antenna locations for adequate signal coverage. Computer-based radio propagation prediction tools are now often used in designing these systems. We assess the performance of such a propagation tool based on ray-tracing and advanced computational methods. We have compared its predictions with outdoor experimental data collected in Manhattan and Boston (at 900 MHz and 2 GHz). The comparisons show that the computer-based propagation tool can predict signal strengths in these environments with very good accuracy. The prediction errors are within 6 dB in both mean and standard deviation. This shows that simulations, rather than costly field measurements, can lead to accurate determination of the coverage area for a given system design     

Finite element beam propagation method for anisotropic opticalwaveguides

A finite element beam propagation method (BPM) for anisotropic optical waveguides is newly formulated. In order to treat a wide-angle beam propagation, a Pade approximant operator is employed and to avoid nonphysical reflection from computational window edges, a transparent boundary condition is extended to anisotropic materials. To show the validity and usefulness of this approach, the numerical results for an anisotropic planar waveguide and a magnetooptic channel waveguide are presented     

A full-vectorial beam propagation method for anisotropic waveguides

An extension of the full-vectorial beam propagation method to anisotropic media is presented. Optical waveguides made of anisotropic materials can be modeled and simulated. The polarization dependence and coupling due to both the material and the geometric effects are considered     

Variational propagation constant expressions for lossyinhomogeneous anisotropic waveguides

Based on reciprocal relationships for the adjoint operator, we derive a variational formulation for the propagation constant satisfying the divergence-free condition in lossy inhomogeneous anisotropic waveguides whose media tensors have all nine components. In addition, with some advantages over previous representations, two variational formulations have been derived for waveguides with the transverse part of the media tensors decoupled from the longitudinal part. However, to obtain a variational formulation for a general lossy reciprocal problem the waveguide must be bi-directional. Each of the variational expressions results in a standard generalized eigenvalue equation with the propagation constant appearing explicitly as the desired eigenvalue. The stationarity of the formulations is shown. It is also shown that for a general lossy nonreciprocal problem the variational functional exists only if the original and adjoint waveguide are mutually bi-directional