Analytical Formulae for Path Loss Prediction in Urban Street Grid Microcellular Environments

Rapid growth in the demand of wireless communications makes the use of microcells essential. Ray tracing models have shown good path loss prediction accuracy in microcellular environments. However, these techniques have great computational and memory requirements. The purpose of this paper is to derive analytical propagation path loss formulae for microcellular communications in urban street grid environments. The formulae are derived based on the geometrical optics and diffraction theory and they take into account multiple reflections along street walls and diffractions around street corners with ground reflections neglected; i.e., a two-dimensional approach. Comparisons between our theoretical results and published measurements in Tokyo and New York Cities show good agreement.     

Computational electromagnetic simulation of smart antenna systems in urban microcellular environments

The paper presents computational electromagnetics (CEM)-based characterization of smart antenna-system performance in urban microcellular environments. Mutual coupling effects between antenna-array elements are modeled using the method of moments (MoM) and the mobile environment is modeled using electromagnetic ray tracing (ERT). The smart antenna systems simulated in several urban microcells (covering a region of downtown Austin, TX) use uniform circular antenna arrays operating at 1.8 GHz. Direction-of-arrival (DOA) distribution information is used to comment on alternative array geometries for urban microcells. Power distributions are given to illustrate the variability of microcell shape using both DOA- and spatial signature-based downlink beamforming. In addition, these power distributions demonstrate how multivariate optimization can be used to modify microcell shape and to compensate for the presence of a blocking cellular tower. Spatial signature-variation information is used to characterize the overall environment and to motivate vector-autoregressive (VAR) prediction of mobile users' spatial signatures using a Kalman filter. Results from this developed prediction technique are provided for mobile users in the urban microcellular environment.     

射线追踪法应用于移动通信信道的特性分析研究

移动通信信道的研究一直是通信系统研究的难点,近年来,射线追踪法的快速发展及其在移动通信信道研究上的应用,为解决这一难点提供了新的可能途径。文中探索了利用射线追踪法分析移动通信信道特性的方法,并通过基于射线追踪法建立了的射线追踪模型,实例仿真分析了城市环境下移动通信信道的特性。     

Shadowing correlation assessment and modeling for satellite diversity in urban environments

Non‐geostationary orbit satellite networks have dynamic, yet deterministic topologies. This paper deals with the consequences of relying on the use of multiple visible satellites to improve availability with time/locations through satellite diversity techniques. The assumption of independent blockage events in two different satellite‐to‐mobile links is generally not accurate and information on shadowing correlation should be taken into account in the assessment of availability.In this paper a shadowing correlation study for urban environments is presented and a model for the real environments, as well as for a generic urban environment is inferred. The model proposed here is simple and can be run on a computer. It also relates urban and constellation geometries thus allowing the identification of those cases for which satellite diversity gain should be expected. As a result of this analysis and modelling, we present empirical analytical expressions describing positive correlation coefficient as a function of satellite angular separation (azimuth and elevation). We also show that an angle exists above which correlation can be negative and satellite diversity can sensibly improve link availability. Copyright © 2002 John Wiley & Sons, Ltd.     

An Enhanced Approach for a Prediction Method of the Propagation Characteristics in Korean Environments at 781 MHz

In high‐speed wireless communications, an analysis of the propagation characteristics is an important process. Information on the propagation characteristics suitable for each environment significantly helps in the design of mobile communications. This paper presents the analysis results of radio propagation characteristics in outdoor environments for a new mobile wireless system at 781 MHz. To avoid the interference of Korean DTV broadcasting, we measure the channel characteristics in urban, suburban, and rural areas on Jeju Island, Republic of Korea, using a channel sounder and 4×4 antenna. The path loss (PL) measurement results differ from those of existing propagation models by more than 10 dB. To analyze the frequency characteristics for Korean propagation environments, we derive various propagation characteristic parameters: PL, delay spread, angular spread, and K‐factor. Finally, we verify the validity of the measurement results by comparing them with the actual measurement results and 3D ray‐tracing simulation results.     

Simulating radio channel statistics for different buildingenvironments

The design of advanced radio systems requires knowledge of higher order channel statistics, such as the time delay spread and the angle of arrival spread. Time delay has been measured in a number of cities, while angle of arrival has been measured in only a few. Since the link geometry is not the same for all measurements, it is not clear how to compare the measured values, or if they are applicable to other building environments, antenna height, etc. To clarify these issues, we have used a three-dimensional ray tracing code, called the vertical plane launch (VPL) method, to simulate time delay spread and angle of arrival spread in different building environments. Results for elevated base station antennas show that the distribution of root mean square (RMS) delay spreads is not sensitive to the statistical properties of the buildings but increases with distance to the mobiles and increases as the base antenna is lowered below the rooftops. In contrast, the distribution of RMS angle spread is sensitive to the distribution of building heights and to the height of the base station antenna but not to the distance to the mobile. The influence of street geometry on delay and angle spread for low base station antennas is also discussed     

Propagation Over Clutter: Physical Stochastic Model

Propagation of radio signals from a base above clutter, such as buildings and trees, to a mobile immersed in clutter is treated theoretically by accounting for random diffuse scattering at the mobile. Small-scale fading and distance-dependent loss are treated in a unified way, as opposed to the heuristic methodologies, which formulate them as separate factors. Closed form expressions are derived for path gain and for angular spectrum at the base in both urban and heavily foliated environments. The resulting predictions are in close agreement with widely accepted models and empirical results. The angular spectrum at the base in urban environments is found to be Lorentzian of width close to that reported for measurements in Aarhus. In foliated environments, vegetation is represented as statistically homogeneous diffuse scattering medium, resulting in a Gaussian-shaped angular spectrum at the base.     

Three-Dimensional Urban EM Wave Propagation Model for Radio Network Planning and Optimization Over Large Areas

A new 3-D urban electromagnetic wave propagation model is presented. It provides fast 3-D deterministic predictions in urban radio configurations and over large areas. The various techniques to make it suitable to the network planning and optimization of large wireless networks are described. The resulting radio propagation maps exhibit seamless coverage between the various environments (dense urban, urban, and suburban). The model efficiently addresses all types of outdoor transmitter configurations (macrocells, minicells, microcells, and picocells) and all types of receiver locations (at ground level, over the rooftop, and at high building floors). It predicts the field strength as well as the dominant specular contributions of the impulse responses to build ray spectra (including delays and angles). Thus, the model may also be used to estimate the performances of new radio systems [diversity and multiple-input–multiple-output (MIMO)]. The narrowband power prediction of the model is evaluated by comparison with microcell measurements. The evaluation stresses the advantage of 3-D modeling compared with the vertical-plane approach or 2-D ray tracing. Finally, the ability of the model to simulate radio wideband characteristics in a complex environment is demonstrated by comparing delay-spread estimates to measurements collected from a high-macrocell transmitter in a hilly city and to arrival angles collected in a suburban macrocell area.      

高性能射线跟踪技术在智能交通领域的应用

随着移动通信技术的快速发展和更新换代,各行各业的信息化、智能化日益依赖于无线通信的强有力保障。因此,准确的信道信息、可靠的无线覆盖至关重要。射线跟踪技术面向不同行业的各类通信场景,通过建立有效的三维场景模型,以材料电磁参数、天线参数为基础,依托高性能计算引擎,将光学的射线技术引入电磁计算领域,能够准确地表征反射、散射、绕射、透射等多种电波传播机理及其对无线系统的影响。本文介绍了作者团队自主研发的高性能射线跟踪仿真平台,围绕高性能射线跟踪技术在智能交通领域的应用案例,阐述了射线跟踪技术在轨道交通、水路交通、公路交通等智能交通领域无线网络规划与优化、无线信道建模及信道特性分析等方面的技术优势,以期以自主可控的高性能射线跟踪仿真技术更好地助力我国交通强国战略的实施。     

Some experimental and modeling results of widely varying urban environments on train mobile radio communication

A comparative study of urban mobile radio wave propagation characteristics in the UHF band has been carried out based on the field strength measurements conducted inside a moving train in two widely varying urban environments. Various prediction techniques are employed to compare the observed path losses with those of predicted ones in both the environments. The major fall out of the present study is the modification of Xia's model, which gave better agreement with the observed results. The deviations of the prediction techniques and their suitability have been discussed. Copyright © 2006 John Wiley & Sons, Ltd.     

基于射线跟踪的小区信号强度估计

基于经验模型的无线信号强度估计方法无法针对具体物理场景,估计结果精度低,无法满足移动通信网络规划和优化的需要。射线跟踪技术能依据场景信息跟踪电波传播路径,但现有的反向跟踪方法在进行室外成片区域信号强度估计时复杂度高,无法实用。为提高估计结果的精度,降低估计方法的复杂度,提出了一种正向跟踪信号强度估计方法,将基站天线处发射的电磁波模拟成离散的射线,在考虑建筑物形状、分布信息的基础上采用基于网格的搜索算法跟踪射线路径,在接收点处对反射、绕射射线接收合并,最终得到基站覆盖区域的信号强度分布。仿真结果表明该方法的场强估计结果和实测数据吻合程度远大于经验模型估计方法,并且80%左右的估计结果和实测数据的误差在12 dBm以内,可应用于移动通信网络规划和优化。     

Quasi-ray Gaussian beam algorithm for time-harmonic two-dimensionalscattering by moderately rough interfaces

Gabor-based Gaussian beam (GB) algorithms, in conjunction with the complex source point (CSP) method for generating beam-like wave objects, have found application in a variety of high-frequency wave propagation and diffraction scenarios. Of special interest for efficient numerical implementation is the noncollimated narrow-waisted species of GB, which reduces the computationally intensive complex ray tracing for collimated GB propagation and scattering to quasi-real ray tracing, without the failure of strictly real ray field algorithms in caustic and other transition regions. The Gabor-based narrow-waisted CSP-GB method has been applied previously to two-dimensional (2-D) propagation from extended nonfocused and focused aperture distributions through arbitrarily curved 2-D layered environments. In this 2-D study the method is applied to aperture-excited field scattering from, and transmission through, a moderately rough interface between two dielectric media. It is shown that the algorithm produces accurate and computationally efficient solutions for this complex propagation environment, over a range of calibrated combinations of the problem parameters. One of the potential uses of the algorithm is as an efficient forward solver for inverse problems concerned with profile and object reconstruction     

Propagation modeling and system strategies in mobile-satelliteurban scenarios

Land mobile satellite (LMS) systems require fade countermeasure techniques since they suffer from limited fade margins and severe channel degradations. In the view of complete statistical models for LMS systems in urban areas, this paper deals with several specific mobile satellite urban configurations, such as a long straight street lined on both sides by buildings and a crossroad. Propagation effects are modeled as time series of received power by means of a ray-tracing method, which is used in combination with an orbit generator. The time series results are then postprocessed to simulate the impact of propagation mechanisms and satellite motion on fade mitigation techniques, satellite handover, and diversity. This original approach inherently accounts for the correlation between a number of very different but simultaneous effects that influence system performance. Exemplary results are finally discussed to stress the capability of the time-series approach     

Propagation factors controlling mean field strength on urban streets

Calculation of mean field strength for urban mobile radio has been made on a ray-theoretical basis assuming an ideal city structure with uniform building heights. The result shows that building height, street width, and street orientation as well as mobile station antenna height are controlling propagation parameters in addition to the ordinary factors. The major theoretical characteristics agree approximately with experimental data including conventional empirical predictions. This suggests a way of theoretically predicting mean field strength in an urban area.     

Parabolic distribution of scatterers for street-dominated mobile environments

We propose a parabolic scattering model (PSM) to complement the widely used circular scattering model for street-dominated environments, where street canyons favor propagation in narrow angular ranges centered on the street direction. The proposed model is based on the recently introduced semi-geometrically based statistical (SGBS) model and the geometric classification (GEC). The SGBS model defines the distribution of scatterers contributing to the final reradiation of multipath components to the receiver and the GEC defines spatio-temporal clusters using a geometric approach, which simulates different propagation classes based on their suitability to specific radio environments. Expressions are then provided for the power azimuthal spectrum (PAS), angular constriction, variance of received power, and Doppler spectrum (DS) using the PSM, all of which are obtained as seen from the mobile unit. Results for the PSM are also compared with the experimental data provided for dense urban macrocells, for which it has been shown that the proposed model produces PAS and DS that closely agree with the measurement.     

Deterministic Wideband Modeling of Satellite Propagation Channel With Buildings Blockage

The article presents an example of satellite propagation modeling, applying the radio channel transfer function analysis as described and experimentally verified in scientific literature. The simulation of a satellite radio channel is executed by employing "ray tracing" and the uniform geometric theory of diffraction-based method for an assumed urban and suburban environment and different polarizations. Derived results regarding the channel transfer function are analyzed via a simulation of the wideband propagation measurement system and the Fourier transform procedures. It has been concluded that, contrary to ground cell radio system situations, where two-ray models usually suffice, a more detailed calculation should be considered for wideband satellite radio systems. Moreover, it is shown that the conclusions derived for the path loss and the delay spread depend not only on the specific propagation scenario, but also on the building permittivity.     

Environment and Movement Model for Mobile Terminal Location Tracking

Mobile terminal position location, tracking and prediction are becomingimportant areas of research for advanced cellular communications.Methods for mobile terminal location are evaluated using simulations. To obtain accurate simulation results, the simulation environment and terminalmotion model must be as realistic as possible. This paper describes a simulation system for mobile terminals located within vehicles in dense urban environments. These are the mobiles with the greatest need for locationpredictions in the environments of greatest interest to network providers. Theradio propagation model is based on well known multipath radio propagationmodels. The motion model combines an accurate kinematic model for vehicular motion with a driver decision model to mimic human driving decisions.Simulatedmobile terminal motion tracks are presented, showing how realistic motionsare generated.     

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     

Path-loss prediction model for microcells

Empirical path-loss formulas for microcells in low-rise and high-rise environments are established from measurements conducted in the San Francisco Bay area. Using the 1-km intercepts and slope indexes of the least square fit lines to the measurements at cellular and personal communication services (PCS) frequencies for three base station heights, simple analytic expressions are obtained. Separate formulas are presented for environments of low buildings and for the high-rise urban core. Following the formula development processes for individual test routes, in low-building environments, a single nonline-of-sight (non-LOS) formula that is applicable to all non-LOS routes is derived. Due to the anisotropic property of wave propagation, cell shape of microcells is no longer circular. As examples, cell shape is presented when base stations are on the street in the middle of a block and when they are placed in the backyard