Prediction of loss characteristics in built-up areas with variousbuildings' overlay profiles

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 concentrate on the influence of buildings' overlay profiles on signal spatial decay, and on path-loss dependence in the frequency domain within UHF/X-band urban propagation channels. Using different buildings' overlay profiles, the field-intensity attenuation along radio paths is examined, taking into account single-scattering and multiple-scattering phenomena, and diffraction from buildings' corners and rooftops, for various positions of receiver and transmitter antennas with respect to surrounding obstacles. The comparison between experimental and theoretical predictions was motivated by the proposed stochastic multi-parametric model and the experimental data obtained for actual areas in Jerusalem (Israel) and Lisbon (Portugal), as well as by other models of multiple diffraction. The discussion is presented for realistic elevations of both terminal antennas to assess the accuracy and limits of the proposed stochastic model. A sensitivity analysis of the influence on the path loss of built-up terrain parameters and the elevation of antennas relative to the buildings surrounding them is presented     

Average field attenuation in the nonregular impedance streetwaveguide

The propagation of electromagnetic (EM) waves in a city with a regularly planned building as a model of a straight street with buildings lining its sides is investigated. The street is considered as a planar two-dimensional (2-D) multislit waveguide with Poisson distributed screens (building walls) and slits (gaps between buildings). The electrical properties of the buildings' walls are taken into account by introducing the electrical impedance as a function of their surface permittivity and conductivity. The average field from the vertical electric dipole placed inside the street lower than rooftop level in the conditions of line-of-sight is investigated using Green's function formalism and real boundary conditions on the building walls. Evaluations show that the total field inside the waveguide can be presented as a superposition of a continuous spectral propagation component, which does not exist in the ideal unbroken waveguide, and a discrete spectral component, which describes the exponential attenuation of reflected and diffracted waves at distances of up to 23 km depending on the width of street. The presented model and evaluated formulas are in a good agreement with experimental data of ultrahigh-frequency (UHF)/L-band wave propagation in urban areas with a crossing-street plan     

SEKE: A computer model for low altitude radar propagation over irregular terrain

SEKE, a new site-specific propagation model for general terrain, makes use of the original Lincoln Laboratory models geometrical optics (GOPT), low altitude propagation spherical earth (LAPSE), and low altitude propagation knife edges (LAPKE) to compute multipath, spherical earth diffraction, and multiple knife-edge diffraction losses. The proper algorithm is selected based on terrain geometry, antenna and target heights, and frequency. Comparison of model predictions with measurements over several paths ranging from level to rough at five frequencies (X-band through VHF) is presented. A brief discussion on the performance of SEKE over general terrain with respect to the expected performance of the two other general terrain-specific models (Longley-Rice and terrain integrated rough earth model (TIREM)) is given.     

Characteristics' prediction in urban and suburban environments

The characteristics of the propagation in the microcellular urban and suburban environments in the 902-928-MHz frequency band in line-of-sight (LOS) conditions is investigated both theoretically and experimentally for the purpose of wireless radio local loop (WRLL) prediction. The path-loss characteristics and the range of a break point, at which the polynomial character of field intensity decay along the street level is changed, are analyzed for various parameters of street widths, for different average building heights, and for the actual electrical impedance properties of building walls. A multislit waveguide with randomly distributed gaps between the sides of buildings is considered as a model of straight streets. Results of experiments for VHF/UHF wave propagation along the straight streets in urban environment in the conditions of direct visibility between receiver and transmitter are compared with theoretical analysis of field intensity decay, path-loss distribution, and dependence of the break point on street topography in LOS conditions     

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     

A canonical problem in electromagnetic backscattering from buildings

In this paper, a geometric and electromagnetic model of a typical element of urban structure is presented, in order to analytically evaluate in closed form its electromagnetic return to an active microwave sensor. This model can be used to understand what information on geometric and dielectric properties of a building can be extracted from microwave remote sensing data. The geometrical model consists of a rectangular parallelepiped whose vertical walls form a generic angle with respect to the sensor line of flight. The parallelepiped is placed on a rough surface. The radar return from such a structure can be decomposed into single-scattering contributions from the (rough) ground, the building roof (a plane surface in our model), and vertical walls and multiple scattering contributions from dihedral structures formed by vertical walls and ground. In our model, single-scattering contributions are evaluated by using either physical optics (PO) or geometrical optics (GO), depending on surface roughness. In order to account for multiple scattering between buildings and terrain, we use GO to evaluate the field reflected by the smooth wall toward the ground (first bounce) or the sensor (second or third bounce) and GO or PO (according to ground surface roughness) to evaluate the field scattered by the ground toward the wall (first or second bounce) or the sensor (second bounce). Finally, the above model is used to analyze the field backscattered from a building as a function of the main scene parameters; in particular, the angle between vertical walls and sensor line of night and the dependence on the look angle are analyzed.     

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.     

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     

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.     

Effect of terrain on path loss in urban environments for wirelessapplications

Path loss prediction algorithms for advanced wireless communication system planning have long considered the effect of electromagnetic propagation over buildings between the base station and subscriber. This phenomena is particularly important in residential areas, where the houses are typically a few stories high. For the most part, the buildings were assumed to lie on level terrain, although shadowing effects by the terrain in the absence of buildings has been included. Previous works have offered a number of methods to quantitatively determine these effects from path profiles. This study examines propagation over buildings when the buildings are located on terrain features (hills). The buildings, which are represented by a series of absorbing half screens, are assumed to lie in rows that are equally spaced along parallel streets, with the streets running perpendicular to the terrain slope. Numerical results are obtained using successive repetition of the Kirchhoff-Huygens approximation. A phenomenological model based on ray optics for diffraction over a smooth surface is proposed as a way to interpret the numerical results. The dependence of the model coefficients on the terrain parameters are obtained from the numerical results     

Propagation characteristics in open-groove waveguides surrounded by rough sidewalls

The radio propagation characteristics in groove-shaped roads surrounded by rough surface sidewalls are presented. Typical sidewalls are snowpack in heavy snow regions or buildings in urban areas. In this analysis, such roads are modeled by a straight groove waveguide with statistically rough sidewalls. A simple geometrical optical approach is applied to calculate the field strength along the longitudinal direction of the road as well as transversely across the road. The theoretical results are compared with previously presented experimental results. The theoretical results show that the surface roughness causes an additional propagation loss in regions far from the transmitting point and that the field strength in the cross section exhibits a cosine distribution with a slightly changing magnitude. These theoretical characteristics agree with the experimental results.<>     

A ray-tracing propagation model for digital broadcast systems inurban areas

A propagation model is presented for characterizing the channel response for digital systems in urban areas where multiple reflections from buildings are encountered. A deterministic ray-tracing propagation model is used to predict the time delay and fading characteristics for the channel in a hypothetical urban area. The analysis shows that due to multiple reflection and diffraction sources, the RMS delay spread of the channel in urban areas can be several hundred nanoseconds, so that very effective equalizers will be required to achieve successful performance of high-data-rate digital systems such as 20-Mb 16-QAM digital HDTV. The channel response results presented also suggest that polarization diversity may be a useful technique for mitigating some of the channel impairments predicted by the propagation model     

A simplified analytical model for predicting path loss in urban andsuburban environments

An analytical propagation model has recently been developed to predict radio signal attenuation in urban and suburban environments. This analytical model explicates the path loss as a result of signal reduction due to free space wavefront spreading, multiple diffraction past rows of buildings, and building shadowing. It is applicable for cellular mobile services as well as personal communications services (PCS) in both macro- and microcellular environments. Good accuracy was found for this analytical model by comparing the predictions with numerous measurements made in various propagation environments. However, since the analytical model involves multiple-dimension integration to calculate the signal attenuation due to multiple diffraction past rows of buildings, the model in its original format does not lend itself to easy implementation into a radio system planning tool. A simplified version of the analytical model is developed in this paper, which can be used for three different propagation scenarios with base-station antenna above, below, and near the average rooftop level     

Preparing an urban test site for SRTM data validation

In this paper, we describe a method to obtain a reliable set of elevation data suitable for data validation on the Shuttle Radar Topography Mission (SRTM), starting from laser scanning measurements on an urban test site: Pavia, Northern Italy. The elevation dataset is obtained through extraction of digital terrain models. The source digital surface model is first filtered by means of a lowpass or morphological kernel. Then, buildings are suppressed through analysis of the height histogram. Finally, a lowpass filter suppresses the surviving elevation artifacts. We show that, starting from a digital surface model at 1-m ground resolution, we end up with a digital terrain model that can be used as a ground truth for SRTM topographic analysis of an urban area.     

A Comprehensive Study on Urban True Orthorectification

To provide some advanced technical bases (algorithms and procedures) and experience needed for national large-scale digital orthophoto generation and revision of the Standards for National Large-Scale City Digital Orthophoto in the National Digital Orthophoto Program (NDOP), this paper presents a comprehensive study on theories, algorithms, and methods of large-scale urban orthoimage generation. The procedures of orthorectification for digital terrain model (DTM)-based and digital building model (DBM)-based orthoimage generation and their mergence for true orthoimage generation are discussed in detail. A method of compensating for building occlusions using photogrammetric geometry is developed. The data structure needed to model urban buildings for accurately generating urban orthoimages is presented. Shadow detection and removal, the optimization of seamline for automatic mosaic, and the radiometric balance of neighbor images are discussed. Street visibility analysis, including the relationship between flight height, building height, street width, and relative location of the street to the imaging center, is analyzed for complete true orthoimage generation. The experimental results demonstrated that our method can effectively and correctly orthorectify the displacements caused by terrain and buildings in urban large-scale aerial images.     

Propagation loss prediction: A comparative study with application to the mobile radio channel

A number of statistical models are available in the literature for the prediction and the calculation of transmission loss, but the main differences between them as well as their usefulness in a particular situation is not easy to assess. In this article, the experimental results of Okumura, as seen through the empirical expression derived by Hata, are compared with the models of Egli, Edwards and Durkin, Blomquist and Ladell, and Allsebrook and Parsons. Comparisons are made for the case of an open region and flat terrain, first without and then with inclusion of a statistical estimation of diffraction losses due to terrain in the models of Blomquist and Ladell, Edwards and Durkin, and Allsebrook and Parsons. The study is also extended to cover the case of irregular terrain and urban areas. The method proposed by Hata, based on Okumura's results, and Allsebrook and Parsons' model, which provides an easy way to take into account the influence of buildings are the most complete and it is suggested to use them with the inclusion, as required, of an estimation of diffraction losses due to terrain. As a conclusion, experimental propagation loss measurements taken in the Ottawa region at 910 MHz are presented and are found to fall very nicely in the range predicted by the above-mentioned methods.     

Precision enhancement in ETSI‐Hata propagation model tuning using experimental data in a dense urban area

In this paper an enhanced ETSI‐Hata propagation model tuning is presented. The three‐dimensional (3D) digital terrain map (DTM) was included in the simulation process. For the enhancement of the model tuning process and precision verification of ETSI‐Hata model, the real 3D map of the buildings of the simulated area was incorporated over the DTM. Multiple knife edge diffraction method and the antenna effective height method were used to calculate the diffraction loss. This method was applied for a real urban scenario. For every sector in the coverage area, a tuned model was exploited. Using a genetic algorithm, frequency planning for the entire urban area was performed, which resulted in an improvement in the quality of service. Copyright © 2009 John Wiley & Sons, Ltd.     

Path loss predictions in the presence of buildings on flat terrain: a 3-D vector parabolic equation approach

Starting from a parabolic approximation to the Helmholtz equation, a three-dimensional (3-D) vector parabolic equation technique for calculating path loss in an urban environment is presented. The buildings are assumed to be polygonal in cross section with vertical sides and flat rooftops and the terrain is assumed to be flat. Both buildings and ground are allowed to be lossy and present impedance-type boundary condition to the electromagnetic field. Vector fields are represented in terms of the two components of Hertzian potentials and depolarization of the fields is automatically included in the formulation. A split-step algorithm is presented for marching the aperture fields along the range. Boundary conditions on the building surfaces are treated by using a local Fourier representation of the aperture fields. Several test cases are considered to check the boundary treatment used in the technique as well as to validate the overall approach. Comparison is shown with uniform theory of diffraction (UTD), exact solutions, as well as with measurements.     

城区机载LIDAR数据滤波方法研究

为了从机载激光扫描数据中获取城区数字地面模型,在分析城区机载激光扫描数据多回波信息特点的基础上,提出一种基于多回波信息的城区数据滤波方法,该方法根据城区机载激光扫描数据的分布特点,将激光脚点划分到具有一定体积的体素中,然后依据滤波准则,剔除地物点,保留地面点,最后得到城区数字地面模型。结果表明,该方法较以往滤波方法不仅能有效提取数字地面模型,而且可以减少机载激光扫描数据处理的计算量,提高海量机载激光扫描数据的运算效率。     

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.