Emanoel Costa

An efficient solution of an integral equation applicable to simulation of propagation along irregular terrain

An efficient algorithm is proposed as a substitute for the one originally used for the solution of an integral equation with applications to propagation studies. The results from the original and the proposed algorithms are compared by means of their application to the same terrain profile. A good overall agreement is displayed between the corresponding results from the two algorithms. Additionally, it is shown that considerable savings in processing time can be obtained with the proposed algorithm.

Extended ionospheric amplitude scintillation model for GPS receivers

Ionospheric scintillation is a phenomenon that occurs after sunset, especially in the low-latitude region, affecting radio signals that propagate through the ionosphere. Depending on geophysical conditions, ionospheric scintillation may cause availability and precision problems to Global Navigation Satellite System users. The present work is concerned with the development of an extended model for describing the effects of the amplitude ionospheric scintillation on GPS receivers. Using the α-μ probabilistic model, introduced by previous authors in different contexts, the variance of GPS receiver tracking loop error may be estimated more realistically. The proposed model is developed with basis on the α-μ parameters and also considering correlation between amplitude and phase scintillation. Its results are interpreted to explain how a receiver may experience different error values under the influence of ionospheric conditions leading to a fixed scintillation level S4. The model is applied to a large experimental data set obtained at Sao Jose dos Campos, Brazil, near the peak of the equatorial anomaly during high solar flux conditions, between December 2001 and January 2002. The results from the proposed model show that depending on the α-μ pair, moderate scintillation (0.5 ≤ S4 ≤ 0.7) may be an issue for the receiver performance. When S4 > 0.7, the results indicate that the effects of scintillation are serious, leading to a reduction in the receiver availability for providing positioning solutions in approximately 50% of the cases.

The effects of ground-reflected rays and atmospheric inhomogeneities on multipath fading

Ray tracing through a single horizontally stratified atmospheric layer has been used to support evidence that defocusing of the direct ray, combined with surface multipath, can have an important effect on the performance of overland microwave line-of-sight (LOS) links. The same link and horizontally stratified layer proposed by A.R. Webster (1983) are used to exhibit the agreement between previous results and the present ones, to display a numerical example of multipath effects on terrestrial microwave LOS, and as a reference for detailed discussions. The effects of the combination of the horizontal stratification with a wave-like structure are analyzed. it is seen that the vertical displacement of the structure across the radio link has a strong impact on the parameters of the direct ray, which is translated into fast variations of the received signal around its average value. >

A simulation of multipath effects on the cross-polarization discrimination in microwave line-of-sight links

A ray-tracing computer model, combining the effects of the curvature of the Earth, of the radiation patterns of the antennas, as well as those of the reflection at the Earth’s surface, has been developed in order to simulate multipath effects on the relationship between cross-polarization discrimination (xpd)and co-polar attenuation (cpa)values occurring in frequency-reuse line-of-sight microwave links. Measured refractive-index vertical profiles have been used as input data to this model, in order to study the dependence of the parameters of the law relatingxpdandcpaon the characteristics of the link. Based on the observed dependence, experimental values for the parameters of this law, available in the literature, have then been analyzed.AnalyseL’auteur présente un modèle de simulation de tracé de rayons combinant les effets de la courbure de la terre, des diagrammes de rayonnement des antennes d’émission ou de réception et de la réflexion à la surface du sol. Le modèle exploite les données obtenues à partir des mesures des profils verticaux d’indice de réfraction afin d’étudier les paramètres de l’expression liant le découplage de polarisation croisée et l’affaiblissement du signal copolaire, en fonction des caractéristiques de la liaison hertzienne à hyperfréquences. Les résultats permettent d’analyser la validité des valeurs expérimentales de ces paramètres, citées dans la littérature.

Analysis of the Effects of Irregular Terrain on Radio Wave Propagation Based on a Three-Dimensional Parabolic Equation

The effects from lateral variations of irregular terrain on the propagation of radio waves are considered by the representation of the vector fields in terms of two scalar Hertz potentials in spherical coordinates. The combination of three-dimensional parabolic equations for these potentials with an impedance boundary condition for the ground, followed by a transformation of variables, will define a boundary-condition problem characterized by equations displaying coefficients that depend on the terrain height function and its partial derivatives. The problem solution through the Crank-Nicolson scheme will lead to a sparse system of linear equations, which will be solved by a direct method. The resulting numerical model will be applied to test cases to show similar features to those from examples described in the literature, taken as references for validation purposes.

A Site-Specific Beam Tracing Model of the UWB Indoor Radio Propagation Channel

A site-specific convex pyramidal beam tracing model of ultrawideband (UWB) indoor propagation channels is described in detail. The model is fast and accurate, since it does not need to apply nontrivial and costly tests to determine all the existing rays between the transmitter and receiver. Predictions from the model are compared with those from corresponding measurements, performed under line-of-sight (LOS) and nonline-of-sight (NLOS) conditions. A good agreement is displayed between predicted and measured impulse responses, as well as of some derived parameters (average power, mean delay, and delay spread), as they vary with the distance between the transmitter and the receiver.

Wave propagation models Comparison of prediction results with measurements

Models that estimate diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands available for digital TV applications will be used to predict field strengths that will be compared with those from the corresponding measurements. A basis for comparison between predictions and experimental data was obtained from a special measurement series performed by BFH-TI (Berne University of Applied Sciences, Engineering and Information Technology, Bienne, Switzerland) [1] to determine the height function of the received field strength. Thousands of path profiles and measurements are incorporated also into the ITU-R DBSG5 database. All these data (BFH-TI and DBSG5) will be described; the mean value and the standard deviation of the difference between measurements and predictions will be presented as functions of their number of main obstacles.

GPS availability and positioning issues when the signal paths are aligned with ionospheric plasma bubbles

The propagation paths of signals through equatorial ionospheric irregularities are analyzed by evaluating their effects on Global Navigation Satellite System (GNSS) positioning and availability. Based on observations during 32 days by a scintillation monitor at São José dos Campos, Brazil, it was noted that there is a dominance of enhanced scintillation events for Global Positioning System (GPS) ray paths aligned with the azimuth angle of 345° (geographic northwest). This azimuth corresponds to the magnetic meridian that has a large westward declination angle in the region (21.4ºW). Such results suggest that the enhanced scintillation events were associated with GPS signals that propagated through plasma bubbles aligned along the direction of the magnetic field. It will be shown that, under this alignment condition, the longer propagation path length through plasma bubbles can result in more severe scintillation cases and more losses of signal lock, as supported by proposed statistics of bit error probability and mean time between cycle slips. Additionally, large precise positioning errors are also related to these events, as demonstrated by precise point positioning experiments.

Equatorial scintillation predictions from C/NOFS Planar Langmuir Probe electron density fluctuation data

Data from the Planar Langmuir Probe onboard Communication/ Navigation Outage Forecasting System will be combined with coherent scatter radar and scintillation measurements to analyze the performance of different propagation models of satellite signals. This work will characterize: (i) the prediction capability of a purely space-based phase-screen scintillation model in comparison with another that represents the variation of the irregularity strength along ray paths in detail; and (ii) how early in time it is possible to detect irregularity structures, estimate their temporal and spatial evolution and predict their effects on propagation through different ionospheric regions at later instants of time.

Digital elevation data and their use for improved broadcast coverage and frequency utilization

Thousands of path profiles incorporated into the ITU-R Study Group 3 (DBSG5) database and those estimated from the shuttle radar topography mission (SRTM) digital elevation model for the same terminal coordinates will be compared. Models that estimate diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands available for digital TV applications will be used to predict field strengths that will be compared with those from the corresponding measurements. The mean value and the standard deviation of the difference between measurements and predictions will be presented for each model and for both the DBSG5 and the SRTM terrain profiles, as functions of their number of main obstacles. A better basis for comparison between predictions and experimental data was obtained from a special measurement series performed by HTI to determine the height function of the received field strength. These measurements will be described, also compared with model predictions and statistically analyzed.