Mauro S. Assis

An Empirical Model for Propagation Loss Through Tropical Woodland in Urban Areas at UHF

A vegetation path loss model was derived from measurements performed in a downtown park in Rio de Janeiro city, from 0.9 to 1.8 GHz. The resulting equation followed the general formulation in ITU-R Recommendation P.833. A comparative analysis was carried out with other empirical models, assessing statistical adherence to the available data. Coherent results were observed.

Search and rescue in a forest environment

The problem of search and rescue in a jungle environment is discussed in this paper. Depending on the relative position between the unknown radio station and the searcher equipment, three propagation mechanisms should be considered in the analysis of the radio path: (a) Both equipments immersed in the jungle; (b) The searcher equipment in a plane or helicopter (ground-to-air link); (c) The searcher equipment on the ground outside the jungle. Once the first two cases are well known, emphasis is given to case (c) where a mathematical model to evaluate the radio wave attenuation is proposed.

Rainfall Rate Duration Study for Performance Assessment of Satellite Communication Links

The duration of rainfall events as a function of precipitation rate is investigated in this paper. The experimental data used in this study were measured along a rain gauge network with 8 pluviographs located in the Amazon region. The most important point to be highlighted in this study is the evidence of a correlation between rain and fade events durations observed in a 12 GHz satellite link. This result is quite important under the engineering point of view, once it can be used in the design of improvement techniques for low availability satellite systems.

Diurnal variation in a long distance VHF tropospheric path in the Brazilian Amazon region

This paper deals with an experimental study carried out in a long distance VHF tropospheric path located in the Brazilian Amazon region. Measurements of the received power in this path were registered for 170 hours and clearly indicate a diurnal variation characterized by the existence of two propagation mechanisms. Scatter propagation during the day and diffraction propagation in night hours. This information, together with the knowledge of the median values of the earth k-factor derived from these measurements are important input data for planning VHF and possibly UHF radio systems in low latitude areas.

Spatial structure of rain in the Amazon region

Based on rain gauge and radar measurements this paper discusses the variability of the spatial distribution of precipitation in the Amazon region. Regarding the horizontal behaviour, the emphasis is given to the dimension and statistical characteristics of rain cells. On the other hand, the problem associated to the vertical extent of rain is stressed with a few examples for different types of precipitation. The importance of the material presented here is highlighted regarding satellite communication systems design. Site diversity configuration and modelling of low and high availability systems are referred to.

Propagation Analysis for Wireless Sensor Networks Applied to Viticulture

Wireless sensor networks have been proposed as a solution to obtain soil and environment information in large distributed areas. The main economic activity of the Sao Francisco Valley region in the Northeast of Brazil is the irrigated fruit production. The region is one of the major agricultural regions of the country. Grape plantations receive large investments and provide good financial return. However, the region still lacks electronic sensing systems to extract adequate information from plantations. Considering these facts, this paper presents a study of path loss in grape plantations for a 2.4 GHz operating frequency. In order to determine the position of the sensor nodes, the research dealt with various environmental factors that influence the intensity of the received signal. It has been noticed that main plantation aisles favor the guided propagation, and the vegetation along the secondary plantation aisles compromises the propagation. Diffraction over the grape trees is the main propagation mechanism in the diagonal propagation path. Transmission carried out above the vineyard showed that reflection on the top of the trees is the main mechanism.

Path loss modeling at UHF band for Wireless Sensor Network deployment in a vineyard

Wireless Sensor Networks (WSNs) can be used to monitor large agricultural areas, as the São Francisco Valley region in the northeast of Brazil. The main economic activity is grape growing for export which demands high quality production in order to attend the market requirements. This work presents an experimental study of path loss in grape plantations located in this region performed based on a measurement campaign. The research will aid the deployment of WSNs in São Francisco Valley region.

Radio wave diffraction by terrain irregularities

This paper deals with the problem of diffraction by terrain irregularities. It is well-known that this problem is quite complex, the general solution requiring an integral equation normally solved by numerical methods. To avoid the difficulties associated to this solution, simplified methods are available for the evaluation of radio wave attenuation in practical cases. However, the accuracy of these methods depends on restrictions imposed by frequency, link parameters (path distance and antenna heights) and terrain profile. Propagation mechanisms such as ground wave over a smooth spherical earth and multiple diffraction by isolated obstacles are examples where the accuracy is closely related to specific topographical features. In this paper emphasis is given to the work that is being carried out in the Study Group 3 of ITU-R (Radiocommunication Sector of the International Telecommunication Union). In the Recommendation ITU-R P.526–10 there are consolidated algorithms to solve the above limiting cases. Nevertheless, an important question remains, i.e., how to handle a situation where the variations of the relief are within the limits between smooth earth and isolated obstacles? Numerical results derived from the solution currently adopted by Recommendation 526–10 to this case do not fit well when compared to experimental data. In this context, the present paper discusses some fundamental points to be taken into account in the development of a possible solution to this problem. The analysis of interaction between the terrain and the propagating wave is based on the concept of penumbra region derived from a mathematical model consisting of a smooth spherical earth surmounted with a knife-edge obstacle. A preliminary conclusion indicates that an empirical hybrid model which considers the two limiting cases referred to in the above comments seems to be the best compromise to solve the problem.