Saúl A. Torrico

Modeling tree effects on path loss in a residential environment

A theoretical model is proposed to compute the path loss in a vegetated residential environment, with particular application to mobile radio systems. As in the past, rows of houses or blocks of buildings are viewed as diffracting cylinders lying on the Earth and the canopy of the trees is located adjacent to and above the houses/buildings. In this approach, a row of houses or buildings is represented by an absorbing screen and the adjacent canopy of trees by a partially absorbing phase screen. The phase-screen properties are found by finding the mean field in the canopy of the tree. Physical optics (PO) is then used to evaluate the diffracting field at the receiver level by using a multiple Kirchhoff-Huygens integration for each absorbing/phase half-screen combination.

A Simplified Analytical Model to Predict the Specific Attenuation of a Tree Canopy

A simplified analytical model is presented to predict the specific attenuation for propagation through a tree canopy in a residential environment for frequencies of up to 2 GHz. In this approach, the canopy of a tree is modeled as an ensemble of leaves and branches all having prescribed location and orientation statistics. The Foldy-Lax discrete scattering theory is used to find the specific attenuation of a tree associated with the mean field. Explicit formulas are presented to calculate the specific attenuation of a tree canopy. It is shown that the specific attenuation of a tree canopy depends on the frequency, polarization, electrical and geometrical characteristics of branches and leaves, biophysical parameters of a tree, and statistical distribution of branches and leaves in reference to the angle of incidence of the plane wave. It is also shown that for deciduous trees, as opposed to coniferous trees, the inclination angle distribution of the branches is more vertical, producing a higher specific attenuation for the vertical-polarization incident wave than for the horizontal-polarization incident wave

Foliage Attenuation Over Mixed Terrains in Rural Areas for Broadband Wireless Access at 3.5 GHz

This paper reports the modeling of foliage attenuation for a broadband wireless access system deployed over mixed terrains in rural areas at 3.5 GHz. The foliage is composed of leaves and leafstalks, and are the dominant scatterers along the transmission paths. The foliage attenuation is determined using the Torrico-Lang model combined with digital topography information. In this model, leaves are modeled as thin lossy circular dielectric discs whereas leafstalks (petioles) are modeled as thin lossy dielectric cylinders. Three measurement campaigns were performed using the mobile WiMAX system (IEEE 802.16 e) deployed in Hetzwege/Abbendorf during winter, spring and mid-summer. Using the winter data as a baseline, the foliage loss due to different degrees of foliation in spring and in winter is studied. The derived foliage loss is then verified and compared with an empirical exponential decay model.

Radiowave Propagation Prediction in Vegetated Residential Environments

This paper proposes a propagation prediction model in vegetated residential areas. The goal is to model the attenuation caused by the tree canopies in vegetated residential areas in a simplified manner. The model is based on the Torrico-Bertoni-Lang model. It describes a vegetated residential area where rows of houses and trees are lying between an elevated transmitting antenna and the receiving antenna that is located at street level. In this scenario, the receiving antenna does not have a direct line of sight (LoS) from the transmitting antenna. Since the transmitting antenna has comparable height to the houses, propagation takes place over the top of the houses. From this viewpoint, the propagation loss is computed by using multiscreen diffraction, where the houses are modeled as absorbing screens, and the trees are modeled as phase screens. Using this approach, the total propagation loss is broken into three components, namely, free-space loss, multiscreen diffraction loss, and rooftop-to-street diffraction loss. In this paper, two main contributions are provided. The first is that a simplified analytical model is proposed to compute the multiscreen diffraction loss in a vegetated residential environment. The second contribution is to include in a simplified manner the effects of vegetation on the rooftop-to-street diffraction loss via the scattering theory of Foldy-Lax. To verify the proposed model, cross-season measurement campaigns at 800 and 3500 MHz were conducted in vegetated residential areas in the north of Germany. The model serves as an important extension of the Walfisch-Bertoni urban model and the COST-231 Walfisch-Ikegami model for applications in vegetated residential areas. The model is valid at the UHF frequency band between 0.5 and 3.5 GHz.

Theoretical investigation of foliage effects on path loss for residential environments

A mobile communications system depends on the propagation loss due to the environment between the transmitter and the mobile receiver located at the street level. A theoretical model is proposed to include the effects of trees as well as buildings/houses on the propagation in residential environments. As in past models, the rows of building/houses are modeled as diffracting cylinders lying on the Earth, but now the canopies of the trees adjacent to and above the building/houses are included in the model. The building/houses are represented as absorbing screens and the trees as phase screens. The phase screen properties are found by representing the trees as a time-invariant ensemble of leaves (discs) and branches (cylinders) all having a prescribed location and orientation statistics. The mean field at the aperture of the absorbing screen depends on the mean field in the canopy, which is calculated using the discrete scattering theory of Foldy (1945) and Lax (1951).

Predicting the radio channel beyond second-generation wireless systems

Ray-optical methods incorporating Geometric Optics (GO) and the Uniform Theory of Diffraction (UTD) are appropriate for the representation of radiowave propagation in cities for frequencies in the UHF band and above, where the wavelength is small compared to building dimensions. Various ray codes have been written to implement the ray representation. Because the rays undergo multiple interactions with the buildings over long distances, the codes make various assumptions to reduce running time. This paper reviews the types of assumptions that have been made, the ways in which the ray procedures have been implemented, and the accuracy that can be expected from the predictions. The paper gives examples of how the computed ray quantities have been used to simulate the characteristics of the radio channel (besides received power) that impact the designs of different radio systems.

Point-to-point backhaul systems at 3.5GHz predictions vs. measurements in a vegetated residential area of Washington, DC, USA

For point-to-point backhaul systems located in a vegetated residential area, the base-station transmitter is located close to the surrounding rooftops; the propagation takes place over the rooftops and through the canopy of the trees. The receivers, in many cases, are also located close to the surrounding rooftops or well below them. The objective of the present paper is to use the Torrico-Bertoni-Lang model to predict the propagation losses and compare them with measurements made at 3.5 GHz in the Washington, DC area. Results show that by using a physical-base propagation model and GIS data, a close correlation between the measurements and the predictions is obtained. In particular, for all the point-to-point links measured the root-mean-square-error (RMSE) is 5.5 dB.

2-D radiative transport theory - forward scattering approximation: Mobile-to-mobile communication in a trunk dominated forest

As a new generation of broadband wireless communication systems is being proposed to meet the increased demand for data capacity, there is a new interest in deploying high-performance microwave backhauls, at millimeter frequencies, to interconnect the wireless network in urban/suburban/forest environments. Deploying high-performance microwave backhauls in urban/suburban/forest environments, however, does not guarantee a direct line-of-sight between the transmitter and receiver base stations. A substantial number of backhaul small cells in urban/suburban or forest settings do not have a clear line-of-sight to the network; they are either blocked by houses, trees, or both. It is of practical interest to determine the effect of attenuation at these millimeter frequencies. The objective of this presentation is to demonstrate that the use of the forward scattering approximation to solve the Radiative Transport (RT) equation at millimeter frequencies is an effective and a practical way of assessing the attenuation in a trunk dominated forest. The solution of the exact RT equation at millimeter wave frequencies is computationally much more intensive than the solution of the RT equation under the forwarding scattering approximation.

2-D radiative transport theory: Propagation loss predictions in a trunk dominated forest

With the emergence of new applications for wireless sensor networks (WSN) in outdoor environments, such as, WSN measuring environmental parameters in forested areas, there needs to be more precise analysis of the propagation loss between transmitters and receivers. The objective of this presentation is to demonstrate the importance of including the incoherent field as part of the total field to predict the propagation loss in a trunk dominated forest. A typical WSN in a forested environment involves an undetermined number of independent nodes where each independent node has many sensors that measure different environmental variables, such as, solar radiation, pressure, and humidity. To link all these nodes to a central node therefore, they need to meet the link reliability between each node and the central node. An accurate propagation loss prediction also needs to be obtained. As it will be shown in the present paper, the propagation loss changes with frequency, with the location of the transmitter and receiver between nodes, and with the biophysical parameters of the forest. In this context, the radiative transport (RT) theory is used to demonstrate the importance of the coherent and the incoherent fields on propagation loss. To check the soundness of the RT theory, a Monte-Carlo (MC) simulation will be employed.

Predicting the propagation loss through a tree canopy at millimeter frequencies — Forward scattering approximation — 3-D vector radiative transport theory

The vector radiative transport theory is used to compute the attenuation produced by a tree canopy containing random located lossy-dielectric leaves and branches at millimeter wave frequencies. Using this approach, the forward scattering approximation is used to simplify the radiative transport equation. The forward scattering approximation is used since at millimeter frequencies, the leaves and branches are large and thick compared to the wavelength; hence, a leaf or a branch scatter energy strongly in the forward direction and weakly in all other directions. The leaves are modeled as flat-circular lossy-dielectric discs and the branches as lossy-dielectric cylinders with prescribe orientation statistics.