Henry L. Bertoni

A new approach to 3-D ray tracing for propagation prediction in cities

A vertical-plane-launch (VPL) technique for approximating a full three dimensional (3-D) site-specific ray trace to predict propagation effects in cities for frequencies in the 300 MHz-3-GHz band is described and its predictions are compared with measurements for Rosslyn, VA. The VPL technique employs the standard shoot and bounce method in the horizontal plane while using a deterministic approach to find the vertical displacement of the unfolded ray paths. This approximation is valid since building walls are almost always vertical. The VPL method shows significant improvement compared with the slant-plane/vertical-plane (SP/VP) method for rooftop antennas. For a base station located at street level, the VPL method gives better predictions than the two-dimensional (2-D) method in locations where propagation over buildings is significant.

Radio propagation characteristics for line-of-sight microcellular and personal communications

To acquire a knowledge of radio propagation characteristics in the microcellular environments for personal communications services (PCS), a comprehensive measurement program was conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three base station antenna heights of 3.2 m, 8.7 m, and 13.4 m and two frequencies at 900 MHz and 1900 MHz. Five test settings were chosen in urban, suburban, and rural areas in order to study propagation in a variety of environments. This paper reports the LOS measurements in different environments, all of which show variations of signal strength with distance that have distinct near and far regions separated by a break point. It was also found that the location of the break point for different frequencies and antenna heights can be calculated based on first Fresnel zone clearance. The regression analysis reveals a slope that is less than two before the break point, while it is greater than two after the break point. This break distance can be used to define the size of microcell and to design for fast hand-off. Beyond the first Fresnel zone break distance the base station antenna height gain was observed to approximately follow the square power law of antenna height. >

Unified approach to prediction of propagation over buildings for all ranges of base station antenna height

Theoretical results for the dependence on base station antenna height of the average received signal for mobiles at street level are presented. The results apply to residential and commercial sections of cities and to all ranges of antenna height from well above to below that of the surrounding buildings. Assuming all buildings to be of equal heights, the range dependence of the average signal is found by evaluating multiple forward diffraction past rows of buildings. The solution for this diffraction problem for sources near to or below the rooftops gives the dependence of the range index on antenna height and base station height gain, which are in agreement with measurements. These results will be of importance for proposed systems for personal communication services, which envision the use of base station antennas at the height of lamp posts, as well as cellular mobile radio. >

Diffraction of cylindrical and plane waves by an array of absorbing half-screens

Multiple forward diffraction past an array of many absorbing half-screens whose separation is large compared to wavelength is examined. Starting with the physical optics approximation for half-planes that are equally spaced and of equal height, the field incident on successive edges is represented by a multidimensional Fresnel integral, which is then expanded into a series of functions studied by Boersma (1978). When the angle of incidence with respect to the plane containing the edges is small, each edge is in the transition region of the previous edge, which precludes the use of the geometrical theory of diffraction and related asymptotic theories. The solution obtained applies for incidence either from above or below the plane containing the edges, and is especially suited to the case of near-grazing incidence. This method of solution allows for numerical evaluation of a large number of half-screens and shows how the multiple diffracted fields are influenced by the physical parameters. Both incident plane waves and incident cylindrical waves can be treated. >

Microcellular propagation characteristics for personal communications in urban and suburban environments

New microcellular systems have been proposed to operate over short radio paths by using low-base station antennas, and transmitting at low power. In order to study radio propagation in the microcellular environments for future personal communications services (PCS), comprehensive radio propagation measurements were conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three transmitting antenna heights of 3.2, 8.7, and 13.4 m and two frequencies in the 900 and 1900 MHz bands. The paper reports the path loss measurements made in urban and suburban areas where the receiving mobile was driven along preselected line-of-sight (LOS), zig-zag, and staircase routes to gather information about direct propagation along streets, as well as diffraction over the roofs in suburban areas, and diffraction around the corners in urban areas. The results obtained for the three antenna heights are studied, and show the height gain that can be expected for microcells in different environments. >

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.

Achievable accuracy of site-specific path-loss predictions in residential environments

The design of future wireless communication systems employing microcells will require a flexible tool for determining the dependence of the coverage area on base-station antenna height and position. In this paper, the accuracy of a ray-based algorithm versus slope intercept models for propagation prediction in residential environments is investigated by comparison with measurements. The measurements were taken in two areas of Trenton, NJ, where building heights ranged from one to three stories. For base-station antennas at or above rooftop levels, the algorithm is shown to give good agreement with the measurements. For these high antennas, the average and standard deviations of the difference between the site-specific prediction and measurement are less than 1 and 5 dB, respectively. For base-station antennas below the rooftops, additional ray paths are required in order to achieve similar prediction accuracy.

Transmission and reflection characteristics at concrete block walls in the UHF bands proposed for future PCS

Buildings such as warehouses, supermarkets and retail department stores typically have walls constructed from concrete (cinder) blocks. The web and void design of the individual blocks and their arrangement within a wall creates a periodic structure, which exhibits frequency dependent transmission and reflections characteristics in the UHF bands proposed for future Personal Communication Systems (PCS). For higher frequencies, higher order Floquet modes excited at the periodic structure can propagate away from the wall, suggesting that significant power can be carried away from the wall in non-specular directions. Indoor propagation prediction models must consider the non-specular paths exited by walls with a periodic nature in order to account for all of the scattered power. In this work, plane wave reflection and transmission characteristics for typical concrete block walls are examined theoretically and experimentally to determine the frequency dependence of the specularly and non-specularly transmitted and reflected fields. >

Reflection from a periodically perforated plane using a subsectional current approximation

The scattering from a zero thickness plane having finite sheet resistance and perforated periodically with apertures is calculated for arbitrary plane wave illumination. The surface current density within the unit cell is approximated by a finite number of current elements having rooftop spatial dependence. The transverse electric field is expressed in terms of the current, and the electric field boundary condition is satisfied in an integral sense over the conductor, generating a finite dimension matrix equation whose solution is the current density. Since the conductor shape is defined through the locations of subsectional current elements, arbitrary shaped apertures can be handled. The reflection coefficient and current distribution are calculated for square apertures in both perfectly conducting and resistive sheets, and for cross-shaped apertures. Finite resistivity is shown to cause the magnitude of the transverse magnetic (TM) reflection coefficient to decrease more rapidly and its phase to decrease less rapidly, as the angle of incidence approaches glancing. Through detailed plots of the current density, the current crowding around the apertures is made clearly evident.

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.