This paper begins with a discussion of multipath interference. The spatial description of the field impinging upon a mobile radio antenna is derived and the power spectrum and other properties of the signal envelope are considered. Next, large scale variations of the average signal are discussed. Measurements of observed attenuation on mobile paths over both smooth and irregular terrain are summarized. The paper concludes with a discussion of methods of predicting the area of coverage from a base station.

Properties of mobile radio propagation above 400 MHz

Propagation of radiowaves over irregular terrain and in an inhomogeneous atmosphere is solved by the parabolic equation method using the split-step Fourier algorithm on a terrain-conformal mesh. A piecewise continuous coordinate system is generated by the specification of: (1) the terrain profile shape at discrete points and (2) an upper height. The resulting mesh is conformal to the terrain at the lower boundary and gradually flattens off at the maximum height. In addition to preserving the number of points on any vertical line between the terrain and the maximum height from one range step to another, the coordinate transformation used in the paper produces a correction term in the refractive index whose gradient diminishes with height. As a result, the sampling requirements over steep terrain are relaxed when compared to the Beilis-Tappert transformation. Formulation and results are given both for the horizontal and vertical polarizations.

A curvilinear coordinate-based split-step parabolic equation method for propagation predictions over terrain

In this paper we describe radio wave propagation within mixed residential area consisting of vegetation and houses. We assume no specific knowledge of the houses and vegetation location, but only of their statistical parameters. A three-dimensional (3D) stochastic approach, which is based on the statistical description of the terrain features, houses and vegetation, and deterministic description of signal decay is presented. The scattering and diffraction from trees and buildings, as well as the diffused reflection from the rough structures of the obstructions are modeled using the statistical description of an array of non-transparent phase screens randomly distributed on the rough terrain. The model, which accounts for single scattering and diffraction phenomena and a similar model, which accounts for multiple scattering effects without effects of diffraction are compared with measurements carried out in typical rural mixed residential areas with vegetation. The accuracy of the theoretical prediction is analyzed accounting possible variations of the terrain features. The approach presented here is applicable in many cases, where specific topographical information is not available.

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Radio propagation in rural residential areas with vegetation

Measurements of signal attenuation were made from a suburban hilltop base station to a mobile vehicle on several streets in the surrounding countryside. Measurements of signal strength were simultaneously made in the winter of 1971 at frequencies of 836 MHz and 11.2 GHz and then repeated in the summer to determine the effects of foliage. The presence of foliage reduced the received signal strength and the effect was more pronounced at X -band than at UHF. In cases where the shadowing obstacle was tree covered, signal levels at UHF might typically be 10 dB lower when the trees were in full leaf, whereas at X -band this additional loss could be as high as 20 dB. The experimental data was compared to values predicted by knife-edge diffraction and reasonable agreement was found.

Some Propagation Experiments Relating Foliage Loss and Diffraction Loss at X-Band and UHF Frequencies

[1] We describe radio wave propagation within terrain with vegetation, based on the measurements performed in a forested areas using low transmitter (TX) and receiver (RX) antenna elevations We continue to investigate 3-D statistical multiparametric model of radio wave propagation above the rough terrain with some modifications made to describe multiple scattering of the signal field from randomly distributed trees, as phase screens, that model the random structure of trees with the rough surfaces and the irregular structure of branches and leaves, and other roughnesses placed on the ground surface The scattering effects of trees and roughnesses are considered using a statistical description of an array of randomly distributed screens placed on a rough terrain At the same time, an empirical short-range path loss model which is based on measurements carried out in typical forested areas in Denmark is considered Comparison between results obtained from the statistical and the empirical models and those obtained from examination of the experimental data, as well as with the results of other existing models, is presented It is shown that both models predict the exponential field intensity decay with the wide range of the power law index variations (from -25 to -43) with accuracy ±6 dB with respect to experimental data and which is better than that obtained from other existing theoretical models

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002RS002600

Prediction of UHF path loss for forest environments

A simplified method of computing knife edge diffraction in the shadow region is presented which is applicable to most obstacle gain paths, that is, paths with a dominant mountain obstacle. The method has been worked out for 1) the four-ray model-specular reflection on each side of the obstacle, 2) the two-ray model-reflection on one side only, and 3) the single-ray model-no reflection on either side. The obstacle can be at any location along the path. The accuracy is within 2 db for path geometries such that the usual diffraction parameter \nu is greater than 1 and the two terminal heights are less than the obstacle height. Curves which further simplify the computation procedure are presented.

L. Trolese

Papers

Simplified method for computing knife edge diffraction in the shadow region