Propagation of the radioelectric waves of terrestrial networks

Radio links on the fixed (FH, WIFI, WIMAX, etc.), mobile (GSM, UMTS, etc.) or very high-speed short-range terrestrial network are located either within the troposphere, which is the site of numerous meteorological and climatic phenomena (presence of refractive index gradients, hydrometeors: rain, snow, fog, etc.), or above the ground with its share of obstacles (buildings, vegetation, etc.), or inside buildings.

To study the balances of such links, we need to take into account the various attenuations (free-space attenuation, excess attenuation, which includes all the additional attenuations due to the various effects of the environment: gas, hydrometeors, buildings, vegetation, etc.) and the various signal reinforcements between transmitter and receiver (antenna gains, focusing, etc.). Different propagation mechanisms come into play: reflection, refraction, transmission, scattering, etc.

Refractive index plays an important role in the troposphere. Refractive index gradients in the vertical profile create guiding layers for electromagnetic radiation. If the horizontal extent of these guiding layers is sufficient, they cause sometimes significant variations in the level of the direct signal, variations in angles of arrival and the appearance of multipaths that interfere at the receiver.

The ground, buildings and vegetation all contribute their share of rays: we can distinguish between rays reflected on the ground, on the various façades of buildings or on the various partitions inside buildings, rays diffracted on high peaks or on the horizontal and vertical edges of buildings located in the axis of the link, rays scattered on the vegetation cover, rays guided in ducts, streets, building corridors, etc.

At frequencies above 10 GHz, electromagnetic waves interact with the neutral atmosphere and various meteorological phenomena such as hydrometeors (rain, snow, hail) to cause energy absorption and scattering, thus weakening transmitted signals.

The ever-increasing needs of telecommunications in terms of throughput require increasingly accurate modeling of the propagation channel in ever more diverse environmental conditions, frequency ranges, bandwidths and so on. This modeling enables us to optimize radio interfaces in terms of quality, to optimize networks during deployment (determination of coverage areas (choice of sites, frequency allocation, definition of power, antenna gains, etc.) and to determine possible interference).

There are different types of model: deterministic, empirical and semi-empirical.

Deterministic models are based on the fundamental laws of physics. They serve as reference models. On the other hand, calculation time is...