Wireless communications between radioelectric systems and communicating objects require a good knowledge of the propagation channel. First it is necessary to evaluate the behaviour of the waves in the environment considered (rural, suburban, urban, dense urban, indoor) to be able to parameterise the emission power, the polarisation and to choose the antennas, the modulation, the transmission protocol, etc.
A first part of this chapter will consist in briefly defining what is a radio wave and then presenting the various phenomena being able to affect it (reflection, transmission, diffraction , diffusion, guidance).
In a second part the difficulties of transmission will be detailed resulting from the interactions of the waves, between them and with the environment, outside and inside buildings (shadowing, interferences , fading, etc).
The last part will approach the available techniques for the study of propagation between communicating objects, mainly with models of propagation in various environments (rural, mountainous, suburban, urban, inside buildings, etc.) macro cell, small cell, micro cell, pico cell , launching and ray tracing models. These two last are more particularly adapted to understand and illustrate the various phenomena, inside and outside the buildings.