Different empirical models for the evaluation of the path loss exist. The following types of models may be mentioned here: long-distance models, Motley-Keenan models (Keenan 1990) and multi-ray models, also referred to as corridor models.
In the case of the long-distance models, the parameters considered are the frequency and the distance between the transmitter and the receiver. Two longdistance models have been advanced: while the first such model (COST 231 1999) assumes a logarithmic dependence of the attenuation on distance, the second model assumes a linear dependence (COST 231 1999). Both models can be used in non line-of-sight situations.
Motley-Keenan models apply to non line-of-sight situations in dense environments, like an office. Like the building penetration loss, the path loss L is expressed as the sum of the free-space loss Lo of the losses due to the different obstacles along the direct line-of-sight path (tiles, walls, doors, windows) and of a constant Lc (Motley 1988). Databases can be used for differentiating between the different obstacles to which specific attenuation values are attached. This model is the most commonly used.
where Nj is the number of walls of type j present along the line-of-sight path, Lj is the losses due to walls of type j, N is the number of types of walls, Nf is the number of tiles present along the line-of-sight path and Lf is the losses due to tiles.
A few typical values of the losses in the 1-2 GHz frequency band for different types of materials used in the internal walls are summarised here in Table 7.3 (COST 231 1999).
The waveguide effect of the corridors imposes to develop specific models taking into account a diffraction term in non line-of-sight situations (Dersch 1994a; La-fortune 1990).
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