InnoWave Telecommunications

R Xec

Figure 10.23. Direct and ground reflected rays, showing the Fresnel ellipse about the direct ray. (From Figure 18, Ref. 21.)

Figure 10.24. Fresnel zone for propagation between transmitter and receiver in clear space between building furnishings and ceiling fixtures. (From Figure 35, Ref. 21.)

related to the Fresnel ellipse. If the Fresnel ellipse associated with the path lies entirely in the clear space, the path loss has LOS properties (1/L2). Now as the separation between the transmitter and receiver increases, the Fresnel ellipse grows in size so that scatters lie within it. This is shown in Figure 10.25. Now the path loss is greater than free space.

Bertoni et al. (Ref. 21) report on one measurement program where the scatters have been simulated using absorbing screens. It was recognized that path loss will be highly dependent on nearby scattering objects. Figure 10.25 was developed from this program. It was found that the path loss in excess of free space calculated at 900 and 1800 MHz for W = 1.5 is plotted in Figure 10.24 as a function of path length L. The figure shows that the excess path loss (over LOS) is small at each frequency out to distances of about 20 and 40 m, respectively, where it increases dramatically.

Propagation between floors of a modern office building can be very complex. If the floors are constructed of reinforced concrete or prefabricated

Figure 10.25. Measured and calculated excess path loss at 900 and 1800 MHz for a large office building having head-high cubical partitions, but no floor-to-ceiling partitions. (From Figure 36, Ref. 21.)

concrete, transmission loss can be 10 dB or more. Floors constructed of concrete poured over steel panels show much greater loss. In this case (Ref. 21), signals may propagate over other paths involving diffraction rather than transmission through the floors. For instance, signals can exit the building through windows and reenter on higher floors by diffraction mechanisms along the face of the building.