Product Info

System Description WipLL Radio Technology - Physical Layer
25030311-08 Airspan Networks Inc. 2-25
2.6.2.2.1. Propagation loss
Propagation is the dispersal of the signal into space as it leaves the antenna. The loss
of this propagation depends on the signal path between the transmitter and the
receiver. Obstructions in the signal path such as trees and buildings can cause signal
degradation. Several models simulate signal attenuation along this path.
Propagation loss should incorporate fading margins to compensate different
phenomenon such as multipath shadowing and climatic behavior of the waves.
Based on this, the parameter path loss can be represented by
PathLoss = L + Fade Margin.
 Free Space model:
Free space propagation loss is valid where the first Fresnel Zone is clear. In this
case, free space propagation loss is given by the following equation:
L
FS
= 32.44 + 20logd
[km]
+ 20logf
[MHz]
 Fade Margin:
Fade margin further introduces fading factor to the propagation loss to cover the
different signal fading and shadow effects, as well as the degradation caused by
interferences. The fading factor depends on the time availability parameter
defined by the operator, and should be calculated according to the ITU 530
model for 99.9% availability.
For simplicity purposes, the ITU model can be replaced by a 10 dB Flat fade
margin as a rough estimation.
 Rainfall:
Radio signals are attenuated by moisture in the atmosphere. The level of
attenuation varies with carrier frequency, the quantity of rainfall, and the
distance from the transmitter to the receiver. The variation of attenuation
with frequency is particularly strong and highly non-linear. At 3 GHz, the
highest attenuation is about 0.06 dB/Km; for a typical WLL path of, for
example, 6 Km, the attenuation is only 0.36 dB. Therefore, for the purpose of
link budget, we can assume that the impact of rainfall is negligible.