The ITU single vegetative obstruction model is a radio propagation model that quantitatively estimates attenuation due to a single plant or tree standing in the middle of a telecommunication link.
[1] Frequency = Below 3 GHz and over 5 GHz Depth = Not specified The single vegetative obstruction model is formally expressed as,
where, A = The Attenuation due to vegetation.
Unit: decibel(dB).
= Specific attenuation for short vegetative paths.
Ri = The initial slope of the attenuation curve Rf = The final slope of the attenuation curve f = The frequency of operations.
Unit: gigahertz (GHz).
k = Empirical constant Initial slope is calculated as:
where, a, b and c are empirical constants (given in the table below).
where, k0 = Empirical constant (given in the table below) Rf = Empirical constant for frequency dependent attenuation A0 = Empirical attenuation constant (given in the table below) Ai = Illumination area Ai is calculated in using any of the equations below.
A point to note is that, the terms h, hT, hR, w, wT and wR are defined perpendicular to the (assumed horizontal) line joining the transmitter and receiver.
where, wT = Width of illuminated area as seen from the transmitter.
wR = Width of illuminated area as seen from the receiver.
hT =Height of illuminated area as seen from the transmitter.
hR = Height of illuminated area as seen from the receiver.
aT = Azimuth beamwidth of the transmitter.
Unit: degree or radian.
aR = Azimuth beamwidth of the receiver.
Unit: degree or radian.
eT = Elevation beamwidth of the transmitter.
Unit: degree or radian.
eR = Elevation beamwidth of the receiver.
dT = Distance of the vegetation from transmitter.
dR = Distance of the vegetation from receiver.
Empirical constants a, b, c, k0, Rf and A0 are used as tabulated below.
The model predicts the explicit path loss due to the existence of vegetation along the link.
The total path loss includes other factors like free space loss which is not included in this model.
Over 5 GHz, the equations suddenly become extremely complex in consideration of the equations for below 3 GHz.