Page 39 - ITU Journal: Volume 2, No. 1 - Special issue - Propagation modelling for advanced future radio systems - Challenges for a congested radio spectrum

ITU Journal: ICT Discoveries, Vol. 2(1), December 2019

The CDF of the excess path loss (EPL) at 150 GHz is
plotted in Fig. 12 for three different values of
vegetation linear loss (VLL). The shown EPL is the
one obtained with highly-directive antennas;
however, the results are very similar with larger
antenna beam widths. The NLoS EPL is about
50 dB higher than non-NLoS. It is hardly impacted
by the VLL value, as the dominant propagation
path is often due to rooftop diffraction, i.e. occurs
above trees. The LoS percentage appears as the left
CDF value in the plain curves: about 20%. The
highest CDF values are associated to the
NloS-Vegetation situation, where the VLL has a
significant impact. As the foliage transmission is
combined with foliage diffraction, the distance Fig. 14 – Standard deviation of the residual path loss
between EPL curves decreases when the VLL
increases, i.e. when the diffracted path becomes The highly-directive EPL can be approximated by a
dominant. log-normal variable, where both the mean value

Fig. 13 shows the resulting EPL fitting functions for and the standard deviation are log-distance
the different VLL values, and Fig. 14 shows the dependent:
standard deviation of the residual path loss. This { } = + × ( ) (2)
residual path loss is very high compared to general
observations at lower frequencies (standard { } = + × ( ) (3)
deviation lower or equal to 10 dB). It globally
increases with distance. The EPL parameters at 150 GHz are given in
Table 2 for NLoS and NLoS-Vegetation situations
(values are zero in LoS). Those values apply on
distances greater than 25 up to 200 meters. They
are proposed as a simplified model for the path
loss experienced in urban street-level sub-THz
fixed backhaul.
When considering different antenna beam widths,
we observe only small changes in the EPL values,
meaning the channel is dominated by a strong path.
Actually, the delay spread is more significantly
impacted. Fig. 15 shows how it is statistically
distributed depending on the antenna beam width
and visibility. The 90% quantile with the isotropic
Fig. 12 – CDF of the excess path loss antenna is between 70 and 90 ns depending on the
visibility condition. It is lower than 0.2 ns with the
6°-beam-width antenna. This is of particular
importance in a backhaul system definition, where
the performance and even the waveform can be
affected by channel wideband properties, flat or
selective. The vegetation scattering has not been
predicted in this work; however, it may cause some
spread in the delay domain even with a directive
antenna, provided the dominant path crosses a
tree.

Fig. 13 – Excess path loss fit

© International Telecommunication Union, 2019 23