Page 38 - 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

considered yet, i.e. the receiver sensitivity. In a
practical system, some of the individual paths that
are distinguished in low frequency bands may be
received at a level inferior to the noise floor at a
sub-THz frequency. The observed wideband
characteristics of the measured channel depend on
the receiver sensitivity or maximum allowed path
loss (MAPL) at each considered frequency. Fig. 9
shows how the LoS and NLoS isotopric median
delay spreads evolve with frequency, but this time,
different MAPL constraints are considered.

Fig. 10 – Propagation paths in office environment with
furniture
The impact of furniture at 150 GHz has been
studied by addition of shelves, boards, screens and
chairs in the same office environment. Some of the
links are subject to changes as shown in Fig. 10.
But globally, as the user terminal is located above
many of the added objects (1.5 m), the channel
properties in terms of path loss, delay or angle
statistics are not significantly modified. This would
have to be further assessed with a lower terminal
antenna.

4.2 In-street scenario
The propagation channel is predicted at 1873
lamp-post-to-lamp-post radio links in a North-
American downtown area. The distribution
between LoS, NLoS and NLoS-Vegetation is shown
in Fig. 11 as a function of the distance. At the
shortest ranges, the poles are mostly in LoS and
NLoS-Vegetation situations, then NLoS occurrences
rapidly increase and become the dominant
configuration after 85 meters. At this distance, the
LoS probability falls below 10%. The NLoS-
Vegetation links are less than 20% at range
200 meters.

Fig. 9 – Median delay spread as a function of MAPL, for an
isotropic antenna at the access point
The conclusion on the delay spread evolution
significantly changes depending on the receiver
sensitivity value. The NLoS median delay spread is
observed as increasing with frequency when the
receiver sensitivity is low, while it rapidly falls to
only few ns in mmWave or sub-THz frequencies in
case of a limited-performance receiver. The way
the wideband channel properties are compared at
different frequencies has to be done carefully. The
delay spread may be strongly reduced in upper
spectrum due to the receiver limitations but not
directly to the propagation channel. Fig. 11 – Visibility condition as a function of the distance

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