Page 34 - 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

Remark that the channel sparsity is further VolcanoUrban (optimized for large-scale outdoor
increased by the use of highly-directive antennas, areas) for the in-street predictions. Some
which will compensate for global higher path loss evolutions have been required for this work, which
at mmWave or sub-THz frequencies. Some multi- are described in the two following subsections.
paths transmitted and/or received out of the
antennas beam width are filtered out. This effect 2.1 Extension of the EM material properties
has been captured by [2] where the 60-GHz delay library up to 200 GHz
and angular spreads do depend on the antenna The original simulator relies on the definition of
beam width. Recommendations [2] and [3] materials permittivity and conductivity
propose a beam width-dependent model for frequencies up to 100 GHz, including those
different scenarios at 28 and 38 GHz in recommended by ITU [8, Table 3]. The current
respectively indoor and outdoor environments. knowledge regarding the sub-THz materials
Only a few scientific publications report today on properties is limited. Therefore, we decided to
channel characterization above 90 GHz. Channel simply consider the ITU models at 100 GHz and
sounding measurements, collected in a shopping extend their application up to 200 GHz. The correct
mall at 28 and 140 GHz, are described and implementation was validated by test simulations
analyzed in [4]. Similar delay spreads and angular that assess the transmission, reflection and
spreads are found in both frequency bands. Paper diffraction coefficients from the four following
[5] reports on indoor measurements in bands V materials: glass, concrete, plasterboard and wood
(60 GHz), E (70 – 80 GHz) and D (126 – 146 GHz). [9]. The plasterboard that is almost transparent
The delay spread is found to be lower in the D- below 6 GHz leads to more than 20 dB loss over
Band. Even if similar propagation paths can be most part of the sub-THz spectrum. Concrete walls
identified in each band, the longest echoes are not are fully opaque above 60 GHz. Strong outdoor-
detected in the D-band (possibly due to limitation indoor isolation, and room-to-room isolation in an
in the measured power dynamic). Paper [6] indoor environment, are expected in sub-THz
presents a large set of measurements in several bands. Also reflection loss is observed constant
bands up to 86 GHz with a focus on delay spread with frequency while diffraction loss is higher.
also. The conclusion is that delay spread does not More precisely, the uniform theory of diffraction
vary much with frequency. (UTD) loss remains the same at the optical
frontiers, but rapidly degrades out of those
Two different scenarios are studied in the present frontiers. Additional degradation between 2 GHz
article, radio propagation for in-office access and and 200 GHz is found to be around 20 dB when
in-street backhaul. Section 2 describes the ray- considering a 90° concrete corner and incidence
based model that has been utilized to produce angle 45°.
channel samples at various frequencies and
situations, and how it has been upgraded. The 2.2 Management of highly-detailed
simulation set-ups are detailed in section 3. The geographical representation
simulation results are reported in section 4, along The VolcanoUrban tool [10] predicts several kinds
with the analysis and the description of the derived of outdoor contribution, resulting from
path loss and delay-spread simplified models. interactions with the building façades, the ground
Conclusions are summarized in section 5. and the building rooftops. The ray-launching
implementations allows for very fast computation
2. PROPAGATION CHALLENGES AND of 3D multiple trajectories that combine reflections
MODELING IN SUB-THZ BAND and diffractions, as well as propagation above

The ray-based engine Volcano that is used to rooftops. The losses due to the rooftop diffraction
create the sub-THz prototype simulator has been (or terrain diffraction) is computed from the well-
successfully employed for more than 15 years in known knife-edge diffraction technique, while the
the sub-6 GHz band, and has already been utilized lateral building diffractions are calculated from
by the industry in the past few years in the UTD. The vegetation obstacles are managed
mmWave domain up to 80 GHz [7]. Two different specifically for frequencies above 6 GHz [11]. Both
versions have been employed in the presented the transmission through the vegetation and the
research: VolcanoFlex (devoted to small 3D diffraction on bottom and top of the foliage are
environments) for the in-office predictions, and considered. The transmission is computed from an
average linear loss (dB/m) that is multiplied by the

18 © International Telecommunication Union, 2019