Page 33 - 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

SUB-THz CHANNEL CHARACTERIZATION FROM RAY-BASED DETERMINISTIC SIMULATIONS
Grégory Gougeon, Yoann Corre, Mohammed Zahid Aslam
Infra Network Design (IND) department, SIRADEL, 2 Parc de Brocéliande, Saint-Grégoire, France

Abstract – Future wireless communication systems will require large network capacities beyond the
capabilities of present and upcoming 5G technology. The trend of considering higher frequencies for their
large bandwidths continues today into the sub-THz domain. The frequencies that are considered in this
article are the ones investigated in the BRAVE beyond-5G project, i.e. in the 90-200 GHz spectrum. A ray-
based deterministic tool is extended to those frequencies, which are then exploited to simulate and
characterize the propagation channel properties in two different scenarios: 1) in-office and 2) in-street. A
particular interest is brought to the path loss and delay spread statistics. The impact of the antenna beam
width is also considered. Using deterministic simulations (even if not yet validated in the target spectrum
but at lower frequencies) is a very convenient way to explore the sub-THz propagation characteristics,
while channel measurements are only very few at those frequencies. Some very simple models have been
derived that may contribute to the elaboration and evaluation of future sub-THz systems.

Keywords Channel modeling, ray-based model, sub-THz

The scientific propagation community is today
1. INTRODUCTION
producing intensive activity on the mmWave bands
Many frequency bands in the so-called millimeter- that are envisaged for 5G applications. These
wave spectrum (mmWave), between 10 and applications include a wide range of different
90 GHz, are allocated today for fixed terrestrial solutions applied in backhauling, access, indoor
communication radio links, and will be further and outdoor environments, large bandwidth and
exploited in 5G for mobile access or backhaul. high antenna directivity scenarios. Recent channel
Some interest of the telecommunication models like WINNER+, METIS, mmMAGIC,
community that is preparing the next generation MiWEBA or 3GPP offer solutions addressing
technologies is now moving to huge bandwidths frequencies above 6 GHz and often up to 100 GHz.
available above 90 GHz. As pointed out in [1], up to The ITU also provides reference attenuation
58.6 GHz bandwidth could be devoted to terrestrial models up to 100 GHz (or beyond) for atmospheric
communication services in spectrum between 90 gases, rain, vegetation and in-building penetration.
and 200 GHz. Those frequencies, on which the A sparse propagation channel is generally
present article is focusing, are either considered as observed in mmWave bands, where the line-of-
part of the THz or sub-THz domain, depending on sight (LoS) direct path is the most dominant
the interpretations. In the following, the term “sub- component. Many propagation paths that bring
THz” is preferred.
significant power at a lower frequency are either
The properties of the radio wave propagation in the attenuated by obstacles or suffer from some
90-200 GHz band are not properly known, and no interactions weakness (diffraction, diffuse
channel model (deterministic or stochastic) has been scattering). That is still true in the sub-THz
formally validated and recognized by the scientific spectrum, and might even be slightly amplified.
community yet. The characteristics of the propagation Nevertheless, some specular strong contributions
channel and its modeling are nevertheless critical are still present, leading to a few propagation
inputs for several research tasks: definition of clusters, along with significant delay and angular
adequate scenarios (cell range, supported propagation spreading. Main contributors are reflections on flat
environments), elaboration of PHY-layer algorithms surfaces such as walls, floors or windows. Because
(e.g. waveform, channel estimation, equalization), the wavelength is lower than 3 mm, small objects,
evaluation and refinement of multi-antenna systems, in particular metallic objects, may also cause a
link and system-level simulations. significant echo due to a reflection or scattering.

© International Telecommunication Union, 2019 17