Page 14 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 7 – Terahertz communications

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 7

Fig. 1 – Possible real‑world scenarios of THz‑enabled drone networks.

applications, while at the same time promises massive waves at 0.35 THz, a larger UAV density is required for a
antenna gains due to shorter wavelengths [9, 10]. certain coverage probability, as compared to lower
However, THz communications are restricted by the carrier frequencies. In [19], THz MIMO‑OFDM communication
absorption loss, which is highest at the sea‑level, as the between two UAVs is studied by analyzing the
atmospheric gas concentration is at the maximum [11, orientation and position estimation error bounds. It is
12]. Consequently, THz communications have been shown that the positioning accuracy at the millimeter
studied mainly for short transmission distances at the levels can be achieved provided that the transmitter to
sea‑level, such as for on‑ chip communications [13] or receiver separation is considerably small.
for connecting data centers within up to 10 m [14].
In [11], we have performed path loss and total usable
THz bands have been recently considered for aerial bandwidth analyses over a THz band (0.75‑10 THz), con‑
communications. Despite the highly mobile nature of sidering constant narrowband noise approach for four
aerial vehicles, a THz band, due to very high frequency, types of aerial vehicles at different altitudes: Drones (at
promises minimized Doppler effect, making massive rate 1 km), jet planes (at 10 km), high altitude UAVs (at 16 km),
communication links realizable within mobile aerial ve‑ and satellites (at 99 km). The path loss analysis shows
hicles by optimal selection of the beam patterns [15]. that the absorption effect diminishes at the higher alti‑
For the razor‑sharp beams due to carrier frequencies in tudes and the total path loss behaves as free space spread
the order of THz, the communication links between loss. Moreover, the total usable bandwidth analysis infers
hovering aerial vehicles have to be highly aligned. The that at the higher altitudes (e.g. high altitude UAVs and
in luence of the micro, small and large‑scale mobility satellites), the entire THz band (0.75‑10 THz) becomes
uncertainties for drones communicating in millimeter feasible as a single transmission window, which is about
wave and THz bands are studied in [16, 17]. It is shown 9.25 THz wide. In our subsequent work [12], we have pro‑
that without adaptive beam‑width control, micro‑scale posed an alternative channel model for THz communica‑
mobility induces negligible link capacity degradation, tions, where, by taking the colored nature of noise Power
whereas small‑scale mobility and large‑scale mobility can Spectral Density (PSD) into account, the commonly lat
induce icant degradation in the link capacity, with bands in path loss (gain) and noise PSD are determined
larger outages. THz‑based drone (Unmanned Aerial for the THz spectrum (0.75‑10 THz), and a variable band‑
Vehicle, UAV) networks are analyzed in [18] by assessing width capacity computation method is proposed as an
coverage probability and area spectrum iciency. It is alternative to the standard capacity computation. Our
concluded that due to massive path loss incurred by THz band extensive capacity analysis of the same four aerial

2 © International Telecommunication Union, 2021