Page 15 - 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

scenarios has shown that under fading channel conditions, Military Applications
the ergodic capacity at the sea‑level is enhanced by an
Drone networks have become an integral part of military
order of magnitude for the drones hovering at 100 m
applications around the globe. With the aid of quickly de‑
altitude supporting multiple Tbps at a range of 10 m,
ployable drone networks, a multitude of military‑related
whereas 10s of Tbps are realizable among jet planes
activities can be performed effectively. Such activities
(10 km altitude) and the high altitude UAVs (16 km
include border patrolling by monitoring high resolution
altitude), and multitude of 100s of Tbps are also real‑time videos. For instance in [21], the concept of Bor‑
achievable for inter‑satellite links (also cubesats) at a
derSense is introduced, which is a new hybrid concept
range of 1 km. In both works [11, 12], it is concluded
of wireless sensor networks, including underground sen‑
that the THz communications is highly viable for
sors, on‑ground sensors, and drones for wireless sensing
non‑terrestrial communications. Motivated by our earlier
from the air. With the BorderSense framework, drones
analyses for THz communications among aerial vehicles in
can provide mobility freedom together with on‑board
[11, 12], in this survey, we review THz band
high resolution cameras and highly sensitive sensors for
communications and sensing for drone networks, more
provisioning an enhanced coverage as per the military
speci ically for DSNs and we highlight the prospects. First,
requirements. Here, for the military applications, band‑
we present applications of THz‑enabled DSNs. Secondly,
width should be provisioned substantially together with
we present capacity results for drone‑to‑ drone links,
an ultra‑reliable low latency service in order to transfer
considering drones at different altitudes and varying
sensitive military data/information within fractions of a
fading conditions. We show that THz communi‑ cations
second [10]. In addition, drones providing such military
can be quite promising even under realistic fading
applications (e.g., air to air and air to ground) will need to
conditions, providing up to many Tbps at 10 m range and
be highly energy ef icient as it will not be realistically pos‑
10s of Gbps at 50 m range. Motivated by the capacity po‑
sible to frequently replace their on‑board power sources
tential, we next discuss the open issues for THz communi‑
(batteries). With THz‑enabled DSNs, a massive THz band‑
cations in DSNs, along with research directions. Lastly, we
width will promise high resolution video monitoring of
highlight Arti icial Intelligence (AI) and Machine Learning
(ML)‑based approaches. sensitive areas, as in BorderSense framework. Moreover,
thanks to the unique propagation characteristics of the
2. APPLICATIONS OF THZ BAND DRONE THz band, THz waves show a unique re lective nature to
NETWORKS the metallic surfaces. Therefore, a THz band can be
effectively utilized in the military surveillance
applications such as detecting certain weapons [22]. The
With the THz band being one of the key enablers of
detection of any possible explosives is also possible
prospective 6G research, we envision employing the
using THz spectral imaging [23]. For instance, THz
THz band for drone networks as expected use cases of
spectral imaging can detect small land mines, while the
6G non‑terrestrial networks. Fig. 2 depicts such possible
ground radars cannot distinguish between such mines
applications of THz‑enabled drone networks, namely
and rocks [24]. THz‑enabled DSNs with mobility freedom
monitoring and surveillance, sensing, localization and
can assist a military by detecting such mines without
on‑ demand network coverage, as elaborated next.
any direct human contact.
It is worth‑mentioning here that within each of the
following applications of the THz band communications,
sensing and localization, it will be important to deploy Disaster Management
the THz‑ enabled drones strategically [6] so as to fully
exploit the THz band for drone networks and DSNs. Drone networks or DSNs can be considered in various
These strate‑ gies include Ultra‑Massive Multiple Input disaster management applications, e.g., for Early War-
Multiple Out‑ put (UM‑MIMO) and Recon igurable ning Systems (EWSs), which perform environmental
Intelligent Surfaces (RIS), which are explained in and structural monitoring and process the collected
Section 4 of this paper, in detail. informa‑ tion for disaster predictions. Such a DSN can
also support Search And Rescue (SAR) missions in the
post disaster management scenarios. DSNs can be utilized
2.1 Monitoring/Surveillance to restore the damaged communication infrastructure in
case of a disaster. Additionally, post‑disaster damage
As 6G research is progressing towards ubiquitous au‑ assessment can be made possible using DSNs with video
tomation, aerial monitoring using drones has become monitoring [25]. THz‑enabled drone networks and DSNs
increasingly popular [20]. Networked state‑of‑the‑art with massive bandwidth can support an aerial
drones will become an essential aerial resource for communication backup for EWS, SAR over the
many real‑world monitoring applications, such as mili‑ disaster‑struck region. Energy ef iciency of the drones
tary surveillance, disaster management, etc. In the will be a critical parameter for such autonomous aerial
following, we cover such practical monitoring applications operations [26], where frequent replacement of the
for THz‑enabled drone networks. on‑board batteries may not be a feasible operation.

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