Page 43 - 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

TERAHERTZ WIRELESS COMMUNICATIONS IN SPACE

1
Meltem Civas and Ozgur B. Akan 1,2
1
Next‑generation and Wireless Communications Laboratory (NWCL), Department of Electrical and Electronics
2
Engineering, Koç University, Istanbul, Turkey , Internet of Everthing (IoE) Group, Department of Engineering,
University of Cambridge, UK
NOTE: Corresponding author: Meltem Civas, mcivas16@ku.edu.tr

Abstract – The New Space Era has increased communication traf ic in space by new space missions led by public space
agencies and private companies. Mars colonization is also targeted by crewed missions in the near future. Due to increasing
space traf ic near Earth and Mars, the bandwidth is getting congested. Moreover, the downlink performance of the current
missions is not satisfactory in terms of delay and data rate. Therefore, to meet the increasing demand in space links, Terahertz
band (0.1‑10 THz) wireless communications are proposed in this study. In line with this, we discuss the major challenges that
the realization of THz band space links pose and possible solutions. Moreover, we simulate Mars‑space THz links for the case
of a clear Mars atmosphere, and a heavy dust storm to show that even in the worst conditions, a large bandwidth is available
for Mars communication traf ic.

Keywords – Deep space communications, inter‑satellite links, terahertz communications

1. INTRODUCTION optical links NASA
will further conduct Deep Space Optical Communications
The start of a New Space Era has led to a paradigm shift
demonstration as a part of Psyche mission to show that
in the space industry. An increasing number of private
higher data rates, 10‑100 times of the current state of the
com‑ panies with space missions have emerged, and
attainable optical wireless communi-
spacecraft are getting smaller and easily deployable
cations The Data Relay Satellite
with the help of enabling technologies. Moreover, the
(EDRS) also employs optical inter‑satellite links, which
non‑terrestrial networks are also recognized by the
can reach data of 1.8 for transmission
future release 17 of the 3rd Generation Partnership
up 45000 from institutional
Project (3GPP) to be studied under the study item
projects, the SpaceX
”Non‑Terrestrial Networks”. Vertical networks are
opti‑ cal communications for space‑to‑space or
expected to be integrated into the next generation 5G
air‑to‑air links of their projects under
and beyond networks. This can lead to many novel
Despite its advan‑ tages, FSO communications have still
paradigms including the Internet of Space Things (IoST)
several challenges. Regarding space links, due to high
[1]. Therefore, available bandwidths are getting
transmission distances Effective Isotropic Radiated
congested. National Aeronautics and Space Ad‑
Power (EIRP) must be high. This enabled
ministration (NASA) estimates that the growth factor of
transmitting op‑
deep space communication capability should be at least
narrow‑beam divergence (∝ / , where is the
10 to meet the growing demand in the next three
wavelength and is the diameter of aper‑ Thus, a
decades [2]. Therefore, high data rate communication
deviation of the optical beam from the tar‑ get results in
technolo‑ gies are required. Free space optical (FSO)
an outage. Considering the same transmit‑ ting antenna
communica‑ tion has been envisioned for space
size, THz systems have looser beam pointing
applications. However, optical communication
requirements compared to FSO links, since we consider
highly depends on atmospheric conditions such as fog,
larger wavelengths.
cloud, and haze where optical links experience
strong attenuation [3]. Moreover, FSO is costly, and
affected atmo‑
beam alignment problems pose several addi‑
spheric conditions haze, atmo‑
tional challenges. Terahertz band (0.1‑10 THz)
spheric turbulence. For less
wireless communications, which can enable high data
than 50 m when dense fog attenuation can be as
rates on the order of Terabits per second, is an
high 350 dB/km, transmission In
alternative to FSO.
case of fog with the same visibility, there are several win‑
The advantages of FSO such as large bandwidth, high dows in the THz band where the attenuation is below
data rate, high security, no spectrum licensing are of 100 dB/km Compared to FSO, THz
growing interest. NASA’s demonstration in 2013 called communications are more robust to weather effects in
Lunar Laser Communication Demonstration proved that Although the attenuation in THz links for
high downlink and uplink transmission rates from lunar long‑distance communication is still a challenge to be
© International Telecommunication Union, 2021 31