IEEE - Aerospace and Electronic Systems - April 2023 - 4

Feature Article:
DOI. No. 10.1109/MAES.2023.3241142
Laser Intersatellite Link Range in Free-Space Optical
Satellite Networks: Impact on Latency
Aizaz U. Chaudhry , Carleton University, Ottawa, ON K1S 5B6, Canada
Guillaume Lamontagne, MDA, Montreal, QC H9X 3R2, Canada
Halim Yanikomeroglu , Carleton University, Ottawa, ON K1S 5B6, Canada
INTRODUCTION
Free-space optical links between satellites or laser intersatellite
links (ISLs) in upcoming satellite constellations,
such as Phase I of SpaceX's Starlink, are envisioned as a
key enabler to realize free-space optical satellite networks
(FSOSNs)-also known as optical wireless satellite networks
[1]. Laser ISLs (LISLs) are also sometimes referred
to as optical ISLs (OISLs). Radio frequency-based ISLs
are already in use between satellites in constellations,
such as Iridium NEXT. However, LISLs offer several
advantages over radio frequency-based ISLs, such as
higher data rates, smaller antenna sizes, smaller terminals
with lower weight and volume, narrower beams, no interference,
higher security, higher directivity, lower transmit
power, and operation in unlicensed spectrum [1]. Laser
communication terminals (LCTs) for creating LISLs will
be essential to interconnect thousands of satellites in the
upcoming satellite constellations to formulate a global
communications network in space.
LCTs for intersatellite data communications over
LISLs are highly sought after by companies, such as
SpaceX and Telesat, who are looking to equip their low
Earth orbit (LEO) and very low Earth orbit (VLEO) satellites
with LISLs. Tesat is among the few companies developing
such terminals. Their SMART LCT can achieve a
Authors' current addresses: Aizaz U. Chaudhry and
Halim Yanikomeroglu are with the Department of Systems
and Computer Engineering, Carleton University,
Ottawa, ON K1S 5B6, Canada (e-mail: auhchaud@sce.
carleton.ca, halim@sce.carleton.ca). Guillaume Lamontagne
is with Satellite Systems, MDA, Montreal, QC
H9X 3R2, Canada (e-mail: guillaume.lamontagne@mda.space).
Manuscript
received 24 December 2021, revised 16 May
2022; accepted 27 January 2023, and ready for
publication 31 January 2023.
Review handled byMichael Cardinale.
0885-8985/23/$26.00 ß 2023 IEEE
4
data rate of 1.8 Gbps over a link distance of 45,000 km.
Another LCT currently being developed by Tesat specifically
for satellites in upcoming LEO constellations is
ConLCT1550, which will offer LISLs with a capacity of
10 Gbps at link distances of 6000 km [2]. Other companies,
such as Mynaric and General Atomics, are also
actively working to develop LCTs for LISLs. Mynaric's
LCT for LEO satellites is promising to provide LISLs
with data rates of 10 Gbps over ISL distances of up to
4500 km [3]. More recently, Mynaric has stated that their
LCT (now called CONDOR) can operate with a reduced
data rate of 5 Gbps at a maximum distance of 7780
km [4]. General Atomic's GA-LCT will have a modular
design in terms of amplifier stages, and will support data
rates of up to 5 Gbps over varying LEO-to-LEO ISL distances
ranging from hundreds to thousands of kilometers
[5]. We define LISL range as the distance within
which a satellite can successfully establish a LISL with
another satellite. For example, the LISL range of
ConLCT1550 will be 6000 km, which means that a satellite
equipped with this LCT will be able to establish an
LISL with another satellite within 6000 km. What is the
impact of LISL range on latency within FSOSNs? We
explore answer to this important question in this work.
The end-to-end delay (i.e., the delay from the source
to the destination) in the network consists of the following
four components: transmission delay, processing delay,
queueing delay, and propagation delay. The transmission
delay is the time taken to transmit all bits of a packet, i.e.,
the time between the transmission of the first and last bits
of a packet onto the communication link. It depends upon
the packet size and the link speed (or data rate). The
queueing delay is the time spent by the packet in the buffer
at a node while it is waiting for transmission onto the communication
link. It depends upon the number of packets
waiting for transmission. In FSOSNs, propagation delay
can be defined as the delay caused by the transmission of
the optical signal along the medium, i.e., the vacuum in
space. The propagation delay is contingent on the end-toend
distance, i.e., the distance between the source and the
IEEE A&E SYSTEMS MAGAZINE
APRIL 2023
https://orcid.org/0000-0002-1145-5604 https://orcid.org/0000-0003-4776-9354
IEEE - Aerospace and Electronic Systems - April 2023

Table of Contents for the Digital Edition of IEEE - Aerospace and Electronic Systems - April 2023
