IEEE - Aerospace and Electronic Systems - April 2023 - 12

Laser Intersatellite Link Range in Free-Space Optical Satellite Networks: Impact on Latency
Furthermore, we observe improvement in average network
latency with increase in LISL range in all scenarios.
We employed the satellite constellation for Phase I of
Starlink in this study to realize an FSOSN. Similar studies can
be conducted to examine the effect ofLISL range on network
latency in FSOSNs formed from other satellite constellations.
However, similar trends are likely to be observed.
At different LISL ranges, we observed different number
of crossing OP neighbors for a satellite. This number
increases with the increase in LISL range. For example,
the number of crossing OP neighbors for satellite x10101
at the equator is 12 and 92 at LISL ranges of 1700 and
5016 km, respectively. The effect of crossing OP LISLs
(i.e., LISLs with crossing OP neighbors) on network
latency is worth studying.
It was seen that longer links led to better shortest paths
and lower network latencies. The satellites in the upcoming
LEO/VLEO satellite constellations are expected to be
energy constrained. Longer LISLs lead to lower latency
paths but require higher transmission power and consume
more energy, and may not be suitable for these energyconstrained
satellites. On the other hand, shorter LISLs
require less transmission power and consume less energy
but result in higher latency paths. The tradeoff arising
from different LISL ranges between network latency and
satellite transmission power (and thereby satellite energy)
in FSOSNs should be investigated.
Due to PAT during establishing an LISL, current LISL
setup times range from a few seconds to tens of seconds [4].
Due to these prohibitive LISL setup times, previous work is
mostly based on next-generation satellite networks that are
expected to become fully operational by the mid to late 2020s
where a satellite will be restricted to form only permanent
LISLs with neighbors that are always within its LISL range.
Once established, such LISLs will have to exist continuously
to avoid LISL setup delays. Our work targets next-next-generation
satellite networks that are likely to come into existence
in the early to mid-2030s where we envision the LISL setup
times to be in milliseconds due to technological advancements.
LCTs that will offer dynamic or on-demand LISLs
will become available, and a satellite will be able to instantaneously
establish an LISLwith any other satellite that is currently
within its LISL range for data communications within
the FSOSN (via intra-OP LISLs or inter-OP LISLs) or
between different FSOSNs (via interorbit LISLs) as well as to
route around a failed satellite. To achieve very low LISL setup
times that are in milliseconds, there is a need for extreme
advancements in LCT PAT technology, satellite attitude control
subsystems, and satellite orbit determination subsystems.
The delay involved in setting up an LISL between a pair
of satellites can be referred to as LISL setup delay. In the
future, it would be interesting to quantify the LISL setup
delay in next-next-generation FSOSNs where the shortest
paths between the source and destination GSs change frequently
and incur the LISL setup delay when one or more
12
new satellites are introduced in a shortest path and new
LISLs need to be established. Furthermore, it would be interesting
to examine the impact ofLISL setup delay on the network
latency ofnext-next-generation FSOSNs.
ACKNOWLEDGMENT
This work was supported by the National Research Council
Canada's (NRC) High Throughput Secure Networks program
(CSTIP Grant #CH-HTSN-625) within the Optical
Satellite Communications Consortium Canada (OSC)
framework. The authors would like to thank AGI for the
STKplatform.
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IEEE A&E SYSTEMS MAGAZINE
APRIL 2023

IEEE - Aerospace and Electronic Systems - April 2023

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