IEEE - Aerospace and Electronic Systems - April 2023 - 9

Chaudhry et al.
Table 3.
Simulation Parameters
Parameter
Number of satellites
Number of OPs
Number of satellites
per OP
Inclination
Altitude
Spacing between
OPs
Spacing between
satellites in an OP
LISL range
GS range
Location of source
GS
Location of
destination GS
Value
1584
24
66
53
550 km
15
5.45
{659.5; 1319; 1500; 1700;
2500; 5016} km
1000 km
New York Stock
Exchange
{London Stock
Exchange; Istanbul
Stock Exchange;
Sydney Stock
Exchange}
Node delay per
satellite
Speed of light in
vacuum
Time slot duration
Simulation duration
1ms
299,792,458 m/s
1 s
3600 s
for satellites on the shortest path are highlighted in pink
color in this figure.
While calculating the shortest path, links with all neighbors
of a satellite that are within its LISL range are considered.
These include crossing OP links (i.e., links with
crossing OP neighbors) sometimes also referred to as crossseam
links [10]. Due to high LISL setup times [4],these
links are currently considered undesirable in next-generation
FSOSNs. However, we envision such links to become feasible
in next-next-generation FSOSNs with advancements in
pointing, acquisition, and tracking (PAT) technology [19].
EFFECT OF LISL RANGE ON NETWORK LATENCY
To study the effect of different LISL ranges on network
latency for three different intercontinental scenarios,
including connections between GSs at New York and
APRIL 2023
London, New York and Istanbul, and New York and Sydney,
we simulate the FSOSN using the well-known satellite
constellation simulator STK Version 12.1 [20].To
realize the FSOSN, we assume LISLs between satellites in
Starlink's Phase I constellation. Distinct IDs are created in
the STK simulator for the 1584 satellites within the satellite
network. For the 24 OPs, the following IDs are created:
x101, x102, x103, ..., x124. Furthermore, distinct IDs
are created for the 66 satellites within each OP. For example,
the following IDs are generated for satellites in the
first OP: x10101, x10102, x10103, ..., x10166. The simulation
parameters are summarized in Table 3.
We run the simulation for one hour, i.e., 3600 seconds
(or time slots). For each LISL range, we calculate the
shortest path between the GSs in two cities over the
FSOSN at every time slot. Table 4 shows average latency
of the shortest paths for New York-London, New York-
Istanbul, and New York-Sydney long-distance intercontinental
connections at different LISL ranges. In this table,
nhop is the average number of hops, dprop and dnode represent
average propagation delay and average node delay in
milliseconds, respectively, whereas dtotal includes propagation
delay as well as node delay and denotes the average
latency (or average network latency) in milliseconds.
The value of nhop, dprop, dnode, and dtotal for an intercontinental
connection at an LISL range in Table 4 is the
average of the numbers of hops, average of the propagation
delays, average of the node delays, and average of the
latencies, respectively, for all shortest paths that are calculated
at all time slots over the one-hour simulation period.
For example, the average latency of the New York-London
inter-continental connection at 1700 km LISL range
in Table 4 is 25.86 ms, which is the average of the latencies
of all shortest paths calculated over all time slots for
this scenario at this LISL range. The average network
latency or dtotal is plotted against the LISL range in
Figure 5 for all three intercontinental connection scenarios
so that trends are apparent.
From the results in Table 4 and Figure 5, we observe that
average number of hops and average latency decrease with
an increase in LISL range for all scenarios. From Tables 1
and 2, wehaveseenthatasthe LISL rangeincreases,the
number of neighbors within the LISL range of a satellite
increases, and more and farther satellites become available
to a satellite for connectivity. As LISL range increases, longer
links with farther neighbors lead to better shortest paths
with fewer LISLs, lesser hops, and lower network latency,
which is reflected in Figures 2-4 and Table 4. For example,
the average latency or dtotal for the New York-Istanbul
intercontinental connection at 659.5 km LISL range is
48.10 ms in Table 4, the average number ofhops or nhop for
this connection at this range is 14.91, and the first shortest
path in Figure 2 for this scenario consists of14 LISLs and 15
hops. At 1700 kmLISL range, dtotal for this scenario reduces
to 36.93 ms, nhop reduces to six, and the number of LISLs
IEEE A&E SYSTEMS MAGAZINE
9
IEEE - Aerospace and Electronic Systems - April 2023

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