IEEE - Aerospace and Electronic Systems - April 2023 - 7

Chaudhry et al.
Figure 1.
Satellite connectivity for satellite x10101 at 2500 km LISL range. At this LISL range, this satellite has connectivity with 38 satellites that are
within its range.
a satellite in this constellation as it provides a reasonable
minimum amount of satellite connectivity where x10101
has four intra-OP neighbors, six adjacent OP neighbors,
and 12 crossing OP neighbors.
The logic for choosing the six LISL ranges shown in
Table 1 to examine the effect of LISL range on network
connectivity in the FSOSN based on Starlink's Phase I
constellation is as follows. We identify 659.5 km as the
minimum LISL range for this constellation as a satellite at
this range is connected to only two intra-OP neighbors. At
1319 km LISL range, a satellite in this constellation is
connected to four intra-OP neighbors. A satellite is connected
to nearest two and nearest six adjacent OP neighbors
at LISL ranges of 1500 and 1700 km, respectively.
The LISL range of 5016 km is identified as the maximum
possible LISL range for a satellite in this constellation.
We also examine the satellite connectivity at an intermediate
LISL range of2500 km.
Table 1 illustrates the number of neighbors within the
LISL range ofx10101 for different LISL ranges when this satellite
is at the equator. Due to the 53 inclination ofStarlink's
Phase I constellation, a satellite in this constellation has more
neighbors (or satellites) within its range at higher latitudes
near the polar regions and less neighbors within its range at
lower latitudes near the equator. For example, the satellite
connectivity for satellite x10101 at 47.33 latitude, shown in
Table 2, highlights this interesting aspect. Note that the satellite
connectivity for x10101 at different LISL ranges at 47.33
latitude is higher than that at the equator (or 0 latitude).
METHODOLOGY FOR CALCULATING NETWORK LATENCY
The speed of light in vacuum is usually denoted by c and its
exact value is 299,792,458 m/s [14]. We consider this value
APRIL 2023
ofc while calculating the latency ofthe shortest path between
a pair of cities over the FSOSN. The propagation delay of a
link (i.e., the propagation delay of an LISL between a pair of
satellites or the propagation delay of the laser link between a
GS and a satellite or the propagation delay of the laser link
between a satellite and a GS) is calculated by dividing the
length ofthat link by the exact value ofc. We consider a node
delay at each satellite (or node or hop), and assume it as 1
ms [15]. This delay is mainly the processing delay due to the
on-board data routing and switching processes of a satellite.
We assume a congestion-free FSOSN with minimal queueing
delay [16]. Also, LISLs with data rates in Gbps are
assumed [2], [3], [4], [5]. Consequently, the queueing and
transmission delays are considered to be negligible, and the
node delay is assumed to encompass these delays.
Each time slot represents a snapshot of the FSOSN at
that time. Using links between satellites and links between
Table 2.
Satellite Connectivity for Satellite x10101 for Different
LISL Ranges at 47.33 Latitude
LISL range (km)
659.5
1319
1500
1700
2500
5016
IEEE A&E SYSTEMS MAGAZINE
29
33
40
70
209
7
# Satellites in LISL range
8

IEEE - Aerospace and Electronic Systems - April 2023

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