Abstract
Communications-integrated satellite-terrestrial networks used for global broadband services have gained a high degree of interest from scientists and industries worldwide. The most convenient structures for such use are low Earth orbit satellites, since they fly closer to the Earth compared to the other orbits, and consequently provide significantly lower latency, which is essential for reliable and safe communications. Among these efforts is the Starlink satellites constellation, developed and partly deployed by the United States Company SpaceX. The constellation is planned to be organized in three spatial shells, each of them made up of several hundreds of small-dimensioned and light-weighted low Earth orbit specially designed satellites to provide broadband services, intending to offer global Earth coverage through their interoperability, combined also with the ground stations as a part of the satellite-terrestrial integrated network. By October 24, 2020, 893 satellites are situated in orbit of altitudes of 550 km under different inclinations, determining the first Starlink orbital shell. Two next generations are planned to be situated at altitudes of 1,110 and 340 km, to complete the appropriate infrastructure of three Starlink satellite shells, toward a global presence of broadband internet services. These three orbital shells offer different space views seen from the ground station (user) because of their different altitudes, thus in this paper a few parameters which describe the satellite’s behavior considered from the ground station’s (user’s) point of view are compared. These parameters in fact stem from the space orbital parameters and are defined as: horizon plane wideness, slant range, latency, and coverage area. A comparison is given for the three Starlink orbit layers, with identification of appropriate drawbacks and advantages as performance indicators. By the end, these parameters are applied to geometrically interpret and confirm the handover process among satellites. This paper may serve to highlight the new challenges of the satellite-terrestrial integrated network, providing some theoretical analysis and performance comparisons for the satellites in different orbit layers seen from the ground station (user) perspective.
Highlights
The orbits of altitudes ranging from 300 km up to around 1,400 km above the Earth’s surface are defined as Low Earth Orbits, and the satellites consolidated to these orbits are known as the low Earth orbits (LEO) satellites
Concerning the communications perspective, from my view, the step taken forward to envelop the Earth with satellites for ubiquitous broadband services represents a very gigantic technological step for worldwide human equality, but with a lot of challenges to be faced in the future
For the continuity of services, more satellites may be involved in communications even from the different shells, adding delay, but in the worst case will still remain under 100 ms, which may be considered as negligible for communications (Gojal et al, 1998; Zong and Kohani, 2019)
Summary
The orbits of altitudes ranging from 300 km up to around 1,400 km above the Earth’s surface are defined as Low Earth Orbits, and the satellites consolidated to these orbits are known as the LEO satellites. The performance in respect to the horizon plane, slant range, and the appropriate latency for communication in between user’s station and the Starlink satellites for different satellite orbital shells will be analyzed (layers). From the single ground station (user location point), the satellite in its orbit is seen differently under different satellite passes of the same orbit, each LEO pass provides different communication durations with the appropriate point on the ground (user) (Cakaj and Malaric, 2007). Seen from the ground station (user) point of view, the satellite’s position in space within its orbit is determined by Azimuth and Elevation angles. Denoting signal delay (latency) by τ, for the satellite path seen from the user, on one way communication, the signal delay ranges as: τmin(due to dmin) < τ < τmax(due to dmax)
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