| Authors: | |
| Beatriz Soret | |
| Israel Leyva-Mayorga | |
| Petar Popovski |
One Sentence Summary:
address the matching problem of finding the interto each other
Abstract:
-Dense constellations of Low Earth Orbit (LEO) in rural or remote areas, where the cellular and other relaying small satellites are envisioned to make extensive use of the inter- networks are out of range [1]. satellite link (ISL). Within the same orbital plane, the inter- Inter-satellite distances are usually preserved within a plane. Isanteclolintteradsits,tatnhceersealarteivpermesoertivoend baentdwetehne plilnaknsesarmearkaetshtehrestinabtelre-. However, inter-satellite distances between different planes are plane ISL challenging. In a dense set-up, each spacecraft has time-variant: longest when satellites are over the Equator, and several satellites in its coverage volume, but the time duration shortest over the polar region boundaries. Moreover, the orbital of each of these links is small and the maximum number of periods are different if the planes are deployed at different active connections is limited by the hardware. We analyze the altitudes, or if these contain a different number of satellites, ImSaLtchfoinrg upnriocbasletmtroafnscmonisnseioctnisn.g Wsaetelplirteessenutsinagndtheevianltueart-eplathnee which results in aperiodic topologies. In a dense set-up, each performance of two solutions to the matching problem with spacecraft has several inter-plane satellites in its coverage any number of orbital planes and up to two transceivers: a volume, which leads to a matching problem of who should heuristic solution with the aim of minimizing the total cost; and a communicate to whom. Markovian solution to maintain the on-going connections as long Although less investigated than the GSL, several works taos psoolsvseiblteh.eTmheatMchainrgkouvipantoal1g0o0ri0thmanreddu1c0es twheithtimreespneecetdetdo have addressed the communication challenges of the ISL. The the optimal solution and to the heuristic solution, respectively, authors in [4] provide a thorough compilation of the latest without compromising the total cost. Our model includes power research efforts in the area of inter-satellite communications, adaptation and optimizes the network energy consumption as the organized in physical, data and network layer. [5] describes the exemplary cost in the evaluations, but any other QoS-oriented main use cases and elements of a LEO constellation for IoT, KPI can be used instead. including the use of the ISL. In [6], a power budget analysis I. INTRODUCTION for CubeSats that includes the ISL is conducted. [7] addresses the communication among a group of independent satellites in Low Earth Orbit (LEO) dense constellations of small satel- an unstructured constellation, treating the spacecraft positions lites, based on the CubeSat architecture, have become an as random variables. attractive solution for Internet of Things (IoT) applications in Matching problems are among the most important problems 5G [1]. The constellation is composed of hundreds of space- in network optimization [8]. For unmanned aerial vehicles crafts plus several ground stations, working all together as a (UAVs), [9] investigates the assignment problem in a Flying relay communication network. The space segment is organized Ad-Hoc Network composed of drones, formulating a dynamic in several orbital planes that can be deployed at different matching game that uses the trajectory of the drones. In this inclinations and altitudes [2] [3]. The satellites are connected paper, we address the matching problem of finding the interto each other via the Inter-Satellite Links (ISL), a two-way plane ISL connections that minimize the total cost of the connection. The ISL can be intra-plane ISL, connecting with constellation at each time instant. The model includes power the satellite in front and the satellite behind in the same plane; adaptation and the power consumption is the exemplary cost, and inter-plane ISL, connecting satellites from different orbital but any other QoS-oriented Key Performance Indicator (KPI) planes. In addition, the satellites are connected to ground sta- can be optimized instead. Differently than [7], we address tions, gateways or end-devices through the Ground-to-Satellite a planned network and solve the combinatorial problem by Link (GSL). LEO satellites move at speeds > 25 000 km/h considering the predictability of the spacecrafts positions. relative to the ground terminals. Therefore, the GSL is only Specifically, we aim to solve the inter-plane matching probavailable for a few minutes before handover to another satellite lem with M orbital planes and for up to two simultaneous occurs. ISLs per satellite. The Hungarian algorithm [10] is known to The use of the ISL unleashes the true potential of a LEO find the optimal pairing in bipartite graphs, which corresponds constellation, ensuring continuous connectivity, and reducing to the case with only M = 2 and one ISL. Furthermore, its the number of required ground stations and the end-to-end la- computational cost is high. Conversely, we take a networktency. One example of application is to use the constellation as wise approach and propose two novel algorithms that provide a relay network, which can dramatically increase the coverage a near-optimal solution to the matching problem with any of machine-type communication (MTC) and IoT deployments M and up to two simultaneous ISLs per satellite without