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LEO Satellite Constellations for 5G and Beyond: How Will They Reshape Vertical Domains?

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LEO Satellite Constellations for 5G and Beyond: How Will They Reshape Vertical Domains? 1 LEO Satellite Constellations for 5G and Beyond: How Will They Reshape Vertical Domains? Shicong Liu, Zhen Gao*, Yongpeng Wu, Derrick Wing Kwan Ng, Xiqi Gao, Kai-Kit Wong, Symeon Chatzinotas, and Bjorn¨ Ottersten Abstract—The rapid development of communication technolo- With the emerging concept referred to as mega- gies in the past decades has provided immense vertical oppor- constellations [5], the era of seamless connectivity is more re- tunities for individuals and enterprises. However, conventional alistic than ever. Tremendous amount of satellites in low Earth terrestrial cellular networks have unfortunately neglected the huge geographical digital divide, since high bandwidth wireless orbit (LEO), medium Earth orbit (MEO), and geostationary coverage is concentrated to urban areas. To meet the goal Earth orbit (GEO) can collaborate together forming SatCons, of “connecting the unconnected”, integrating low Earth orbit which completely changes the static topology in conventional (LEO) satellites with the terrestrial cellular networks has been terrestrial networks and enables flexible network deployment. widely considered as a promising solution. In this article, we Despite the fact that 3 GEO satellites are enough to provide first introduce the development roadmap of LEO satellite con- stellations (SatCons), including early attempts in LEO satellites seamless coverage across the globe, the associated latency and with the emerging LEO constellations. Further, we discuss the low area spectral efficiency are generally intolerable in most unique opportunities of employing LEO SatCons for the delivery 5G application scenarios. Hence, exploiting LEO satellites of integrating 5G networks. Specifically, we present their key becomes a better option as operating on a lower orbit provides performance indicators, which offer important guidelines for lower latency and higher service density. the design of associated enabling techniques, and then discuss the potential impact of integrating LEO SatCons with typical In recent years, new launching and propulsion technologies 5G use cases, where we engrave our vision of various vertical have drastically reduced the cost, and advanced volume manu- domains reshaped by LEO SatCons. Technical challenges are facturing technologies have paved the way for the deployment finally provided to specify future research directions. of mega constellations, especially for LEO satellites. For LEO, the lower orbital altitude leads to a lower latency for delay- sensitive tasks such as video calls and streaming, while the I. INTRODUCTION high density constellation guarantees service capacity globally. HE unprecedented development of communication tech- Therefore, the amalgamation of satellite access and conven- T nology in the past few decades has demanded an expo- tional terrestrial networks is an inevitable convergence for B5G nential growth in the overall transmission rate [1], [2]. Unlike and even 6G in meeting the increasing demands. previous mobile communications, from 1G to 4G, 5G networks After this introduction, the article first introduces the aim for ubiquitous connections to help digitize the economy roadmap of LEO SatCons development, after which the oppor- and contribute towards the global digital transformation, rather tunities of employing LEO SatCons are discussed. We further than barely improving the overall data rate. The driving force discuss the technical challenges and highlight the research for further beyond 5G (B5G) even 6G research is the demand- directions, and finally summarize our conclusion. intensive vertical industries, which can be classified as one or a mix of the following usage scenarios: enhanced mo- bile broadband (eMBB), massive machine type communica- II. DEVELOPMENT ROADMAP OF LEO SATCONS arXiv:2106.09897v1 [eess.SP] 18 Jun 2021 tions (mMTC), and ultra reliable low latency communications (URLLC) [3]. The idea of communicating via commercial LEO satellites Affected by the COVID-19 pandemic, vertical applications dates back to the early 1990s. Since the earliest launch in 1957, such as media, public safety, and eHealth have attracted satellites used for data transmission are mainly GEO satellites widespread attention, and are expected to become a new and the majority of them served as data broadcasting satellites, normality in the future. According to the report of international whose applications include satellite TV programs, positioning, telecommunication union (ITU), nearly half of the population etc. With the increasing demands for higher system capacity still remains unconnected [4], whereas eliminating the blind and lower latency, the concept of constellation composed of areas by deploying much more terrestrial base stations (BSs) LEO satellites has been proposed [5]. Early designs of LEO will impose a heavy burden on the telecom operators. On satellites typically included a small number of satellites to the other hand, the coverage of non-deployable areas such ensure that every part of Earth is covered by at least one as aero and maritime lanes remains to be solved. Against satellite. In this section, we provide a comprehensive overview the aforementioned constraints, space-based satellite constel- and comparison on the existing SatCons. Table II gives a lations (SatCons) emerge as the times require. brief summary of the most well-known commercial satellite communication systems that utilize constellations to support *: Corresponding author. wide-area coverage. 2 TABLE I COMPARISON OF SELECTED CONSTELLATIONS Constellation Regime Orbital height Quantity Bands Services Est. data rate Iridium Gen. 1 LEO 781 km 66 L Voice, data 2.4 Kbps Globalstar LEO 1414 km 48 S, L Voice, data ∼9.6 Kbps Orbcomm Gen. 1 LEO 700 ∼ 800 km 36 VHF IoT & M2M∗ communication 2.4 Kbps Skybridge LEO 1457 km 64 Ku Broadband Internet 60 Mbps Teledesic LEO 1375 km 288(840) Ka Broadband Internet 64 Mbps Iridium NEXT LEO 781 km 66 L, Ka Voice, data 1.5 Mbps, 8 Mbps Orbcomm Gen. 2 LEO 700 ∼ 800 km 18 VHF IoT & M2M communication 4.8 Kbps O3b MEO 8063 km 20 Ka Broadband Internet 500 Mbps OneWeb LEO 1200 km 648 Ku Broadband Internet 400 Mbps Starlink Gen. 1 335:9 ∼ 570 km 11926 V LEO Broadband Internet 100 Mbps Starlink Gen. 2 328 ∼ 614 km 30000 Ku, Ka, E Telesat Phase. 1 298 LEO 1015 ∼ 1325 km Ku, Ka Broadband Internet - Telesat Phase. 2 1373 Hongyan LEO 1100 km 320 L, Ka Voice, broadband Internet 100 Mbps Kuiper LEO 590 ∼ 630 km 3236 Ka Broadband Internet - * : Internet of Things and machine to machine. A. Overview of Early LEO Satellites Starlink intends to launch around 42000 LEO satellites, In the late 20th century, network operators and companies which make up the largest constellation ever, on several have made their initial attempts to deploy LEO constellations. different altitudes of orbits. At the initial stage of arrange- Although most of the early attempts ended with bankruptcy, ment, around 12000 satellites with 2 groups of orbital height their experiences provide valuable lessons for the ventures. (335:9 ∼ 345:6 km for 7518 satellites and 540 ∼ 570 km 4408 Iridium went into operation by Motorola in 1998 as one for satellites) will be deployed, whereas 30000 more of the earliest LEO constellations adopting the Walker con- satellites awaiting approval will be deployed at the final stellation pattern. 11 satellites are uniformly distributed on 6 stage. As an emerging SatCon, it is the first constellation orbital planes with a height of 780 km, and are able to work that has applied for the use of V-band and E-band to support in both time division multiple access (TDMA) and frequency its advanced services in broadband Internet access globally, division multiple access (FDMA) modes. including commercial, residential, and governmental scenarios. Apart from Starlink, several developing or designing LEO Different from Iridium, Globalstar adopted the Walker 1 Delta pattern, which is also known as Rosette, achieved the SatCons are in progress. OneWeb targets at seamless global best coverage diversity at mid-latitudes, but no coverage at coverage with customer demonstrations and commercial ser- poles, and became commercially available in late 1998. 48 vices in the upcoming future, and has launched 74 of 648 LEO satellites are designed at the altitude of 1414 km adopting planned satellites to date. It is expected to provide up to 400 30 code division multiple access (CDMA) for satellite phones and Mbps downlink and Mbps uplink rate through special narrow band data communication services. user terminals (UTs) or gateways. On the other hand, Telesat also seeks to provide global coverage and high throughput Teledesic also started its operation in 1998 and initially broadband capacity on LEO constellation in polar and inclined attempted to build the largest constellation with 840 satel- orbits. Its first LEO satellite was launched in 2018, and is lites at the altitude of 700 km supporting the space-based now supporting live demonstrations of satellite services across broadband Internet access. After several reorganizations and a variety of markets and applications. The project Kuiper merging, Teledesic progressively scaled down the number of is an initiative that proposes to build an LEO constellation its satellites to no more than 288. with 3236 satellites for providing broadband connectivity to The past verticals were underdeveloped to nurture a mature the uncovered users. The related detail of other constellation LEO commercial operation in the last century. Therefore, in competitors can also be found in
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