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Sổ tay của các mạng không dây và điện toán di động P22

A low earth orbit (LEO) satellite constellation consists of a set of satellites orbiting the Earth with high constant speed at a relatively low altitude (a few thousand kilometers) [1]. Each satellite is equipped with a fixed number of antennas that allow it to communicate with ground transmitters/receivers and with other satellites. One of the major advantages of LEO satellites (as opposed to geostationary—GEO—satellites) is that they are closer to the Earth’s surface. | Handbook of Wireless Networks and Mobile Computing Edited by Ivan Stojmenovic Copyright 2002 John Wiley Sons Inc. ISBNs 0-471-41902-8 Paper 0-471-22456-1 Electronic CHAPTER 22 Topological Design Routing and Handover in Satellite Networks AFONSO FERREIRA JÉRÔME GALTIER andPAOLO PENNA Mascotte Team INRIA CNRS UNSA Sophia Antipolis France 22.1 INTRODUCTION Alow earthorbit LEO ssteilitecons ellation consirttolWc set of satellites orbiting the Earthwithlugh constantspeedat arelativelylow altitude a few thousand kilometers 1 Each satellite is equipped with a fixed number of antennas that allow it to communicate with ground transmitters receivers and with other satellites. One of the major advantages of LEO satellites as opposed to geostationary GEO satellites is that they are closer to the Earth s surface. This reduces the communication delay and the energy required to directly connect a user with a satellite. On the other hand two major issues arise due to their lowaltitude.kftst beckuue a single satellite can only cover a small geographical area called footprint at the Earth s surface many satellites are required to provide global cov-erage.SecoeKl. hie lootprintol eachsatellite movcscontiimously.iniplying ihiglimobility oi tOie whoVe network. Oo noclraut withoihyc celleVursystcmv. In tUetoihiwing. wewill eeu howVOytopcVogyoCLyOeonutelletiono iotimtlodby leiyoibulcosistiuoms.Thnncvc wilt uecsvwhovvtnc selactons ppvc Seen takcnintoaccui.int lg tOodesign oCnoutmoondOaodoverpolicics. 22.2 TOPOLOGIES Durinv thevysVemgOssignphacUiOVverat enrtoKnni scoioc lmo pigg such uvsbte tiles al-OiguOninnmyev oi oateViiVes number oforOiCvmtdsaCel-ttes per orbit how to deploy the orbits andhowOembereonnect thevoOeiliOec. AllsuchfegVorrdvIenninoOhe topo logy yOVhs ne-work soshownm tOis secdem 22.2.1 Orbits Acloseelookat thefeasible types of orbits shows that unless the orbits have the same altitude and inclination their relative positions change so often that intersatellite links 473 474