Georgian Electronic Scientific Journal: Computer Science and Telecommunications 2006|No.3(10) 29 A Handover Modelling for Globe Cover Telecommunications Merabtine Nadjim, Aris Skander, Benslama Malek Electromagnetism and Telecommunication Laboratory, Department of Electronics, Faculty of Engineering. Constantine University, Constantine 25000 Algeria. merabtinenadjim@yahoo.fr, arisskander@yahoo.fr, malekbenslama@hotmail.com Abstract The use of different satellite systems throughout the world has known a wide expansion, not only by the services it proposes, but by the large scale communication networks as it is possible to communicate in any point around the globe. Nowadays the increasing importance of the telecommunications systems in the satellite domains relies on the Low Earth Orbit (LEO) satellites. The aim of this paper is a main main survey of the communications networks with a particular concern of the satellite constellations constitutions and the different interfering factors: the orbit numbers, the satellite numbers in each orbit, the altitude, hence modelling the HANDOVER problems. Keywords: handover; cover; satellite systems; networks; modelling; triggering probability 1 Introduction The satellite systems based on the Low Earth Orbit (LEO) satellites have a major advantage over the earth (land) networks as far as the globe cover is concerned. They allow the users to have at their disposal telecommunication services extended over a very large zone and to be able to carry on a communication while moving in regions that are not covered by the land systems such as the GSM. However, these systems are characterized by a very high rate of Handover temptations which can significantly deteriorate their performances. The orbit altitude is considered as an essential element of the network. The constellations are defined with 1-1 High Earth-Orbit (HEO) They are elliptic orbits at about 500 km altitude and an apogee at about 50000 km altitude and have a 63° inclination. 1-2 Geostationary orbits (GEO) The geostationary orbits have a circular orbit of 42164Km radius in a plane in the neighbourhood of the equator and their angular speed is equal to the earth rotation. 1-3 Medium Earth-Orbits (MEO) The Medium Earth-Orbit have an altitude of about10000Km and a 50°, the satellite revolution period is 6hours with a constellation of 10 to 15 satellites we can assure a global cover of the earth. 1-4 Low earth-orbits (LEO) They are orbits situated at an altitude comprised between a few hundreds kilometres and 2000 km from the earth surface with a signal propagation delay of the order of 10 to 20ms. 2 Earth cover notion The cover is the land zone covered by the satellite also called print: