Architecture of an Integrated GSM-Satellite System

The integration of satellite systems with cellular networks permits to provide wider and more efficient area coverage. This paper deals with the network aspects related to a full integration between the Global System for Mobile communications (GSM) pan-European cellular network and a spot-beam geostationary satellite. The basic requirements of full integration are that the insertion of the satellite system does not entail any modification on the already existing GSM network and that the satellite system reuses, as far as possible, the same equipment and protocols, i.e. the same hardware and software, as the GSM network. In the fully integrated system the user need not be aware whether the actual connection goes through the satellite or the cellular network. In particular, this paper identifies the satellite system counterpart of the GSM functional areas (cell, location area, MSC area, PLMN area) and deals with the problems and the relevant solutions related to the extension of the GSM procedures (e.g. call set-up, cell selection/reselection, handover, initial acquisition, tracking) to the integrated network. This paper is partly based upon the work performed by the author in the framework of an European Space Agency (ESA) study on the compatibility between satellite systems and the GSM cellular network (Telespazio is the prime contractor of this study) and partly results from the cooperation of the author with the INFOCOM department of the University of Rome ''La Sapienza''. The opinions herewith reported are not necessarily those of ESA.