Non geostationary satellite procedures for the third generation mobile communication system

Synopsis - The European project for third generation mobile communication, known as UMTS envisions the satellite component as a means of completing terrestrial and global coverage objectives, particularly where terrestrial networks are not competitive, not applicable or not developed at all. Non-geostationary satellite constellations are interesting as far as mobile systems are concerned, because spacecraft fly at low altitudes, permitting more effective communication. Intelligent satellites, i. e. satellite systems characterized by wide on-board processing capabilities are starting to be considered for commercial use. This work is about the project and the high level realization of mobility procedures for constellations of intelligent satellites within the UMTS project. Acknowledging the hypothesis that satellites are interconnected with inter-satellite links and present on-board functionalities that manage the switching of the data circuits regarding the terminals roaming in the area covered by the satellites, UMTS mobility procedures have been extended to the intelligent satellite segment, taking into account the constraint of minimizing the radio traffic between the satellites and the network. The procedures have been realized using UMTS tools and techniques, in the framework of the RACE program, according to MONET project, following the methodology outlined in STORMS. In order to achieve good system performance, ii has been necessary to develop a new specific procedure, the place switching, responsible for transferring the control data among the satellites of the constellation setting with respect to the service area and those rising on the area. Subsequently the mobility procedures realized for intelligent satellites have been compared to terrestrial network procedures of the same type and the impact of place switching on the system has been studied in terms of processing load and data requirement. Examining the procedures it is evident that, while the terminals remain in the satellite service area, constellations of intelligent satellites require few user or session data transferred from the terrestrial segment to the satellite one during particular phases of the sessions and vice-versa. As a result, the integration of the intelligent satellite constellations and the terrestrial network works fine; these constellations may be used to extend the network access functionality, and they can manage some elaboration load almost independently from the network.