A Geographical Location Based Satellite Selection Scheme for a Novel Constellation Composed of Quasi-Geostationary Satellites Tarik Taleb, Umith Dharmaratna, Nei Kato, and Yoshiaki Nemoto Graduate School of Information Sciences, Tohoku Univ., Japan Email: {taleb, umith}@nemoto.ecei.tohoku.ac.jp, kato@it.ecei.tohoku.ac.jp, nemoto@nemoto.ecei.tohoku.ac.jp Abstract— In order to realize the dream of global broadband coverage, the need for satellite communication systems has grown rapidly during the last few years. Several Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Geostationary(GEO) satellite constellations have been thus proposed in the recent literature. However, these constellations either require a potential number of satellites or are unable to provide data transmission with high elevation angles. This paper proposes a new satellite constellation composed of Quasi Geostationary Satellites. The main advantage of the constellation is in its ability to provide global coverage with a significantly small number of satellites while, at the same time, maintaining high elevation angles. Since end-terminals can be simultaneously covered by plural satellites in the proposed constellation, a scheme is proposed to select the most appropriate satellite for communication. The selection is based on the geographical location information of end-terminals. The efficiency of the proposed scheme is verified through a set of simulations. Simulation results reveal the good performance of the proposed method in reducing the delay, the delay variation, and ultimately improving the overall quality of service. I. I NTRODUCTION New multimedia services require more cost-effective, high-quality, and high-speed telecommunication technologies. Large-scale deployment of these wide-band services in a metropolitan area with a potentially large number of users is a challenging task for terrestrial technologies. Satellite network systems are seen as an attractive solution to realize the vision of a global broadband multimedia infrastructure [1]. This is because of their extensive geographic reach, flexible and rapid deployment features, and inherent multicast capa- bilities. Furthermore, given the recent advances and ongoing improvements in satellite technologies, broadband satellite based multimedia services are likely to open a promising and strong market for service providers and operators in the near future [2] [3] [4]. In the recent literature, a number of Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Geostationary (GEO) satellite constellations have been proposed to provide broad- band services. For more than two decades, GEO satellite systems have been used for providing commercial services. They have, however, failed in providing data transmission with high elevation angles over high latitude regions. In Tokyo, for example, the elevation does not exceed 48 ◦ . In GEO systems, end-terminals, mainly mobile users, experience consequently frequent cut-offs of propagation signals due to high buildings and mountains. The proposed LEO and MEO satellite constel- lations require, on the other hand, a large number of satellites for global coverage. They are thus characterized by frequent handover occurrences [5] [6]. Additionally, their satellites can be used for only a short life span . As a remedy to the above issues, this paper proposes a novel constellation composed of long-life span Quasi-Geostationary Orbit (Quasi-GSO) satellites. The strength of the constellation is in its ability to provide global coverage with a significantly small number of satellites while, at the same time, maintaining high elevation angles. The architecture of the proposed constellation is dynamic in its nature, yet exhibits significantly less mobility than LEO or MEO constellations. Nevertheless, to deal with issues related to the initial set-up of connections or handover phenomenon, end-terminals should be acquired with the ability of selecting the most appropriate satellite. Applying the baseline satellite selection procedure [7], the most widely used method for research on LEO and MEO satellite constellations, to the proposed constellation results in unnecessarily longer delays and higher levels of delay variation. To deal with such an issue, the coverage area of the constellation is divided into a number of regions and a satellite selection scheme is developed based on information related to the geographical location of end-terminals. The remainder of this paper is structured as follows. Section II gives a brief description of the Quasi-GSO satellite systems and highlights some of their main merits. The key design philosophy and distinct features that were incorporated in the proposed constellation are presented in Section III. Following this, Section IV portrays in detail the satellite selection scheme proposed for the considered Quasi-Geostationary satellite con- stellation. In Section V, the proposed satellite selection method is evaluated through a set of simulations. Simulation results are discussed in the same section. The paper concludes in Section VI with a summary recapping the main advantages and achievements of the proposed constellation. II. QUASI -GEOSTATIONARY ORBIT SATELLITE SYSTEM For more than three decades, satellite systems have been successful in providing some commercial services. Currently, there are two types of broadband satellite systems: low-altitude earth orbit and geostationary satellite systems. The former requires a huge infrastructure investment and has created some doubts on its economical practicality mainly after the recent financial failure of the Iridium system. The latter, on the 0-7803-8939-5/05/$20.00 (C) 2005 IEEE