Satellite systems performance with TCP-IP applications

Mobile access to the Internet is becoming extremely popular because users depend on the Internet for many activities in their daily routine. Satellites are well suited for mobile Internet applications because of their ability to enhance coverage and support long-range mobility. Satellites are an attractive alternative for mobile (pedestrian and, more importantly, vehicular) access to the Internet in sparsely populated areas where high bandwidth UMTS cells cannot be economically deployed or in regions where deployment of terrestrial facilities remains impractical. In this paper, we analyze various mobile Internet applications for both GEO and LEO satellite configurations (Iridium-like and Globalstar-like) using an enhanced version of \´ns2\´ (Network Simulator 2). As part of enhancing ns2, we developed a channel propagation model that includes shadowing from surrounding building skylines. The model incorporates actual data measurements collected in a built-up area. We compute via simulations the performance of FTP applications as perceived by mobile users traveling along "urban canyons" in LEO and GEO configurations. The results show that throughput and delay performance is strongly affected by skyline shadowing and that shadowing degradation can be compensated by satellite diversity, such as provided by Globalstar. For all the experiments, we compared the performance of different TCP schemes (Reno, SACK, Westwood).