CAC-TCP cross-layer interaction in a HAPS-satellite integrated scenario

The integration of a satellite system with a HAPS segment appears very suitable to provide communication services, including Internet access, for a large set of applications. In fact, the-satellite capability to provide wide coverage and broadband access can be enhanced by the use of cost-effective, mobile/portable and low-power consuming user terminals, when HAPS acts as an intermediate repeater. Moreover, also TCP-based applications, which suffer from long latency introduced by the satellite link and in general by errors, can get benefits in terms of end-to-end performance. In this frame, this paper deals with the introduction, on board the HAPS, of an efficient CAC scheme in order to guarantee an optimal utilization of the precious radio resources. In particular, we propose an innovative TCP driven CAC algorithm, which shall take into account not only the QoS requirements, but also TCP statistics obtained through a proxy installed on the HAPS. Results show that the overall system performance in terms of both average throughput and blocking probability is significantly improved

Analyze TCP Protocol Performance in Satellite Communications

This research is mainly about the influence of protocols on the performance of Satellite Communication. It is widely recognized that satellite communications are affected by some peculiar problems, which penalize heavily the performance and efficiency of the Transmission Control Protocol (TCP). In fact, wireless satellite channels are usually characterized by link-asymmetry and higher Round Trip Time and Bit Error Rate in comparison to wired links. It means that TCP, which was developed for wired channels, exhibits often poor performance in a satellite scenario (unfair bandwidth allocation, low throughput and long file-transfer delay).We have studied and compared many TCP variants recently proposed. In particular we have compared TCP-Reno standard implementation with TCP-SACK, TCP-Westwood, TCP-Vegas and TCP-Tibet. We tested the different protocols on a simulated satellite scenario, with the support of NS2, a well-know network simulator platform, annotating the advantages and drawbacks of various protocols in order to improve the transmission of IP data packets over satellite channels. Keywords: Satellite link, Performance analysis, TCP behaviors

Satellite Systems Performance with TCP-IP applications

Satellites are well suited for mobile Internet applications because of their capability to enhance coverage and support long-range mobility. Satellites are an attractive alternative for providing mobile access to the Internet in sparsely populated areas where high bandwidth UMTS cells cannot be economically deployed or in impervious regions where deployment of terrestrial facilities is not practical. In this paper we analyze various mobile Internet applications for both GEO and LEO satellite configurations (Iridium-like and Globalstar-like.) For the simulations, we use ‘ns2 ’ (Network Simulator 2), enhanced to support LEO and GEO satellites and mobile terminals. As part of the ns-2 upgrade, we developed a channel propagation model that includes shadowing data from surrounding building skylines. We compute via simulations the performance of FTP applications when users are mobile, traveling along “urban canyons”. 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. 1