Abstract
Arising from the fact that the terrestrial network is becoming more IP-centric, it is crucial to be able to support IP services over the satellite component of UMTS as well to achieve close synergy with the terrestrial counterpart for seamless communication. Nevertheless, the direct utilization of the IP protocol suite in a mobile environment is not straightforward, and when coupled with the additional constraints and shortcomings that satellite-based systems pose, it imposes additional challenges to the integration of satellite systems into the IP-based T-UMTS and the global Internet. In this thesis, we study the feasibility of establishing multimedia sessions over S-UMTS based on the SIP protocol, and investigate efficient solutions to transport SIP signalling, taking into account not only the larger satellite propagation delay but also the impact of the S-UMTS radio interface arid channel impairment. The preservation of maximum commonality between T- & S-UMTS is the aim of our work to facilitate an effective integration of both segments. Given that a dedicated channel needs to be used for the transport of SIP signalling, the Random Access Channel (RACH) is first investigated. The impact of the different RACH transmission control parameters on the access performance over S-UMTS is studied with their trade-offs identified. It is further demonstrated how QoS differentiation could be provided on the RACH through Access Service Classes (ASCs). Two schemes have also been proposed to decrease the risk of code/signature collision, where it has been shown that when network-wide synchronization is already in place, these schemes perform better than the ETSI S-UMTS scheme as the access rate increases. By incorporating a link layer retransmission based on the RLC-AM mechanisms, it has been shown that SIP session establishment can work acceptably well over S-UMTS with performance comparable to the circuit-switched call setup. It is further demonstrated that with proper configuration of RLC parameters and retransmission options, the session setup performance under various channel conditions can be substantially improved. Two schemes that mitigate the inefficiencies of the existing UMTS RLC-AM procedure for session setup over S-UMTS have also been proposed. The main advantage of the first scheme lies in its ability to recover the missing last radio segments in a single round-tip whilst minimizing the feedback and avoiding redundant retransmissions. The second approach minimises redundant retransmissions when more than one feedback report trigger is configured, where improved system performances are obtained. Finally, in the joint study of SIP's own reliability mechanisms and RLC retransmission scheme, it has been shown that precious radio and network resources can be saved by making SIP and RLC 'more co-operative' through different degree of awareness of each other. Key words: S-UMTS, IP, Session Initiation Protocol, Random Access Charmel, Radio Link Control.