Design and performance of a 3G mobile satellite system

摘要

This paper describes the design and performance of a geo-synchronous mobile satellite system based on enhancements to terrestrial 3GPP specifications. The corresponding 3G satellite air interface developed by Hughes is called GMR-1 3G and has been standardized at ETSI and ITU standards bodies. System architecture is based on Release-7 all-IP architecture with satellite specific enhancements primarily in the access stratum. This allows the use of COTS core network and COTS Non-Access Stratum (NAS) software to be implemented in user terminal. System provides IP data services with data rates up to 590 kbps. Consistent with 3G specifications, the system provides differentiated Quality of Service (QoS) both across users as well as across applications. In this framework, a given user terminal can invoke multiple applications simultaneously, each receiving their appropriate Quality of Service treatment. The system permits both user mobility and terminal mobility across spot-beams within the satellite system as well as between satellite system and terrestrial systems. The terrestrial 3G standard was significantly enhanced to achieve better spectral efficiency and improved throughput for satellite operation that is characterized by long delays, spectral scarcity and limited link margins. Enhancements were primarily in the radio specific layers, namely physical layer, MAC/RLC layer and PDCP layer, to achieve the necessary spectral efficiency and throughput improvement. The system implements IMS based services, including VoIP with circuit-switched spectral efficiency, IP data with delay optimized Bandwidth on Demand (BoD), dynamic link adaptation (DLA), Link Layer ARQ, multiple levels of QoS, TCP Performance Enhancing Proxy, policy based resource management, load balancing and, position based admission control, billing, emergency call handling and legal interception. System supports multiple terminal types such as hand-held, vehicular and portable terminals. System also suppor-n-nts security at the transmission layer and permits L3, L4 and application layer security.