CONTRIBUTION FROM INMARSAT TO ASMS TECHNICAL WORKING GROUP. SYSTEM ARCHITECTURE FOR ADVANCED SATELLITE MOBILE SYSTEMS Draft 1.

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1 Ref: ASMS_02_T10_0.doc CONTRIBUTION FROM INMARSAT TO ASMS TECHNICAL WORKING GROUP SYSTEM ARCHITECTURE FOR ADVANCED SATELLITE MOBILE SYSTEMS Draft /5/ Introduction During the ASMS task force meeting # 2, the technical working group was tasked to propose mobile satellite system (MSS) architecture which can provide the users requirements for the short term (year ~2004), defined by the commercial group (CG) (1). In this draft report system architecture and related issues applicable to the short term are covered. Due to the long deployment period of satellite systems, the most applicable architectures are the ones either deployed (e.g. Inmarsat, Aces, Thuraya, Iridium, Globalstar, etc.) or under development (e.g. Inmarsat-4 broad band global area network). The latter have some flexibility in terms of incorporating trends such as mobile-broadcast convergence. Harmonisation and standardisation efforts should consider a suitable evolutionary path for existing operators. A typical MSS architecture comprises of a space segment, a fixed segment and a mobile segment interconnected to each other through radio links and to partner terrestrial networks through interfaces installed at gateways. Depending on the orbit deployed and the service area, the space segment comprises of one or more satellites illuminating the service area through multiple spot beams. The fixed segment comprises of one or more gateways connected to the public, and optionally, to private networks. The gateways also interface to a business management centre to assist billing and customer services; to a network control centre to support management and monitoring of network performance; and with each other in some types of architectures,. The mobile segment comprises of various types of mobiles supported in the network. Several existing and planned system have built inter-operability with terrestrial mobile standards such as GSM, GPRS and UMTS. Further, with a growing convergence of broadcast and the fixed network, it is likely that future MSS architecture will include broadcast/multicast components. Due to lack of agreed standards, technical solutions tend to be propriety with the result that a variety of systems are in use and the industry has perhaps not been able to benefit from economy of scale in a market which is rather limited anyway. Due to the long lead time in introducing MSS technology, it would appear that operators may continue to use individual solutions in the short term. However standardisation will enable better inter-operability in the long term.

2 2.0 Space segment The function of the space segment is to provide the necessary radio resources to support the desired communications, signalling and connectivity. The space segment comprises of a satellite constellation whose size and design depends on orbital altitude, service area (country-wide, regional or global), type of service and the desired connectivity. For LEO satellites satellite systems have already been deployed in operational systems; for medium earth orbit satellite systems are expected within the next few years; and depending on whether the system has a regional or world-wide coverage, 1-4 satellites are deployed for geo-stationary systems. Hybrid orbits comprising of combination of inclined, circular different altitude have also been proposed. Space segment deploying non-geostationary orbit are more complex due to motion of satellites relative to the Earth and hence a need of tracking, handover and dynamic routing. Network routing within the MSS segment can be implemented through inter-satellite links. Example of non-geostationary satellite systems are Iridium (low earth orbit), Globalstar (low earth orbit) and the new ICO (medium earth orbit) while examples of geostationary orbit systems are Inmarsat (world-wide), Thuraya and Aces (regional). To support communication to mobiles, high powered, multi-spot beam satellites are necessary. Multi-spot beam and high power satellites reduce call cost and increase system capacity by improving spectral efficiency and spacecraft power utilisation. The satellites are transparent or regenerative, with or without intersatellite links (ISL). Spacecraft capacity is a trade-off between user throughput, constraints imposed by - mobile transmitter power and sensitivity; and spacecraft antenna and high power amplifier technology. Due to non-uniform geographical distribution of traffic, dynamic allocation of power and spectrum is an inherent component of a payload design. Table 1 summarises transponder characteristic of a recent MSS geostationary satellites. [Long term goals larger number of spot beams; regenerative transponders; agile/adaptive beams, higher satellite power ] 3.0 Ground segment 3.1 Gateways The fixed part of the ground segment comprises of one or more gateways to access the space segment, transport the necessary signalling, control and communications and support inter/intra system mobility. The location of gateway depends on operator s preferred selection criteria. Factors considered include proximity to the terrestrial traffic, desired network connectivity and routing arrangements, Gateways comprise of a radio system to support transport over the satellite system and a network switching system to interconnect to the terrestrial network. The gateway are interfaced to various terrestrial networks such as Public Switched Telephone Network (PSTN), Public Land Mobile Network (PLMN) such as GPRS or UMTS, Internet, private network, etc. The service providers, responsible for end-to-end service provision, access the satellite network through the appropriate interfaces.

3 In some networks separate network control stations are used for call set up and radio resource management. [Need to develop interfaces GPRS, UMTS,DVB..] 3.2 Mobiles The service link connects user terminals with the gateway. The user terminals consists of a radio part comprising of an antenna system and associated radio frequency circuits for accessing the radio link and a terminal equipment which supports the application, user interface, network protocols, and other functions such as encryption. Technological constraints arise from the stringent size, weight and cost requirements. Several MSS systems have already demonstrated feasibility of speech to hand-held terminals and 64 kbps to briefcase terminals. Dual and multi-mode terminals have been demonstrated by some MSS operators. Mobile technology can benefit substantially from terrestrial mobile technology deriving benefits from device/dsp technologies software radio, adaptive antennas, etc,. A part of the terrestrial traffic can be transported over a MSS terminal by concentrating local traffic (e.g. on a ship). Blue tooth and wireless LAN are relevant technologies in this respect. Low terminal cost is vital. 3.3 Network control centre The network control centre (NCC) monitors and manages the network performance. Its functions include traffic and radio-frequency monitoring, management of system bulletin board, fault diagnosis, maintenance of network RF integrity, generation of payload change requests, real time and long term radio resource/traffic planning and management, etc. Due to the complexity of MSS networks it is necessary that the NCC provide monitoring and performance data in an easily comprehensible format to the operators, necessitating advanced data processing, graphical display and GUI. The NCC together with the satellite control also has the task of managing real-time spacecraft switching in response to traffic demands, while maintaining spectrum efficiency. This necessitates a combination of off-line and real-time optimisation techniques. [Enabling technologies frequency planning, optimisation.] 3.4 Business segment The business segment is responsible for managing products and services of the network. These functions include billing, customer care, revenue collection, service provisioning, customer management and interconnect billing system. Operators generally have their propriety billing/customer management system 4.0 Radio interface

4 The radio interface, comprises of accessing and control mechanism and ensures efficient transport over the satellite network for circuit or packet mode as necessary. Functions associated with the radio interface include call-control, radio resource management during a session and at call set-up, quality of service management, power control, mobility management, data adaptation and others. A number of accessing techniques are in use. These include FDMA, TDMA, CDMA, random access and their variants. Table 2 demonstrates example link budgets for palmtop, notebook and briefcase terminals to support the specified bit rates for a FDMA/TDMA geostationary satellite system operating in C/L band. For a given user requirements, spacecraft sensitivity (G/T), Effective Isotropic Radiated Power (EIRP) and available spectrum set practical bounds on system capacity. [Technologies: Improved accessing/modulation/coding techniques, optimised radio resource management methods, QOS mangement, integration of broadcast and MSS air interface ] 5.0 Network A layered architecture supports efficient partitioning of functionality and network interfaces. It permits MSS specific functionality to be segregated, allowing transparent transport across networks via appropriate interface. To permit interoperability with terrestrial networks it is necessary to adapt their protocols to the satellite network to enable a seamless end-end connectivity. Some of the issues in this respect include effects of satellite network on performance of protocols and applications (e.g. TCP/IP, voice over IP). [Include layered MSS network architecture here] As mentioned, several MSS operators now interface their network to public land mobile network (PLMN), the Internet and other IP networks in addition to the PSTN/ISDN and possibly to the broadcast network. The logical architecture within the satellite network can be separated into a number of domains, e.g. service, control and transport. Depending on an operator s preference, mobility management functions can be integrated or separated from the terrestrial PLMN. Three types of functional entities or planes can be identified for partitioning information flow and protocols transmission, signalling and management. The transmission plane contains flow of end-user information and protocol necessary for transport of the information across the network through appropriate interfaces. The signalling plane contains flow of control information for establishment, operation, modification and termination of connections and resources in the network for each session The management plane contains the flows of information and protocols of information and protocols to control the configuration, reconfiguration and management of different functional units, including accounting, performance monitoring and fault management. Intra-system network connectivity is possible through inter-satellite link or terrestrial links. Call routing is relatively simple in geostationary orbit systems,

5 while a number of techniques are used for call and packet routing in nongeostationary orbits. 6.0 Conclusions Requirements specified by CG can be met in the short term by existing or planned system provided some technologies are developed (List of technologies in need of development). Low call and terminal costs are desirable. As solutions are disparate market segmentation is inevitable. Standardisation and (perhaps) spectrum is an issue.

6 Table 1 State of art of geo-stationary transponder characteristics ( ). Spacecraft EIRP (dbw) > 73 Number of spot beams Service link G/T (db/k) Feeder link G/T (db/k) -11

7 Table 1(a) Example forward link budget Terminal Size Palm top Lap top Brief-case Bit rate (Kbps) Modulation/coding QPSK(co de rate?) 16 QAM, turbo-code 16 QAM, turbo-code EIRP (dbw) Path loss (db) GHz, 5 Deg elevation ) Fading and other loss (db) Satellite G/T C/No (Up) (db-hz) C/IM 0 (db-hz) Transponder gain (db) Satellite EIRP (dbw) Path loss (db) (@1.5 GHz, 5 Deg Elevation) Fading and other loss (db) LES G/T (db/k) C/No(Down) (db Hz) C/N (Total) (db Hz) C/No (Required) (db Hz)

8 Table 1(b) Example return link budget Terminal Size Palm top Lap top Brief-case Bit rate (Kbps) Modulation/coding QPSK/ 16 QAM, 16 QAM, Code rate? turbocode turbo-code EIRP (dbw) Path loss (db), L-band, 5 Deg Elev Fading and other loss (db) Satellite G/T (db/k) C/N 0 (Up) (db-hz) C/IM 0 (db-hz) Transponder gain (db) Satellite EIRP (dbw) Path loss (db), C-band, 5 Deg Elev Fading and other loss (db) LES G/T (db/k) C/N 0 (Down) (db) C/N 0 (Total) (db) C/N 0 (Required) (db)

9 Reference 1. Internal Report of the Commercial Group of the Advanced Satellite Mobile System Task Force Commercial requirements for the third generation of mobile satellite systems and beyond, April 2001, CNES Toulouse 2. Inmarsat contribution to Meeting #2 PMC system. 3. Inmarsat contribution to Meeting #2 Technologies for advanced satellite mobile system.