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Survey of Satellite-Based Internet

Seminar Telematiksysteme in der Raumfahrt. Survey of Satellite-Based Internet. 20. November 2003 M.Sc. Lei Ma M.Sc Rajesh Shankar Department of Informatics VII Bayerische Julius-Maximilians Universität Würzburg. Content. Introduction Satellite Communication Fundamentals

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Survey of Satellite-Based Internet

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  1. Seminar Telematiksysteme in der Raumfahrt Survey of Satellite-Based Internet 20. November 2003 M.Sc. Lei Ma M.Sc Rajesh Shankar Department of Informatics VII Bayerische Julius-Maximilians Universität Würzburg

  2. Content • Introduction • Satellite Communication Fundamentals • Satellite-Based Internet Architectures • Some Examples of Satellite Systems • Technical Challenges Survey of Satellite-Based Internet

  3. Introduction • Source Material: • Y.Hu and V.Li. Satellite-based Internet: a Tutorial, IEEE Comm., March 2001. • J.Farserotu and R.Prasad. A Survey of Future Broadband Multimedia Satellite Systems, Issues and Trends, IEEE Comm., June 2000. • E.Lutz, M.Werner and A.Jahn. Satellite Systems for Personal and Broadband Communications, Springer, Berlin, 2000. Survey of Satellite-Based Internet

  4. Introduction • Technical challenges to Internet development • Proliferation of applications • Expansion in the number of hosts • User impose • High-speed high-quality services needed to accommodate multimedia applications with diverse quality of service Survey of Satellite-Based Internet

  5. Introduction • Satellite Network • Global coverage • Inherent broadband capability • Bandwidth-on-demand flexibility • Mobility support • Point-to-multipoint, multipoint-to-multipoint comm. • Satellite communication system is a excellent candidate to provide broadband integrated Internet services to globally scattered users Survey of Satellite-Based Internet

  6. Satellite Communication Fundamentals • Construction of a satellite system • Space segment: satellites • Geostationary orbit (GSO) • Nongeostationary orbit (NGSO) • Medium earth orbit (MEO) • Low earth orbit (LEO) • Ground segment • Gateway stations (GSs) • Network control center (NCC) • Operation control centers (OCC) Survey of Satellite-Based Internet

  7. Orbit Selection • GSO option: Larger Coverage (1/3 of Earth’s Surface) • Distance challenge: • Large delay (round-trip delay 250-280 ms) • Large propagation loss (requires higher transmitting powers and antenna gains) • NGSO option: Smaller Delay (LEO round-trip delay ~20ms) • Variable looking angle challenge: • Requires sophisticated tracking techniques or, most of the times, omni-directional antennas. • Requires support to handoff from one satellite to another. Survey of Satellite-Based Internet

  8. Frequency Bands • C Band (4-8 GHz): very congested already. • Ku Band (10-18 GHz): Majority of DBS systems, as well as current Internet DTH systems (DirectPC and Starband). • Ka band (18-31 GHz): Offers higher bandwidth with smaller antennas, but suffers more environmental impairments and is less massively produced as of today (more expensive) when compared to C and Ka. Survey of Satellite-Based Internet

  9. Satellite Payload • Bent pipe • Satellites act as repeaters. Signal is amplified and retransmitted but there is no improvement in the C/N ratio, since there is no demodulation, decoding or other type of processing. No possibility of ISL, longer delay due to multiple hops. • Onboard processing (OBP) • Satellite performs tasks like demodulation and decoding which allow signal recovery before retransmission (new coding and modulation). Since the signal is available at some point in baseband, other activities are also possible, such as routing, switching, etc. Allows ISL implementation. Survey of Satellite-Based Internet

  10. Satellite-Based Internet Architectures • The satellite-based Internet with bent pipe architecture • Lack of direct communication path • Low spectrum efficiency and long latency • The satellite-based Internet with OBP and ISL architecture • Rich connectivity • Complex routing issues Survey of Satellite-Based Internet

  11. The satellite-based Internet with bent pipe architecture Survey of Satellite-Based Internet

  12. The satellite-based Internet with OBP and ISL architecture Survey of Satellite-Based Internet

  13. Next Generation Satellite Systems Survey of Satellite-Based Internet

  14. Case Study: Teledesic • Constellation consists of 288 satellites in 12 planes of 24 satellites. • Ka-band system. Uplink operates at 28.6–29.1 GHz, downlink at 18.8–19.3 GHz. It uses • Signals at 60 GHz for ISLs between adjacent satellites in each orbital plane. • Full OBP and OBS (on-board switching). • "Internet in the sky." • Offers high-quality voice, data, and multimedia information services. QoS performance designed for a BER < 10–10. • Multiple access is a combination of multifrequency TDMA (MF-TDMA) on the uplink and asynchronous TDMA (ATDMA) on the downlink. Survey of Satellite-Based Internet

  15. Case Study: Teledesic • Network capacity planned to be 10 Gb/s. User connections of 2 Mb/s on the uplink and 64 Mb/s on the downlink possible. • Minimum elevation angle of 40.25 enables achievement of an availability of 99.9 percent. • Enormous complexity to the table in terms of untried technology, onboard switching and inter-satellite capabilities. Survey of Satellite-Based Internet

  16. Technical Challenges • Multiple Access Control • Routing Issues in Satellite Systems • Satellite Transport Survey of Satellite-Based Internet

  17. Technical Challenges (MAC) • Multiple Access Control (MAC) • Performance • Schemes • Implementation Survey of Satellite-Based Internet

  18. Technical Challenges (MAC) • Performance of MAC - Depends on shared communication media and traffic. - Long latency in Sat-channels excludes some MAC schemes that are used in terrestrial LAN - Limited power supply on board constrains computational capacity - Implementation of priorities required Survey of Satellite-Based Internet

  19. Technical Challenges (MAC) • MAC Schemes • Fixed Assignment • Random Access • Demand Assignment Survey of Satellite-Based Internet

  20. Technical Challenges (MAC) • Fixed Assignment • Techniques include FDMA,TDMA and CDMA • FDMA and TDMA uses dedicated channels • In CDMA, each user is assigned a unique code sequence • Data signal is spread over a wider brand width than the required to transmit the data. Survey of Satellite-Based Internet

  21. Technical Challenges (MAC) • Random Access In RA schemes, each station transmits data regardless of the transmission status of others. Retransmission after collision creates - Packet delay - Frequent collisions Survey of Satellite-Based Internet

  22. Technical Challenges (MAC) • Demand Assignment - DAMA protocols dynamically allocate systembandwidth in response to user accounts - Resource Reservation can be made - PODA and FIFO combine requests Survey of Satellite-Based Internet

  23. Technical Challenges (Routing Issues) • Routing Issues in LEO Constellation • IP Routing • ATM Switching at the satellites • External Routing Issues Survey of Satellite-Based Internet

  24. Technical Challenges (Routing Issues) • Routing Issues in LEO Constellation • Dynamic Topology - Handles Topological variations - ISL Maintenance • DT-DVTR - Works offline - Sets time intervals and remains constant until next time interval - No of consecutive routing tables are stored and then retrieved when topology changes • VN -Hiding of topology changes from routing protocols Survey of Satellite-Based Internet

  25. Technical Challenges (Routing Issues) Survey of Satellite-Based Internet

  26. Technical Challenges (Routing Issues) IP Routing at Satellites • Seems to be straightforward • Dealing with variable-length packets • Scalability problems • Computational and processing capacity • Research yet to be made on this scheme Survey of Satellite-Based Internet

  27. Technical Challenges (Routing Issues) ATM Switching at the satellites • Many proposed systems use ATM as the network protocol • An ATM version of DT-DVTR is investigated • Modified S-ATM packet Survey of Satellite-Based Internet

  28. Technical Challenges (Routing Issues) External Routing Issues • Internal routing done by Autonomous systems • Internal routing is handled by AS’s own internal routing protocol Survey of Satellite-Based Internet

  29. Technical Challenges (Satellite Transport) TCP/IP UDP/IP These 2 protocols will continue for now as they have tremendous legacy • Performance will be any way affected by long latency and error prone characteristics of satellite links • Researchers are still working in NASA on TCP/IP • TCP performance will definitely improve Survey of Satellite-Based Internet

  30. Technical Challenges (Satellite Transport) • TCP performance over satellite - Positive feedback mechanism - Achieve rate control and reliable delivery • Performance enhancement - TCP selective acknowledgement - TCP for transaction - Persistent TCP connection - Path Maximum Transfer Unit Survey of Satellite-Based Internet

  31. Conclusion • Bent pipe and OBP were discussed • MAC, IP routing were investigated • Important research issues - IP QoS support - Traffic and congestion control Survey of Satellite-Based Internet

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