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 Seminar Telematiksysteme in der Raumfahrt

Survey of Satellite-Based Internet2 Content Introduction Satellite Communication Fundamentals Satellite-Based Internet Architectures Some Examples of Satellite Systems Technical Challenges

Survey of Satellite-Based Internet3 Introduction Source Material:  Y.Hu and V.Li. Satellite-based Internet: a Tutorial, IEEE Comm., March  J.Farserotu and R.Prasad. A Survey of Future Broadband Multimedia Satellite Systems, Issues and Trends, IEEE Comm., June  E.Lutz, M.Werner and A.Jahn. Satellite Systems for Personal and Broadband Communications, Springer, Berlin, 2000.

Survey of Satellite-Based Internet4 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 Internet5 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 Internet6 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 Internet7 Orbit Selection GSO option: Larger Coverage (1/3 of Earth’s Surface)  Distance challenge: Large delay (round-trip delay 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 Internet8 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 Internet9 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 Internet10 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 Internet11 The satellite-based Internet with bent pipe architecture

Survey of Satellite-Based Internet12 The satellite-based Internet with OBP and ISL architecture

Survey of Satellite-Based Internet13 Next Generation Satellite Systems

Survey of Satellite-Based Internet14 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 Internet15 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 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 Internet16 Technical Challenges Multiple Access Control Routing Issues in Satellite Systems Satellite Transport

Survey of Satellite-Based Internet17 Technical Challenges (MAC) Multiple Access Control (MAC) 1. Performance 2. Schemes 3. Implementation

Survey of Satellite-Based Internet18 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 Internet19 Technical Challenges (MAC) MAC Schemes 1.Fixed Assignment 2.Random Access 3.Demand Assignment

Survey of Satellite-Based Internet20 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 Internet21 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 Internet22 Technical Challenges (MAC) Demand Assignment - DAMA protocols dynamically allocate system bandwidth in response to user accounts - Resource Reservation can be made - PODA and FIFO combine requests

Survey of Satellite-Based Internet23 Technical Challenges (Routing Issues) Routing Issues in LEO Constellation IP Routing ATM Switching at the satellites External Routing Issues

Survey of Satellite-Based Internet24 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 Internet25 Technical Challenges (Routing Issues)

Survey of Satellite-Based Internet26 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 Internet27 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 Internet28 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 Internet29 Technical Challenges (Satellite Transport) TCP/IPUDP/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 Internet30 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 Internet31 Conclusion Bent pipe and OBP were discussed MAC, IP routing were investigated Important research issues - IP QoS support - Traffic and congestion control