Survey of Satellite-Based Survey of Satellite-Based Internet Internet 20. November 2003 20. November 2003 M.Sc. Lei Ma M.Sc. Lei Ma M.Sc Rajesh Shankar M.Sc Rajesh Shankar Department of Informatics VII Department of Informatics VII Bayerische Julius-Maximilians Universität Würzburg Bayerische Julius-Maximilians Universität Würzburg Seminar Telematiksysteme in der Raumfahrt Seminar Telematiksysteme in der Raumfahrt
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 - PowerPoint PPT Presentation
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Survey of Satellite-Based InternetSurvey of Satellite-Based Internet
20. November 200320. November 2003M.Sc. Lei Ma M.Sc. Lei Ma
M.Sc Rajesh ShankarM.Sc Rajesh Shankar
Department of Informatics VIIDepartment of Informatics VIIBayerische Julius-Maximilians Universität WürzburgBayerische Julius-Maximilians Universität Würzburg
Seminar Telematiksysteme in der RaumfahrtSeminar Telematiksysteme in der Raumfahrt
Survey of Satellite-Based Internet 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 developmentProliferation of applicationsExpansion in the number of hostsUser imposeHigh-speed high-quality services needed to
accommodate multimedia applications with diverse quality of service
Satellite communication system is a excellent Satellite communication system is a excellent candidate to provide broadband integrated Internet candidate to provide broadband integrated Internet services to globally scattered usersservices to globally scattered users
Survey of Satellite-Based Internet 6
Satellite Communication Fundamentals
Construction of a satellite systemSpace segment: satellites
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.
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Satellite-Based Internet Architectures
The satellite-based Internet with bent pipe architectureLack of direct communication pathLow spectrum efficiency and long latency
The satellite-based Internet with OBP and ISL architectureRich connectivityComplex routing issues
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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
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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 usesSignals 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)
1. Performance
2. Schemes
3. 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
1. Fixed Assignment
2. Random Access
3. 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