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Satellite-Based Internet

Joe MontanaIT 488 Fall, 2003

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Source Material:IEEE published material:

Satellite-based Internet: a Tutorial (Yurong Hu and Victor O.K. Li), IEEE Comm., March 2001.A Survey of Future Broadband Multimedia Satellite Systems, Issues and Trends (John Farserotu & Ramjee Prasad), IEEE Comm., June 2000.Broadband Satellite Systems (Daniel Bem et.al) IEEE Surveys, 1st Quarter 2000.

Internet research:http://www.irwincom.com/idvs-summary.txt (Irwin Consulting Report – Internet Delivery via Satellite, June 1999)

Dr. Jeremy Allnutt class notesLeila Z. Ribeiro Class HandoutsStudents research papers:

Kwabena Konadu & Rafael ChaparroKim WeeSemirames Miranda

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Introduction

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Internet Services

“Defined as any service in which data traffic originates from, travels over, or is destined for the public Internet -- growing from approximately 5.4 Gbps by year-end 1999 to an estimated 21 Gbps by 2003.”

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Service Options

 Internet backbone interconnection provisioning. (Intelsat, Loral-Orion, PanAmSat, etc). Great fraction of revenue source in current systems.Last mile (end-user access points): more recent approach. Some systems already operating (DirectPC and Starband). Many systems proposed for future.

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Backbone Interconnection“Point-to-point Internet backbone interconnection services represent the single largest identifiable market for satellite Internet services today.  As new fiber is continually deployed worldwide, the addressable market for point-to-point satellite Internet services will gradually diminish. In the long term, satellite services that leverage the inherent strengths of satellite communications systems (broadcasting) will be the most successful.

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Last Mile SolutionsConsists of connecting users to network access points directly.Satellite networks have clear advantages against other terrestrial systems with respect to its inherent capability to reach customers anywhere, anytime.The main challenges for “last mile” solutions rely on providing enough bandwidth in two directions (two-way broadband capability) to low cost end user equipment.Providing Internet service to mobile end users constitutes another challenge by itself.

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Scope of DiscussionMobile Applications: Broadband Internet access over mobile (3G). GSO or NGSO options.

Currently supported with limitations: low data rate.Future support by: Teledesic, Inmarsat(Extension of mobile voice systems discussed in previous classes)

Fixed applications (Direct-to-Home): Typically GSO systems, some NGSO systems. Examples:

Current systems: DirectPC and StarbandFuture: Teledesic, Astrolink, Spaceway-GEO and Skybridge

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System Design

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Orbit SelectionGSO option: Advantage Larger Coverage

Distance challenge:• Large delay (trouble for interactive real-time

applications)• Large propagation loss (requires higher transmitting

powers and antenna gains)

NGSO option: Advantage Smaller DelayVariable looking angle challenge:

• Requires sophisticated tracking techniques or, most of the times, omni-directional antennas.

• Requires support to handoff from one satellite to another.

Hybrid option: Network including some GSO and some NGSO satellites in order to get the best of both worlds. Ex. Spaceway

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Frequency BandsMost commonly used: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.

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ArchitecturesBent pipes: 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.On-Board-Processing: 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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Architecture with Bent Pipe

Satellite-Based Internet: A TutorialYurong Hu and Victor O. K. Li, The University of Hong KongIEEE Communications Magazine - March 2001

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Architecture with OBP and ISL

Satellite-Based Internet: A TutorialYurong Hu and Victor O. K. Li, The University of Hong KongIEEE Communications Magazine - March 2001

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Terminals and User Asymetry Interactive terminals: can both transmit and receive data directly to/from satellite. Still expensive for DTH users (e.g. Starband terminal costs $400 + $200 installation fee).Initial DBS Internet services offered went for one-way option, with satellite receive-only user units, and upstream sent via terrestrial link. Ex. DirectPC first generation.Since Internet traffic is becoming progressively LESS asymmetrical, one way solutions don’t have great chances for success in the near future.

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Multiple Access ControlTo support QoS provisioning for data traffic, a requires priorities. Real-time traffic has the highest priority.

Three implementation groups:Fixed Assignment: Pre-assigned channels based on FDMA, TDMA or CDMA implementation options.Random access: Contention based (Aloha and its variations). Each station transmits when needed. Collisions occur for simultaneous transmissions.Demand Assignment (DAMA): Resource negotiation phase prior to data transmission. Bandwidth allocated on demand using FDMA, TDMA or CDMA schemes.

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Routing Schemes

GSO Routing over terrestrial network (no ISL).LEO Routing:

Dynamic Topology: Support to inter-satellite handover, inter-beam handover.Availability of ISL form a mesh network topology in the sky. Intra-plane and Inter-plane ISL may be supported.

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Transport ProtocolTCP/IP over satellite links present some issues that require modifications on the protocol implementation:

Typical slow start TCP implementation could be replaced by larger initial windows.Spoofing to compensate larger Round-trip time (RTT) inherent to satellite links (mainly GSOs), by sending “false” ACKs to trick TCP into continuing transmission.

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Case Studies

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Future Systems:

A Survey of Future Broadband Multimedia Satellite Systems, Issues and TrendsJohn Farserotu, CSEM &Ramjee Prasad, Aalborg UniversityIEEE Communications Magazine June 2000

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Future Systems:

Satellite-Based Internet: A TutorialYurong Hu and Victor O. K. Li, The University of Hong KongIEEE Communications Magazine - March 2001

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Astrolink (2003)The Astrolink satellite constellation contains nine GEO satellites Ka-band satellite system. The uplink is 28.35–28.8 GHz and 29.25–30.0 GHz. The downlink is 19.7–20.2 GHz.System designed to support high-speed multimedia communication.Employs OBP for increased efficiency and OBS for flexibility. Each satellite is an integral part of the communication network, as opposed to being a bent-pipe relay.Data rates range from as low as 16 kb/s to 9.6 Mb/s. 384 kb/s are supported to 90 cm dishes, which makes Astrolink potentially suitable for large mobile platforms.

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Cybestar (2001)Ka-band constellation consisting of three GEO satellites.Originally planned to deploy a Ku/Ka-band fleet of three Ka-band satellites with as many as 48 LEO Ku-band satellites. While the company is still planning to build a Ka-band system, its primary focus is on successfully implementing its Ku-band service offering, which uses Loral Skynet's Telstar 5 to deliver broadband services to businesses.Cyberstar-Ka is designed to provide IP multicasting services to Internet service providers (ISPs), large and small business organizations, and multimedia content providers.The capacity of the Cyberstar-Ka network is 9.6 Gb/s. IP multicasting is implemented based on frame relay and ATM technology.

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SpacewayMay get confusing as there are many phases and configurations to what is called “Spaceway”.The Spaceway final configuration plans for 16 GEO and 20 medium earth orbit (MEO) satellites.Hughes Electronics Corp. has committed $1.4 billion to Hughes Spaceway for the launch three GEO Ka-band satellites for service starting in 2001, which will be the platform for the next generation DirecPC. Under the Hughes H-Link proposal filed with the FCC, 22 MEOs (2 spares) will be launched using Ku-band to offer broadband services.The HughesNET proposal consists of 70 Ku-band LEOs for packet-switched and circuit-switched Internet access.

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Spaceway (2002)The Spaceway final configuration plans for 16 GEO and 20 medium earth orbit (MEO) satellites.Ka-band system designed to support high-speed data, Internet access, and broadband multimedia information services.The Spaceway satellite architecture is based on conventional bent-pipe relay.It offers high QoS (bit error rate, BER < 10–10) to users with terminals as small as 0.66 m, at data rates starting at 16 kb/s up to 6 Mb/s.The Spaceway system is compatible with ATM, integrated services digital network (ISDN), frame relay, and X.25 terrestrial standards.

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SkyBridge (2002)Skybridge, the only one of the major players that has a LEO-based Ku-band solution, has expanded from a proposed constellation of 64 LEO Ku-band satellites to 80 satellites for a total of $4.2 billion. Besides the decision to use Ku-band, Skybridge is excluding any complex switching-in-the-sky and inter-satellite link capabilities.Constellation consists of 80 satellites in circular LEO at 1469 km. The orbital inclination is 53s.The system is intended to support advanced information services (e.g., interactive multimedia) at data rates from 16 kb/s to as high as 60 Mb/s.SkyBridge satellite design is based on a bent-pipe relay architecture.

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SkyBridge (cont.)Unlike the other systems described so far, SkyBridge is a Ku-band system. The uplink operates at 12.75–14.5 GHz, and the downlink is 10.7–12.75 GHz. The choice of Ku-band is due to the availability of Ku-band technology. SkyBridge gateway stations interface with terrestrial networks via ATM switches. The majority of services are expected to be IP-based. SkyBridge employs a combined code-/time-/frequency-division multiple access (CDMA/TDMA/ FDMA) waveform; however, the satellites themselves are transparent (i.e., bent-pipe).Spot beams, with frequency reuse in each beam, are employed to enhance capacity. SkyBridge is designed to accommodate traffic from over 20 million simultaneous users.

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Teledesic (2004)The Teledesic constellation consists of 288 satellites in 12 planes of 24 satellites. Teledesic is a Ka-band system. The uplink operates at 28.6–29.1 GHz, and the downlink at 18.8–19.3 GHz. It uses signals at 60 GHz for ISLs between adjacent satellites in each orbital plane. Teledesic employs full OBP and OBS (on-board switching). The system is designed to be an "Internet in the sky." It offers high-quality voice, data, and multimedia information services. QoS performance is 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.

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Teledesic (cont.)The capacity of the network is planned to be 10 Gb/s. User connections of 2 Mb/s on the uplink and 64 Mb/s on the downlink are possible.A minimum elevation angle of 40.25 enables the Teledesic system to achieve an availability of 99.9 percent. Teledesic's 288 LEO Ka-band satellites bring enormous complexity to the table in terms of untried technology, on-board switching and inter-satellite capabilities. While this complexity may translate into more service flexibility over time, we expect to see further adjustments to Teledesic’s business plan as the system continues to be developed.

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iSky (2001)iSky, formerly KaStar, is focused on providing broadband data and Internet services to North America (regional solution). This Ka-band system is designed to support high-speed two-way Internet access, direct broadcast services (DBS), and future personal communications systems (PCS) to homes and offices via small aperture (e.g., 26 in) antennas.The initial constellation consists of two GEO satellites. The uplink frequency is 19.2–20.0 GHz, and the downlink 29.0–30.0 GHz.Data rates up to 40 Mb/s are envisioned, with typical rates in the range of 1.5–5 Mb/s.

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Other “Last Mile” Satellite Systems

Other planned broadband systems include:

Ka-band payloads on Koreasat 3, which will carry three Ka-band transponders;Astra-1H, the first of two SES Ku/Ka-band satellites, originally planned for 1999.Tokyo-based Space Communications Corp.'s Superbird 2B replacing Ka-band satellite Superbird B (originally planned 2000)Telespazio is offering a broad menu of multicast and broadcast solutions including high speed IP connectivity.

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Regulatory IssuesThe worldwide regulatory trend is towards deregulation of telecommunications, and most World Trade Organization (WTO) countries are adopting non-exclusive licensing arrangements for telecommunications service providers in response to the WTO Basic Telecommunications Agreement.

The European Union (EU) also has made substantial progress in opening its markets to satellite communications and reducing trade barriers, with the eventual goal of creating a single market for satellite services.

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Regulatory Issues (cont.)Access to most Asian markets requires not only landing rights, but also some form of political clout because the Internet and broadcasting regulations are politically charged issues. Bilateral and regional agreements are promoting a gradual though uneven opening of markets in Latin America. Regulatory issues in areas like Africa and the Middle East tend to be more related to infrastructure development and the high costs of Internet services, as well as government attitudes towards open access to the Internet.

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Market Analysis DBS system operators can take advantage of the growing demand for Internet content by using surplus bandwidth to deliver direct-to-user Internet services.Current services, which have experienced slow consumer uptake, are combining Internet content delivered via satellite with a terrestrial return path, in conjunction with traditional television content.The biggest challenge facing the Ka-band industry is not technology development, but rather business and service development, as well as financing.Because the networking market changes rapidly over time, the need for these ventures to remain flexible in terms of types of services and applications that can be provided is key.By the end of 2001, we expect to see approximately 1000 direct-to-user Ka-band sites providing 2-way Internet services, with this figure growing to over 100,000 by the end of 2003.

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Market AnalysisOther options available to end user for Internet broadband access include:

DSLCable ModemMMDS and LMDS (wireless)Terrestrial 3G systems in the case of mobile applications.

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Options for Home Internet AccessDSL is a modem technology that transforms ordinary phone lines into high-speed digital lines for internet access. It transmits data in both directions simultaneously, at over 1.5 Mbps over copper wires up to 18,000 feet (about one third of a mile). The main limitation of DSL is that the user must be within 18,000 feet of a telephone company’s exchange office. Cable modem is a device that allows high-speed internet access via a cable TV network. To communicate with a user, the network allocates one television channel ( 50-750 MHz range) for downstream traffic and another channel (5-42 MHz band) for upstream signals. The limitation of the cable service is that as the number of users on the same cable modem termination system (CMTS) increases the communication speed will slow down considerably.MMDS wireless broadband network has a fixed wireless headend that connects to a central antenna which broadcasts data to users. The two main limitations of wireless MMDS are the line-of-sight transmission and broadcast range.

From (adapted): Research Paper – TCOM 507 (Student: Katherine Wee)

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SummaryFuture satellite systems will offer an array of advanced information services.The trend is toward high-speed Internet access and broadband multimedia and IP-based services over IP and/or IP/ATM networks. Services may range from email and voice to broadband multicasting and interactive video. Satellite architectures may employ OBP, OBS, and/or OBR to augment capacity, or traditional bent-pipe transponders for simplicity and flexibility.Constellations may be LEO, MEO, GEO, or combinations thereof, dependent on the coverage required and the services to be supported.

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Summary (cont.)The use of Ka-band and even higher frequencies will be increasingly common as available spectrum becomes more scarce.Higher frequencies also enable the use of smaller terminals and, potentially, greater mobility. Integration of emerging and future satellite systems with terrestrial networks can help bridge the last mile and expand the reach of Internet-based services to business and homes.