Transcript TCOM 507 Class 2

Satellite-Based Internet
Joe Montana
IT 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 notes
Leila Z. Ribeiro Class Handouts
Students research papers:
Kwabena Konadu & Rafael Chaparro
Kim Wee
Semirames 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 pointto-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 Solutions
Consists 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 Discussion
Mobile 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 Starband
Future: Teledesic, Astrolink, Spaceway-GEO and Skybridge
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System Design
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Orbit Selection
GSO 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 Delay
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.
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 Bands
Most 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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Architectures
Bent 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
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implementation.
Architecture with Bent Pipe
Satellite-Based Internet: A Tutorial
Yurong Hu and Victor O. K. Li, The University of Hong Kong
IEEE Communications Magazine - March 2001
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Architecture with OBP and ISL
Satellite-Based Internet: A Tutorial
Yurong Hu and Victor O. K. Li, The University of Hong Kong
IEEE 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 Control
To 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 intersatellite handover, inter-beam handover.
Availability of ISL form a mesh network
topology in the sky. Intra-plane and Interplane ISL may be supported.
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Transport Protocol
TCP/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 Trends
John Farserotu, CSEM &Ramjee Prasad, Aalborg University
IEEE Communications Magazine June 2000
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Future Systems:
Satellite-Based Internet: A Tutorial
Yurong Hu and Victor O. K. Li, The University of Hong Kong
IEEE 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 bentpipe 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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Spaceway
May 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 Kaband 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 highspeed 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 Issues
The 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 Analysis
Other options available to end user for
Internet broadband access include:
DSL
Cable Modem
MMDS and LMDS (wireless)
Terrestrial 3G systems in the case of
mobile applications.
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Options for Home Internet Access
DSL 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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Summary
Future 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.
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