inter satell!te l!nk
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!NTER SATELL!TE L!NK
SEASON 1“It’s all about global coverage”
Sanjeev Kumar
2006H124469
Note: I(Part 2) along with Mr. Sanjeev Gupta (Part 1) delivered this presentation , during our
MS (ME/Mtech) in Communication Engineering at Birla Institute of Technology and Science
Pilani India
Dated : November 2007
Place: Birla Institute of Technology and Science Pilani India
Agenda for Season 1
• What is Inter Satellite Link (ISL) ?
• The Need of ISLs and IOLs !
• Satellite Cancellations and examples !
• Constellation and Table
• Constellation Characteristics
• Band of Working !
• Applications of ISL and IOL !
• Pros and Cons of ISL
• Types of ISL !
• Optical Inter Satellite Link !
• MIT Lincoln Laboratory‟s 1 Gbps DPSK test-bed !
• Case Study Of Iridium
What is Inter Satellite Link (ISL) ?
• A service providing links between artificial satellites.
• Inter-satellite links (ISL) within the constellation, or
inter-constellation links with other data relay satellites
to carry traffic and signaling.
• Also known as cross link.
• Abbreviated as ISL
• ISL operates in the Ka-band at frequencies in the range
23.18– 23.38 GHz.
The Need of ISLs and IOLs !
• Satellites can be used to connect with each other,
through the use of ISL or inter-orbit links (IOL),
which when combined with on-board routing
facilities, can be used to form a network in the
sky. (Known as Satellite Personal
Communication Network – S PCN)
• The more sophisticated the space segment, the
less reliant it is on the ground network, thus
reducing the need for gateways.
• More will be in Application Episode.
Satellite Cancellations and examples !
• A constellation is a group of similar satellites working
together in partnership to provide a network of useful
service.
• Each satellite in a constellation, for example, acts as a
switching node and is connected to nearby satellites by
inter satellite links. An example is the two LEOs cross-
linked in Fig. S1.1
• Examples
• U.S Defense satellite operational network called FLTSATCOM
(Fleet satellite communications system)
• SBIRS (Space-based infrared system)
• Iridium
• Teledesic networks
Satellite Cancellations and examples !
Fig S1.1a A sketch of SBIRS, an example of inter satellite links and
satellite constellation.
Applications of ISL and IOL !
Figure S1.2 Possible S-PCN architectures for global coverage.
•To connect GEO and possibly non-GEO satellites to each other.
•The commercial application of ISLs is for the Iridium system, and
these employ Ka-band.
Positives and Negatives with ISL
Positives /Advantages
• Adds further dimensions to the definition of location areas
and mobility management in satellite networks
• Calls may be grounded at the optimal ground station
through another satellite for call termination – reducing the
length of the terrestrial „tail‟ required.
• A reduction in ground-based control may be achieved with
on-board baseband switching – reducing delay (autonomous
operation).
• Increased global coverage – oceans and areas without Earth
stations.
• Single network control centre and Earth station.
Positives and Negatives with ISL
Negatives/Problems
• The complexity and cost of the satellites will be increased.
• Power available for the satellite/user link may be reduced.
• Handover between satellites due to inter-satellite dynamics
will have to be incorporated.
• Replenishment strategy.
• Frequency co-ordination.
• Cross-link dimensioning.
“Despite these disadvantages, the advantage of routing traffic
in the sky independently of the ground infrastructure,
makes the use of ISLs an attractive solution.”
Types of ISL !
There are two types of ISL
•RF ISL
•Optical ISL
• RF is generally not used now a days , the whole research
community is working on Optical ISL because of the
advantages it provide
Optical Inter Satellite Link !
• Space-based optical communications
• High data rate (many Gbps) space-earth links
• Much narrower beam-width than the RF system
• Potential for interference to or from adjacent satellites
will be reduced
• Requirements for more accurate pointing
• Pointing, acquisition and tracking (PAT) and the impact
that this may have on the spacecraft could impose an
unwelcome burden
• The optical spectrum is currently unregulated
Japan‟s Communications Research
Laboratory (CRL)
Fig. S1.4. Japanese Optical Communications System Plan (CRL).
Japan‟s Communications Research
Laboratory (CRL)
• Fairly broad-ranging program
• Current plans call for investigation of multichannel
medium bit rate (300 Mbps) systems using 0.8 μm
wavelength technology
• Simultaneously developing high rate (1.2 Gbps) systems
using 1.5 μm technology
• The plan is for operational 10 Gbps/channel systems.
MIT Lincoln Laboratory‟s 1 Gbps DPSK test-
bed
Fig. S1.6. Lincoln Laboratory 1 Gbps test-bed system.
MIT Lincoln Laboratory‟s 1 Gbps DPSK
testbed
• Programs for U.S. military optical communications needs
• Based upon a 1.55 μm wavelength
• Erbium-doped fiber amplifier technology
Case Study Iridium
•Deployed in 1998
•Consists of 66 satellites in six orbital planes
•Each satellite has 48 spot beams
•The inter-satellite links operate in the 23.18- to 23.38-GHz
band
•The uplink and downlink frequency bands to the gateways
are 29.1 to 29.3 GHz and 19.2 to 19.6 GHz, respectively
Case Study Iridium
•A satellite-based, wireless personal communications network
• Providing a robust suite of voice and data features all over the globe
•Comprised of three principal components
-- the satellite network
--the ground network
--Iridium subscriber products, including phones and
data modems.
Case Study Iridium
•More than 99 percent of calls placed through Iridium handsets were
successfully connected compared to 51.3 percent of all calls from a
competitor's handset.
•98.1 percent of calls on Iridium handsets were successfully
connected and completed without being dropped during a three-
minute period compared to 36.2 percent of calls on a competitor's
handset.
REASONS OF ITS ADVANTAGES
•More satellites than any other commercial constellation
• Constantly in view of every part of the Earth.
•With no service gaps, Iridium users should be able to pick up and
hold a strong communications signal
Case Study Iridium
•Iridium is often used as a backup to cellular data modems –
many businesses that need a very reliable connection automatically
switch over to Iridium when their GSM data service fades or is
unavailable.
•With terrestrial mobile systems only covering about 15 percent of
the
Earth's surface (and certainly not the sky, oceans or poles), Iridium is
the only connection available to many parts of the world.
Even in urban and suburban environments, Iridium data solutions are
providing reliable backup.
Case Study Iridium
Future Network
•Plans for 288 satellites to be deployed in a number of polar
orbits
•Each satellite is interconnected to eight adjacent satellites to
provide tolerance to faults and adaptability to congestion.
•The earth is divided into approximately 20,000 square
„„supercells‟‟, each 160 km long and comprised of 9 square cells.
• Each satellite‟s beam covers up to 64 supercells
Agenda of Season 2
• ISL Design
• ISL Trade Offs
• Issues in ISL
• Simulation and Simulation Strategies
• Architecture
• Topology
• Defining Constellation
• Routing and Routing Algorithms
• Routing Approach for Simulation
• Simulation Parameters
• Evaluation Tools
• Research Related Tools in ISL
• Conlcusion
ISL Design
Constrained in ISL design
• Low transmitting power Pt
• Low figure of merit (G / T) values.
• Satellite EIRP.
• Size of antenna on satellite.
• Other Trade offs to be discussed in subsequent
sections.
ISL Design
Fig. S2. A model of an inter satellite link
D, Antenna Diameter
Φc, Beam width pointing to
each other
h, altitude of the orbit
Dc, propagation distance
γs,,angle
Te, equivalent noise
temperature
Pt, Transmitted power ( A to
B)
Assumptions:
Same orbit, no aerodynamic
drag, identical antenna, exact
position of each other
ISL Design
• Then by geometry
• Eq 1
• At maximum line of sight the propagation
distance is
• Eq 2
• At higher altitudes h >> Re => 2h Eq 3
• Φc ,dependent on antenna diameter and
propagation frequency, i.e.
• Eq 4
• We know that receiving antenna gain is related
to the aperture area.
ISL Design
• There fore transmitting and receiving antenna
gains are resp.
• Eq 5
• Eq 6
• Also,
• Eq 7
• From the above equations carrier-to-noise ratio
C=N delivered to the receiving satellite over the
ISL as
ISL Design
• In practice, satellite cross-links are typically in
the K-band in the GHz frequency range, we can
conveniently express the propagation wavelength
λ as (0.3 / f), where f is in GHz. Hence,
• From this expression, the most practical means of
delivering high C/N to the receiving satellite over
ISL is by one of the following because in practice
we are constrained by the size of the antenna that
can be deployed……………
ISL Design
• Decreasing the separation distance dc
• Increasing the transmission frequency f
• Lowering the system front-end noise
temperature Te since N is directly proportional
to Te .
Issues in ISL !
• Telecommunication industry faced a challenge to provide
a variety of new, broadband multimedia services for users
equipped with fixed and mobile terminals.
• Requirements for higher capacity and lower propagation
delay made non-geostationary satellite constellations
appealing, especially with advances in technology which
enabled the implementation of ISLs.
• Many satellite communication systems have been
proposed in the last few years, both for the provision of
mobile telephony and internet-in-the sky.
• Several of these proposals already incorporate ISLs
suitable for traffic interconnection in the satellite segment
of the network. (like iridium)
Issues in ISL !
• However, non-geostationary satellite systems with ISLs
still lack
• efficient routing algorithms,
• adaptive to inherent dynamics of topology and traffic load.
• Current solutions are mainly reusing algorithms
developed and optimized for the use in terrestrial
networks with static topology, thus having only limited
capability to grasp the characteristics of non-geostationary
satellite system.
• In addition, dynamic topology of satellite networks and
variations in traffic load in satellite coverage areas due to
the motion of satellite in their orbits, pose stringent
requirements to routing algorithms
Simulation and Simulation Strategies !
• Various simulations have been carried out to study the
performance of different routing algorithms in MEO and
LEO satellite networks.
• In general, the simulation models consist of the following
components:
• The satellite system dynamics components which describe
the satellite constellation characteristics;
• The traffic simulation component which considers the
geographical distribution of traffic sources and the daily
variation of their traffic intensity as well as the traffic
source generation;
• The ISL network component which studies the
performance of simulated routing algorithm under various
network conditions.
Topology
Constellation Topology
Up/ Down Links Topology
Ground Topology
Fig S2. The Topology Module
Next Step Define a Constellation ……..
Defining Constellation !
• The Parameters needed to define Constellations are:
• Number of orbital planes;
• Declination of orbital planes;
• Ascension angle at the seam;
• Orbit altitude;
• Number of satellites per orbit;
• Phase between the corresponding satellites of each orbit.
Routing and Routing Algorithms !
• Static and Adaptive Routes
• Isolated and Non isolated Routes
• Pre Computed and On Demand Routes
• Centralized, Decentralized and Distributed
Routing
Laurent Franck, Gerard Maral, "Routing in Networks of Intersatellite Links", IEEE Transactions On Aerospace
And Electronic Systems Vol. 38, No. 3 July 2002
Evaluation Tools !
• NETWORK SIMULATOR 2
• MATLAB
• UNIX/C
• OPNET
• BoNeS (BoNeS SATLAB)
• LeoSim (simulator for routing)
• GaliLEO
• CONSIMTM (tool for reliability)
• AristoteLEO
• SEESAWS
Research Related Issues in ISL !
• Routing Algorithm
• Congestion Control Algorithms
• Resource Allocation and Utilization
• QoS related Issues
• Constellation topologies
• ISL‟s protocol models
• TCP / IP and ISL
• Satellite IP
Conclusion !
• ISL and IOL adds one more option to the wireless
communication networks.
• They not only provide higher data rates but also
provide global coverage.
• TCP/IP like networking protocols are giving boost
to satellite internet access.
• The different issues discussed earlier, are the
major challenges related to ISL.
• Efficient network utilization is needed in ISL like
routing algorithms, congestion control
mechanisms.
References !
• Michael O. Kolawole, "Satellite Communication
Engineering", Marcel Dekker, Inc.,2002
• Ray E. Sheriff and Y. Fun Hu, "Mobile Satellite
Communication Networks", John Wiley & Sons,
2001
• Y. Fun Hu, Gerard Maral and Erina Ferm,
"Service Efficient Network Interconnection via
Satellite",John Wiley & Sons, 2002
• Bruce R. Elbert, "The Satellite Communication
Handbook", Artech House, Inc.,2004
References !
• www.iridium.com
• www.nasa.gov.in
• http://www.wtec.org/loyola/satcom2/03_06.htm
• http://telecom.esa.int/telecom/www/object/index
.cfm?fobjectid=431
References !
• P.V.Gatenby, "Optical Inter satellite Links For Military
Satellite Communications”
• R. Ferrier, A. D. Johnson, G. D. Fletcher, Marconi
Spaci, "Inter satellite Coherent Optical
Communication”
• Erich Lutz, “Issues in satellite personal communication
systems”, Wireless Networks 4 (1998) 109–124 109
• Jaeook Lee, Sun Kang,“Satellite over Satellite (SOS)
Network: A Novel Architecture for Satellite Network”,
IEEE Infocom 2000
• Laurent Franck, Gerard Maral, "Routing in Networks
of Intersatellite Links", IEEE Transactions On
Aerospace And Electronic Systems Vol. 38, No. 3 July
2002
!NTER SATELL!TE L!NK
Season 3 (Back Up)“It’s all about global coverage”
Sanjeev Kumar & Ashwini Patankar
2006H124469 & 2006H124470
Satellite Cancellations and examples !
• FLTSATCOM
• U.S. Navy and Air Force units (except for the polar regions)
• Four satellites.
• Injected into a near-geosynchronous equatorial orbit
• positioned at longitudes 100oW, 23oW, 71:5oE, and 172oE.
• Each satellite overlaps in coverage with the adjacent
satellite.
• The coverage is between the latitudes of 70oN and 70oS.
• Primary Navy‟s broadcast and ship interchange
communications system.
• Vital communications to the Allied Forces worldwide.
Satellite Cancellations and examples !
• SBIRS
• U.S. missile defense
• system: a sort of missile shield [3]. SBIRS would comprise
a network of
• satellites: LEO, HEO, and GEO (see Fig. 2.7). In theory,
the GEO forms the
• frontline satellites that provide the first warning of
missile launches over the
• equator and HEO satellites cover the North Pole.The
information received the frontline satellites is then passed
via dedicated defense support program
• (DSP) satellites to earth terminals. The DSP satellites are
programmed to look
• for the launch flares of a missile taking off or the
distinctive double flares that
• mark the explosion of a nuclear weapon. The details of the
missile trajectories
Routing And Use of ATM
• The inclusion of a satellite on-board switch with
some ATM functionality was considered for the
satellite architecture within COST253. These
switches would route packets (or ATM cells) using
the information in the header. Options on-board
the satellite for routing, include routing via
individual spotbeams to ground stations, or via
ISLs to other satellites which will further route
the packets.
Economy of (your country)
• Explain which goods and
services are produced in
your country. How do
people typically provide for
the needs of themselves
and their families?
top related