inter satell!te l!nk

!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

http://www.bits-pilani.ac.in/

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


Fig S1.1a A sketch of SBIRS, an example of inter satellite links and

satellite constellation.


Fig S1.1b. satellites in Iridium Cancellation

Constellation and Table !

Constellation Characteristics !

Band of Working

“ISL operates in the Ka-band at frequencies in the range

23.18–23.38 GHz.”

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).


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.


Laboratory (CRL)

Fig. S1.5. Performance targets.

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

Case Study Iridium

•What is Iridium ?

•How it works ?

•Network Performance!

•Whats Next ?

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


SEASON 2“It’s all about global coverage”

Ashwini Patankar

2006H124470

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 .

ISL Trade Offs

• Separation distances and angles for different

satellites. (Eq 1)

ISL Trade Offs

• Graph produce for better view

ISL Trade Offs

• Date rate

• D, antenna diameter

ISL Trade Offs

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.

Architecture

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

Routing Approach For Simulation !

Fig S2. ISL Routing Approach

Simulation Parameters !

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


Season 3 (Back Up)“It’s all about global coverage”

Sanjeev Kumar & Ashwini Patankar

2006H124469 & 2006H124470


• 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.


• 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

The Need of ISLs and IOLs !

ISL Design and Trade Offs !

• Pointing Error

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.

Routing And Use of ATM

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?