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# CSE475 Satellite and Space Networks - PowerPoint PPT Presentation

CSE475 Satellite and Space Networks. ÖMER KORÇAK omer . korcak @ marmara .edu.tr Marmara University Department of Computer Engineering Satellite Networks Research Laboratory (SATLAB) Department of Computer Engineering, Boğazi ç i University Istanbul, Turkey. OUTLINE. Satellites

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### CSE475SatelliteandSpace Networks

ÖMER KORÇAK

omer.korcak@marmara.edu.tr

Marmara University

Department of ComputerEngineering

Satellite Networks Research Laboratory (SATLAB)

Department of Computer Engineering,

Boğaziçi University

Istanbul, Turkey

• Satellites

• GEO, MEO, LEO

• High Altitude Platforms

• Integration Scenario

• Problem Definition & Solution Approach

Distance: 378.000 km

Period: 27.3 days

• Satellites in circular orbits

• attractive force Fg = m g (R/r)²

• centrifugal force Fc = m r ²

• m: mass of the satellite

• R: radius of the earth (R = 6370 km)

• r: distance to the center of the earth

• g: acceleration of gravity (g = 9.81 m/s²)

• : angular velocity ( = 2  f, f: rotation frequency)

• Stable orbit

• Fg = Fc

24

satellite

period [h]

velocity [ x1000 km/h]

20

16

12

8

4

synchronous distance

35,786 km

10

20

30

40 x106 m

• elliptical or circular orbits

• complete rotation time depends on distance satellite-earth

• inclination: angle between orbit and equator

• elevation: angle between satellite and horizon

• LOS (Line of Sight) to the satellite necessary for connection

 high elevation needed, less absorption due to e.g. buildings

• Uplink: connection base station - satellite

• Downlink: connection satellite - base station

• typically separated frequencies for uplink and downlink

• transponder used for sending/receiving and shifting of frequencies

• transparent transponder: only shift of frequencies

• regenerative transponder: additionally signal regeneration

plane of satellite orbit

satellite orbit

perigee

d

inclination d

equatorial plane

Elevation:

angle e between center of satellite beam

and surface

minimal elevation:

elevation needed at least

to communicate with the satellite

e

footprint

• Parameters like attenuation or received power determined by four parameters:

• sending power

• gain of sending antenna

• distance between sender and receiver

• gain of receiving antenna

• Problems

• varying strength of received signal due to multipath propagation

• interruptions due to shadowing of signal (no LOS)

• Possible solutions

• Link Margin to eliminate variations in signal strength

• satellite diversity (usage of several visible satellites at the same time) helps to use less sending power

L: Loss

f: carrier frequency

r: distance

c: speed of light

Attenuation of

the signal in %

Example: satellite systems at 4-6 GHz

50

40

rain absorption

e

30

fog absorption

20

10

atmospheric absorption

10°

20°

30°

40°

50°

elevation of the satellite

SatelliteOrbits 2

GEO (Inmarsat)

HEO

MEO (ICO)

LEO (Globalstar,Irdium)

inner and outer Van

Allen belts

earth

1000

10000

Van-Allen-Belts:

ionized particles

2000 - 6000 km and

15000 - 30000 km

above earth surface

35768

km

• No handover

• Altitude: ~35.786 km.

• One-way propagation delay: 250-280 ms

• 3 to 4 satellites for global coverage

• Mostly used in video broadcasting

• Example: TURKSAT satellites

• Another applications: Weather forecast, global communications, military applications

• Disadvantages: Long delay, high free-space attenuation

• Altitude: 10.000 – 15.000 km

• One-way propagation delay: 100 – 130 ms

• 10 to 15 satellites for global coverage

• Infrequent handover

• Orbit period: ~6 hr

• Mostly used in navigation

• GPS, Galileo, Glonass

• Communications: Inmarsat, ICO

• Global Positioning System

• Developed by US Dept. Of Defence

• Became fully operational in 1993

• Currently 31 satellites at 20.200 km.

• Last lunch: March 2008

• It works based on a geometric principle

• “Position of a point can be calculated if the distances between this point and three objects with known positions can be measured”

• Four satellites are needed to calculate the position

• Fourth satellite is needed to correct the receiver’s clock.

• Selective Availability

• Glonass (Russian):24 satellites, 19.100 km

• Galileo (EU): 30 satellites, 23.222 km, under development (expected date: 2013)

• Beidou (China): Currently experimental & limited.

• Altitude: 700 – 2.000 km

• One-way propagation delay: 5 – 20 ms

• More than 32 satellites for global coverage

• Frequent handover

• Orbit period: ~2 hr

• Applications:

• Earth Observation

• GoogleEarth image providers (DigitalGlobe, etc.)

• RASAT (First satellite to be produced solely in Turkey)

• Communications

• Globalstar, Iridium

• Search and Rescue (SAR)

• COSPAS-SARSAT

• Satellite phone & low speed data comm.

• 48 satellites (8 planes, 6 sat per plane) and 4 spares.

• 52˚ inclination: not covers the polar regions

• Altitude: 1.410 km

• No intersatellite link: Ground gateways provide connectivity from satellites to PSTN and Internet.

• Satellite visibility time: 16.4 min

• Operational since February 2000.

• 315.000 subscribers (as of June 2008)

• Currentlysecond-generation satellites arebeingproduced (by Thales Alenia Space) and 18 satelliteslaunched in 2010 and 2011.

• 66 satellites (6 planes, 11 sat per plane) and 10 spares.

• 86.4˚ inclination: full coverage

• Altitude: 780 km

• Intersatellite links, onboard processing

• Satellite visibility time: 11.1 min

• Satellites launched in 1997-98.

• Initial company went into bankrupcy

• Technologically flawless, however:

• Very expensive; Awful business plan

• Cannot compete with GSM

• Now, owned by Iridium satellite LLC.

• 280.000 subscribers (as of Aug. 2008)

• Multi-year contract with US DoD.

• Satellitecollision (February 10, 2009).

COSPAS-SARSAT(Search And Rescue Satellite Aided Tracking)

• An international satellite-based SAR distress alert detection & information distribution system.

• 4 GEO, 5 LEO satellites

• Aircraft & maritime radiobeacons are automatically activated in case of distress.

• Newest beacons incorporate GPS receivers (position of distress is transmitted)

• Supporters are working to add a new capability called MEOSAR.

• The system will put SAR processors aboard GPS and Galileo satellites

Since 1982, 30.713 persons rescued in 8.387 distress situation.

• GEOs have good broadcasting capability, but long propagation delay.

• LEOs offer low latency, low terminal power requirements.

• Inter-satellite links and on-board processing for increased performance and better utilization of satellites

• From flying mirrors to intelligent routers on sky.

• Major problem with LEOs: Mobility of satellites

• Frequent hand-over

• Another important problem with satellites:

• Infeasible to upgrade the technology, after the satellite is launched

High Altitude Platforms (HAPs)

• Aerial unmanned platforms

• Quasi-stationary position (at 17-22 km)

• Telecommunications & surveillance

• Cover larger areas than terrestrial base stations

• No mobility problems like LEOs

• Low propagation delay

• Smaller and cheaper user terminals

• Easy and incremental deployment

• Immature airship technology

• Monitoring of the platform’s movement

• HAPs have significant advantages.

• Satellites still represent the most attractive solution for broadcast and multicast services

• Should be considered as complementary technologies.

• Integration of HAPs and mobile satellites

• Establishment of optical links

HAPs

Satellites

Optimal Assignment of Optical Links

CONSTRAINTS:

• A satellite and a HAP should have line of sight in order to communicate with each other.

• Elevation angle between HAP and satellite should be larger than a certain εmin value.

• Number of optical transmitters in satellites is limited.

• A satellite can serve maximum of Hmax HAPs.

• One to many relation between HAPs and satellites.

AIMS:

• As much HAP as possible should be served (Maximum utilization)

• Average of elevation angles between HAPs and satellites should be maximized.

Optimal Assignment of Optical Links (cont.)

SOLUTION APPROACHES

• This optimization problem can be represented as an Integer Linear Programming (ILP) problem

• ILP solution approaches: Exclusive search, Branch-and-bound algorithms, etc.

• Exponential time complexity

• Not feasible for large networks

• Optimization algorithm should be applied repeatedly

• In periodic manner: every ∆t time unit

• In event-driven manner: When a link becomes obsolete

• Faster algorithm is necessary.

• There exists a polynomial time solution approach

• Example scenario

• Three satellites & seven HAPs

• Visible pairs are connected

• Elevation angles are given on the links

• Bipartite graph

• First group: Node for each satellite transmitter

• Second group: Node for each HAP

• Edge exists between a HAP and each transmitter of a satellite, if they are visible to each other.

• Weights: Elevation angles

Maximum weighted maximum cardinality matching

• Matching: A subset of edges, such that no two edges share a common node.

• Maximum cardinality matching: Matching with maximum number of edges.

• Maximum weighted maximum cardinality matching: Maximum cardinality matching where the sum of the weights of the edges is maximum.

• Hungarian Algorithm: O(n3)

100 HAPs (height: 20 km)

10 MEO Satellites: ICO (height: 10350 km, inclination: 45˚)

Total time: 1 day, Δt=1 minute

• Matching with maximum “average elevation angle” may result in frequent optical link switching

• Switching from one satellite to another is an expensive operation.

• Reduction of switching = Increasing the link durations

• Method: Favor existing links with a particular amount γ

• Weights of utilized edges are incremented by γ

εmin=-2

“Efficient Integration of HAPs and Mobile Satellites

via Free-space Optical Links,” Computer Networks, 2011

More on Satellites

• Hand-over

• Satellite-fixed / Earth-fixedfootprints

• Network MobilityManagement

• Routing

Handover in satellitesystems

• Several additional situations for handover in satellite systems compared to cellular terrestrial mobile phone networks caused by the movement of the satellites

• Intra satellite handover

• handover from one spot beam to another

• mobile station still in the footprint of the satellite, but in another cell

• Inter satellite handover

• handover from one satellite to another satellite

• mobile station leaves the footprint of one satellite

• Gateway handover

• Handover from one gateway to another

• mobile station still in the footprint of a satellite, but gateway leaves the footprint

• Inter system handover

• Handover from the satellite network to a terrestrial cellular network

• mobile station can reach a terrestrial network again which might be cheaper, has a lower latency etc.

Satellite Fixed Footprints

(asynchronous handoff)

Earth Fixed Footprints

(synchronous handoff)

Routing is carried out without considering the movement of satellites

A satellite corresponds to a VN in a time.

• Physical network topology is dynamic

• Virtual Node topology is fixed

• One solution: inter satellite links (ISL)

• reduced number of gateways needed

• forward connections or data packets within the satellite network as long as possible

• only one uplink and one downlink per direction needed for the connection of two mobile phones

• Problems:

• more complex focusing of antennas between satellites

• high system complexity due to moving routers

• higher fuel consumption

• thus shorter lifetime

• Iridium and Teledesic planned with ISL

• Other systems use gateways and additionally terrestrial networks

• Effects of satellite mobility

• Topology is dynamic.

• Topology changes are predictable and periodic.

• Traffic is very dynamic and non-homogeneous.

• Handovers are necessary.

• Limitations and capabilities of satellites

• Power and onboard processing capability are limited.

• Implementing the state-of-the-art technology is difficult.

• Satellites have a broadcast nature.

• Nature of satellite constellations

• Higher propagation delays.

• Fixed number of nodes.

• Highly symmetric and uniform structure.

• Considering these issues various routing & MM techniques are proposed. Main ideas are:

• To handle dynamic topology changes with minimum overhead.

• To prevent an outgoing call from dropping due to link handovers

• To minimize length of the paths in terms of propagation delay and/or number of satellite hops.

• To prevent congestion of some ISLs, while others are idle (Load balancing).

• To perform traffic-based routing.

• To provide better integration of satellite networks and terrestrial networks.

• To perform efficient multicasting over satellites.

“Exploring the Routing Strategies in Next-Generation Satellite Networks”

IEEE Wireless Communications, 2007

Any questions?