mobile satellite communication
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Himanshu Singh, 2011EET3679
10/11/2012Himanshu Singh, 2011EET3679, IIT Delhi 2
Appl.
Handoff
Intro
How it Works
Routing
SatellitesTypes
A satellite is an object that orbits another large object like planet.
A communication satellite is a station in space that is used for telecommunication, radio and television signals.
In simplest form , a satellite communication can be thought of as a big microwave repeater in the sky.
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They are used for mobile applications such as communication to ships, vehicles, planes, hand-held terminals and for TV and radio broadcasting.
A satellite works most efficiently when the transmissions are focused with a desired area.
The earth station should be in a position to control the satellite if it drifts from its orbit it is subjected to any kind of drag from the external forces.
Transmission cost is independent of distance.
The power and bandwidth of these satellites depend upon the preferred size of the footprint, complexity of the traffic control protocol schemes and the cost of ground stations.
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Satellites orbit around the earth◦ Orbits can be circular or elliptical.
Important parameters ◦ inclination and elevation angles
Inclination angle (δ): Between the equatorial plane and the plane described by the satellite orbit.
Elevation angle (ε): Between the centre of the satellite beam and the plane tangential to the earth’s surface. ◦ Footprint can be defined as the area on earth where the
signals of the satellite can be received.
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International Telecommunication Union (ITU) Three regions ◦ Region1: Europe, Africa and Mongolia ◦ Region 2: North and South America and Greenland ◦ Region 3: Asia (excluding region 1 areas), Australia and
south-west Pacific. Three common bands (in GHz):◦ C-band: 4-8 - Fixed Satellite Service ◦ Ku-band: 12-18 - Direct Broadcast Satellite Services ◦ Ka-band: 25-40 – Military & Scientific Research
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Geostationary or geosynchronous earth orbit (GEO)
Quasi - Zenith satellite
Low Earth Orbit (LEO) Medium Earth Orbit (MEO) Highly Elliptical Orbit (HEO)
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Earth
GEOHEO
MEOLEO
Synchronous with respect to earth Footprint is covering almost 1/3rd of the Earth ◦ 3-4 Satellites are enough to cover the earth
Circular Orbit, Satellite visibility 24 hour Altitude : 36,000 km Inclination Angle : 0 Applications: ◦ TV and radio broadcast◦ Weather forecast ◦ Backbones for the telephone networks
Issues◦ Shading of the signals ◦ High latency (270 ms)◦ Transferring a Satellite into GEO is very expensive ◦ Cannot be used for small mobile phones (High transmit power
needed )
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Circular orbit at 45 degree to equator Altitude 36000 km One satellite fixed near zenith in Japan 3-4 satellites are required Applications:◦ mobile applications◦ Communications-based services Video audio, data◦ Positioning information.
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Quasi-Zenith satellite orbit
Altitude 500-2000km Satellite visibility 10-20m, Orbital period 5-8 hour Delay : relatively low (approx 10 ms) Smaller footprints of LEOs allow for better frequency reuse, similar to
the concepts used for cellular networks Applications:◦ Remote sensing ◦ Mobile communication services (due to lower latency).
Issues◦ 48 and above satellites required to cover whole earth◦ Short life: 4-10 years◦ Larger Handoffs
Examples: ◦ Iridium (start 1998, 66 satellites) Bankruptcy in 2000, deal with US DoD for free use
◦ Globalstar (start 1999, 48 satellites) Not many customers (2001: 44000)
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Earth
LEO
Altitude 10000km-20000km Orbital period 6-12 hour 10-15 satellites required Satellite visibility 2-4 hrs Propagation delay less Set-up cost is medium MEO can cover larger populations, so requiring fewer
handovers than LEO Issues◦ Larger Delay: 70–80 ms ◦ Need higher transmit power ◦ Special antennas for smaller footprints
Example: ◦ ICO (Intermediate Circular Orbit, Inmarsat) start ca. 2000
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Earth
MEO
Altitude 40000km Orbital period 8-24 hour 2-3 satellites required Large propagation delay Satellite lifetime 20-25 yrs HEO orbits offering visibility over Earth's polar regions,
which most geosynchronous satellites lack
Example◦ Molniya◦ Tundra
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base stationor gateway
Inter Satellite Link (ISL)
Mobile User Link (MUL) Gateway Link
(GWL)
footprint
small cells (spotbeams)
User data
PSTNISDN GSM
GWL
MUL
PSTN: Public Switched Telephone Network
Satellite Segment
End User
GroundSegment
Modulation: Three major classes of digital modulations◦ Amplitude – Shift Keying◦ Frequency – Shift Keying◦ Phase – Shift Keying
Multiple access techniques◦ Frequency Division Multiple Access (FDMA)◦ Time Division Multiple Access (TDMA) ◦ Code Division Multiple Access (CDMA) WCDMA (3G )
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Benefits◦ Less complex Switching circuits are on the ground and the satellites are just reflectors
◦ Easier to operate Most of the call is transferred over the public telephone network,
◦ Reduces the cost of the system. Technical problems to be fixed on the ground
Issues◦ Gateway must be in the line of sight of the satellite◦ Significant number of ground gateways to provide direct satellite links
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Benefits◦ Minimizes the cost of the ground segment & long distance and interconnect
fees◦ 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 Issues ◦ More complex focusing of antennas between satellites ◦ High system complexity due to moving routers◦ Higher fuel consumption, thus shorter lifetime
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Mechanisms similar to GSM Gateways maintain registers with user data◦ HLR (Home Location Register): static user data◦ VLR (Visitor Location Register): (last known) location of the mobile
station◦ SUMR (Satellite User Mapping Register): Satellite assigned to a mobile station Positions of all satellites
Registration of mobile stations◦ Localization of the mobile station via the satellite’s position◦ Requesting user data from HLR◦ Updating VLR and SUMR
Calling a mobile station◦ Localization using HLR/VLR similar to GSM◦ Connection setup using the appropriate satellite
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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.
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Due to high mobility, handoff are extremely frequent in LEO, causing high failure rate
How to Deal ??◦ Prioritised handover call over new call Allocating guard channel Queuing the handover request Channel reservation in advance
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Current Status
Evaluation of 3G Satellite System from GMR Standard
• GMR1, GMR2• Thuraya, AceS and Inmarsat systems
S-CDMA to S-WCDMACDMA based evolution of 3G satellite system
• Followed 3G and developed the standard of S-UMTS• Adaptive modifications for wireless transmission conditions.• MOUS of USA for military application
Technical evolution of Satellite system from 3G to B3G
• Referring to the LTE Trends
Weather Forecasting Radio and TV Broadcast Military App Navigation App Global Telephone Connecting Remote Areas Global Mobile Communication
And Much More ……
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