Mobile satellite communication

Intro

Appl.

Types

Satellites
Handoff

How it
Works
Routing

Himanshu Singh, 2011EET3679, IIT Delhi 10/11/2012 2

 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.


 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.


 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.


 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


 Geostationary or geosynchronous earth orbit (GEO)
GEO
HEO
 Quasi - Zenith satellite
LEO
MEO
 Low Earth Orbit (LEO)
Earth
 Medium Earth Orbit (MEO)
 Highly Elliptical Orbit (HEO)


 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 )


 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 Quasi-Zenith satellite orbit

◦ Positioning information.


 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).
LEO
 Issues
◦ 48 and above satellites required to cover whole earth
◦ Short life: 4-10 years Earth
◦ 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)


 Altitude 10000km-20000km
 Orbital period 6-12 hour MEO

 10-15 satellites required Earth
 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


 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


Satellite
Segment
Inter Satellite Link
(ISL)
Mobile User
Link (MUL) MUL Ground
Gateway Link
(GWL) Segment
GWL

small cells
(spotbeams)

base station
or gateway
footprint

ISDN PSTN GSM

PSTN: Public Switched User data
Telephone Network
End User


 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 )


 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


 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


 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


 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.


 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


Current Status

Evaluation of 3G S-CDMA to S-WCDMA Technical evolution of
Satellite System from CDMA based evolution of Satellite system from 3G to
GMR Standard 3G satellite system B3G

• GMR1, GMR2 • Followed 3G and • Referring to the LTE Trends
• Thuraya, AceS and developed the standard
Inmarsat systems of S-UMTS
• Adaptive modifications
for wireless transmission
conditions.
• MOUS of USA for
military application


 Weather Forecasting
 Radio and TV Broadcast
 Military App
 Navigation App
 Global Telephone
 Connecting Remote Areas
 Global Mobile Communication

And Much More ……


Mobile satellite communication

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