mobile satellite communication

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.


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)

Quasi - Zenith satellite

Low Earth Orbit (LEO) Medium Earth Orbit (MEO) Highly Elliptical Orbit (HEO)


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 )


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.


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)


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


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



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 )


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 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 ……


mobile satellite communication

Technology