FU Berlin

Institute of Computer Science

Mobile Communications

Chapter 5: Satellite Systems

Prof. Dr.-Ing. Jochen H. Schiller

2002 5.1

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.1

Mobile Communications

Chapter 5: Satellite Systems

• support mobile communications

• global coverage without wiring costs for base stations

• implementation of varying population densities

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.2

Basics

Satellites in circular orbits

attractive force Fg = m g (R/r)²

centrifugal force Fc = m v²/r

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)

v: satellite speed

Stable orbit

Fg = Fc

r = g R²/v²mgR²/r² = mv²/r

FU Berlin

Institute of Computer Science

Mobile Communications

Chapter 5: Satellite Systems

Prof. Dr.-Ing. Jochen H. Schiller

2002 5.2

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.3

Satellite period and orbits

10 20 30 40 x106 m

24

20

16

12

8

4

radius

satellite

period [h]velocity [ x1000 km/h]

synchronous distance

35,786 km

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.4

Inclination

inclination d

d

satellite orbit

Perigee (closest point to the earth)

plane of satellite orbit

equatorial plane

FU Berlin

Institute of Computer Science

Mobile Communications

Chapter 5: Satellite Systems

Prof. Dr.-Ing. Jochen H. Schiller

2002 5.3

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.5

Elevation

Elevation:

angle e between center of satellite beam

and surface

eminimal elevation:

elevation needed at least

to communicate with the satellite

LOS (Line of Sight) to the satellite

necessary for connections.

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.6

Atmospheric attenuation

Example: satellite systems at 4-6 GHz

elevation of the satellite

5° 10° 20° 30° 40° 50°

Attenuation of

the signal in %

10

20

30

40

50

rain absorption

fog absorption

atmospheric

absorption

e

FU Berlin

Institute of Computer Science

Mobile Communications

Chapter 5: Satellite Systems

Prof. Dr.-Ing. Jochen H. Schiller

2002 5.4

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.7

Four different types of satellite orbits:

GEO: geostationary orbit,

ca. 36000 km above earth surface

LEO (Low Earth Orbit):

ca. 500 - 1500 km

MEO (Medium Earth Orbit) or

ICO (Intermediate Circular Orbit):

ca. 6000 - 20000 km

HEO (Highly Elliptical Orbit) elliptical orbits

Orbits I

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.8

Orbits II

earth

km

35768

10000

1000

LEO

(Globalstar,

Irdium)

HEO

inner and outer Van

Allen belts

MEO (ICO)

GEO (Inmarsat)

Van-Allen-Belts:

ionized particles

2000 - 6000 km and

15000 - 30000 km

above earth surface

FU Berlin

Institute of Computer Science

Mobile Communications

Chapter 5: Satellite Systems

Prof. Dr.-Ing. Jochen H. Schiller

2002 5.5

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.9

base station

or gateway

Classical satellite systems

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

Some satellites have

special antennas to

create smaller cells

using spot beams

(e.g. 163 spot beams

per Satellite in then

ICO-system)

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.10

Satellites

• Iridium (LEO)

• Globalstar (LEO)

• ICO (MEO)

The have all gone

Bankrupt!

LEO: low earth orbit

MEO: medium earth orbit

FU Berlin

Institute of Computer Science

Mobile Communications

Chapter 5: Satellite Systems

Prof. Dr.-Ing. Jochen H. Schiller

2002 5.6

End

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.11