1. Satellite Systems
•Global Coverage without wiring costs
•Independent of population density
•Chiefly for broadcast TV
•Useful addition to exisiting services – e.g. with UMTS
History
 Basics
 Localization

Handover
 Routing
 Systems


2. History of satellite communication
1945 - Arthur C. Clarke “Extra Terrestrial Relays“
1957 - first satellite USSR’s SPUTNIK
1960- first reflecting communication satellite ECHO
1962 – Telstar launched, an important step
1963 - first geostationary satellite SYNCOM
1965 - first commercial geostationary satellite “Early
Bird” (INTELSAT I 68 kg): 240 duplex telephone
channels or 1 TV channel, 1.5 years lifetime
1967-69 – Intelsat II, III; 1200 phone channels
1976 - three MARISAT satellites for maritime
communication; 40W power, 1.2 m antenna

3. History (Contd)
1982 first mobile satellite telephone system
INMARSAT-A
1988 first satellite system for mobile phones and data
communication INMARSAT-C; 600 bps, interface to
X.25
1993 INMARSAT-M - first digital satellite telephone
system; still very heavy equipment
1998 global satellite systems for small mobile phones –
Iridium & Globalstar
Currently about 200 geo satellites.

4. Applications
Traditional
 Weather, radio and TV broadcast
 military satellites – espionage, warning system
 navigation and localization (GPS)
 Telecommunication – ‘cable in the sky’
 global telephone connections & mobiles
 backbone for global networks
 remote/rural areas
 extend cellular systems (AMPS, GSM UMTS),
need low orbit satellites.


5. Satellite Functions
Transponder
 Receive on one frequency, repeat on
another frequency (transparent
transponder)
 May amplify or regenerate (regenerative
transponder)
 Inter satellite routing
 Error correction is essential


6. Classical satellite systems
Inter Satellite Link
(ISL)
Mobile User
Link (MUL)
Gateway Link
(GWL)
MUL
GWL
small cells
(spotbeams)
base station
or gateway
footprint
ISDN
PSTN: Public Switched
Telephone Network
PSTN
User data
GSM

7. Satellite Networks

8. SATELLITE RECEPTION
Footprint – area on earth’s surface where signal can
be received
 LOS (Line of Sight) to the satellite necessary for
connection
 Attenuation depends on distance, elevation,
frequency of carrier and atmosphere
 High elevation means less absorption due to rain,
fog, atmosphere and buildings; at least 10 degrees
needed.


9. Signal Loss Calculation (qualitative only)
Attenuation or power loss is
determined by
gain of sending/receiving
antennae
 distance between sender
and receiver
 Carrier frequency
 This affects data rates
achievable
Only 10 bps may be achievable
with GEOs, compared to 10
Kbps at 100 km, 2GHz carrier

 4π r f 
L=

 c 
L: Loss
f: carrier frequency
r: distance
c: speed of light
2

10. Atmospheric attenuation
Attenuation of
the signal in %
Example: satellite systems at 4-6 GHz
50
40
rain absorption
30
fog absorption
ε
20
10
atmospheric
absorption
5° 10°
20°
30°
elevation of the satellite
40°
50°

11. Satellites - features
 GEO:
geostationary, ~ 36000 km from the
earth
 LEO (Low Earth Orbit): 500 - 1500 km
 MEO (Medium Earth Orbit) or ICO
(Intermediate Circular Orbit): 6000 - 20000 km
 HEO (Highly Elliptical Orbit) elliptical orbits
 Microwave, line of sight; GHz range
 Uplink and downlink – different frequencies

12. Satellite orbit altitudes

13. Orbits II
GEO (Inmarsat)
HEO
MEO (ICO)
LEO
(Globalstar,
Irdium)
inner and outer Van
Allen belts
earth
1000
10000
35768
km
Inner & outer Van-Allen-Belts: ionized particles
2000 - 6000 km, 15000 - 30000 km altitude

14. Table 17.1 Satellite frequency bands
Band
Downlink,
GHz
Uplink,
GHz
Bandwidth,
MHz
L
1.5
1.6
15
S
1.9
2.2
70
C
Ku
4
11
6
14
500
500
Ka
20
30
3500

15. Satellites in geosynchronous orbit
Telephony, broadcast TV, Internet backbone

16. Geostationary satellites
35,786 km, equatorial (inclination 0°), 15 yrs life
 24 hr period, synchronous to earth rotation
 fix antenna positions, no adjusting necessary
 large footprint (up to 34% of earth), limited frequency
reuse; 3 satellites are enough to cover
 bad elevations in areas with latitude above 60°
 high transmit power 10KW, high latency (0.25 s)
 not for global coverage for small mobile phones and
data transmission,
 suitable for radio & TV


17. MEOs – used for GPS
18000 km altitude
24 to cover the earth
6 hrs to orbit
GPS based on
‘triangulation’ – need
distance from 4 points
Used widely by all sorts of
users

18. LEO – global telephony
Polar orbits, 500-2000 km
5-8 years lifetime
90-120 min to orbit
20000 – 25000 km/hr
8000 km diameter footprint
System of satellites = network of switches
 Little Leos - < 1GHz, low data rate messaging
 Big Leos (1-3 GHz) – Globalstar, Iridium
 Broadband Leos (like fibre) - Teledesic

19. LEO systems
visibility ~ 10 - 40 minutes, period of 95-120 min
 global radio coverage possible, 50-200 satellites
 latency similar to terrestrial long distance: 5 - 10 ms
 smaller footprints (i.e. cells), better frequency reuse
 handover necessary from one satellite to another
 High elevation even in polar regions
 more complex systems due to moving satellites
 Need for routing


20. LEOS
ISL Inter Satellite Link
GWL – Gateway Link
UML – User Mobile Link

21. Iridium 1998 - present
66 satellites, 6 orbits, altitude
750 km.
Originally for global voice, data,
fax, paging, navigation
Spectrum - 1.6 G, ISL 23 G
66 x 48 spot beams or cells
2000 cells to cover the earth
240 channels of 41 KHz each,
can support 253 440 users.
Applications – telephony ($7 per minute) and data
2.4 kbps (10 kbps under new ownership)
Inter satellite links for routing 25 Mbps
Complex software for call routing via ISL

22. Globalstar
48 Satellites, 6 orbits
Altitude of 1400 km
Relaying uses earth stations as well as
satellites – ‘bent pipe’.
Ground stations can create stronger signals
Voice and data at 4.8 kbps

23. Teledesic – planned but never materialised
288 satellites, 12 polar orbits,1350 km
BB channels – Internet in the sky
8 satellites form a unit, earth stations are also used
Earth divided into several 10k’s cells, each assigned a
time slot to transmit
User terminals to communicate directly
155 M/1.2G up/down links – Ka band

24. Routing between satellites, gateways, fixed
networks: ISL or terrestrial?
Reduced
number of gateways needed with ISL
Best to 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

25. PROBLEMS - ISL
more complex focusing of antennas between satellites
 satellites need routing software
 high system complexity due to moving routers
 higher fuel consumption, shorter lifetime
 Iridium and Teledesic planned with ISL

Other systems use terrestrial gateways and also terrestrial
networks

26. Localization of mobile stations
Mechanisms similar to GSM, except ‘base stations’ are
satellites.
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

27. Localisation of Mobiles
Registration of mobile stations
 Mobile’s signal received by several satellites,
reported to gateway(s)
 Localization of the mobile station is 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 SUMR & the appropriate
satellite

28. Handover in satellite systems
 More
complex, due to motion of 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

29. Handover (Contd.)
 Gateway
handover
Handover from one gateway to another
mobile station still in the footprint of a satellite,
but satellite moves away from the current gateway
 Inter system handover
Handover from the satellite network to a
terrestrial cellular network
mobile station can use a terrestrial network again
which might be cheaper, have a lower latency.

30. Overview of LEO/MEO systems
# satellites
altitude
(km)
coverage
min.
elevation
frequencies
[GHz
(circa)]
access
method
ISL
bit rate
# channels
Lifetime
[years]
cost
estimation
Iridium
66 + 6
780
Globalstar
48 + 4
1414
ICO
10 + 2
10390
Teledesic
288
ca. 700
global
8°
±70° latitude
20°
global
20°
global
40°
1.6 MS
29.2 ↑
19.5 ↓
23.3 ISL
FDMA/TDMA
1.6 MS ↑
2.5 MS ↓
5.1 ↑
6.9 ↓
CDMA
2 MS ↑
2.2 MS ↓
5.2 ↑
7↓
FDMA/TDMA
19 ↓
28.8 ↑
62 ISL
yes
2.4 kbit/s
no
9.6 kbit/s
no
4.8 kbit/s
4000
5-8
2700
7.5
4500
12
yes
64 Mbit/s ↓
2/64 Mbit/s ↑
2500
10
4.4 B$
2.9 B$
4.5 B$
9 B$
FDMA/TDMA