Satellite Communications

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Satellite Communications
Satellite Communications
Ashaad Rambharos
CSE, Intelsat
Date: October 2014
1
Guidelines
• Mobile phones – kindly switch to silent
• Bathrooms
• Questions – please ask
• Health Breaks and Lunch
2
Agenda
• Satellite project
• Satellite Launch
• Orbits
• Satellite Eclipse
• Sun Outage
• Frequency allocations
• Polarisation
3
Satellite Launch
4
Launch Trajectories
Mission Sequence
Stabilization
Multiple burns to achieve GEO orbit
5
Launch Trajectories
Successive LAM/LAE burns achieve the final geostationary orbit
Generic
Transfer Profile
Generic Transfer Orbit
Profile
6
• Show IS20 Launch
• Show video of launch
7
Satellite orbits
8
Communication Satellite Orbits
• To understand satellite systems better, we must know
something about their orbits
• Satellites circle the earth in orbits, balancing gravity
against centripetal force
MEO
LEO
GEO
9
Satellite Orbits
MEO
LEO
GEO
Type
Description
Height
Signal Availability
LEO
MEO
GEO
Low Earth Orbit
Equatorial or polar orbit
Medium Earth Orbit
Equatorial or Polar orbit
Geostationary Earth Orbit
Equatorial orbit
100-500 miles
6000-12000 miles
22,282 miles
15 min
2-4 hrs
24 hrs
Advantages
Lower launch costs
Short round trip signal delay
Small path loss
Tracking antenna
Moderate launch cost
Small round trip delays
Tracking antenna
Covers as much as 42.2% of the earth's surface
Ease of tracking
No problems due to doppler
Disadvantages
Shorter life, 5-8 years
Encounters radiation belts
Larger delays
Greater path loss than LEO's
Very large round trip delays
Expensive Earth Stations due to weak signals
10
GEO ORBIT
• The orbit must be geosynchronous. Having an
orbital period of ≈ 24Hrs.
• The orbit must be a circle.
The orbit must lie in the earth's equatorial plane
11
Satellite Orbits
• GEO Inclined Orbit
• Antenna tracking system required
• Uplink beam coverage changes
• Downlink beam coverage changes
12
Orbital Drift
• A satellite intended for radio communications among fixed earth
stations must meet two criteria:
• The satellite must remain at a fixed position in the sky, this means
that the satellite must move in a geostationary orbit. The owners of
most geostationary satellites try to maintain their satellites within a
box measuring 0.1° x 0.1°
• The satellite must be maintained at the proper attitude. This term
describes the orientation of the satellite within its box. If the satellite
is not maintained at the proper attitude, its antennas will not be
aimed properly.
• Unfortunately, once a satellite is placed in proper position and
attitude, it doesn't stay there: it tends to drift.
13
DRIFT
• Drift degrades satellite performance in two ways: the satellite
may move out of position, or it may assume an improper
attitude.
• Drift results from external forces. While there are hundreds of
external forces acting on the satellite, the primary forces are
these:
• The gravitational pull of the sun. The intensity and direction of
this force changes continuously, in daily and yearly cycles.
• The gravitational pull of other objects in the solar system.
Although these forces are considerably weaker than the sun's
gravity, their effects can be measured and predicted.
• The uneven distribution of land mass on the surface of the
earth.
14
Satellite Eclipse
15
Eclipse
During the spring and fall equinoxes the sun passes
through the equatorial plane
When the Earth is between the sun and the satellite
the solar panels do not have sun light - Thus they can
not provide power
Earth
Sun
Satellite is powered by batteries during the eclipse
period
16
Sun Outage
17
Sun Outage
• During the Spring and Fall equinoxes the sun passes
through the equatorial Plane
Sun
When both the sun and satellite are in the ground
stations field of view, the RF energy from the sun
overpowers the satellite signal
18
Sun Outage (cont)
Impact period lasts for Several Days Around the
Spring and Fall Equinox
Latitude and Longitude of the ground station and
Longitude of the satellite determines when the sun
outage will occur
Per Site Impact Period Lasts 3-10 Days
Duration 1 – 10 minutes per Day
– Antenna Size (Beam Width)
– Satellite Transmit Power (EIRP)
To calculate sun outage times go to:
http://ww2.intelsat.com/resources/satellites/sun.aspx
http://www.satellite –calculations.com
19
ITU Satellite Frequency Allocations
20
Satellite Frequency Allocations
Fixed
mobile
2010 2025
2110 2120
2160 2170
2290
2200
2300
2483.5
2500
2520
~
~
1980
~
~
1710
2535 2655
Fixed
mobile
Radar
REGION 1
REGION 2
REGION 3
~
~
1675
~
~
Aeronautical,
Radio-nav.,
Fixed mobile
Fixed
mobile
~
~
~
~
~
~
~
~
S-Band, C-Band and X-Band Satellite Frequency Allocations in MHz
3400
3700
4200
4500
4800
S-Band
5725 5850
6425
6725
7025
7250
C-Band
7750 7900
8400
X-Band
~
~
~
~
Ku-Band Satellite Frequency Allocations in MHz
Aeronautical
Radar
~
~
~
~
Radar
10700
10950
11200
11450
11700
12200
12500
12750
13250
REGION 1
REGION 2
REGION 3
13750
14500
14800
17300
17800
18100
~
~
Ka-Band Satellite Frequency Allocations in MHz
~~
REGION 1
REGION 2
REGION 3
17700
Legend
19700
20100
21200
29500
27500
27000
30000
31000
FSS Down
Extended FSS Down
FSS Allotment Plan Down
Government FSS Down
Space Operation/Earth Exploration/Space
Research Down (Co-Primary)
Space Research Down
FSS Up
Extended FSS Up
FSS Allotment Plan Up
Government FSS Up
Space Operation/Earth Exploration/Space
Research Up (Co-Primary)
Space Research Up
MSS Down
Meteorological Down
FSS/MSS Up (Co-Primary)
MSS/Radiodetermination Up
(Co-Primary)
MSS/Government FSS Down (Co-Primary)
BSS Plan Down
MSS Up
Meteorological Down/
MSS Up (Co-Primary)
FSS/BSS Up (Co-Primary)
MSS/Government FSS Up (Co-Primary)
BSS Plan Up
L-Band Satellite Frequency Allocations in MHz
~
~
REGION 1
REGION 2
REGION 3
1525
1530
1533
1544
1545
1555
~
~
1492
1559
1610 1626.5 1631.5
1634.5
Legend
1645.5
1646.5
1656.5
REGION
2
MSS Down
Maritime/Land Mobile Down (Co-Primary)
Emergency/Distress Down
MSS Up
Maritime/Land Mobile Up (Co-Primary)
Emergency/Distress Up
Maritime Mobile Down
Land Mobile Down
Aeronautical Mobile Down
Maritime Mobile Up
Land Mobile Up
Aeronautical Mobile Up
BSS = Broadcast Satellite Service FSS = Fixed Satellite Service MSS = Mobile Satellite Service
1660.5
REGION
1
REGION
3
REGION
3
ITU Regional Definitions
21
Frequency allocations
C-Band
- Transmit 5.925 - 6.425 GHz (U.S.)
5.625 – 6.425 GHz (I.T.U.)
- Receive 3.700 - 4.200 GHz (U.S.)
Ku-Band
3.400 – 4.200 GHz (I.T.U.)
- Transmit 14.00 - 14.50 GHz (U.S.)
13.75 – 14.50 GHz (I.T.U.)
- Receive 11.70 – 12.20 GHz (U.S.)
11.20 – 11.70 GHz (ITU)
•Ka-Band
- Transmit 27.5 – 30.0 GHz
- Receive 17.7 – 20.0 GHz
22
C-Band
•Advantages
– Wide footprint coverage
– Minor effects from rain
– Lower cost for earth station antenna
Disadvantages
– Requires larger antennas
– Requires larger RF power amplifier
– Effected by terrestrial interference (TI)
– Difficult to obtain transmit license
• Frequency clearance
23
Ku-Band
Advantages
– Smaller antennas
– Smaller RF power amplifiers
Disadvantages
– Greater effect from rain
– Smaller footprint (beam) coverage
24
Ka-Band
Advantages
– Smaller antennas
– Smaller RF power amplifier
Disadvantages
– Greater effect from rain
– Smaller footprint (beam) coverage
– High equipment cost
25
Polarization
26
Polarization
Provides increased satellite capacity
(Allows frequency reuse)
The directional aspects of the electrical field of a radio signal
Linear (90o Out of Phase)
- Horizontal (H)
- Vertical (V)
- All Ku-Band satellites are Linear
Circular (180 o Out of Phase)
-Right Hand Circular (RHCP)
-Left Hand Circular (LHCP)
27
Linear Polarization
Linear Polarization
– The electrical field is wholly
in one plane containing the
direction of propagation
Horizontal
– Field lies in a plane parallel
to the earth’s surface.
• Vertical
• Field lies in a plane
perpendicular to the
earth’s surface.
28
Circular Polarization
Circular Polarization
– The electrical field radiates energy in both the horizontal and vertical
planes and all planes in between
Right Hand Circular Polarization (RHCP)
– the electric field is rotating clockwise as seen by an observer towards
whom the wave is moving
• Left Hand Circular Polarization (LHCP)
• the electric field is rotating counterclockwise as seen by an observer
towards whom the wave is moving
29
Linear Polarization
• Advantage
• Lower Cost Antenna System
• Feed Assembly (OMT)
• Better Cross-Pol Isolation
Disadvantage
–
–
–
–
Polarization Adjustment Required
Polarization changes depending on Latitude and Longitude
Greater chance of problems due to cross-pol interference
Faraday rotation in the ionosphere
30
Circular Polarization
•Advantage
•
No polarization adjustment required
•
•
Fixed by Ortho-Mode-Transducer (OMT)
Less chance of cross-Pol interference
Disadvantage
– Higher cost antenna systems
• Feed Assembly (OMT)
– Slightly lower cross-Pol isolation
31
• Questions
32

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