Transcript Transmission Planning

Satellite Communication
Fundamentals
History of International
Communication
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1850
1901
1926
1945
1945
1956
- Submarine Telephone cable (UK & France)
– Transoceanic Long Wave Communication (Europe & America)
– Short wave communication (UK & Europe)
– Microwave Transmission System (Europe & America)
– Geo stationery Satellite concept by Arthur C Clarke
– Co-axial multi channel submarine cable (UK & USA)
1957 – First man made satellite Sputnik by USSR
1964 – Formation of Intelsat Organization (UK, USA, Australia,
Japan, Germany, Italy & France)
1965 – First Communication Satellite (Intelsat - 1)
Satellites
► Arthur
C. Clarke’s vision:
 3 Geostationary satellites illuminate the
Earth Satellite 3
17.4°
Illumination Lines
Satellite 1
Satellite 2
Satellites
► Three
Basic Orbits
Inclined
Orbit
Polar
Orbit
Equator
Equatorial
Orbit
Satellites
► What
does Geostationary mean?
 Geo = Earth, Stationary = Not Moving
 Satellite is a Fixed Point in the Sky
►Rotation
of the Satellite = Rotation of the Earth
(~24 Hrs/Rot)
►Equatorial Plane (only possible orbit)
►35,786 km above the Earth’s surface
(only possible distance)
Satellites
► Geostationary
Orbits
 Satellite needs to stay within designated area:
►Station-keeping
box
Variation due to
Orbital Ellipticity
Station-keeping
Box
Latitudinal
Variation
+0.1°
m
5k
6
,1
42
Equatorial Plane
Longitudinal
Drift
+0.1°
Nominal
Satellite
Location
Communications Satellites
► What
is a Communications Satellite?
 A “Radio Relay” in the Sky
► Receives,
amplifies and re-directs analog and digital
signals carried within a carrier frequency
Transmit Antenna
Transponder
(incl. Switching
Matrix)
“3-Axis Stabilized”
Receive Antenna
“Spinner”
Communications Satellites
► What
are the Satellite Components?
 Main subsystems:
Antenna Payload
Communication
Spacecraft Control/Propulsion
Electrical Power
Communication Satellite
Satellite
(m)
Centrifugal Force
At equilibration
mV2/R
mV2/R=GmM/R2
Since
V=R ω
Gravitational Force
GmM/R2
R=(GM)1/3/ω 2/3
Resolving
R=42,000 km
Earth
(M)
From Surface of Earth
R’=42,000km-6,378km=35,786km
Satellite Stabilization
► Spin Stabilization
► Three Axis Stabilization
Spin Stabilization For (cylindrical shape)
rotation
satellite
wheel
• Motor applies torque to wheel (red)
motor
• Reaction torque on motor (green)
causes satellite to rotate
Three Axis Stabilization (For cubical shape)
► Geostationary
Orbits (especially 3-Axis
Stabilized S/C)
N
 Station-keeping for East-West & NorthSouth drift
Yaw
Orbital Path
(South - North Drift)
S
Roll
Local Vertical
Pitch
(East-West Drift)
Satellite Position
Communications Satellites
► What
identifies a S/C?
 Each satellite is defined by its Sub Satellite Point (SSP)
Longitude (Long=342° for IS-705)
N
Latitude (Lat=0° for all Intelsat Satellites)
Sub Satellite Point
S
Satellite Architecture
Communications data passes through a satellite using
a signal path known as a Transponder.
► Typically satellites have between 24 and 72
transponders.
► A single transponder is capable of handling up to 155
million bits of information per second.
► Simple voice or data to the most complex and
bandwidth-intensive video, audio and Internet
►
content.
Radio frequency bands
Band
UHF
L
S
C
X
Ku
K
Ka
Frequency/(GHz)
0.3 – 1.0
1.0 – 1.5
1.5 – 3.9
3.9 – 8.0
8.0 – 12.5
12.5 – 18.0
18.0 – 26.5
26.5 – 40.0
Communications Satellites
► Why
do we use satellites?
Global reach
Distance insensitive
Mobility and flexibility
Rapid deployment of ground equipment /
ease of expansion
 Bundling of applications




Communications Satellites
► Where
are the satellites located?
 Three Orbital Regions
► AOR,
IOR/APR, POR
Indian/APR
Ocean Region
33°E
60°E
62°E
64°E
66°E
83°E
85°E
110.5 °E
157 °E
Atlantic
Ocean Region
304.5°E
307°E
310°E
325.5°E
328.5°E
330.5°E
332.5°E
335.5°E
Pacific
Ocean Region
340°E
342°E
359°E
174°E
176°E
178°E
180°E
Co-located S/C
Communications Satellites
► How
is simultaneous operation of satellites
possible?
 Spacing (2-degree, 3-degree)
 Coverage (different footprints)
 Frequency (C-band, Ku-band, Ka-band …)
► How
close can simultaneous satellites operate?
 At different frequency bands:
► Co-location:
typically at 0.2° (~ 120 km)
Communications Satellites
► Spacing
 Why is the satellite spacing important?
►Pointing
error (E/S mispointing)
 System margins (small error => BIG mistake)
S/C 1
Distance between 2-degree Satellites:
~ 1200 km
S/C 2
Distance between 3-degree Satellites:
~ 1900 km
2°
3°
E/S
S/C 3
Communications Satellites
► Spacing
 Why is the satellite spacing important?
(Continued)
►Antenna
size (radiation pattern)
 Small E/S (wide beam, low gain)
 Large E/S (narrow beam, high gain)
Antenna Peak Gain
 What to keep in mind?
►Interference
margins (ASI)
Small E/S
Large E/S
Communications Satellites
► Satellite
Spacing:
 Desired and un-desired
DESIRED
SATELLITE SPACING
UNDESIRED
SATELLITE
SPACING
WANTED SIGNALS
SATELLITE ANTENNA
UNWANTED SIGNALS
RADIO LINK
Communications Satellites
► What
is a Footprint?
Composite Plot/IBN
1-dB Contour Plot
Composite Plot / Satellite Guide
Communications Satellites
► How
to visualize a footprint?
Like Mountain’s Profile:
+
Antenna Radiation Pattern: Cartesian Representation
Full Gain Grid - 1 dB steps
Satellite Communication
► How
can so many beams co-exist?
 Frequency isolation
► Multiple
72 MHz and 36 MHz transponders
Frequency Slots: 1-2 to 9
Hemi
Global
Zone
10 to 12
Satellite Communication
► Why
C- and Ku-band?
 ITU-assigned frequency band: 1 - 30 GHz
 Low rain degradation
 Low sky noise
Oxygen
Resonance
60 GHz
Sky Temperature (Degrees Kelvin)
1000
Galactic
Background
100
Microwave
Window
Sky Temp
(Total)
10
1
Water Vapor
Resonance
22 GHz
0.5
5
Frequency GHz
(Ka-Band)
Atmosphere
Absorption
10
C-Band
50
Ku-Band
Satellite Communication
► What
is Polarization?
 Linear (vertical / horizontal)
►All
Intelsat Ku-band
►C-band on [email protected]°E, APR-1@83°E and [email protected]°E
=> When used Simultaneously: Double the
Bandwidth
 Circular (left-hand / right-hand)
►C-band
on most Intelsat satellites
=> When used Simultaneously: Double the
Bandwidth
Linear Polarization
Horizontal Polarization
Vertical Polarization
Circular Polarization
Communications Satellites
► Why
do we need solar panels?
 Convert sunlight into electric power
►Primary
power supply
►Only 10% - 14% of sunlight can be converted
 Charge satellite battery system
►Ceases
during eclipse
Communications Satellites
► What
is the
impact of an
eclipse?
 No solar power
 Error in earth
sensor
 Service outages
Spring
Eclipse: 21 March
Max. Outage = 70 min.
+ preceding & following days
Summer
Autumn
Eclipse: 23 September
Max. Outage = 70 min.
+ preceding & following days
Winter
Satellite Communication
► What





is the Communication Subsystem?
Transponder – satellite bandwidth
Receiver – satellite antenna (G/T)
Amplifier – TWTA/SSPA (wattage)
Switching matrix – connectivity
Transmitter – transmit power (D/L e.i.r.p.)
Full Transponder Layout:
Satellite Communication
► Some
typical carriers
 Voice:
►8
kb/s
► 16 kb/s
► 64 kb/s
 Data:
► 64
kb/s
► up to 155 Mb/s
 Video:
►2
Mb/s
► 8 Mb/s
Satellite Communication
► What
to keep in mind?
 Time delay
►One-way
delay: location dependant
 Sub-satellite point: 119.3 ms
 Horizon: 138.9 ms
►Path length:
 Location dependant (elevation angle)
► Sub-satellite
point: 71,572 km
► Horizon: 83,360 km
Horizon
 Dependant on actual elevation angle
► C-band:
~200 dB
► Ku-band: ~206 dB
SSP
Earth Station Technology
Earth Station Equipment For Data
TRANSMIT PATH
RECEIVE PATH
HPA
HPA
LNA
LNA
RF COMB
RF COMB
RF DIV
RF DIV
U/C
U/C
D/C
D/C
IF COMB
IF COMB
IF DIV
IF DIV
MOD
MOD
DEMOD
DEMOD
RHCP
LHCP
RHCP
LHCP
Earth Station Equipment For TV
TRANSMIT PATH
RECEIVE PATH
HPA
HPA
LNB
LNB
RF COMB
RF COMB
RF DIV
RF DIV
U/C
U/C
D/C
D/C
IF COMB
IF COMB
IF DIV
IF DIV
ENCODER
ENCODER
DECODER
DECODER
RHCP
LHCP
RHCP
LHCP
Typical Parameters for Earth
Station Antennas: C Band
Intelsat
Standard
G/T (dB/°K)
Antenna
Diameter
(typical)
A
35 (35 + 20 Log f/4)
18 - 21 m
B
31.7
11 - 13 m
F3
29
9 – 10 m
F2
27
6.5 – 7.3 m
F1
22.7
3.7 – 4 m
H
22.1 for H4
18.3 for H3
15.1 for H2
3.7 m
2.4 m
1.8 m
Typical Parameters for Earth
Station Antennas: Ku Band
Intelsat
Standar
d
C
E3
E2
E1
K3
K2
G/T (dB/deg K)
37
34
29
25
23.3
19.8
Antenna
Diameter
(typical)
11 m
7-8m
3.7 – 4.5 m
2.4 - 3.7 m
1.8 m
1.2 – 1.5 m
Earth Station Antenna Configurations
► Common
Antenna Feed Systems
FEEDER PHOTO REQUIRED
HYPERBOLOID
FOCAL FEED PARABOLOID
CASSEGRAIN FEED SYSTEM
ELLIPSOID
PARAXIAL FOCUS
GREGORIAN FEED SYSTEM
SPHERICAL REFLECTOR
Prime Focus & Cassegrain Antenna Optics
Antenna Radiation Pattern (1)
Satellite Communication
► Transmission
via satellite
 Modulation (change of properties of an electrical
signal)
 Coding (change an analog signal to a digital
signal)
 Multiplexing (combine several signals)
 Up/Down converter (change of frequency)
 Amplifier (enhance signal strength)
 Multiple access techniques (procedure to access
the satellite)
Types of Propulsion
 Chemical Propulsion
► Performance is energy limited
► Propellant Selection
 Electric Propulsion
► Electrostatic—Ion Engine
► Electro thermal—Arc Jet
► Electromagnetic—Rail gun
 Solar Sails
► Would use large (1 sq. km.) reflective sail (made of thin
plastic)
► Light pushes on the sail to provide necessary force to change
orbit.
► Still on the drawing board, but technologically possible!
 Nuclear Thermal
Launching
Geo stationary orbit
Parking orbit
Va
Earth
Vp
Transfer orbit
Launching
N
Orbital velocity
Equator
E
W
Geo St. velocity
Velocity accelerated
by
Apogee motor
S