communications payload design and satellite system architecture: bent pipe and digital...
DESCRIPTION
This four-day course, ATI Courses.com's Communications Payload Design and Satellite System Architecture course , provides communications and satellite systems engineers and system architects with a comprehensive and accurate approach for the specification and detailed design of the communications payload and its integration into a satellite system. Both standard bent pipe repeaters and digital processors (on board and ground-based) are studied in depth, and optimized from the standpoint of maximizing throughput and coverage (single footprint and multi-beam). Applications in Fixed Satellite Service (C, X, Ku and Ka bands) and Mobile Satellite Service (L and S bands) are addressed as are the requirements of the associated ground segment for satellite control and the provision of services to end users.TRANSCRIPT
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COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-2
Objectives and Approach
• Instructor:
– Bruce Elbert, President, Application Technology Strategy, Inc.
– Hughes Satellite, 1972 - 1999
– BEE, City Univ. of NY, MSEE, Univ. of Md., MBA, Pepperdine Univ.
– Contact: tel +1 (310) 918-1728, email [email protected]
• Objectives:
– Develop a systems engineering approach for satellite communications
– Explain the techniques and tools used to design commercial communications payloads
– Provide the framework for the overall system and ground segment
• Approach:
– Blend the theoretical with the practical
– Provide both the big picture and a detailed view
– Interact and exchange concepts and methodologies
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-3
Course Outline
• Comm Payloads and Service Requirements
• Systems Engineering to Meet Service Requirements
• Bent-pipe Repeater Design
• Spacecraft Antenna Design and Performance
• Comm Payload Performance Budgeting
• On-board Digital Processor Technology
• Multi-beam Antennas
• RF Interference and Spectrum Management
• Ground Segment Selection and Optimization
• Earth Station and User Terminal Tradeoffs
• Performance and Capacity Assessment
• Satellite System Verification Methodology
Satellite System Definitions
VSATs or other user terminals
Space segment
Ground segment
TT&C earth station
Satellite
control
center
Hub or gateway earth station
COPYRIGHT © 1997 • BRUCE R. ELBERT
(satellite operator)
(network operator or user)
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-5
Kepler’s Laws of Planetary Motion
• First Law: The orbit of each planet is an ellipse, with the Sun at one focus.
• Second Law: The line joining the planet and the Sun sweeps out equal areas in equal times.
• Third Law: The square of the period of a planet is proportional to the cube of its mean distance from the Sun.
v
h
P = 1.659 10-4 (6378 + h)3/2
minutes
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-6
Earth Satellite Orbit Options
Orbit definition Altitude range, km Period, hrs
• Low earth orbit (LEO) 150 - 1,000 1.5 - 1.8
• Medium earth orbit (MEO) 5,000 - 10,000 3.5 - 6
• Geosynchronous earth orbit 36,000 24
– Inclined
– Geostationary earth orbit (GEO)
LEO
MEO
GEO
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-7 COPYRIGHT © 2000 • BRUCE R. ELBERT
Plasma sheet
Polar wind
Plasma sphere
Polar
cusp
Bow shock
Magnetosheath
Magnetopause
Solar wind
Van Allen Belts
Space Environment
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-8
Radiation Dose vs. Altitude (5 mil Al thickness)
0 2000 4000 6000 8000 10000
10
103
105
107
109
Dose,
Rads/yr
Altitude, km
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-9
Orbit Period and Delay vs. Altitude
0
5
10
15
20
25
0 10000 20000 30000 40000
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 500 1000
LEO
Altitude, km Altitude, km
Hours
7.5 75 150 225 270
Delay, ms
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-10
LEO Constellation for Iridium
• 66 satellites
• 6 polar orbits
• Inter-satellite links
Iridium Spacecraft (Motorola and Lockheed-Martin)
PD-1-01-11
PD-1-12
http://www.faqs.org/sec-filings/100602/Iridium-
Communications-Inc_8-K/dex992.htm
GEO Orbit “Slot” for Domestic Service
COPYRIGHT © 1999 – 2001 • BRUCE R. ELBERT
• 24 hour orbit requires stationkeeping operations – Maintain orbit in equatorial plane (N/S stationkeeping)
– Compensate for east-west drift and eccentricity
– Satellite service defined by antenna beam coverage
• Lifetime determined by stationkeeping fuel reserve
PD-1-01-13
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-14
Antenna Beam Options
Area Coverage Multiple Spot Beams
GW
GW
GW
GW
GW
GW
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-15
Star and Mesh Topologies
Hub
Remote
Remote
Remote Remote
Remote
Remote
Peer
node
Peer
node
Peer
node
Peer
node
Control
In either topology, links can be established on demand or fixed
Large-capacity GEO Spacecraft
PD-1-01-16
Boeing 702
15 kW
4700 kg at launch
SS/Loral 1300S
19 kW
6200 kg at launch
EADS Astrium
14 kW
6000 kg at launch
LM A 2100 AX
3600 kg at launch
Major Satellite Components
• Payload subsystems
– Repeater (receivers, multiplexers, amplifiers, processing and switching)
– Antennas (reflectors, feeds, feed networks, support structure and pointing mechanisms)
• Bus subsystems
– Tracking, telemetry, command and ranging (TTC&R)
– Solar panels
– Batteries
– Reaction control system (propulsion)
– Attitude and spacecraft control processing
– Thermal control and structure
PD-1-01-17
Lockheed-Martin A2100 Three-Axis Spacecraft
PD-1-01-18
Lockheed-Martin A2100 Block Diagram
PD-1-01-19
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-20
Typical Spacecraft Mass Allocation
• Geostationary orbit
• 15 year mission
• Three axis spacecraft
• ~2000 kg total dry mass
• ~8000 watts total (EOL)
• Standard payload type
Repeater Antenna Power
TT&C ACS Propulsion
Thermal Structure Harness
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-21
Typical Spacecraft Power Allocation
• GaAs solar cells
• Flat solar panels
• NiH2 batteries
• 15 year operation
• ~8000 watts EOL
Repeater TT&C ACS
Propulsion Power Thermal
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-22
Satellite Size v. Capabilities
Hypothetical
class of satellite
Conceptual
number of
Transponders
General Range
of EOL Power
General Range
of Launch
Mass, kg
“Small” 24 to 36 4 to 6 kW 1500 to 2500
“Medium” 48 to 72 8 to 10 kW 3000 to 4000
“Large” 90 to 120 12 to 22 kW 4500 to 6000
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-23
UHF L S C X Ku Ka Q V
1 10 100 GHz 0.1
Microwave
30 3
Microwave Spectrum (log scale)
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-24
Total
attenuation
toward
zenith, dB
Propagation Effects on
Satellite Systems at
Frequencies Below 10 GHz,
NASA Publication 1108(02) 1987 Frequency, GHz
H2O
O2
O2 H20
Clear Air Attenuation
sin
w0a
a2a8A
Variation of total
attenuation as a
function of elevation
angle, >10
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-25
ITU-DAH Rain Model
75
55
37
26
14
25
mm/hr, .01% of the time
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-26
Elevation Angle Dependence
Rain Cell
(rain rate)
),,( FplrrfA
pl
el
el
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-27
Rain Attenuation (temperate climate)
Availability
99.5%
98.0%
10°
20°
45°
10°
20°
45°
1 10 100
Frequency, GHz
Elevation
angle
2 4 8 20 40 80
50
40
30
20
10
0
Attenuation,
dB
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-28
Typical Margin for Rain Fade (12 GHz)
Rain Intensity Margin region mm/hr at 99.8%
A 6 0.3
B 12 0.5
C 15 0.7
D 19 0.9
E 22 1.1
F 28 1.4
G 30 1.5
H 32 1.7
J 35 1.8
K 42 2.2
L 60 3.2
M 63 3.4
N 98 4.8
P 145 5.8
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-29
Rain Attenuation Solutions
• Ku band (14/12 GHz) – Link margin
» Satellite EIRP
» Dish size
– Uplink power control
– Automatic Gain Control (AGC) in spacecraft
– Antenna feed blower
– Site selection (rain zone)
• Ka band (30/20 GHz)
– Link margin
» Satellite EIRP
• Spot beams
• Dynamic power
» Dish size
– Uplink power control
– AGC
– Dynamic data/coding rate
– Antenna feed blower
– Radome
– Site selection
» Rain zone
» Diversity
• Site
• Satellite
Site (Space) Diversity
D
D
PD-1-30
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-31
Further Details on Propagation
• Ionospheric effects (below 10 GHz) – Faraday rotation of linear polarization – day to night variation
greatest during peaks of sun spot cycle
– Ionospheric scintillation – most pronounced near the geomagnetic equator (tropical regions) – frequency selective fading during evening and morning transitions of the F layers
• Tropospheric effects (low elevation angles) – Absorption
– Scintillation
– Ducting (Horizontal path)
– Rain – ITU-R Dissanayake, Allnut, Haidara (DAH) model
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-32
Maximum Ionospheric Effects [US one-way paths at 30 elevation, NASA 1108(2) Table 2.2]
Effect 100 MHz
300 MHz
1 GHz 3 GHz 10 GHz
Faraday rotation
30 rotations
3.3 rotations
108° 12 1.1°
Excess time delay
25 s 2.8 s 0.25 s 28 ns 2.5 ns
Absorp (polar)
5 dB 1.1 dB .05 dB .006 dB .0005 dB
Absorp (mid Lat)
<1 dB .1 dB <.01 dB <.001 dB <.0001 dB
Disper .4 ps/Hz .015 ps/Hs
.0004 ps/Hz
.000015 ps/Hz
.0000004 ps/Hz
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-33
Communication Payload Technology (Analog and Digital)
Analog repeater
– Bent pipe (no change in format; uplink and downlink noise combine)
– Supports any modulation and multiple access
– Limited routing capability
– Excellent dynamic range; impairments can aggregate
Digital processing repeater
– Channel routing or packet
switching
– Tailored to multiple access
(and modulation)
– Separates uplink from
downlink
– Excellent routing (and
switching) capability
– Limited dynamic range
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-34
Analog (Bent-pipe) Repeater
• Standard design for FSS and BSS satellites
• Simple design, simple operation
• Very flexible
• Network optimization limited
Wideband
receiver
(500 MHz bandwidth)
F1 Pre A F1
F3 Pre A F3
F5 Pre A F5
F6 Pre A F6
F4 Pre A F4
F2 Pre A F2
LPF
5.925-6.425 GHz
3.7-4.2 GHz
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-35
Frequency Plan for Bent Pipe Repeater
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
Uplink frequency range
Downlink frequency range
Fup(low) Fup(hi)
Fdwn(low) Fdwn(hi)
Channel spacing Transponder bandwidth Guardband
Not to scale: guardband typically 10% of channel spacing
Translation frequency
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-36
The Spacecraft Antenna System
• Area coverage antenna – Most common approach for bent pipe repeaters
– Coverage area is similar to local broadcasting (but with less variation of received signal power)
• Coverage is defined by the antenna gain pattern
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-37
Digital Signal Processing Repeater Design
• Need for flexible payload architecture – Channel routing
– On-demand reconfiguration
– Demod/remod performance
– Beam forming, multiple and flexible
• Constraints – Signal structure (multiplex, modulation and multiple access)
– Bandwidth
– Processor speed and complexity
– Power and weight
– Impairments
– Dynamic range
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-38
Broadband Processing Payload
Rcv feed net- work
Tx feed net- work
Rcvr
Rcvr
Rcvr
Rcvr
Rcvr
Rcvr
HPA
HPA
HPA
HPA
HPA
HPA
Digital Processor:
A/D Demod
Routing and Switching
Multiplexing Modulation
Beam forming D/A
Rece
ive feeds
and a
pert
ure
Tra
nsm
it feeds
and a
pert
ure
Low-power transmission line High-power transmission line
Active redundancy not shown
Upconv or driver
Upconv or driver
Upconv or driver
Upconv or driver
Upconv or driver
Upconv or driver
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-39
Inmarsat-4 Global Coverage
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-40
Course Outline
• Comm Payloads and Service Requirements
• Systems Engineering to Meet Service Requirements
• Bent-pipe Repeater Design
• Spacecraft Antenna Design and Performance
• Comm Payload Performance Budgeting
• On-board Digital Processor Technology
• Multi-beam Antennas
• RF Interference and Spectrum Management
• Ground Segment Selection and Optimization
• Earth Station and User Terminal Tradeoffs
• Performance and Capacity Assessment
• Satellite System Verification Methodology
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-41
The Microwave Link in Satellite Communications
• Frequencies above 1 GHz (but less than 60 GHz)
• Line-of-sight propagation
• Low received signal level due to large distance
P r P t
R0 2
P r R0 P t
Power
Flux
Density,
Watts/sq meter
P r A
= P t
4 p R0 2
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-42
Path Geometry (GEO Link)
coscos29577.01107.42643 3
0 R
R0
h
km
Where
R0 = slant range (distance between satellite and earth station)
h = GEO altitude (35,788,293 meters)
= Earth station latitude
= Earth station relative longitude
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-43
Gain and Effective Area of a Circular Aperture
p
p
p
4
4
2
2
2
GAA
DAG
E
D
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-44
Antenna “Capture” Area
• Receive antenna “captures” power through its effective area
• Transmit antenna is a reciprocal device (yielding the same performance as in receive)
R P t AE
2
2
2
4
4
4
p
p
p
RGPP
GAA
AR
PP
rtr
rE
Et
r
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-45
Polarization of the EM Wave
Linear polarization: (a) vertical
(b) horizontal
Circular polarization (c) Left hand
(d) Right hand
(d)
λ
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-46
Vertically polarized horn
Horizontally polarized horn
a
b
Waveguide and Horn Polarization (Linear Polarization)
c =2a
b ~ a/2
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-47
Co and CrossPolarization
Co-polarized
signal component
Cross-polarized
signal component
Relative polarization angle, degrees
Relative
received
signal
0 10 20 30 40 50 60 70 80 90
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-48
Linear CrossPolarization Isolation
Cross-Polarization Isolation
0
10
20
30
40
50
60
0 1 2 3 4 5 6 7 8 9 10 11
Feed offset angle, degrees
Iso
lati
on
, d
B
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-49
Properties of Circular Polarization
• Special case of elliptical polarization
• Polarization sense established within the transmit feed system
• Little or no impact from the Ionosphere
• Isolation properties generally inferior to linear
Axial ratio = 20 log (a/b)
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-50
Polarization Coupling
Polarization type Linear Circular
Linear -10log [Cos2] dB -3 dB
Circular (elliptical) -3 dB Graph
Ref: Johnson, Antenna
Engineering Handbook,
FIG 23-7, p 23-9
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-51
Depolarization in Rain (Ku – Ka)
Cloud and Rain Cell Geometry
affect V and H polarizations differently
Circular Polarization is composed
of V and H polarizations
COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-52
Link Degradation
http://descanso.jpl.nasa.gov/Propagation/1082/1082ch1.pdf