Communications Payload Design and Satellite System Architecture: Bent Pipe and Digital Processor-based Course Sampler

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ATI's CONOPS:
Satellite Communications Payload Design
and System Architecture
Instructor:
Bruce Elbert

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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
bruce@applicationstrategy.com
• 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

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)

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

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-1-7COPYRIGHT © 2000 • BRUCE R. ELBERT
Plasma sheet
Polar wind
Plasma sphere
Polar
cusp
Bow shock
Magnetosheath
Magnetopause
Solar wind
Van Allen Belts
Space Environment

Radiation Dose vs. Altitude
(5 mil Al thickness)
0 2000 4000 6000 8000 10000
10
103
105
107
109
Dose,
Rads/yr
Altitude, km

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

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

Antenna Beam Options
Area Coverage Multiple Spot Beams
GW
GW
GW
GW
GW
GW

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

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

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

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

UHF L S C X Ku Ka Q V
1 10 100 GHz0.1
Microwave
303
Microwave Spectrum
(log scale)

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
w0
a
a2a8
A
Variation of total
attenuation as a
function of elevation
angle,  >10

ITU-DAH Rain Model
75
55
37
26
14
25
mm/hr, .01% of the time

Elevation Angle Dependence
Rain Cell
(rain rate)
),,( FplrrfA
pl
el
el

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

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

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

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

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

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

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

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 bandwidthGuardband
Not to scale: guardband typically 10% of channel spacing
Translation frequency

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

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

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
Receivefeedsandaperture
Transmitfeedsandaperture
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

Inmarsat-4 Global Coverage

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

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
Pr
Pt
R0
2
Pr
R0Pt
Power
Flux
Density,
Watts/sq meter

Pr
A
= Pt
4pR0
2

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

Gain and Effective Area of a Circular
Aperture




















p



p


p
4
4
2
2
2
G
AA
DA
G
E
D

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
Pt AE
2
2
2
4
4
4






p


p


p

R
GPP
G
AA
A
R
P
P
rtr
r
E
E
t
r

Polarization of the EM Wave
Linear polarization:
(a) vertical
(b) horizontal
Circular polarization
(c) Left hand
(d) Right hand
(d)
λ

Vertically polarized horn
Horizontally polarized horn
a
b
Waveguide and Horn Polarization
(Linear Polarization)
c =2a
b ~ a/2

Co and CrossPolarization
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

Linear CrossPolarization 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
Isolation,dB

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)

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

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

Link Degradation
http://descanso.jpl.nasa.gov/Propagation/1082/1082ch1.pdf

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Communications Payload Design and Satellite System Architecture: Bent Pipe and Digital Processor-based Course Sampler

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Communications Payload Design and Satellite System Architecture: Bent Pipe and Digital Processor-based Course Sampler