Post on 18-Dec-2015
Communications Payload Engineering
Owen Clarke
© EADS Astrium2 October 2004
Aims
To describe the main components of the Communications satellite payload and explain how designs are impacted by the changing needs of the user
© EADS Astrium3 October 2004
Contents
1 Introduction
2 Payload Function
3 Payload Constraints
4 Payload Specifications
5 Payload Configurations
6 Payload Equipment
© EADS Astrium4 October 2004
Communications Payload Function
Repeater
Uplink Downlink
Communications Payload = Antenna Sub-System + Repeater
Receive
Antenna
Transmit
Antenna
© EADS Astrium5 October 2004
Essential Communication Payload Functions
Antenna Functions- To provide highly directional receive and transmit beams
Repeater Functions- Power Amplification- Frequency Conversion
© EADS Astrium6 October 2004
Antenna Types and Functions
Reflector Antennas
- Parabolic Reflector with Off-set Feed
- With Gregorian or Cassegrain Sub –reflector
- Gridded Reflectors for Polarisation Discrimination
- Dual Gridded Assemblies for dual plane polarisation Direct Radiating Phased Arrays Shaped Beams
- Shaped Reflector Surfaces
- Multiple Feeds with Beamforming Network Generation of Multiple Beams from the same Aperture Reflectors with De-focused Feed Arrays
© EADS Astrium7 October 2004
Typical Repeater Functions
Receive and filter uplink signals Provide minimum C/No degradation Provide variable high gain amplification Downconvert Frequency for re-transmission Filter high power downlink signal and re-transmit Provide high reliability in functionality Beam-to-beam interconnectivity Functional re-configurability Beamforming
© EADS Astrium8 October 2004
Why Filter?
Elimination of Spurious Transmissions Elimination of Self Interference Elimination of Image Bands introduced by Mixing Processes Elimination of Alias Bands before and after Sampling Processes Partitioning of Spectrum to allow Channelised Amplification Partitioning of Spectrum for usage by Different Services Partitioning of Spectrum for use on Different Routes
© EADS Astrium9 October 2004
Why High Reliability?
Everyone wants machines, tools, people, services to be reliable What is special about Communications Satellites? Inaccessibility of the orbits used
- LEO – Generally highly inclined
- GEO – High altitude means: High potential energy AND High kinetic energy
- Either way large high energy launch vehicles required Very expensive to launch in the first place Inaccessible to astronauts or remote control vehicles Repair by external intervention virtually impossible The design must be tolerant of internal failures
© EADS Astrium10 October 2004
Payload Constraints
Accommodation- Physical size, must fit on spacecraft platform, compatibility with launch
vehicle fairing Thermal Dissipation
- Limited ability of spacecraft to radiate heat, radiator area Mass
- Impacts fuel, life, cost, functionality Power consumption
- Impacts thermal design, mass of power sub-system Thermal Control
- Comms. performance versus mass of thermal control hardware Received Noise
- Thermal noise- Transmitter Noise
- Includes: Passive Intermodulation, Multipaction Noise
© EADS Astrium11 October 2004
Quality of the Receive System – G/T
The quality of the satellite receive system, in terms of its ability to receive a given signal with a high signal to noise ratio is usually expressed as:
Ga/ Ts Where:
Ga = Antenna Gain (Relative numerically to that of an isotropic radiator and referenced to an arbitary interface at the
output of the antenna)
Ts = The Noise Temperature of the complete System (Referenced to the same interface at the output of the antenna)
© EADS Astrium12 October 2004
Noise Temperature
Ts = Ta + T1 + T2 / G1 + T3 / (G1.G2) +
T4 / (G1.G2.G3) ……... Ta = Antenna Noise Temperature
1 2 3 4
Concatenation of Noise Sources Ts = Noise Temperature of the Complete System
© EADS Astrium13 October 2004
E.I.R.P.
Effective Isotropic Radiated Power
EIRP = (Gain of Transmit Antenna)x(Transmit Power)
© EADS Astrium14 October 2004
Payload Constraints
Spurious Products- Mixing products: From Frequency Converters- Intermodulation products: Non linearity in active devices- Passive intermodulation products (PIMP): Transmit chain, post High
Power Amplification
- In Band: Directly impacts C/N0
- Out of Band: Interference to other transponders or systems
© EADS Astrium15 October 2004
Payload Constraints – Spurious Products
10
11
12
13
14
-50 -48 -46 -44 -42 -40 -38
Input Power dBW
Ou
tpu
t P
ow
er d
bW
Typical Saturation Characteristic e.g. Solid State Power Amplifier
© EADS Astrium16 October 2004
Payload Constraints – Spurious Products
- Linear devices can be characterised by:
Sout = aSin
- Memoryless Non-linear devices can be approximated over a limited signal range by a polynomial relationship such as:
Sout = a1Sin + a2Sin2 + a3Sin
3 + a4Sin4 + …
If 2 signals are applied such that:
Sin = Asinω1t + Bsinω2t
Then Sout is found to contain frequency components as follows:
ω1, ω2, (ω1 - ω2), (ω1 + ω2), 2ω1, 2ω2, (2ω1 - ω2), (ω1 - 2ω2), 3ω1, 3ω2…
© EADS Astrium17 October 2004
Intermodulation Products (2)
Order of a product is m = n + k for frequency nf2 - kf1 for 2 carriers
For many closely spaced carriers, IMPs are distributed contiguously 3rd order products most important in band (C/I3) multi-carrier = (C/I3) 2carrier - 8 dB
f1 f2
5 th Order Products
5x(f2-f1)3x(f2-f1)
f1 f2
3rd Order Product
© EADS Astrium18 October 2004
Intermodulation Products (3)
Type of product Order Number of products of thetype
N=5 N=10
2F1 – F2 3 N(N-1) 20 90F1 + F2 – F3 0.5N(N-1)(N-2) 30 3603F1 – 2F2 5 N(N-1) 20 902F1 + F2 – 2F3 N(N-1)(N-2) 60 7203F1 – F2 – F3 0.5 N(N-1)(N-2) 30 3602F1 + F2 – F3 – F4 0.5 N(N-1)(N-2)(N-3) 60 2520F1 + F2 + F3 – 2F4 0.5 N(N-1)(N-2)(N-3) 60 2520F1 + F2 + F3 – F4 – F5 0.5 N(N-1)(N-2)(N-3)(N-4) 120 15120Total 400 21780
© EADS Astrium19 October 2004
Intermodulation Products (1)
-20 -15 -10 -5 0-20
-15
-10
-5
0
-35
-30
-25
-20
-15
Input Back Off (dB)
Output Back Off (dB) IMP Level (dB)
N=1
N=3
N=10
F1+F2-F3
2F1-F2
© EADS Astrium20 October 2004
Spurious Products
Bit Error Rate Of QPSK For One Interferer
8 9 10 11 12 13 14 151E-7
1E-6
1E-5
1E-4
1E-3
1E-2
Eb/No (dB)
BER
S/I = INF
S/I = 25 dB
S/I = 20 dB
S/I = 15 dB
S/I = 12 dB
S/I = 10 dB
© EADS Astrium21 October 2004
Transmit Filtering
Reasons for filtering after the High Power Amplifiers
- To reject Out Of Band Spurious (which might adversely affect other systems)
- To reject Intermodulation Noise which would fall in adjacent channels
- To reject transmit noise which would fall in receive bands on the same satellite
- To provide theoretically loss less recombination of amplification channels into a single signal path prior to transmission
- This is achieved using an Output Multiplexer(OMUX)
© EADS Astrium22 October 2004
Payload Constraints
Transmit Characteristics- Gain v frequency
- Gain slope
- Gain ripple
- Group delay v frequency- Group delay slope
- Group delay ripple
- AM/PM conversion- AM/PM transfer
- AM modulation of one carrier transferred to PM modulation of another
© EADS Astrium23 October 2004
Effects of Combinations of Distortions
Gain v Frequency Slope followed by AM to PM Transfer
- Results in Intelligible Cross Talk Group Delay v Frequency Slope followed by AM to PM Transfer
- Similar effects
© EADS Astrium24 October 2004
Gain Slope
0 0.5 1 1.5 20
0.2
0.4
0.6
0.8
1
1.2
Gain Slope (dB)
Degradation (dB) At A BER of 1E-6
4-PSK
16-QASK
8-DPSK
16-PSK
© EADS Astrium25 October 2004
Group Delay Slope
0 0.1 0.2 0.3 0.40
0.5
1
1.5
2
Delay Slope (d/T)
Degradation (dB) At A BER Of 1E-6
4-PSK
8-DPSK
16-QASK
16-PSK
© EADS Astrium26 October 2004
Payload Constraints
Electromagnetic Compatibility- Radiated and conducted- Emissions and susceptibility
Ionising Radiation Reliability
© EADS Astrium27 October 2004
Reliability
Reliability, R, defined as: (Number of Success)/(Number of Trials) For a single mission R = Probability of the success of the mission Failure Rate, λ, measured in failure instances in 109 hours (FITS) For a single mission of duration of t hours:
Reliability, R, is found to be:
R = e- λT
where T = t/109
For items in a functional chain (where each link must succeed for overall success):
- Failure rates add to give total failure rate- Reliabilities multiply to give overall reliability
© EADS Astrium28 October 2004
Improvement of Reliability by Use of Redundancy
Probability of mission failure of an equipment is (1-R) If a system uses 2 identical equipments in parallel, the probability
of failure is the probability of both failing. This is (1-R)2
Reliability of the system is the probability of one or none failing. This is is 1 – (1-R)2 = 2R – R2
“Cold” Redundancy If an equipment is switched off, λ typically decreases by a factor of
ten Thus if non-active equipments are switched off reliability can be
improved further In such a situation with a choice of 1 from 2,
then RT = 11R – 10R1.1
© EADS Astrium29 October 2004
Payload Specification
Max mass 55Kg Phase noise level -49dBc at 100Hz
Max power consumption 500W -70dBc at 1KHz
Max thermal dissipation 400W -100dBc at 10KHz
No of channels 4 Transmission reqts:
Input power level (per channel)
-100 dBW Gain variation (with life, temperature)
1.5 dB
Output power level (per channel)
+14 dBW Gain variation over any 36MHz
0.5dB
Operating freqs (MHz) Input Output Group delay variation (with life, temp)
3nS
Channel 1 14000-14036 12000-12036 Group delay variation over any 36MHz
1nS
Channel 2 14040-14076 12040-12076 AM/PM conversion 50/dB
Channel 3 14080-14116 12080-12116 Linearity C/I3 with 2 nominal carriers
10dB
Channel 4 14120-14156 12120-12156 Reliability over 10 yrs 0.9
Thermal noise temp 260K
© EADS Astrium30 October 2004
Payload Configurations - Basic Elements
InputFilter
Low NoiseAmplifier
Mixer
LocalOscillator
Filter MediumPower
Amplifier
HighPower
Amplifier
OutputFilter
© EADS Astrium31 October 2004
Payload Configurations - Channelisation
© EADS Astrium32 October 2004
Payload Configurations - Redundancy
Sw
itch Netw
ork
Sw
itch Netw
ork
© EADS Astrium33 October 2004
Payload Configurations - Eutelsat 2
© EADS Astrium34 October 2004
Payload Configurations – Inmarsat 3
C-BAND
Rx HORN
LHCP
RHCP
C-BAND
RECEIVER
LHCP
RHCP
FORW ARD
I.F.
PROCESSOR
L-BAND Tx
ANTENNA
BEAM
FORMEROUTPUT
NETW ORK
22 OFF
SSPAs
L-BAND TRANSMIT SECTION
L-BAND Rx
ANTENNA
22-OFF
LOW NOISE
AMPLIFIERS
RETURN
COMBINER
RETURN
I.F.
PROCESSOR
LHCP
RHCP
C-BAND
SSPAs OMUXLHCP
RHCP
C-BAND
Tx HORN
TT & C
~~~~~~
© EADS Astrium35 October 2004
Payload Configurations – Trends
Mobile SS MARECS INMARSAT 2 INMARSAT 3 INMARSAT 4
Payload Mass (Kg) 100 130 208 932
Payload Power (W) 500 660 1725-2138 9000
Design Lifetime (Years) 7 10 13 13
Launch Periods 1981-84 1990-92 1996-97 2004
No of S/C in Series 3 4 5 2 + 1
FSS/DBS ECS EUTELSAT 2 HOTBIRD W3A
Payload Mass (Kg) 117 208 268 507
Payload Power (W) 638 2090 4188 6900
No Of Channels 12/14 16 20/22 50
Design Lifetime (Years) 7 8-10 12-15 12+
Launch Periods 1983-88 1990-95 1996-98 2004
No of S/C in Series 5 6 6 1
© EADS Astrium36 October 2004
On-board Processing – Why?
Beamforming Beam-to-beam interconnectivity Improved link performance More flexibility Improved immunity to interference Multi-rate communications Reduced complexity of earth stations
© EADS Astrium37 October 2004
On-board Processing – Why Not?
Power dissipation Mass Thermal dissipation Packaging Radiation hardness Reliability Difficult to make “Future Proof” Should not do processing onboard which could be done on the ground
by reconfiguring the overall system
© EADS Astrium38 October 2004
Transparent- Channel to beam routing flexibility in multi-beam coverage- Uplink to Downlink frequency mapping flexibility- Channel Bandwidth flexibility
Regenerative- Independent optimisation of uplink and downlink access, modulation
and coding- Link advantage through isolation of uplink and downlink noise and
interference effects- Data rate conversion and signal reformatting- Packet level switching- Security features
Transparent Or Regenerative
© EADS Astrium39 October 2004
Typical Digital Processor Architecture
Rx AAF A/D DEMUX LC DBFN SWITCH FRC MUX D/A AIF SSPA
D/C D/C U/C
Feeder Link
Phased
Array
1
•
•
•
•
•
N
1
N•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
© EADS Astrium40 October 2004
Inmarsat 4
C-Band Rx Horn
Rx
L-BandRx/TxFeedArray
L-BandRx/Tx
Reflector
120
C-BandPayloadReceiveSection
Mobileto
Feeder
FeedertoMobile
ForwardProcessor
Mobile
to Mobile
Postprocessor& L-BandPayloadTransmitSection
DSP
ReturnProcessor
C-BandUp-
Converter
C-BandDown-
Converter
NavigationalPayload
CentralisedFrequencyGenerator
LOs
Pilot ToneInjection
Unit
C to L Integrity CheckerC-Band
Downlink
156
156C-BandPayloadTransmitSection
2
12
12
2
Automatic Level Control
2 120
120
C-Band Tx Horn
Tx
4
2
C-Band to
C-Band
4Preprocessor
& L-BandPayloadReceiveSection
Nav L-Band Tx Antennas
L1
L5
© EADS Astrium41 October 2004
Payload Equipment - Receivers
© EADS Astrium42 October 2004
Payload Equipment – Multi-Chip Module (MCM) Technology
© EADS Astrium43 October 2004
Payload Equipment - Input Multiplexers
© EADS Astrium44 October 2004
Payload Equipment - Input Multiplexers
© EADS Astrium45 October 2004
Payload Equipment - Output Multiplexers
© EADS Astrium46 October 2004
Payload Equipment - Channel Amplifier
© EADS Astrium47 October 2004
Payload Equipment – Dual Travelling Wave Tube Amplifier (TWTA) Direct Thermally Radiating Type
© EADS Astrium48 October 2004
Payload Equipment - Frequency Generator
© EADS Astrium49 October 2004
Multi- Chip Module (MCM) Technology
© EADS Astrium50 October 2004
INMARSAT 4 Digital Signal Processor
© EADS Astrium51 October 2004
Astra 2B In Anechoic Chamber
© EADS Astrium52 October 2004
Astra 2B Repeater
© EADS Astrium53 October 2004
Astra 2B Repeater Panels