communications payload engineering owen clarke october 2004 © eads astrium 2 aims to describe the...

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


Contents

1 Introduction

2 Payload Function

3 Payload Constraints

4 Payload Specifications

5 Payload Configurations

6 Payload Equipment


Communications Payload Function

Repeater

Uplink Downlink

Communications Payload = Antenna Sub-System + Repeater

Receive

Antenna

Transmit

Antenna


Essential Communication Payload Functions

Antenna Functions- To provide highly directional receive and transmit beams

Repeater Functions- Power Amplification- Frequency Conversion


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


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


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


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


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


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)


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


E.I.R.P.

Effective Isotropic Radiated Power

EIRP = (Gain of Transmit Antenna)x(Transmit Power)


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


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


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…


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



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



-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


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


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)


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


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


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


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


Payload Constraints

Electromagnetic Compatibility- Radiated and conducted- Emissions and susceptibility

Ionising Radiation Reliability


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


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


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


Payload Configurations - Basic Elements

InputFilter

Low NoiseAmplifier

Mixer

LocalOscillator

Filter MediumPower

Amplifier

HighPower

Amplifier

OutputFilter


Payload Configurations - Channelisation


Payload Configurations - Redundancy

Sw

itch Netw

ork

Sw

itch Netw

ork


Payload Configurations - Eutelsat 2


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

~~~~~~


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


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


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


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


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•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•


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


Payload Equipment - Receivers


Payload Equipment – Multi-Chip Module (MCM) Technology


Payload Equipment - Input Multiplexers


Payload Equipment - Output Multiplexers


Payload Equipment - Channel Amplifier


Payload Equipment – Dual Travelling Wave Tube Amplifier (TWTA) Direct Thermally Radiating Type


Payload Equipment - Frequency Generator


Multi- Chip Module (MCM) Technology


INMARSAT 4 Digital Signal Processor


Astra 2B In Anechoic Chamber


Astra 2B Repeater


Astra 2B Repeater Panels

communications payload engineering owen clarke october 2004 © eads astrium 2 aims to describe the...

Documents

eads astrium

antenna slide

payload constraints

beamforming slide

payload specifications

payload configurations

payload equipment

user slide