Download presentation
Presentation is loading. Please wait.
1
Communications Payload Engineering
Owen Clarke
2
Aims To describe the main components of the Communications satellite payload and explain how designs are impacted by the changing needs of the user 2 EADS Astrium
3
Contents Introduction Payload Function Payload Constraints
Payload Specifications Payload Configurations Payload Equipment 3 EADS Astrium
4
Communications Payload Function
Transmit Antenna Receive Antenna Repeater Uplink Downlink Communications Payload = Antenna Sub-System + Repeater 4 EADS Astrium
5
Essential Communication Payload Functions
Antenna Functions To provide highly directional receive and transmit beams Repeater Functions Power Amplification Frequency Conversion 5 EADS Astrium
6
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 6 EADS Astrium
7
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 7 EADS Astrium
8
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 8 EADS Astrium
9
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 9 EADS Astrium
10
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 10 EADS Astrium
11
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) 11 EADS Astrium
12
Noise Temperature 1 2 3 4 Concatenation of Noise Sources
Ts = Noise Temperature of the Complete System 1 2 3 4 Ts = Ta + T1 + T2 / G1 + T3 / (G1.G2) + T4 / (G1.G2.G3) ……... Ta = Antenna Noise Temperature 12 EADS Astrium
13
E.I.R.P. Effective Isotropic Radiated Power
EIRP = (Gain of Transmit Antenna)x(Transmit Power) 13 EADS Astrium
14
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 14 EADS Astrium
15
Payload Constraints – Spurious Products
Typical Saturation Characteristic e.g. Solid State Power Amplifier 15 EADS Astrium
16
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 + a3Sin3 + 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… 16 EADS Astrium
17
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 17 EADS Astrium
18
Intermodulation Products (3)
18 EADS Astrium
19
Intermodulation Products (1)
19 EADS Astrium
20
Spurious Products 20 EADS Astrium
21
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) 21 EADS Astrium
22
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 22 EADS Astrium
23
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 23 EADS Astrium
24
Gain Slope 24 EADS Astrium
25
Group Delay Slope 25 EADS Astrium
26
Payload Constraints Electromagnetic Compatibility
Radiated and conducted Emissions and susceptibility Ionising Radiation Reliability 26 EADS Astrium
27
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 27 EADS Astrium
28
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 28 EADS Astrium
29
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 Group delay variation over any 36MHz 1nS Channel 2 AM/PM conversion 50/dB Channel 3 Linearity C/I3 with 2 nominal carriers 10dB Channel 4 Reliability over 10 yrs 0.9 Thermal noise temp 260K 29 EADS Astrium
30
Payload Configurations - Basic Elements
Input Filter Low Noise Amplifier Mixer Filter Medium Power Amplifier High Power Amplifier Output Filter Local Oscillator 30 EADS Astrium
31
Payload Configurations - Channelisation
31 EADS Astrium
32
Payload Configurations - Redundancy
Switch Network Switch Network 32 EADS Astrium
33
Payload Configurations - Eutelsat 2
33 EADS Astrium
34
Payload Configurations – Inmarsat 3
34 EADS Astrium
35
Payload Configurations – Trends
Mobile SS MARECS INMARSAT 2 INMARSAT 3 INMARSAT 4 Payload Mass (Kg) 100 130 208 932 Payload Power (W) 500 660 9000 Design Lifetime (Years) 7 10 13 Launch Periods 2004 No of S/C in Series 3 4 5 2 + 1 FSS/DBS ECS EUTELSAT 2 HOTBIRD W3A 117 268 507 638 2090 4188 6900 No Of Channels 12/14 16 20/22 50 8-10 12-15 12+ 6 1 35 EADS Astrium
36
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 36 EADS Astrium
37
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 37 EADS Astrium
38
Transparent Or Regenerative
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 38 EADS Astrium
39
Typical Digital Processor Architecture
Rx AAF A/D DEMUX LC DBFN SWITCH FRC MUX D/A AIF SSPA D/C D/C U/C 1 1 • N N • • • • • • Phased Array Feeder Link 39 EADS Astrium
40
C to L Integrity Checker
Inmarsat 4 C to L Integrity Checker C-Band Downlink L-Band L-Band Automatic Level Control Rx/Tx Rx/Tx Feed Reflector Feeder to Mobile Array C-Band Rx Horn C-Band Payload Receive Section C-Band Down- Converter Forward Processor Postprocessor & L-Band Payload Transmit Section Rx 156 120 2 4 12 C-Band to 2 2 Mobile to Centralised Frequency Generator C-Band Tx Horn Tx LOs C-Band Up- Converter Preprocessor & L-Band Payload Receive Section C-Band Payload Transmit Section 2 4 120 12 156 Return Processor Mobile to Feeder DSP Pilot Tone Injection Unit 120 L1 Navigational Payload Nav L-Band Tx Antennas L5 40 EADS Astrium
41
Payload Equipment - Receivers
41 EADS Astrium
42
Payload Equipment – Multi-Chip Module (MCM) Technology
42 EADS Astrium
43
Payload Equipment - Input Multiplexers
43 EADS Astrium
44
Payload Equipment - Input Multiplexers
44 EADS Astrium
45
Payload Equipment - Output Multiplexers
45 EADS Astrium
46
Payload Equipment - Channel Amplifier
46 EADS Astrium
47
Payload Equipment – Dual Travelling Wave Tube Amplifier (TWTA) Direct Thermally Radiating Type
47 EADS Astrium
48
Payload Equipment - Frequency Generator
48 EADS Astrium
49
Multi- Chip Module (MCM) Technology
49 EADS Astrium
50
INMARSAT 4 Digital Signal Processor
50 EADS Astrium
51
Astra 2B In Anechoic Chamber
51 EADS Astrium
52
Astra 2B Repeater 52 EADS Astrium
53
Astra 2B Repeater Panels
53 EADS Astrium
Similar presentations
