Post on 16-Mar-2020
MUHAMAD ASVIALCenter for Information and Communication Engineering Research (CICER)
Electrical Engineering Department, University of IndonesiaKampus UI Depok, 16424, Indonesia
asvial@ee.ui.ac.idhttp://www.ee.ui.ac.id/cicer
Basic Satellite System
Lecture 2
1
– Satellite Classification
– Basic Satellite System• Earth Station or Ground Segment
• Space Segment or Satellite
• Satellite Spacing
– Satellite Repeater/Transponder
– Satellite Link Models
– LNA/HPA Characteristics
– Hypothetical Reference Circuit
Objectives
2
Satellite CommunicationsSatellite Communications--IIII
• SATELLITE CLASSIFICATION– Basic Definitions
• Roll, Pitch, and Yaw
3
Satellite CommunicationsSatellite Communications--IIII
• SATELLITE CLASSIFICATION– Spinner Satellites use the angular mome
ntum of its spinning body to provide roll and yaw stabilization
• Less common type
• Mostly used in relatively high-altitude geosynchronous or Molinya orbits
• Intelsat VI Satellite, DSP (Defense Support Program) Satellite of USA
• its (Intelsat VI) body (lower part having solar panels around) spins like a top at approx. 15 rpm around pitch axis. The upper part, containing communication payload, is de-spun relative to the rest of the body to keep its antennas pointing continuously towards Earth
Intelsat VI SatelliteDSP Satellite
4
– Three-Axis Stabilized Satellites keep their body fixed relative to Earth’s surface and an internal subsystem provides roll and yaw stabilization
• Their body is roughly box-shaped and have deployable solar-array panels
• Examples: Defense Meteorological Satellite Program (DMSP), Japanese Earth Resources Satellite (JERS), Russian Communication Satellite, Gorizont.
• All these keep their bodies stable thru inertia except for a slow motion about one axis to keep their payload antennas and sensors continuously pointing towards Earth. The solar panels are counter-rotated to track the sun.
• However, European Infrared Space Observatory (ISO), does not need any such adjustment due to restriction on attitude or low power requirement
Satellite Classification
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User interface User interfaceTerrestrial interface Terrestrial interface
User interface
Figure: Structure of a satellite system
Basic Satellite System
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– Configurations
• Star
• Mesh
Figure: Network topology star
(a)
…………………………
(b)
Figure: Mesh network topology
Satellite System Configurations
7
Figure: Basic communications satellite components
Solar panels
System Components
8
– Spatial separation between any two satellites depends on several factors that include: [1o-2o]• Beam widths and side-lobe radiation of both satellite antennas and earth station• RF carrier frequency• Encoding and modulation technique used• Acceptable limit of interference• Transmit carrier power
θ = cos-1[dA2 + dB2 - 2 r2 (1 – cosβ)]/2 dAdB
where,θ: angular separation between satellites as viewed by the earth stationsβ: angular separation between the satellites as viewed from the center of the earth i.e., β is simply the difference in the longitudinal positions of the two satellites
Figure: Satellite separation
Signal to satellite B
2@6/4 GHz1.5@14/12GHz
Satellite Spacing in Orbit
9
– Functions and Types
• Signal Amplification (≈ 110 dB Gain)
• Frequency Down-Conversion Figure : Types of transponders (a)conventional transparent (non― regenerative satellite, and (b) processing (regenerative) satellite
Tran
spar
ent
Pro
cess
ing
Transponder (A Repeater)
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• SATELLITE Transponder (A Repeater in the Sky)– Transparent Transponder
• Amplification and Frequency Translation and No Processing
Figure Transparent Transponders
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– Processing/Regenerative Transponder
• Amplification and Frequency Translation along with Signal Processing
Figure : A regenerative repeater for digital signals
Mod. HPA BPFft
Mixer
Local oscillator
fr ft
fl
Dem.LNA Regeneration.
Carrierregeneration.
Transponder
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Frequency Translation• Up-Conversion – IF frequency (70 MHz/140MHz) translated to Higher Frequen
cy using Single or Double Stage Conversion Process
Figure: Up-converter schematic diagram (a) single conversion (b) double conversion (c)frequency spectrum
BPF1
Product modulator
ω0
ωl
IF carriercos(ω0t + φ)
cos(ω0t + φ) cosωlt
ωl > ω0
ωu BPF1
Mixer 1
ω0
ωll
ωuBPF2
Mixer 2
ωl2
IF = ωll + ω0
Transponder
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Frequency Translation• Up-Conversion – IF frequency (70 MHz/140MHz) translated to Higher Freque
ncy using Single or Double Stage Conversion Process
Transponder
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Frequency Translation• Down-Conversion – RF Frequency is translated to IF frequency (70 MHz/14
0MHz) using Single or Double Stage Conversion Process
BPFωu
ωl
ω0 BPF2ωu
ωl2
Mixer 2
BPF1
ωl1
Mixer 1
ω0
Mixer
(a) (b)
(c)
Figure : Down-converter schematic diagram (a) single conversion, (b) double conversion (c)frequency spectrum
Transponder
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Classification based Frequency Conversion• Single Conversion Transponder
Figure : Simplified single-conversion transponder for 6/4 GHz band
BPF
Pre-amplifier
Mixer
Local oscillator
fr ft
fl
BPF
6 GHz uplink antenna
ft
4 GHz downlink antenna
6 GHz band-pass filter
4 GHz band-pass filter
LNA LPA HPA
2225 MHz
BPF
4 GHz band-pass filter
Transponder
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Classification based Frequency Conversion• Double Conversion Transponder
Figure : Simplified double-conversion transponder (bent pipe) for 14/11 GHz band
14 GHz LNA
IF Amplifier
1st Local oscillator 13 GHz
1st Mixer
frfIF
fl1
BPF2
11 GHz HPA
BPF3ft
2nd Mixer
fr ft
fl2
2nd Local oscillator 10 GHz
14 GHz uplink antenna
1 GHz amplifier
Up converter
11 GHz downlink antenna
BPF1
Transponder
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Classification based Frequency Conversion• Broadband Multiple-Channel Transponder
Figure : Broadband multiple-channel repeater
fr ft
BPF F1
BPF F1
BPF Fn
BPF Fn
Mixer
Local oscillator
1 2 n-1 n
nB
n-1
B
F1 F2 Fn-1 Fn
Combiner5925 MHz -6425 MHz
3700 MHz -4200 MHz
2.225 GHz
500 MHz bandwidth
LNA
500 MHz bandwidth amplifier
F1 HPA
Fn HPA
Channelization
Transponder
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Classification based Frequency Conversion• Multi-Channel Receiver Transponder
Figure : Multi-channel receiver transponder example
Mixer
LNA BPF HPA BPFBPF F1
LO
LNA BPF HPA BPFBPF Fn
Mixer
LO
Demux
Combiner
2.225 GHz
2.225 GHz
5925 MHz -6425 MHz 3700 MHz -
4200 MHz
Transponder
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A Satellite System Basic Sections: Uplink, Satellite Transponder, and Downlink• Satellite Uplink Model
Satellite Link Model
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– A Satellite System Basic Sections: Uplink, Satellite Transponder, and Downlink
• Transponder (Transmitter + Responder) Model
RF-to-RF Repeater
Tunnel Diode
Satellite Link Model
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A Satellite System Basic Sections: Uplink, Satellite Transponder, and Downlink• Downlink Model
Tunnel Diode/Parametric Amplifier
Satellite Link Model
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• SATELLITE LINK MODEL– Cross-Link or Inter-Satellite Link (ISL) Model
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• LNA Characteristics– LNA-a non-linear device
• 1-dB Compression Point
• 3rd order Intercept point-a hypothetical power level where the operating power of the 3rd order inter-modulation product (generated by the amplifier when two equal level signals at frequency ω1 and ω2 are applied and it generates a third order inter-modulation product 2 ω1 - ω2) is equal to the power of ω1 and ω2
Power output
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• HPA Characteristics– HPA-a non-linear device
– HPA Devices
• TWT Amplifier- most commonly used, BW=500 MHz, BW Efficiency = 10%
• Klystron Tube- Better BW Efficiency (2%) and Higher Gain but at Smaller BW
• Solid State Power Amplifier (SSPA) – IMPATT Diodeuse as final stage Amplifier for lower frequencies and low power applications
Operating point
Figure 4.9.1-1 Transfer characteristics of TWTA
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• HPA Characteristics– Back-Off Loss
Lbo is reduction in Rated O/P Power of HPA to bring it into Linear Region
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• Hypothetical Reference Circuit– Hypothetical Reference Circuit Connection (HRX)-the total le
ngth of HRX, end-to-end, of 64 kbps circuit is 27,500km27,500 km
Local National International National Local
S LE
PC
SC
TC
ISC
ISC
ISC
ISC
ISC
TC
SC PC LE S
S: SubscriberLE: Local ExchangeTC:Tertiary CenterPC:Primary CenterSC: Secondary CenterISC:International Switching Center Switch: Transition element
Figure Digital hypothetical Reference Circuit (HRX)
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• Hypothetical Reference Circuit– HRX Quality Demarcation- The international section, from terminal I
SC to terminal ISC, is considered as stretching 2500km and providing a high grade of service
27,500 km
1250 km25,000 km
1250 kmNote 2 Note 2LE LE
T-reference point (Note 1)
Local grade
Medium grade
High grade
Medium grade
Local grade
Note 1: The T-reference point is an ITU-T defined subscriber/network ISDN interfaceNote 2: This point may be at the LE, PC, SC, TC or ISC depending on the country size
Figure HRX quality demarcation
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• Hypothetical Reference Circuit– Gateway Earth Station in HRX – an important part of high-grade int
ernational section covering about 12, 500 km, leaving 12, 500 km for backhaul and/or international transit sections
Figure Sample 64 kb/s connection including a satellite link
Sub Sub
LE ISC ISC LE
3000km 240km
Local grade
Mediumgrade
High grade Medium grade
Local grade
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