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

5

User interface User interfaceTerrestrial interface Terrestrial interface

User interface

Figure: Structure of a satellite system

Basic Satellite System

6

– 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

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– 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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