Transcript
CONTENTS • Types of Ground Stations • Architecture • Subsystems – – – –
GROUND SEGMENT
Antenna, Tracking Station Parameters: G/T, EIRP Polarisation Components of Ground Stations
Otto Koudelka
• Very Small Aperture Terminals (VSATs) • TV Receive-only Terminals
Institute of Communication Networks and Satellite Communications Graz University of Technology, Austria
• Topologies
[email protected] ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
1
FREQUENCIES • • • •
TYPES OF GROUND STATIONS
C-Band: 4 / 6 GHz X-Band: 8 / 10 GHz Ku-Band: 11 / 14, 12 / 14 GHz Ka-Band: 20 / 30 GHz
• Large stations (operators’ head-ends, TV feeder links, hub stations) • VSATs (very small aperture terminals) – one-way – interactive
• TV Receive-Only (TVRO)
• Always higher uplink frequency (efficiency reasons)
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
2
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
3
MEDIUM-SIZED STATIONS
LARGE STATIONS • INTELSAT-A • TV, telephony, data • up to 32 m
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
4
• VSAT hubs • TV uplinks • up to 9.5 m antenna diameter
Satellite Communications Systems 5
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 6
1
VSATs
FIXED MEDIUM-SIZE STATIONS
Very Small Aperture Terminals • up to 3.7 m antennas • typically 1.2...1.8 m
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
7
LOW-COST TERMINAL
8
TRANSPORTABLE STATIONS Trailer-mounted Terminal
Satellite News Gathering Terminal
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
9
NOMADIC TERMINAL
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
10
MOBILE TERMINAL
Satellite Communications Systems 11
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 12
2
MOBILE ANTENNA
TV RECEIVE ONLY (TVRO) • 35...120 cm (Ku) • 3 m (C)
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
13
ARCHITECTURE
14
RX: 12.5 GHz
Receiver Low Noise 12.5 GHz Amplifier (LNA)
Antenna
14 GHz
1st IF= 750 MHz
2nd IF= 70 MHz
BW=40 MHz
70 / 140 MHz or 950…2050 MHz
Frequency Downconverter
Polarisation OMT separation High Power Amplifier
DOWNCONVERTER
LNA
Demodulator FEC Decoder
DEMOD
Data out
OMT
LO1R: 11.75 GHz
HPA Driver
BW=40 MHz
Transmitter 70 / 140 MHz or 950…2050 MHz
Frequency Upconverter
FEC Encoder Modulator
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Data in
Satellite Communications Systems
LO2R: 680 MHz
UPCONVERTER
MOD TX: 14.0 GHz
LO2T: 13.25 GHz
LO1T: 680 MHz
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
15
12.5 GHz
TEST TRANSLATOR
16
12.5 GHz
LNA
TEST TRANSLATOR
LNA DOWNCONVERTER
DOWNCONVERTER
OMT
OMT
1.5 GHz
1.5 GHz
UPCONVERTER 14.0 GHz ERASMUS-IP Professor Horst Cerjak, 19.12.2005
UPCONVERTER 14.0 GHz
HPA Satellite Communications Systems 17
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
HPA Satellite Communications Systems 18
3
DOWNCONVERTER DEMOD 1
12 GHz x
ANTENNAS • Horn antenna
UPCONVERTER MOD 1 diplexing OMT 14 GHz
SIMULTANEOUS OPERATIONS UPCONVERTER
y
MOD 2 12 GHz
12 GHz
20 GHz
DOWNCONVERTER
transport of electromagnetic energy
DEMOD 2 ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Waveguide (“transmission line” for microwaves)
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
19
20
PARABOLIC ANTENNAS
OFFSET ANTENNA
• Primary focus feed Primary focus offset
Offsetantenne hier Primärfokus und asymmetrischer Reflektor
• With subreflector – Cassegrain – Gregory – Advantage: feed close to RF equipment
Offset - CassegrainAntenne
Offset-Cassegrain
Subreflektor
Offset - GregoryOffset-Gregory Antenne
Offset-Gregory
Subreflektor ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
21
22
OFFSET ANTENNAS
ANTENNA PATTERN • •
• higher efficiency, less shielding • antenna angle steeper, less risk of snow remaining in dish • electrical elevation angle is not mechanical elevation angle (subtract antenna offset ~20° !)
Gain plotted versus azimuth (or elevation) angle Antenna sidelobes below certain mask – G= 29-25logΘ
Main lobe
Gain Reduction [dB]
Azimuth angle ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 23
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 24
4
ANTENNA GAIN
DUAL POLARISATION
• Depends on diameter, wavelength, efficiency • G…antenna gain [dB] λ...wave lenghth [m] , λ = c/f η...efficiency (depends on surface accuracy, shielding)
• Orthogonal polarizations used, same frequency can be used twice – Horizontal / vertical (linear) – Left-hand / right-hand (circular) • Ortho-mode Transducer (OMT) separates polarised waves – must have a good cross-polar discrimination (XPD) – 25 dB minimum – 30...35 dB (@1 deg. off boresight) • Otherwise cross-talk, interference to other users • Proper alignment of OMT vital
Example: D = 2.4 m, f = 14 GHz, η = 60 %
⎞ ⎛ ⎟ ⎜ 2 2 ⎛ π 2 D2 ⎞ ⎜ π 2.4 ⎟ G = 10 log⎜⎜η = 48.7 dB 2⎟ ⎟⎟ = 10 log⎜ 0.6 λ2 ⎠ ⎝ ⎛ 3E 8 ⎞ ⎟ ⎜ ⎜ ⎟ ⎟ ⎜ ⎝ 14 E 9 ⎠ ⎠ ⎝ ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
25
26
OMT
EIRP • Effective isotropic radiated power: power emitted by an isotropic antenna to produce same peak power density (in far field) as a (directional) antenna in the direction of maximum gain
Low-cost OMT XPD: 25 dB
receive port
• EIRP [dBW] = P[dBW] + G[dB]
antenna port
High-performance OMT XPD: 48 dB
transmit port antenna port
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
27
FIGURE OF MERIT
28
ANTENNA POINTING
• Relationship between antenna gain and receiver noise temperature • G/T [in dB/K] • G/T [dB/K] = G [dB] – 10 log T [K]
• manual • motor-driven (can be used for tracking)
• Good value for a 2.4 m antenna with 80 K LNA : 28 dB/K • Receive signal/noise ratio derived from link budget:
• beacon signal from satellite used to optimize pointing
Eb No
= EIRP[ dBW ] − Lall [ dB ] +
(G / T )
[ dB / K ]
– azimuth – elevation – polarization
− k [ dBJ / K ] − B[ dBHz ]
L…sum of all losses, k…Boltzman constant, B…bandwidth ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 29
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 30
5
1) determine local position (GPS) 2) calculate azimuth, elevation, polarisation angles 3) adjust elevation angle (inclinometer) 4) coarse alignment of azimuth (compass, GPS) 5) search for beacon (spectrum analyzer) 6) fine adjustment of elevation, azimuth for maximum signal level 7) adjust polarisation
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
TRACKING • for larger earth stations – compensation of small half-power beamwidth – satellite movement – compensation of wind force
• inclined-orbit satellites
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
31
METHODS
32
PROGRAM TRACK
• program track • step-track • monopulse system
• employ orbit calculations • enter spacecraft orbital elements
• beacon signal to find maximum RX signal strength
• calculate azimuth, elevation • use data to control azimuth/ elevation actuators
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
– updated regularly – after orbital maneuver
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
33
STEP TRACK
34
ANTENNA MOUNTS
• simple algorithm • antenna moved a discrete step
• stable • withstand wind load • non-penetrating mount with frame for semi-permanent installations • should have azimuth/ elevation reading
– if signal increases, carry on in this direction – if signal decreases, go back
• satisfactory for most applications • grounding!
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 35
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 36
6
ANTENNA HEATING
COMPONENTS
• surface heated by foils • remove ice, snow – high attenuation – distortion of antenna diagram Mixer: analogue multiplier
• control system to keep temperature constant
Phase-locked oscillator
XTAL reference oscillator
Waveguide switch
Amplifier ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
37
38
VSAT
VERY SMALL APERTURE TERMINALS -VSATs
LNA
Downconverter DE MOD
• RF Front-end cost-optimised • Small outdoor unit, directly mounted on or near feed of antenna
OMT
– Low noise downconverter block (LNB) – Upconverter and high-power amplifier
OUTDOOR UNIT HPA
2nd Down converter
1st IF= 950... 2050 MHz
INDOOR UNIT
Upconverter MOD 1st Upconverter
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
39
LOW NOISE AMPLIFIER • • • • • •
Solid-state GaAs-FET, HEMT High gain Low noise power T= 65, 80, 120, 160 K (Ku) T = 30 K (C)
40
HIGH POWER AMPLIFIER (HPA) • SSPA (solid state power amplifiers) – 1,2,4,8,16,40, 80, 100 W for Ku-band – up to 300 W for C-band
• Higher power: – Travelling Wave Tube TWTA (100 W...kW) • bandwidth: 0.7 GHz (Ku), 3 GHz (Ka)
– Klystrons (very high power: up to 3 kW)
LNA
• bandwidth: 150 MHz
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 41
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 42
7
HIGH POWER AMPLIFIER
TV RECEIVE-ONLY (TVRO) • • • • •
simple low-cost outdoor mount water-tight receiver unit single cable for intermediate frequency, power, control
High-Power Amplifier 16 W
Upconverter / Driver
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
43
44
LOW-NOISE BLOCK
TVRO
950...2050 MHz
Feed
Mixer POLAR SELECT
Filter
LNB
Dielectric Resonator Oscillator
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
SET-TOP BOX
Amplifier
LNA
Low Noise Block
Antenna
950..2050 MHz
TUNER
Power for LNB via RF cable
DEMOD
TV DECOD
Control signals: - Polarisation - Selection of Band
9.75, 10, 10.75, 11.3 GHz Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
45
Satellite Communications Systems 46
LNB / SET-TOP BOX
TOPOLOGIES
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 47
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 48
8
STAR
POINTTOPOINT
Central Hub Station: responsible for capacity assignment network management
Internet
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems
49
50
STAR / MESH • Star topology suitable if data flow is always to/from central site (e.g. Internet via satellite) • If satellite terminals need to communicate with each other, traffic has to be routed via central hub station • Double satellite hop (ca. 500 ms) prohibits interactive applications (voice, video conference,…)
MESHED MODE
• In mesh mode only single hop (250 ms) • Any terminal can communicate with any other terminal without a hub
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 51
ERASMUS-IP Professor Horst Cerjak, 19.12.2005
Satellite Communications Systems 52
9
