SKS09en 11-12 Applications

Transcription

9. Applications
FER-Zagreb, Satellite communication systems 2011/12
Topics
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Introduction
Satellite television
Satellite telephony
Satellite radio
Satellite internet
Satellite amateur radio
VSAT
Weather satellites
Scientific satellites
Military satellites
Solar power satellites
Satellite navigation
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Introduction
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Satellite communication systems are used for transmission of
data, voice, pictures, etc....
The largest application of satellite communications is TV. In
Europe there are more than 3000 TV channels.
In northern American continent satellite radio is widespread,
but not in Europe.
Satellites can be used for a broadband internet access to rural
area.
Satellites are also used in many other services, such as
weather prognosis, remote sensing, military and scientific
applications.
They are also used in astronomy and in future for solar power
exploitation.
Another important application is VSAT Very Small Aperture
Terminal.
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Technology
Satellite are mostly placed in GEO orbit above equator.
Angular difference between satellites should be at least 1
degree.
Earth satellite stations transmit signal from large parabolic
antennas (9 m).
Satellite receives signal on one frequency and retransmits it
back to Earth on another in order to avoid interference.
Usually satellite has 32 transponders, and channel bandwidth
of 27 MHz.
On receiving side, parabolic antenna (45-90 cm) receives
signal from satellite, LNB down-converts the frequency and coaxial cable leads it to satellite receiver.
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DVB-S Digital Video Broadcasting Satellite
DVB-S (EN 300 421) standard determines modulation
procedures and coding for satellite television.
It is a communication system for distribution of video and
audio over satellite.
It uses MPEG-2 coding, QPSK modulation and concatenated
convolutional and RS coding (204, 188, T=8).
Convolutional coding has code rates: 1/2, 2/3, 3/4, 5/6 and
7/8.
It works mostly in Ku band (11.7 to 12.7 GHz in downlink, 1414.5 GHz in uplink) and also in Ka bad (27.5 to 31 GHz in
downlink, 18.3-18.8 GHz and 19.7 to 20.2 GHz in uplink).
In Europe the largest provider is SkyTV and in USA it is
EchoStar and DirecTV.
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DVB-S
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DVB-S2
Next generation DVB-S2 (EN 102 376) uses new methods of
coding and modulation (HDTV, MPEG 4) for higher flexibility
and capacity without increasing the complexity of the system.
Compatible with MPEG-2 and MPEG-4.
Uses QPSK, 8PSK, 16APSK and 32APSK modulation.
Instead of convolutional coding uses LDPC coding.
Code rates are 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9
and 9/10.
While DVB-S has roll-off factors α = 0.35, DVB-S2, can have
roll-ff factor also equal to 0.25 and 0.2 for more bandwidth
limitation.
DVB-S2 has 30% more capacity than DVB-S system in the
same transmission environment.
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DVB-S2
modulations
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LDPC coding
LDPC codes are linear block codes with rare parity bits in matrix H(N-K)xN
where every block of information bits is coded into code word with size N.
In the example, LDPC code has code word N = 8 and code rate 1/2.
Decoder must determine transmitted bit values.
It is done with bit nodes communications and parity bits (check nodes).
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Comparison of DVB-S and DVB-S2
Transponder with 36 MHz bandwidth with DVB-S and DVB-S2
SATELIT EIRP 51 dBW
SATELIT EIRP 53.7 dBW
DVB-S
DVB-S2
DVB-S
DVB-S2
Symbol rate
27.5 Mbauds
0.35
30.9 Mbauds
0.20
27.5 Mbauds
0.35
29.7 Mbauds
0.25
Modulation
QPSK 2/3
QPSK 3/4
QPSK 7/8
8PSK 23
Bit rate
33.8 Mb/s
46 Mb/s (+36%)
44.4 Mbps
58.8 Mbps(+32%)
Number of
SD channels
7 SDTV MPEG2
15 SDTV h.264
10 SDTV MPEG2
21 SDTV h.264
10 SDTV MPEG2
20 SDTV h.264
13 SDTV MPEG2
26 SDTV h.264
Number of
HD channels
1 HD MPEG2
3 HD h.264
2 HD MPEG2
5 HD h.264
2 HD MPEG2
5 HD h.264
3 HD MPEG2
6 HD h.264
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Using adaptive coding
and modulation
Figure shows how can
adaptive coding and
modulation achieve
higher throughput
compared to the constant
coding and modulation.
Bad weather which
affects the satellite
communication is present
only in small percentage
if observed throughout
whole year.
Adaptive Coding
and Modulation
Constant Coding
and Modulation
ACM Throughput:
67.56 Mbps
Averaged over Year
CCM Throughput:
27.6 Mbps
Averaged over Year
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Satellite telephony
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Fixed satellite telephony
Satellites enable telephony from point to point as
complementary service to terrestrial services.
Users are business men/companies and people in remote
areas.
Duplex is used for two way communication.
It uses one GEO or several LEO or MEO satellites.
Transmission rate is fixed, but only for a limited duration of
call.
It is possible to use PAMA or PRMA method for higher traffic.
The most widely spread systems are: Intelsat, Eutelsat,
Inmarsat, Globalstar, Iridium, ICO, Ellipso and Odyssey.
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Satellite telephony
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Mobile satellite telephony - Globalstar
Uses CDMA technology.
It has 40 satellites in LEO orbit (1414 km), covering 80% of
Earth surface, and 4 satellites in reserve. LEO orbit ensures
small signal delay.
Earth Gateway are used when signal is blocked from building
or terrain, thus ensuring the continuous communications.
Thuraya
Seated in Abu Dhabi, UAE
2 GEO satellites produced by Boeing cover 2.3 bil. people.
Capacity is 13750 calls at the same time.
Works in L band (1.5 – 1.7 GHz) and C band (3.4 – 3.7 GHz).
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Satellite telephony
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Thuraya
Telephone (GSM,
satellite, GPS).
In Croatia roaming:
VIP.
With additional
equipment enables
communication in
closed areas
(Indoor Enabler).
Thuraya SG-2520 –
10991 kn (VIP)
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Satelitski radio
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Satellite digital audio radio service - SDARS
Satellites are placed in GEO orbits.
Frequency of use is from 300 MHz do 4 GHz which is much
more than both AM and FM systems.
Antenna, built into the roof af a car, must always be visually
connected with the satellite. In other cases, the
communication is enabled through the terrestrial repeaters.
SDARS antennas receive signal from one or more satellites
at the same time.
SDARS is more suitable for rural than for urban areas.
Services are commercial and require a decoder.
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Satelitski radio
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SDARS antennas
Antenna needs to receive signal from satellites and terrestrial transmitters
at the same time – two antennas necessary.
Terrestrial TER antenna is usually monopole and satellite SAT antenna is a
circularly polarized structure.
Antennas are best placed on the roof 15 cm away from the edge.
Figure shows SAT antenna as a ceramic patch antenna with lenses. TER
antenna is a λ/4 monopole placed in the centre.
Lenses increase gain of patch antenna at low elevation angles (20° to 30°)
by increasing beam width.
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Satelitski radio
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XM
XM system uses two satellites
(Rock and Roll) in GEO orbit.
It also uses terrestrial
repeaters.
It covers USA.
XM signal uses 12.5 MHz Sband from 2332.5 MHz to
2345.0 MHz.
There are 6 separate carriers.
Whole program has 2 carriers
and other 4 are copy of the
same program for
redundancy.
It uses QPSK and COFDM.
It has delay and error
correcting codes.
XM
12.5 MHz
1.84 MHz
1.84 MHz
2.53 MHz
2.53 MHz
1.84 MHz
1.82 MHz
Rock 1
Roll 1
Ter 1
Ter 2
Rock 2
Roll 2
2332.5 MHz
2345.0 MHz
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Satellite internet
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It can in one direction (only download) and two direction (modem needed).
Tooway - two direction internet over satellite HOTBIRD 13 ° E
Satellite antenna required (68 cm) as well as satellite modem – Softbeam
Works in Ka band – uplink (27.5-30 GHz), downlink (17.7 – 20.2 GHz) and
Ku band uplink (12.75-14.5 GHz), downlink (10.7 – 12.75 GHz).
Link is realized through Eutelsat centre in Torino.
Speed: upload 1-4 Mb/s, download 6-10 MB/s.
App. 30-100 EUR per month.
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http://www.n2yo.com/ - page for tracking satellites
There are many radio amteur satellites
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KitSat-OSCAR 23 has FM repeater with uplink on 145.85 MHz and
downlink on 435.175 MHz.
OSCAR designation: KitSat-OSCAR 23
International designation: 1992-052B
Common name: KITSAT1
Satellite type: micro satellite
Launch date: August 10, 1992
Launch site: French Guyana
Rocket: Ariane 4
Apogee: 1320 km
Perigee: 1312 km
Organization: Korean Science and Technology Institute
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VSAT
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Very Small Aperture Terminal
Small intelligent earth satellite stations working in a system with one larger
HUB earth station and a satellite in GEO orbit.
VSAT stations have antennas from 0.75 m, while HUB has antennas from 6
to 9m in diameter.
Usable for banks, airplane companies, oil and gas industry, news gathering,
telemedicine, etc...
The price of VSAT terminal is about 1000 EUR.
Terminals can just receive signal, just send signal or both.
VSAT uses PAMA (Pre-Assigned Multiple Access) and DAMA (Demand
Assignment Multiple Access) with TDMA, FDMA, CDMA and ALOHA protocol.
Users are arranged in star, mesh or point to point network.
Usually works in Ku band (downlink 12.5-12.75 GHz, uplink 14.0-14.25
GHz), with EIRP of 50 dBW.
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VSAT
Mobile VSAT vehicle for crisis and news gathering.
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VSAT
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Terminals in a star network
Weak signal from remote earth station is amplified at satellite and resend
to earth station HUB.
Downside is that if two VSAT station need to communicate, two hops
over satellite are necessary which increases delay.
GEO satellite
VSAT 1
VSAT star network
HUB
VSAT 2
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VSAT
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Terminals in a mesh network
This network enables connection of terminals without HUB. It is
appropriate for large companies and their remote offices.
GEO satellite
VSAT 1
VSAT mesh network
VSAT 3
VSAT 2
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Weather satellites
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Satellites for observing weather and climate conditions on Earth.
Orbits are polar (860 km) or geostationary (36000 km).
Even though clouds are observed most, other interest include volcanoes,
snow and ice, ocean currents, etc...
Sensors are visible, infrared and laser. Typical resolution is 1 km.
Visible spectrum is usable during day, but infrared is also usable at night.
Infrared sensors are used for temperature and water vapor images. The
wind in upper atmosphere can be determined.
Microwave images do not depend on day or night and pass through the
clouds. They work on frequencies from 3 GHz to 15 GHz.
Lasers are also used–LIDAR (Laser
imaging and detection). They are
however still expensive and not
very often yet.
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Weather satellites
Microwave image
of tropical storm
Dean on 19th
August 2007 at
7:17 hrs.
Warm color
represent
strongest storm.
Visible spectrum
Infrared spectrum - vapor
Infrared spectrum – temp.
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Weather satellites
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EUMETSAT
Member of EUMETSAT is
Meteorological and
Hydrological Service of
Croatia (DHMZ).
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Satellites for gathering information on Earth, its magnetic
field, Sun, planets in Solar systems and celestial bodies
outside Solar system.
Astronomical satellites such as Hubble and WISE
Scientific experiments in space are not under the influence of
atmosphere, gravity, air pollution etc...
Satellites are equipped with different measuring instruments
(radars, accelerometers, spectrometers, photometers,
plasma detectors, optical, infrared and gamma telescopes,
and so on.
Typical missions are earth exploration: ERS (European
Remote Sensing Satellite), GOCE (Earth gravity), LANDSAT
(Earth observing), Double star (Earth magnetic field), SOHO
(Solar and Heliospheric Observatory) and many others.
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Military satellites
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Satellites for gathering intelligence, navigation, detection of nuclear
experiments and military communications.
Usually have sensors in all spectrums.
From around 4000 satellites sent into space between 1957 and 1999, half
was partially or completely military.
Navstar Global Positioning System (GPS) is the most accurate satellite
navigational system.
Satellites with weapons (lasers or such) do not exist yet, but are not
impossible in the future.
KH series of USA satellites.
KH-12 supposedly have resolution 2 cm.
Enlargement of Eiffel Tower, Paris, France
Acquired March 20, 1966
KH-7 Mission 4026
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Solar power satellites
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SPS satellites (GEO) will collect solar power and send it to Earth at 2.4 GHz.
There is a problem of environment and exposure of humans and animals to
microwave radiation. Power density in centre of antenna will be 25 mW/cm2.
There could also be a problem of interference with other terrestrial services.
Sun collectors should be 1km in diameter (50t), and receiving earth antenna
10 km wide and 13 km long. Atmosphere can divert the beam from satellite.
Another problem is focusing. Angle
error of only 0.0005° leads to linear
error of 305 m.
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Satellite navigation
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Known systems are Navstar GPS (USA) and Glonass (Russia). European
system Galileo is under development.
System works both in day or night at or in the vicinity of Earth surface.
GPS does not require subscription for users.
GPS has 24 satellites in MEO orbit (20000 km–12 hrs period).
Signal from three satellites is required to calculate 2D position and
movement, and from four satellites for height as well.
Accuracy of GPS is about 15 m for civil users.
EIRP of satellite is 50 W.
It operates on frequency of 1575.42 MHz for civil users.
The accuracy is effected by ionosphere, multipath, accuracy of clock and
intentional error by American ministry of defense.
GLONASS is less accurate than GPS (55 to 70 m for civil
users). It has 21 satellite at 19100 km (MEO) and period
of 11h15min. It works on 1.6 GHz.
Galileo will have 30 satellites in MEO orbit (23222 km).
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SKS09en 11-12 Applications

Transcription

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