What is VSAT ........................................................ ? VSAT history .………………………………………………………… VSAT application …………………………………………………… Orbit type ……………………………………………………………… What are bands of v-sat ......................................... ? Equipments …………………………………………………………… Concept ………………………………………………………………… SCPC- TDMA ..………………………………………………………
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What is VSAT........................................................ ?
VSAT history .…………………………………………………………
VSAT application ……………………………………………………
Orbit type ………………………………………………………………
What are bands of v-sat......................................... ?
Equipments ……………………………………………………………
Concept …………………………………………………………………
SCPC- TDMA ..………………………………………………………
What is VSAT?
VSAT is the term (Very Small Aperture Terminal) refers to a small fixed earth station.
VSATs provide the vital communication link required to set up a satellite based
communication network. VSATs can support any communication requirement be it
voice, data, or video conferencing.
The VSAT comprises of two modules - an outdoor unit and an indoor unit. The
outdoor unit consists of an Antenna and Radio Frequency Transceiver (RFT) and
the antenna size is typically range from 1.8 meter to 3.4 meter in diameter,
although smaller antennas are also in use. The indoor unit functions as a modem
and also interfaces with the end user equipment like standalone PCs, LANs,
Telephones or an EPABX.
The antenna, along with the attached low-noise converter (LNB-which receives
satellite signals) and the transmitter (BUC-which transmits the radio waves signals)
make up the VSAT outdoor unit (ODU), one of the two components of a VSAT earth
station.
VSAT is a two-way satellite ground station or a stabilized maritime V-sat antenna, Data
rates typically range from 56 kbps up to 4 Mbps. VSATs access satellites
in geosynchronous orbit to relay data from small remote earth stations (terminals) to
other terminals (in mesh configurations) or master earth station "hubs" (in star
configurations).
VSATs are most commonly used to transmit narrowband data (point of sale transactions such as credit card, polling or RFID data; or SCADA), or broadband data (for the provision of Satellite Internet access to remote locations, VoIP or video). VSATs are also used for transportable, on-the-move (utilizing phased array antennas) or mobile maritime communications.
VSAT history
The first recorded fictional depiction of a satellite being launched into orbit is a short
story by Edward Everett Hale, The Brick Moon. The story was serialized in The Atlantic
Monthly, starting in 1869, the idea surfaces again in Jules Verne's The Begum's
Millions (1879).
In 1903 Konstantin Tsiolkovsky (1857–1935) published (The Exploration of Cosmic
Space by Means of Reaction Devices), which is the first academic treatise on the use
of rocketry to launch spacecraft.
He calculated the orbital speed required for a minimal orbit around the Earth at 8
km/s, and that a multi-stage rocket fueled by liquid propellants could be used to
achieve this. He proposed the use of liquid hydrogen and liquid oxygen, though other
combinations can be used.
In 1928 Herman Potočnik (1892–1929) published his sole book, (The Problem of Space
Travel — the Rocket Motor), a plan for a breakthrough into space and a permanent
human presence there. He conceived of a space station in detail and calculated its
geostationary orbit. He described the use of orbiting spacecraft for detailed peaceful
and military observation of the ground and described how the special conditions of
space could be useful for scientific experiments. The book described geostationary
satellites (first put forward by Tsiolkovsky) and discussed communication between
them and the ground using radio, but fell short of the idea of using satellites for mass
broadcasting and as telecommunications relays.
In a 1945 Wireless World article the English science fiction writer Arthur C. Clarke
(1917-2008) described in detail the possible use of communications satellites for mass
communications.
Clarke examined the logistics of satellite launch, possible orbits and other aspects of
the creation of a network of world-circling satellites, pointing to the benefits of high-
speed global communications. He also suggested that three geostationary satellites
would provide coverage over the entire planet.
Telstar, launched by NASA on board a Delta rocket from Cape Canaveral on July 10, 1962, was the first
Privately sponsored space launch and the first active satellite with a microwave receiver and transmitter to
Transmit live television and telephone conversations across the Atlantic.
In July 2004, one of the biggest communication satellites, Akin F2, was launched on board an Ariane 5G
Rocket. With a weight of almost 6 tons, Akin F2 carried 94 transponders (38 Ka-band, 32 Ku-band and 24 C-band transponders)
VSAT application
Applications:-
Communication (Trucking call)
Teleconference
Telemedicine
TV Broadcasting
Data communication
Telemetry (TEC, Remote sensing etc)
Weather telecast
Navigation
GPS
Security/Calamity monitoring
Standard Tm
Orbit type
Several typesLEOs - Low Earth Orbit
MEOs - Medium Earth Orbit
HEOs – Highly Elliptical Orbit
GEO - Geostationary Earth Orbit
LEOsLow Earth Orbit
200-3,000 km
High orbit speed
Many satellites
Predominately mobile
Iridium, Global star
(space shuttle orbit)
MEOs
Medium Earth Orbit
6,000 – 12,000km
New generation
About 12 satellites
Voice and mobile
ICO (Odyssey), Orbcomm , Ellipse
HEOs
HEOs – Highly Elliptical OrbitHEOs: Molnya and TundraMolnya TundraPeriod 12 h 24 hApogee 39500 km 46300 km
Perigee 1000 km 25300 kmInclination 63.4° 63.4°
GEOs
Originally proposed by Arthur C. Clarke
Circular orbits above the equator
Angular separation about 2 degrees - allows 180 satellites
Orbital height above the earth about23000 miles/35786.16km
Round trip time to satellite about 0.24 seconds
GEO satellites require more power for communications
The signal to noise ratio for GEOs is worse because of the distances involved
A few GEOs can cover most of the surface of the earth
Note that Polar Regions cannot be “seen” by GEOs
Since they appear stationary, GEOs do not require tracking
GEOs are good for broadcasting to wide areas
Currently 329 GEO are in orbit
What are bands of v-sat?
There are 3 bands for the V-Sat which are C-band, KU-band and the Ka-band.
All Satellite communication systems are subject to international agreements and
regulations. The International Telecommunication Union (ITU) regulates frequency
use and defines "bands"
The C-Band:
C-band was the first band to be used for satellite communication systems.
However, when the band became overloaded (due to the same frequency being
used by microwave links) satellites were built for the next available frequency
band, the Ku-band.
Today C-Band also gets disturbed by wireless radio links in particular uncontrolled
spreading in Africa. Interferences can get reduced by cost intensive microwave
filters level 421 generally recommends each customer who plans to use C-Band.
The C-band frequency range has one significant problem. It is the frequency
region assigned to microwave radio communication systems. There are an
emerging number of these microwave systems located all over the world and
they carry a large volume of commercial communications. Consequently, the VSAT
locations needed to be restricted in order to prevent interference with the
microwave communication systems. As mobile phones get used more and more in
countries all over Africa as well, the use of C-Band in future will possibly certainly
rather decrease than increase. At the current point of time - C Band nevertheless
is widely used. In particular as KU band capacity over some regions is quite
limited.
Commercially it is fact that hardware for C Band is significantly more expensive
while the capacity is cheaper. So customers with large bandwidth requirements
preferably choose this technology.
Downlink: 3.7 – 4.2 GHz
Uplink: 5.9 – 6.4 GHz
Advantages:
- Less disturbance from heavy rain fade
- Cheaper Bandwidth
Disadvantages:
- Needs a larger satellite dish (diameters of minimum 2-3m)
- Powerful expensive RF unit
- More expensive hardware
- Possible Interference from microwave links
Ku-band:
Ku-band is typically used for broadcasting and 2-way Internet connections
The Ku-band frequency range is allocated to be exclusively used by satellite
communication systems, thereby eliminating the problem of interference with
microwave systems. Due to higher power levels at new satellites Ku-band allows
for significantly smaller earth station antennas and RF units to be installed at the
VSAT location.
KU Band on the other hand operates with small antennas and less expensive
equipment, while the capacity price is higher than C Band.
Downlink: 11.7 – 12.2 GHz
Uplink: 14.0 – 14.5 GHz
Advantages:
- No interference from microwave links and other technologies
- Operates with a smaller satellite dish (diameters from 0.9m) -> cheaper and
more easy installation
- Needs less power -> cheaper RF unit
Disadvantages:
- More expensive capacity
- Sensitive to heavy rain fade (significant attenuation of the signal) / possibly can
be managed by appropriate dish size or transmitter power.
The Ka band:
The Ka band is a portion of the K band of the microwave band of the
electromagnetic spectrum.
Ka-band roughly ranges from 18 to 40 GHz. The 20/30 GHz band is used in
communications satellites, downlink 18.3–18.8 GHz and 19.7–20.2 GHz. The term
Ka-band is frequently used to refer to the recommended operating frequencies of
WR-28 rectangular waveguide, which is 26.5 to 40.0 GHz.
Ka band in future will allow a broader application field in the V-SAT Industry. At the
moment only very few capacity possibilities are available in Ka Band.
Those commercial projects available suffer from the global warming and
the resulting climatic change.
You will ask why? Very simple: The increase of rain and strong weather
conditions terrible affect service stabilities in KA band. Due to stronger and longer
bad weather periods outages of services in KA Band have dramatically increased
in the last 3 years.
However it's quite exciting to get more bandwidth out of a smaller required space
segment - KA band related services still will have to proof that they really will play
a major role in futures satellite communication business.
Equipments
- Mobile
-
- THURAYA
- BJAN
- SNG
- Marine system
- Satellite dish
-
The Satellite Dish Consists of:-
Dish
BUC
LNB
How does VSAT works?
HERE’S HOW THE PROCESS WORKS - IN 5 EASY STEPS TO
UNDERSTAND:
End user computer is connected to your network, which in turn is connected to
the Internet by VSAT Systems. You open a web browser, and type in a web
address. End user computer sends a request for a transfer of data both
transmit and receive.
That request is sent from the end user PC, through their home network, to the
indoor satellite modem which modulates the signal and passes it to the VSAT
dish. The VSAT dish converts this signal to an RF signal and sends it to a
satellite located in the geostationary orbit at the speed of light - 186,000 miles
per second.
The satellite in the geo-stationary orbit receives this signal and sends it to one
of the VSAT Systems teleports This illustrates the fact that although the
packets of information travel tremendous distances via the space segment,
the packets hop fewer networks due to the large reduction in the number of
inter domain and intra domain routers giving an opportunity to minimize
latency.
The request then goes to VSAT Systems’ NOC, which retrieves the requested
website from the web server, across the Internet backbone.
The whole cycle is then reversed and the requested data is available to the
user. A 90,000 mile journey, through millions of dollars of infrastructure and
sophisticated equipment, all in less than 700 milliseconds.