SATELLITE COMMUNICATION

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					                           SATELLITE COMMUNICATION
1 A brief history of space communication
The idea of radio transmission through space was first conceived in 1911. In 1945 British author-scientist
Arthur C. Clarke suggested the use of a geo synchronous earth satellite for the purpose. His assumption of a
manned space station was later revised by a US engineer, J R Pierce, in April 1955, who was also the first
one to analyze unmanned communication satellites. This idea later led to the great success of satellite
communications.
The first artificial satellite "SPUTNIK I" was launched by the erstwhile USSR, in 1957. This began a series
of space initiatives by USA and USSR. The first satellite communication experiment was the US
government's project SCORE (Signal Communication by Orbiting Relay Equipment), which launched a
satellite on December 18, 1958. This satellite circled the earth in an elliptical orbit and retransmitted
messages recorded on a magnetic tape. It lasted for about 13 days after which the batteries ran out!!

2 Types of Satellites
       Anti-Satellite weapons, sometimes called "Killer satellites" are satellites designed to destroy
"enemy" satellites, other orbital weapons and targets.

         Astronomical satellites are satellites used for observation of distant planets, galaxies, and other
outer space objects.

        Biosatellites are satellites designed to carry living organisms, generally for scientific
experimentation.

          Communications satellites are an artificial satellite stationed in space for the purposes of
telecommunications. Modern communications satellites typically use geosynchronous orbits, Medium earth
orbits or low Earth orbits.

          Miniaturized satellites are satellites of unusually low weights and small sizes. New
classifications are used to categorize these satellites: mini-satellite (500–200 kg), micro-satellite (below 200
kg), nano-satellite (below 10 kg).

          Navigation satellites are satellites which use radio time signals transmitted to enable mobile
receivers on the ground to determine their exact location. The relatively clear line of sight between the
satellites and receivers on the ground, combined with ever-improving electronics, allows satellite
navigation systems to measure location to accuracies on the order of a few meters in real time.


3 Altitude Classifications:

3.1Low Earth Orbit (LEO):
Geocentric orbits ranging in altitude from 0 - 2,000 km (0 - 1,240 miles). Low Earth Orbit (LEO) refers to a
satellite which orbits the earth at altitudes between (very roughly) 200 miles and 930 miles. Low Earth
Orbit satellites must travel very quickly to resist the pull of gravity -- approximately 17,000 miles per hour.
Because of this, Lowe Earth Orbit satellites can orbit the planet in as little as 90 minutes. Low Earth Orbit
satellite systems require several dozen satellites to provide coverage of the entire planet. Low Earth Orbit
satellites typically operate in polar orbits. Low Earth Orbit satellites are used for applications where a short
Round Trip Time (RTT) is very important, such as Mobile Satellite Services (MSS).

3.2 Medium Earth Orbit (MEO) :
 Geocentric orbits ranging in altitude from 2,000 km (1,240 miles) - to just below geosynchronous orbit at
35,786 km (22,240 miles). Also known as an intermediate circular orbit. Medium Earth Orbit (MEO) refers
to a satellite which orbits the earth at an altitude below 22,300 miles (geostationary orbit) and above the
altitude of Low Earth Orbit (LEO) satellites. Medium Earth Orbit represents a series of tradeoffs between
geostationary orbit (GEO) and Low Earth Orbit (LEO). Medium Earth Orbit enables a satellite provider to
cover the earth with fewer satellites than Low Earth Orbit, but requires more satellites to do so that
geostationary orbit.

          Medium Earth Orbit terrestrial terminals can be of lower power and use smaller antennas than the
 terrestrial terminals of geostationary orbit satellite systems. However, they cannot be as low power or
 have as small antennas as Low Earth Orbit terrestrial terminals. Medium Earth Orbit satellite systems
 offer better Round Trip Time (RTT) than geosynchronous orbit systems, but not as low as Low Earth
 Orbit systems.

3.3High Earth Orbit (HEO) :
Geocentric orbits above the altitude of geosynchronous orbit 35,786 km (22,240 miles).

3.4 Geosynchronous Orbit (GEO)
Orbits with an altitude of approximately 35,786 km (22,300 miles). Geostationary orbits are often referred
to as geosynchronous or just GEO. A geosynchronous orbit with an inclination of zero. To an observer on
the ground this satellite would appear as a fixed point in the sky. A geostationary satellite is any satellite
which is placed in a geostationary orbit. Satellites in geostationary orbit maintain a constant position
relative to the surface of the earth. Geostationary satellites do this by orbiting the earth approximately
22,300 miles above the equator. This orbital path is called the Clarke Belt, in honor of Arthur C. Clarke. In
other words, if a satellite in a geostationary orbit is in a certain place above the earth, it will stay in that
same spot above the earth. Its latitude stays at zero and its longitude remains constant and one satellite can
cover almost 1/3 of earth surface Geostationary satellites are commonly used for communications and
weather-observation. The typical service life expectancy of a geostationary satellite is ten to fifteen years.


                          LOW EARTH ORBIT
                          450 km – 1000 km
                                                                                   MEDIUM EARTH
                                                                                   ORBIT (15000 km)




                                 GEO STATIONARY
                                 ORBIT(36000 km)

                                   Fig. 1 Different Orbits of Satellite

4 Important Frequency Bands For Satellite Communication
C- Band :
Up Link Frequency                    :      5.925 – 6.425 GHz.
Down Link Frequency                  :      3.7 – 4.2 G Hz.
                                            Total 500 M Hz BW.
Extended C- Band :
Up Link Frequency                    :      6.725 – 7.025 GHz.
Down Link Frequency                  :      4.5 – 4.8 G Hz.
                                            Additional 300 MHz BW
Ku band :
Up Link Frequency                     :      14.0 - 14.5 G Hz.
Down Link Frequency                   :      10.95 – 11.2 and 11.45 - 11.7 GHz.
                                             A total of 500 MHz BW in Ku band.
1.       Advantages of Satellite Communications
•          Wide coverage
           Almost one third of the earth except the polar regions is visible from a geostationary satellite. It is,
therefore, possible to cover wide geographical area irrespective of intervening terrain using a single
satellite. Satellite media is the only alternative for remote areas inaccessible through terrestrial routes. By
suitable design and configuration of earth station equipment, satellite links can be used for thin and heavy
traffic routes in a cost effective manner.

•         Suitable for both Digital and Analog Transmission
          Same satellite can be used for both digital and analog communication links. Satellite is transparent
to the type of service being provided.

•        High Quality
         Satellite links are designed high quality of performance. The links are free from atmospheric
disturbances and fading. As only one repeater is involved, the reliability is very high.

•          Flexibility
           In terrestrial links, the topology of the network gets tied down to the installed equipment. On the
other hand, a satellite can be accessed from any point on the earth from where it is visible. The earth
stations can be relocated and reconfigured providing complete flexibility of operation and utilization of the
satellite capacity.

•        Quick Provision of Services
         Compared to the terrestrial links, earth stations can be installed in much shorter period and,
therefore, services can become available faster.

•        Mobile and Emergency Communication

         An earth station can be mounted on a vehicle to provide mobile communication services. Using
small air lift able earth station terminals, telecommunication services can be extended to any location in
emergency

6 Ku Band VSAT of BSNL
         The Ku band ("kay-yoo" K-under band) is a portion of the electromagnetic spectrum in the
microwave range of frequencies from 11 to 18 GHz. VSAT technology is a secure and reliable medium to
connect geographically dispersed locations and represents a cost effective solution for users seeking an
independent communication network connecting to the global network. In a situation where other
connectivity options are not feasible, Ku Band VSAT offer value added satellite based services capable of
supporting internet, Local Area Network, voice, Fax and can also provide powerful dependable private
communication solutions.

7 What is VSAT?
          VSAT stands for Very Small Aperture Terminal. VSAT is a device (also known as an “earth
station”) that is used to send and receive wireless transmissions by satellite. Millions of VSATs are in use
around the world, allowing people to send and receive two-way data, voice or video transmissions by
bouncing signals off of satellites in orbit. The "very small" component of the VSAT acronym refers to the
size of the VSAT “antenna” or “dish” - typically about 2 to 5feet (0.55-1.8 meters) in diameter for Ku-band
systems - that is mounted on a roof, attached to a wall or placed on the ground and is capable of both
receiving and sending satellite signals. VSAT systems can be designed to serve both broadcast and
interactive applications whether data, voice or video, which are now being served by terrestrial lines and
can be operated in either single or multi-user environment. In single-user mode it would interface directly
to the customer's PC. In multi-user mode, it will seamlessly integrate into a local area network with its built
in Ethernet Interface RJ-45 (10/100) and also acts as an access router to support services to connecting PCs.
VSAT Equipment is mainly consist of-
              • ODU ( Outdoor Unit )
              • IDU ( Indoor Unit ) as shown in Fig.2
7.1 Outdoor Unit (ODU):
    The outdoor unit system is specifically optimized for use with the Indoor Unit and consists of:
    • Transmit / Receive Dish (Antenna) (0.75m - 1.8m)
    • Block Up-converter (BUC) (1W-2W)
    • Low Noise Block-Down-converter (LNB)
    • Feed Assembly

                       ODU                                           IDU



                                                                                       SAT Tx

                                                                                      SAT RX
                                 Dish
                                                                                      USB

          LNB                                                                   Ethernet 10/100
                                                                                BaseT (RJ-45)

                                                                                Telephone Jack
                                                                                for VoIP (RJ-11)


        BUC
                     Feed                                                        100-240 VAC
                     horn                                                        (Optional -48V
                                                                                 DC)




                                               Fig. 2 ODU & IDU
    BUC: - Block up-converter converts incoming I.F. (from IDU) to R.F. transmitting frequency,
    amplifies it and passes it to feed.
     LNB: - LNB amplifies incoming R.F.(Radio Frequency) from feed using low noise amplifier,
    converts it to I.F. and passes it to IDU

7.2 IDU (Indoor Unit):
         On receiving side, converts I.F. (Intermediate Frequency) from ODU to base band signals which
may be data, video or voice. On transmitting side, converts base band signals to I.F. and passes them to
ODU. I.F. is generally in L band. R.F. can be in C, Ku or Ka bands.
         The indoor unit may be a small desktop box, or it may be (as in this case) a network module
integrated with a router providing VSAT network connectivity just as any other network module and
provide flexible Interfaces like Ethernet 10/100 BaseT (RJ45), USB with maximum download speed of up
to 4 Mbps and maximum upload speed of up to 2 Mbps.

8 Features Broadband V-SAT system of BSNL:-
    •    Maximum Trans / Receive Data up to 2 Mbps / 4 Mbps with 10/100 Mbps Base-T Ethernet
         interfaces.
    •    Supports all IP V4 protocols
    •    Shared and customized Bandwidth for customers requirements (i.e. dedicated or shared
         Bandwidth)
    •    Supports Video Conferencing
    •    Built in GRE Tunneling
    •    Dynamic Link Allocation (DLA) technology which automatically adjusts modulation, coding,
         and gain based on the link environment (such as during rain) to achieve maximum availability
    •    VPNs can be created with VSAT Network, MLLN nodes, MPLS nodes of BSNL
    •    VoIP telephony with add on ATA (Analog Telephone Adaptor)
    •    Transparent to IP Sec protocols
    •    Embedded CPU Turbo Product Coding
    •    Dynamic Link Allocation (DLA) Support ( unique to BSNL Gateway, which no other VSAT
         service provider can support in India as on date)
    •    Connectivity to Broadband Internet

9 Broadband V-SAT ARCHITECTURE:
     V-SAT networks can be arranged in point to point, star, mesh, star/mesh, and broadcast configurations.
The preferred arrangement depends on the kind of information flow the network will service. A point to
point network allows two-way communications between two VSAT sites. A star network allows any
number of VSAT sites to have two-way communication with a central hub. A mesh network allows two-
way communications between any VSAT sites in a network. A central hub is not necessary. Each site
communicates to another site with a single satellite hop.
     VSAT Broadband (Ku band VSAT) networks of BSNL designed in a hub-and-spoke fashion as shown
in fig. 3, with customer locations connecting directly over the air to a central “hub” facility. The equipment
at a customer site is a VSAT receiver/router (similar to a DSL or cable modem), attached to a small dish
mounted on top of or outside the building. At the central hub facility, a large dish and sophisticated hub RF
components receive and transmit to the remote sites, and route information to and from the Internet or
private networks via leased line.




                                   Satellite




        INTERNET

                                                                           VSAT
                                                                           VSAT
                                                                                   IDU
                                                                                   IDU

         MPLS

                         HUB

                                                                     IDU    HUB     ATA
                                                                                    ATA
                                    Ku Band BSNL
                                     Ku Band
        MLLN                          Gateway,
                                     HUB/Gateway
                       VoIP                                          ATA- Analog Telephone Adapter
                                                                     ATA- Analog Telephone Adapter
                                      Bangalore

                                Fig.3 Ku band V-SAT ARCHITECTURE
          Internet router is connected to BSNL National Internet Backbone using multiple 2 Mbps leased
line. All Remote VSAT locations are having private IP so that remote VSAT users can connect to Internet.
     MLLN customers will connect directly to this routers using lease line and they will be able to access
the VSAT remote terminals. Customers may take 64 kbps or multiple of it for their main office
connectivity.
    MPLS: It will be connected to BSNL MPLS cloud using multiple 2 MB lease lines. MPLS router will
work as CE routers for the MPLS cloud.
    BSNL’s Ku Band HUB (Earth Station) at BANGALORE consists of :
    • Satellite antenna of 8.1 m – Cassegrain feed type.
    • Ku Band RF equipment and its control systems.
        GATEWAY Networking Equipment with interfaces to Terrestrial Networks like MLLN, MPLS
and NIB.


10 V-SAT SERVICES OFFERED
         The V-SAT Broad VSAT network allows secure, reliable and cost effective data, voice and video
transmission and enables an organization to deploy nationwide different services over IP using the shortest
time span.
         LEASED LINES Through V-SAT on IP PLATFORM: 4Kbps onwards
         High speed Broadband Internet
         VPN Networking
         VOIP Telephony
         Facsimile
         Telemedicine
         E-learning
         IP multicasting
         Video conferencing
          Video streaming
         Facsimile
         Distance Education
         Banking
         E-learning
         On-demand services for WAN backup/disaster recovery etc.
11 Architecture for High Speed Broadband Access
     As shown in fig.4 V-SAT (User Terminals) are capable to provide similar broadband and high speed
Internet capabilities available on terrestrial lines anywhere in India i.e. download speed of up to 4 Mbps
and maximum upload speed of up to 2 Mbps. It delivers bandwidth on demand allowing efficient use of
bandwidth making it ideal for broadband access rollout to Small and Medium Enterprises, Internet Cafes,
apartments and individual users. It allows dedicated or shared bandwidth to match the user’s requirement. It
fully supports standard Internet connection and any IP applications. VSAT broadband offers top of the line
VPN encryption for the security of your personal information and data. They also offer full services for
things like web hosting, net meeting, etc. A public IP address is assigned to both the VSAT network
module and the router satellite interface. Network Address Translation (NAT) is implemented on the
Ethernet interface of the router, so that multiple clients can be connected and use the service.
                                   Satellite




         INTERNET




                          Ku Band BSNL
                             Ku Band                                 User Terminal
                            Gateway,
                           HUB Station
                            Bangalore



                                                         User Terminal


                                                                           Internet Cafes
                                         User Terminal
                                                          HOME

Fig.4 Architecture for High Speed Broadband Access

				
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