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Lecture 4: Satellite Communication

Lecture 4: Satellite Communication. Introduction. In general terms, a satellite is a smaller object that revolves around a larger object in space . Ex. moon is a natural satellite of earth .

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Lecture 4: Satellite Communication

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  1. Lecture 4: Satellite Communication

  2. Introduction • In general terms, a satellite is a smaller object that revolves around a larger object in space. Ex. moon is a natural satellite of earth. • Communication refers to the exchange (sharing) of information between two or more entities, through any medium or channel. • If the communication takes place between any two earth stations through a satellite,  satellite communication • It is helpful in telecommunications, radio and television along with internet applications.

  3. Need of Satellite Communication • In the satellite communication, satellites provide communication for long distances, which is well beyond the line of sight. • Ground wave and Sky wave propagation: The maximum hop or the station distance is limited to 1500KM • Satellite communication overcomes this limitation

  4. Satellite Network • A satellite network is a combination of nodes, some of which are satellites, that provides communication from one point on the Earth to another. • A node in the network can be a satellite, an Earth station, or an end-user terminal or telephone

  5. Communication Satellite • Communications satellite is an artificial satellite stationed in space for the purpose of telecommunications. • It is nothing but a microwave repeater station in space. • A repeater is a circuit, which increases the strength of the received signal and then transmits it. But, this repeater works as a transponder. • That means, it changes the frequency band of the transmitted signal from the received one.

  6. Uplink and Downlink Channels and Frequency

  7. Uplink and Downlink Channels and Frequency • Uplink the link or channel from earth station up to a satellite. • Downlink the link or channel from a satellite down to one or more earth station. • Uplink frequency is the frequency at which, the first earth station is communicating with satellite. • The satellite transponder converts this signal into another frequency and sends it down to the second earth station. This frequency is called as Downlink frequency

  8. Frequency Bands for Satellite Communication • The frequencies reserved for satellite microwave communication are in the gigahertz (GHz) range. • The following table gives the band names and frequencies for each range

  9. Satellite's Footprint • Satellite's footprint is the area which receives a signal of useful strength from the satellite. • The signal power at the center of the footprint is maximum. • The power decreases as we move out from the footprint center. • The boundary of the footprint is the location where the power level is at a predefined threshold.

  10. Satellite's Footprint • There are two types of footprint: moving foot print and fixed footprint ( fixed only for a period of time).

  11. Orbits • The path of satellite revolving around the earth is known as orbit • The orbit can be equatorial, inclined, or polar

  12. Categories of Satellites • Based on the location of the orbit, satellites can be divided into three categories: geostationary Earth orbit (GEO), low-Earth-orbit (LEO), and middle-Earth-orbit (MEO)

  13. Categories of Satellites • The following figure shows the satellite altitudes with respect to the surface Below an altitude of 2000 km

  14. GEO Earth Orbit Satellites • A satellite in a geostationary orbit appears to be in a fixed position to an earth-based observer. • A geostationary satellite revolves around the earth at the same angular velocity of the earth itself, 360 degrees every 24 hours in an equatorial orbit, and therefore it seems to be in a fixed position over the equator.

  15. GEO Earth Orbit Satellites • To provide full global transmission, a minimum of three satellites equidistant from each other is needed. • GEO Satellites are used for weather forecasting, satellite TV, satellite radio and other types of global communications.

  16. MEO Satellites • Medium-Earth-orbit (MEO) satellites are positioned between the two Van Allen belts. • A satellite at this orbit takes approximately 6-8 hours to circle the Earth. • Signals transmitted from a MEO satellite travel a shorter distance. • the signal strength is good  smaller and light weight receiving terminals. • Ten or more MEO satellites are required in order to cover entire earth. • One example of a MEO satellite system is the Global Positioning System (GPS)

  17. MEO Satellites -- GPS • Constructed and operated by the US Department of Defense. • Orbiting at an altitude about 18,000 km (11,000 mi) above the Earth. • The system consists of 24 satellites in six orbits. • are designed in such a way that, at any time, four satellites are visible from any point on Earth • is used for land, sea, and air navigation to provide time and locations for vehicles and ships.

  18. LEO Satellites • Low-Earth-orbit (LEO) satellites have polar orbits. • The altitude is between 500 and 2000 km, with a rotation period of 90 to 120 min. • The satellite has a speed of 20,000 to 25,000 km/h. • The footprint normally has a diameter of 8000 km. • Because LEO satellites are close to Earth, the round-trip time propagation delay is normally less than 20 ms, which is acceptable for audio communication

  19. LEO Satellites • LEO satellites are mainly classified into three categories:little LEOs, big LEOs, and Mega-LEOs. • The little LEOs operate under 1 GHz. They are mostly used for low-data-rate messaging. • The big LEOs operate between 1 and 3 GHz. • Mega-LEOs operates in the 20-30 GHz range. They are mostly used for of real-time, low delay video transmission

  20. Pros of Satellite Communication • Following are the advantages of using satellite communication: •  Area of coverage is more than that of terrestrial systems •  Each and every corner of the earth can be covered •  Transmission cost is independent of coverage area •  More bandwidth and broadcasting possibilities

  21. Cons of Satellite Communication • Following are the disadvantages of using satellite communication: •  Launching of satellites into orbits is a costly process. •  Propagation delay of satellite systems is more than that of conventional terrestrial systems. •  Difficult to provide repairing activities if any problem occurs in a satellite system. •  Free space loss is more. •  There can be congestion of frequencies.

  22. Applications of Satellite Communication • Radio broadcasting and voice communications • TV broadcasting such as Direct To Home (DTH) • Internet applications such as providing Internet connection for data transfer, GPS applications, Internet surfing, etc. • Military applications and navigations • Remote sensing applications • Weather condition monitoring & Forecasting

  23. Any Questions?

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