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    Satellite Communication: Anuj Dandona

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    anujdandona
    Satellite communication uses satellites as relay stations to transmit signals between two earth stations that are too far for conventional terrestrial communication. Satellites receive uplink signals from one station and transmit downlink signals to the other. Satellites offer advantages like global coverage and independence from transmission distance, but also have disadvantages like high launch costs and limited bandwidth. Different types of satellite orbits like GEO, LEO, and MEO are used depending on the application. GEO satellites remain fixed over one spot but have weak signals, while LEO and MEO satellites provide stronger signals but require more satellites for coverage.

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    Satellite Communication: Anuj Dandona

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    anujdandona
    59 views22 pages
    Satellite communication uses satellites as relay stations to transmit signals between two earth stations that are too far for conventional terrestrial communication. Satellites receive uplink signals from one station and transmit downlink signals to the other. Satellites offer advantages like global coverage and independence from transmission distance, but also have disadvantages like high launch costs and limited bandwidth. Different types of satellite orbits like GEO, LEO, and MEO are used depending on the application. GEO satellites remain fixed over one spot but have weak signals, while LEO and MEO satellites provide stronger signals but require more satellites for coverage.

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    Satellite communication uses satellites as relay stations to transmit signals between two earth stations that are too far for conventional terrestrial communication. Satellites receive uplink signals from one station and transmit downlink signals to the other. Satellites offer advantages like global coverage and independence from transmission distance, but also have disadvantages like high launch costs and limited bandwidth. Different types of satellite orbits like GEO, LEO, and MEO are used depending on the application. GEO satellites remain fixed over one spot but have weak signals, while LEO and MEO satellites provide stronger signals but require more satellites for coverage.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    59 views22 pages

    Satellite Communication: Anuj Dandona

    Uploaded by

    anujdandona
    Satellite communication uses satellites as relay stations to transmit signals between two earth stations that are too far for conventional terrestrial communication. Satellites receive uplink signals from one station and transmit downlink signals to the other. Satellites offer advantages like global coverage and independence from transmission distance, but also have disadvantages like high launch costs and limited bandwidth. Different types of satellite orbits like GEO, LEO, and MEO are used depending on the application. GEO satellites remain fixed over one spot but have weak signals, while LEO and MEO satellites provide stronger signals but require more satellites for coverage.

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    of 22

    Satellite Communication

    Anuj Dandona

    Overview

    Basics of Satellite Types of Satellite Capacity Allocation

    Basics: How do Satellites Work

    Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means. The two stations can use a satellite as a relay station for their communication One Earth Station sends a transmission to the satellite. This is called a Uplink. The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink.

    Basics: Advantages of Satellites

    The advantages of satellite communication over terrestrial communication are:


    The coverage area of a satellite greatly exceeds that of a terrestrial system. Transmission cost of a satellite is independent of the distance from the center of the coverage area. Satellite to Satellite communication is very precise. Higher Bandwidths are available for use.

    Basics: Disadvantages of Satellites

    The disadvantages of satellite communication:


    Launching satellites into orbit is costly. Satellite bandwidth is gradually becoming used up. There is a larger propagation delay in satellite communication than in terrestrial communication.

    Basics: Factors in satellite communication

    Elevation Angle: The angle of the horizontal of the earth surface to the center line of the satellite transmission beam.

    This effects the satellites coverage area. Ideally, you want an elevation angle of 0 degrees, so the transmission beam reaches the horizon visible to the satellite in all directions. However, because of environmental factors like objects blocking the transmission, atmospheric attenuation, and the earth electrical background noise, there is a minimum elevation angle of earth stations.

    Basics: Factors in satellite communication (cont.)

    Coverage Angle: A measure of the portion of the earth surface visible to a satellite taking the minimum elevation angle into account. R/(R+h) = sin(/2 - - )/sin( + /2) = cos( + )/cos()
    R = 6370 km (earths radius) h = satellite orbit height = coverage angle = minimum elevation angle

    Basics: Factors in satellite communication (cont.)

    Other impairments to satellite communication:

    The distance between an earth station and a satellite (free space loss). Satellite Footprint: The satellite transmissions strength is strongest in the center of the transmission, and decreases farther from the center as free space loss increases. Atmospheric Attenuation caused by air and water can impair the transmission. It is particularly bad during rain and fog.

    Basics: How Satellites are used

    Service Types

    Fixed Service Satellites (FSS)

    Example: Point to Point Communication Example: Satellite Television/Radio Also called Direct Broadcast Service (DBS). Example: Satellite Phones

    Broadcast Service Satellites (BSS)


    Mobile Service Satellites (MSS)

    Types of Satellites

    Satellite Orbits

    GEO LEO MEO Molniya Orbit HAPs

    Frequency Bands

    Geostationary Earth Orbit (GEO)


    These satellites are in orbit 35,863 km above the earths surface along the equator. Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth.

    GEO (cont.)

    Advantages

    A GEO satellites distance from earth gives it a large coverage area, almost a fourth of the earths surface. GEO satellites have a 24 hour view of a particular area. These factors make it ideal for satellite broadcast and other multipoint applications.

    GEO (cont.)

    Disadvantages

    A GEO satellites distance also cause it to have both a comparatively weak signal and a time delay in the signal, which is bad for point to point communication. GEO satellites, centered above the equator, have difficulty broadcasting signals to near polar regions

    Low Earth Orbit (LEO)

    LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 1,500 km above the surface. LEO satellites dont stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass. A network of LEO satellites is necessary for LEO satellites to be useful

    LEO (cont.)

    Advantages

    A LEO satellites proximity to earth compared to a GEO satellite gives it a better signal strength and less of a time delay, which makes it better for point to point communication. A LEO satellites smaller area of coverage is less of a waste of bandwidth.

    LEO (cont.)

    Disadvantages

    A network of LEO satellites is needed, which can be costly LEO satellites have to compensate for Doppler shifts cause by their relative movement. Atmospheric drag effects LEO satellites, causing gradual orbital deterioration.

    Medium Earth Orbit (MEO)


    A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the earths surface. MEO satellites are similar to LEO satellites in functionality. MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours. MEO satellites have a larger coverage area than LEO satellites.

    MEO (cont.)

    Advantage

    A MEO satellites longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network. A MEO satellites distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite.

    Disadvantage

    Other Orbits

    Molniya Orbit Satellites


    Used by Russia for decades. Molniya Orbit is an elliptical orbit. The satellite remains in a nearly fixed position relative to earth for eight hours. A series of three Molniya satellites can act like a GEO satellite. Useful in near polar regions.

    Other Orbits (cont.)

    High Altitude Platform (HAP)

    One of the newest ideas in satellite communication. A blimp or plane around 20 km above the earths surface is used as a satellite. HAPs would have very small coverage area, but would have a comparatively strong signal. Cheaper to put in position, but would require a lot of them in a network.

    Frequency Bands

    Different kinds of satellites use different frequency bands.


    LBand: 1 to 2 GHz, used by MSS S-Band: 2 to 4 GHz, used by MSS, NASA, deep space research C-Band: 4 to 8 GHz, used by FSS X-Band: 8 to 12.5 GHz, used by FSS and in terrestrial imaging, ex: military and meteorological satellites Ku-Band: 12.5 to 18 GHz: used by FSS and BSS (DBS) K-Band: 18 to 26.5 GHz: used by FSS and BSS Ka-Band: 26.5 to 40 GHz: used by FSS

    Thank You

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