Satellite Communication : Satellite Communication http://www.final-yearprojects.co.cc/ Satellite : Satellite A satellite is an object that orbits another object (known as its primary). The term is often used to describe an artificial satellite (as opposed to natural satellites, or moons).
Because all objects exert gravity, the motion of the primary object is also affected by the satellite. (This observation allows for the discovery of extra solar planets.) If two objects are sufficiently similar in mass, they are generally referred to as a binary system rather than a primary object and satellite. The general criterion for an object to be a satellite is that the center of mass of the two objects is inside the other object.
All masses that are part of the solar system, including the Earth, are satellites of the Sun, or satellites of those objects, such as the Moon. Why Use Satellite? : Why Use Satellite? Satellite communication is just one example of wireless communication systems. Familiar examples of wireless systems are all around us, such as radio and television broadcasting and mobile and cordless telephones. These systems rely on a network of ground-based transmitters and receivers and for this reason they are often referred to as "terrestrial" systems.
One major use of satellites familiar to everyone is satellite television broadcasting.
Other applications of satellite communications include high speed internet, telephony and corporate networks for multinational businesses. One major use of satellites familiar to everyone is satellite television broadcasting. The Satellite Communication : Satellite Communication Satellite Communication : Satellite Communication A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications using radio at microwave frequencies. Most communications satellites use geosynchronous orbits or near-geostationary orbits, although some recent systems use low Earth-orbiting satellites. A place on the ground with satellite dishes used to transmit to or receive from these is called an earth station. Slide 7: Communications satellites provide a technology that is complementary to that of fiber optic submarine communication cables. Unlike fiber optic communication, satellite communication has a propagation delay (also called a path delay) of at least 270 milliseconds, which is the time it takes the radio signal to travel 35,800 km from earth to a satellite and then back to earth. Satellite Internet connections average a 600 to 800 millisecond delay, about ten times that of a terrestrial Internet link. This delay is a challenge for highly interactive applications such as video phones, VOIP or first-person shooter online video games. Introduction : Introduction In 1962, the American telecommunications giant AT&T launched the world's first true communications satellite, called Telstar. Since then, countless communications satellites have been placed into earth orbit, and the technology being applied to them is forever growing in sophistication Frequency Bands : Frequency Bands Selection of the band : Selection of the band The selection of the band is not something that individual service providers decide, but is rather chosen by large satellite operators based on different factors:
Availability: C-band is still the most widely available worldwide. Ku-band is becoming more available recently in regions which were less covered in the past (South America, Asia, Africa)
C-band is more prone to interference from other transmission services that share the same frequencies (adjacent satellites or terrestrial transmissions) than the higher bands
While the C-band technology is cheaper in itself, it requires larger dishes (1 to 3 m) than Ku- and Ka-band (0.6 to 1.8 m) and therefore imposes relatively higher (installation) costs on the end-user Slide 11: Ku- and especially Ka-band make better use of satellite capacity
Higher frequency bands (Ku- and especially Ka-) suffer significantly more from signal deterioration caused by rainfall: to ensure availability in bad weather conditions, the signal has to be much stronger. Note that 0.1% of unavailability means in fact that the service will be interrupted for almost 9 hours over a 1-year period. 1% unavailability represents 90 hours or almost 4 full days Bands of Interest : Bands of Interest C-band is the oldest allocation and operates in the frequency range around 6 GHz for transmission (uplink) and between 3.7 and 4.2 GHz for reception (downlink).Ku-band is the most common transmission format in Europe for satellite TV and uses around 14 GHz for uplink and between 10.9 and 12.75 GHz for downlink.Ka-band uses around 30 GHz up- and between 18 and 20 GHz downlink frequency.C-band and Ku-band are becoming congested by an increasing amount of users, so satellite service operators are more and more turning to the use of Ka-band. Satellite Communications : Satellite Communications 3 Satellite Constellations: (microwave, straight line signal propogation)
Low Earth Orbit (LEO) not synchronised (600 to 1600km)
Medium Earth Orbit (MEO) not synchronised (10000Km)
Geosynchronous Earth Orbit (GEO) (35,200 km) -also known as Geostationary) The Orbits : The Orbits Orbits: GEO, MEO, LEO The GEO : The GEO The most common type of communications satellites, particularly the broadcast satellites like AfriStar, Intelsat, PanAmSat, Eutelsat and ASTRA, are in geosynchronous orbit (from geo = Earth + synchronous = moving at the same rate). That means that the satellite always stays over one spot on Earth. It does this by placing the satellite in a position 35,786 km out in space perpendicularly above the equator. Slide 16: Geostationary Earth Orbit 36,000 km Rapid deployment - instant infrastructure Affordability The MEO : The MEO A medium Earth orbit (MEO) satellite is one with an orbit from a few hundred miles to a few thousand miles above the Earth's surface. Satellites of this type are in a higher orbit than low Earth orbit (LEO) satellites, but lower than geostationary (GEO) satellites. The orbital periods (the time in between two successive passes over one particular place on Earth) of MEO satellites range from about 2 to 12 hours. The LEO : The LEO A low Earth orbit (LEO) satellite system consists of a large number of satellites each in a circular orbit at a constant altitude between 320 and 800 km. Because they orbit so close to Earth, they must travel very fast so gravity does not pull them back into the atmosphere. Satellites in LEOs circle around the Earth at 27,359 km per hour. The orbits take the satellites over the geographic poles. Each revolution takes from less than 90 minutes up to a few hours. The fleet is arranged in such a way that from any point on the surface at any time at least one satellite is in line of sight. The LEO : The LEO Types of Satellites : Types of Satellites Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects.
Communications satellites are artificial satellites stationed in space for the purposes of telecommunications using radio at microwave frequencies. Most communications satellites use geosynchronous orbits or near-geostationary orbits, although some recent systems use low Earth-orbiting satellites. Slide 21: Earth observation satellites are satellites specifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc.
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 metres in real time. Slide 22: Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications.
Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities - instead, other vehicles are used as transport to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years. Slide 23: Weather satellites are satellites that primarily are used to monitor the weather and/or climate of the Earth.
Drag-free satellites are satellites that offers an environment that is as isolated as possible from the forces of nature. A properly designed drag-free-satellite proof mass is uncoupled from the rest of the Universe to a remarkable degree.
Miniaturized_Satellites are satellites of unusually low weights and small sizes. New classifications are used to categorieze these satellites: minisatellite (500-200kg), microsatellite (below 100kg), nanosatellite (below 10kg). A Selective Communications Satellite Chronology : A Selective Communications Satellite Chronology 1945 Arthur C. Clarke Article: "Extra-Terrestrial Relays"
1955 John R. Pierce Article: "Orbital Radio Relays"
1956 First Trans-Atlantic Telephone Cable: TAT-1
1957 Sputnik: Russia launches the first earth satellite.
1960 1st Successful DELTA Launch Vehicle Slide 25: 1960 AT&T applies to FCC for experimental satellite communications license
1961 Formal start of TELSTAR, RELAY, and SYNCOM Programs
1962 TELSTAR and RELAY launched
1962 Communications Satellite Act (U.S.)
1963 SYNCOM launched
1964 INTELSAT formed
1965 COMSAT's EARLY BIRD: 1st commercial communications satellite Slide 26: 1969 INTELSAT-III series provides global coverage
1972 ANIK: 1st Domestic Communications Satellite (Canada)
1974 WESTAR: 1st U.S. Domestic Communications Satellite
1975 INTELSAT-IVA: 1st use of dual-polarization
1975 RCA SATCOM: 1st operational body-stabilized comm. satellite
1976 MARISAT: 1st mobile communications satellite Slide 27: 1976 PALAPA: 3rd country (Indonesia) to launch domestic comm. satellite
1979 INMARSAT formed.
1988 TAT-8: 1st Fiber-Optic Trans-Atlantic telephone cable Basic Elements : Basic Elements Satellite communications are comprised of 2 main components: The Satellite
The Ground Station. The Earth Station : The Earth Station The Earth Station : The Earth Station Earth station is the common name for every installation located on the Earth's surface and intended for communication (transmission and/or reception) with one or more satellites.
Earth stations include all devices and installations for satellite communications: handheld devices for mobile satellite telephony, briefcase satellite phones, satellite TV reception, as well as installations that are less familiar, eg VSAT stations and satellite broadcast TV stations.
The term Earth station refers to the collection of equipment that is needed to perform communications via satellite: the antenna (often a dish) and the associated equipment (receiver/decoder, transmitter). Earth Stations : Earth Stations High Capacity Stations - Costly, complex
Services communities large enough to require
feeder line access to the Earth Station
Mid-Capacity SES - Used by Corporations for Private Networks
Videoconferencing, electronic mail, data,
Voice Services. Each earth station can be
connected to any other station in the network.
VSAT Network - One Master Earth Station and many VSAT
terminals sharing the MES. Limited to data
transmissions, digital voice and digital video.
Receive-Only Earth Station - Voice only, Data only, TV Receive only or a
combination. The parts in the sky : The parts in the sky The two main parts in the sky common to all satellites are called the payload and the bus.Payload: transponders, antennasBus: physical platform, remote control The Payload : The Payload The payload represents all equipment a satellite needs to do its job. This can include antennas, cameras, radar and electronics.
The payload is different for every satellite. For example, the payload for a weather satellite includes cameras to take pictures of cloud formations, while the payload for a communications satellite includes large antennas to transmit TV or telephone signals to Earth. The Transponder : The Transponder The transponder is the key component for satellite communications: it is the part of the payload that takes the signals received from the transmitting Earth station, filters and translates these signals and then redirects them to the transmitting antenna on board. Communications satellites carry a large number of transponders on board (normally from six to more than 24), enabling them to deliver multiple channels of communication at the same time. These channels are called carriers. The Antenna : The Antenna Antennas that receive the original signal from the transmitting Earth station and re-transmit this signal to the receive stations on Earth.
The antennas that were used in the past to do this were omni-directional (transmitting signals in every direction) and not very effective. They were replaced by more efficient high-gain antennas (most often dish shaped) pointing quite precisely towards the areas they were servicing. The Bus : The Bus The bus is the part of the satellite that carries the payload and all its equipment into space. It is the physical platform that holds all the satellite's parts together and that provides electrical power, navigation, control and propulsion to the spacecraft. The bus also contains equipment that allows the satellite to communicate with Earth, a kind of 'remote control'. Slide 37: The GPS : The GPS The nominal GPS Operational Constellation consists of 24 satellites that orbit the earth in 12 hours. There are often more than 24 operational satellites as new ones are launched to replace older satellites. The satellite orbits repeat almost the same ground track (as the earth turns beneath them) once each day. The orbit altitude is such that the satellites repeat the same track and configuration over any point approximately each 24 hours (4 minutes earlier each day). There are six orbital planes (with nominally four SVs in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane. This constellation provides the user with between five and eight SVs visible from any point on the earth. So What is The Internet ? : So What is The Internet ? It is a complex web of networks.
Each network can have millions of inter-connected computers which use telephone infrastructure to communicate
No one ‘owns’ the Internet - Its backbone, through which information flows, is owned by a number of private companies
Messages are transmitted through the Internet via a computer language called ‘transmission control protocol - TCP/IP.
Each message travels as a packet and has a coded address which tells the network its destination and also has a block of data content Slide 42: This packet is transmitted via variety of routes
Data travels more efficiently using digital techniques
Telstra has been (slowly) digitising its public switched telephone network
How do home computers link to the Internet ?
Normally via an Internet Server Provider (ISP) - a monthly fee is charged for connection and maintenance
These ISP’s are connected to a larger network service - Network Service Providers (NSP’s) which are connected using fibre optic cable OR satellite links. Slide 43: There are about 900 ISPs operating in Australia
Telstra has a large share of the Internet wholesale market
Most ISPs are small and operate a single point presence or ‘POP’ - this is a location which comprises modems and a network connection into which an ISP’s customers dial to make an Internet connection.
High speed Internet requires ISDN Applications of SattComm : Applications of SattComm Radio and TV Broadcasting
Business radio and TV
Thin route or trunk telephony
Mobile satellite telephony
Data, broadband and multimedia services
IP over satellite for ISPs
Corporate or institutional VSAT networks
End-user services for home or small office
Mobile data communications Radio and TV Broadcasting : Radio and TV Broadcasting The most familiar use of satellites is television broadcasting. TV satellites deliver hundreds of television channels every day throughout the world. These satellites are even used to supply television signals to terrestrial transmitters or cable-head end stations for further distribution to the home, or to exchange signals between television studios. The bandwidth required to transmit multiple programmes at the same time can easily be provided using satellites. Satellite Dish Antenna : Satellite Dish Antenna The Eutelsat HotBird position at 13 Degrees East : The Eutelsat HotBird position at 13 Degrees East Business radio and TV : Business radio and TV Digital television has made it possible to distribute information within organisations and companies that are geographically dispersed, or to deliver distance education. Similarly, digital radio allows for the delivery of radio services to relatively small closed user groups. Thin route or trunk telephony : Thin route or trunk telephony Telecom operators have been using satellite communications for many years to carry long-distance telephone communications, especially intercontinental, to complement or to bypass submarine cables. To the end-user this is transparent: the phone calls are routed automatically via the available capacity at any given moment Mobile satellite telephony : Mobile satellite telephony Mobile telephony allows the user to make telephone calls and to transmit and receive data from wherever he/she is located. Digital cellular mobile telephony such as GSM has become a worldwide standard for mobile communications, but its services lack coverage over areas that are sparsely populated or uninhabited (mountains, jungle, sea), because it is not economically viable or practical for the network operators to build antennas there. Satellite telephony seems to be able to provide a possible solution to the problem of providing voice and data communications services to these other locations LEO-based telephony : LEO-based telephony Another mobile satellite communications system is the Globalstar satellite telephone network. Globalstar, which was established in 1991 and began commercial service in late 1999, offers service from virtually anywhere across over 100 countries, as well as from most territorial waters and several mid-ocean regions. Globalstar deploys handheld telephone sets that switch between the terrestrial wireless telephone network (GSM) and a LEO-based satellite network in places where no terrestrial GSM network is available. GEO-based telephony : GEO-based telephony An alternative approach to satellite telephony uses a geostationary satellite instead of the LEO. This results in longer delays (approximately half a second) but switching on board the satellite reduces this inconvenience as much as possible. The Thuraya mobile satellite system was launched in 1991, its satellite maintains a geo-synchronous orbit at 44 degrees East. Thuraya operates effectively in both satellite and GSM environments. Its satellite network capacity is about 13,750 telephone channels. When within reach of a GSM network, Thuraya's mobile phone acts as an ordinary GSM handset. Satellite Phones : Satellite Phones IP over satellite for ISPs : IP over satellite for ISPs Telecoms and connectivity providers have started using satellite communications to bypass the increasingly clogged terrestrial and submarine networks to complement their backbone connectivity or to supplement them where they are not yet available. This approach takes advantage of the fact that satellite is not a real point-to-point connection like cable, but a connection that allows the delivery to multiple points at the same time. This allows for simultaneous updating of multiple caching, proxy or mirroring servers. Slide 59: In Much the same way, it is possible to push Internet content to and even over the edges of existing networks. When it is necessary to provide large amounts of content to places that are poorly connected to the Internet, it is now possible to push content to local PoPs (Point of Presence) edge servers. These can then in turn serve as ISPs to the local users or user communities Corporate or institutional VSAT networks : Corporate or institutional VSAT networks VSAT stands for Very Small Aperture Terminal and refers to combined send/receive terminals with a typical antenna diameter of 1 to 3.7 m linking the central hub to all remote offices and facilities and keeping them all in constant immediate contact. VSAT networks offer solutions for large networks with low or medium traffic. They provide very efficient point-to-multipoint communication, are easy to install and can be expanded at low extra cost. VSAT networks offer immediate accessibility and continuous high-quality transmissions. They are adapted for any kind of transmission, from data to voice, fax and video. VSAT Star-shaped Networks : VSAT Star-shaped Networks Slide 62: A VSAT network, a corporation can communicate freely and constantly with branch offices:
Voice and fax transmissions
Local Area Network interconnection
In-house training VSAT Mesh-shaped Networks : VSAT Mesh-shaped Networks One-way Satellite Internet Connection : One-way Satellite Internet Connection Two-way Satellite Internet Connection : Two-way Satellite Internet Connection Slide 66: Thank You