Satellite Communication System

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Satellite Communication SystemD.C. Agarwal

Evolution and Growth of Communication Satellite Synchronous satellite idea was conceived by Arthur C. Clarke in 1945 He point out: satellite

in a circular equatorial orbit with a radius of about 42,242 km would have an angular velocity matching that of the earth Three satellites spaced 120 degree apart could cover the whole atmosphere Electrical power for satellite can be obtained from sun radiation by means of solar cells

History

1957

October 4, 1957: - First satellite - the Russian Sputnik 01 First living creature in space: Sputnik 02

1958

First American satellite: Explorer 01 First telecommunication satellite: This satellite broadcast a taped message: ScoreFirst meteorology satellite: Explorer 07

1959

1960 First successful passive satellite: Echo 1 First successful active satellite: Courier 1B First NASA satellite: Explorer 08 April 12, 1961: - First man in space 1962 First telephone communication & TV broadcast via satellite: Echo 1 First telecommunication satellite, first real-time active, AT&T: Telstar 1 First Canadian satellite: Alouette 1 On 7th June 1962 at 7:53p the two-stage rocket; Rehbar-I was successfully launched from Sonmiani Rocket Range. It carried a payload of 80 pounds of sodium and soared to about 130 km into the atmosphere. With the launching of Rehbar-I, Pakistan had the honour of becoming the third country in Asia and the tenth in the world to conduct such a launching after USA, USSR, UK, France, Sweden, Italy, Canada, Japan and Israel. Rehbar-II followed a successful launch on 9th June 1962 1963 Real-time active: Telstar 2 1964

1965

Intelsat 1 becomes first commercial comsat: Early Bird First real-time active for USSR: Molniya 1A First geostationary meteorology payload: ATS 3

1967

1968 First European satellite: ESRO 2B July 21, 1969: - First man on the moon

1970

First Japanese satellite: Ohsumi First Chinese satellite: Dong Fang Hong 01 First UK launched satellite: Prospero ITU-WARC for Space Telecommunications INTELSAT IV Launched INTERSPUTNIK - Soviet Union equivalent of INTELSAT formed First direct broadcasting satellite: ATS 6 MARISAT - First civil maritime communications satellite service started EUTELSAT - European regional satellite ITU-WARC for Space Telecommunications in the Satellite Service Creation of Inmarsat

1971

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1996

INMARSAT III launched - first of the multibeam mobile satellites (built by GE/Marconi) Echostar begins Diresct Broadcast Service IRIDIUM launches first test satellites ITU-WRC'97 AceS launch first of the L-band MSS Super-GSOs - built by Lockheed Martin Iridium Bankruptcy - the first major failure? Globalstar begins service Thuraya launch L-band MSS Super-GSO XM Satellite Radio begins service Pakistans 2nd Satellite, BADR-B was launched on 10 Dec 2001 at 9:15a from Baikonour Cosmodrome, Kazakistan Sirius Satellite Radio begins service Paksat-1, was deployed at 38 degrees E orbital slot in December 2002, Paksat-1, was deployed at 38 degrees E orbital slot in December 2002 Teledesic network planned to start operation Intelsat and Panamsat Merge VUSat OSCAR-52 (HAMSAT) Launched CubeSat-OSCAR 56 (Cute-1.7) Launched K7RR-Sat launched by California Politechnic University Prism was launched by University of Tokyo COMPASS-1; a project of Aachen University was launched from Satish Dawan Space Center, India. It failed to achieve orbit.

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International Regulation and Frequency Coordination

Specialized agency of UN Develop a series of radio regulations for frequency allocations Four permanent organs General

Secretariat International frequency registration board (IFRB) International radio consultative committee (CCITT) International telegraph and telephone consultative committee (CCITT)

General SecretariatLocated in GENEVA Responsible for the executive management and technical cooperation

International frequency registration board (IFRB)Responsible for recording frequencies and orbital positions For advising member countries on operation of the maximum practical number of radio channels in portions of the spectrum where harmful interference my occur

International radio consultative committee (CCITT)

Responsible for studying technical and operational questions relating to radio communication, Reports,

recommendations, resolutions and decisions published

International telegraph and telephone consultative committee (CCITT)

Responsible for studying technical, operational and tariff questions relating to telegraphy and telephony and for adopting reports and recommendations

World Administrative Radio Conference (WARC)

Held in 1979 Allocation of frequency bands for satellite communications Describes various satellite services under 17 categories 1. Aeronautical Mobile Satellite 2. Aeronautical Radio navigation Satellite 3. Amateur Satellite 4. Broadcasting Satellite 5. Earth-exploration Satellite 6. Fixed Satellite 7. Inter-satellite 8. Land Mobile Satellite 9. Maritime Mobile Satellite 10. Maritime Radio navigation Satellite 11. Meteorological Satellite 12. Mobile Satellite 13. Radio determination 14. Radio navigation Satellite 15. Space Operations 16. Space Research 17. Standard Frequency and time signaling Satellite

WARC also Divided globe into three geographic regions for the purpose of frequency allocations Region

1

Europe, Africa, USSR and Mongolia

Region

2

North and South America and Greenland

Region

3

Asia, Australia and southwest pacific

Satellite Frequency Allocations and Band SpectrumBand Downward bands MHz 250 270 (approx) 3700 4200 7250 7750 11700 12200 17,700 21200 20200 21200

Uplink Bands MHz 292 312 (Approx) 5925 8400 7900 8400 14000 14500 27500 30,000 43500 - 45500

Six frequency bands allocated for the use satellite communications

Uhf Military C Band Commercial X Band Military Ku Band Commercial Ka Band Commercial Ka Band Military

Characteristics of a satellite system

Satellite in space links earth stations User is connected to earth station through terrestrial network (telephone switch or a dedicated link to the earth) The user generates baseband signal that is processed and transmitted to the satellite (received rf carriers) at the earth station Uplink (signal transmitted from earth to satellite) and downlink (signal received from satellite to earth station) Uplink and down link frequency spectrum is different in order to avoid interference

Advent of Digital Satellite Communication

Ease and efficiency of multiplexing multiple signals or handling digital messages in packets for convenient switching The relative insensitivity of digital circuits to retransmission noise, commonly a problem with analog system Potential for extremely low error rates and high fidelity through error detection and correction Communication privacy Flexibility of digital hardware implementation which permits the use of microprocessors and miniprocessors, digital switching and the use of large scale ICs.

Modulation technique

Analog communication system uses FDMM-FM-FDMA has been widely used and provided good quality satellite links

But no of earth station is limited

Digital satellite system uses QPSK-TDMA,

which accommodate large no. of earth stations with small loss in transponder capacity. Quickly respond to traffic variations

Recent technique is CDMA

Allowed micro earth station (0.5m antenna) Extremely low cost Provides good quality service Further enhance the importance of digital communication networking with satellite

ISDN

Active and Passive satellites

Comparison of the comm capability of active and passive satellite is the amount of power radiated toward the receiving ground station by the satellie. Passive satellite

The ground transmitting system beams power at the reflector. Receiving ground system receives a fraction of power that has been intercepted by the reflector and reradiated Receives a fraction of the energy beamed towards it by the ground transmitting system and the received power is amplified by active electronic mean.

Active satellite

Comm capability is much greater in active systems with directional antennas than passive satellite as the altitude is increased Passive systems are advantages for military systems Modern comm satellites are active systems

Long life electronic equipment are available and these have enhanced the capability of active satellite system

Advantages of Satellite Communication

Satellite relays are inherently wide area broadcast

Point to multipoint

Where terrestrial links are point to point

Satellite circuits can be installed rapidly

Once satellite is in position, earth stations can be installed and communication my be established in days or even hours Station my be removed relatively quickly from one location and reinstalled elsewhere

Mobile communicationUnique degree of flexibility in interconnecting mobile vehicles

Terrestrial networks interconnect mobiles vehicles by cellular radios.

Economical advantages Satellite

costs are independent of distance, where terrestrial network costs are proportional to distance Compared to fiber optic cable,

Quality of transmitted signal and locations of stations sending and receiving information are independent of distance

As long as two stations a