Satellite Communication Theory

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Satellite Communication Theory

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1. 1. SATELLITE COMMUNICATION by Naveen Jakhar, ITS
2. 2. Indian Space Research Organization  Design and development of satellites for earth observation, communication, navigation, meteorology and space science ; design of launch vehicles .  Indian National Satellite (INSAT) programme for meeting telecommunication, television broadcasting and developmental applications.  Indian Remote Sensing Satellite (IRS) programme for management of natural resources and monitoring of environment using space based imagery.  Space based Applications for Societal development and Disaster Management Support.
3. 3. Communication Satellites  Indian National Satellite (INSAT) -largest domestic communication satellite systems in Asia-Pacific region .  Established in 1983 with commissioning of INSAT-1B.  Currently operational communication satellites are INSAT-3A, INSAT-3C, INSAT-3E, INSAT-4A, INSAT-4B, INSAT-4CR, GSAT-8, GSAT-10 and GSAT-12.  Total of 195 transponders in the C, Ext C and Ku-bands provide service to telecommunications, television broadcasting, satellite news gathering, societal applications, weather forecasting, disaster warning and Search & Rescue operations.
4. 4. Communication Satellites Launch Date Launch Mass Power Launch Vehicle GSAT-16 Dec 07, 2014 3181.6 kg (GSO) 6000 Watts Ariane-5 VA-221 GSAT-14 Jan 05, 2014 1982 kg 2600 W GSLV-D5 GSAT-7 Aug 30, 2013 2650 kg 3,000 W Ariane-5 VA-215 INSAT-3D Jul 26, 2013 2060 Kg 1164 W Ariane-5 VA-214 GSAT-10 Sep 29, 2012 3400 kg 6474 Watts Ariane-5 VA-209 GSAT-12 Jul 15, 2011 1410 kg 1430 Watts PSLV-C17 GSAT-8 May 21, 2011 3093 kg 6242 Watt Ariane-5 VA-202 GSAT-5P Dec 25, 2010 2310 kg GSLV-F06 GSAT-4 Apr 15, 2010 2220 Kg GSLV-D3 INSAT-4CR Sep 02, 2007 2,130 kg 3000 W GSLV-F04 INSAT-4B Mar 12, 2007 3025 Kg 5859 W Ariane5
5. 5. GSAT -16  Advanced communication satellite, positioned at 55 deg East longitude in the Geostationary orbit .  The designed on-orbit operational life of GSAT-16 is 12 years.  GSAT-16 is configured to carry a total of 48 communication transponders –  24 Nos. in C-band  12 Nos. in Ext C-band  12 Nos. in Ku-band All transponders of 36MHz bandwidth Footprint covers Indian mainland and Andaman & Nicobar islands  GSAT-16 carries a Ku-band beacon to help accurately point ground antennas towards the satellite.
6. 6. GSAT – 10  Communication satellite, configured to carry 30 transponders & GPS Aided GEO Augmented Navigation (GAGAN) payload.  GAGAN payload provides Satellite-based Navigation services with accuracy required for civil aviation applications.  Transponders –  12 Nos. in Ku-band  12 Nos. in C-band  6 nos. in Ext C-band Each with 36 MHz usable bandwidth Footprint covering Indian mainland and islands.
7. 7. GSAT -8  Communication satellite  Configured to carry  24 high power transponders in Ku-band and  two-channel GPS Aided Geo Augmented Navigation (GAGAN) payload
8. 8. Earth Observation Satellites  Starting with IRS-1A in 1988, ISRO has launched many remote sensing satellites.  Eleven operational satellites are in orbit – RESOURCESAT-1 and 2, CARTOSAT-1, 2, 2A, 2B, RISAT-1 and 2, OCEANSAT-2, Megha-Tropiques and SARAL.  Data from these satellites is used for applications covering agriculture, water resources, urban planning, rural development, mineral prospecting, environment, forestry, ocean resources and disaster management.
9. 9. Earth Observation Satellites Launch Date Launch Mass Power Launch Vehicle Orbit Type SARAL Feb 25, 2013 407 kg 906 W PSLV-C20 LEO RISAT-1 Apr 26, 2012 1858 kg 2200 W PSLV-C19 LEO Megha- Tropiques Oct 12, 2011 1000 kg 1325 W PSLV-C18 LEO RESOURCESAT- 2 Apr 20, 2011 1206 kg 1250 W PSLV-C16 LEO CARTOSAT – 2B Jul 12, 2010 694 kg 930 W PSLV-C15 LEO Oceansat-2 Sep 23, 2009 960 kg 1360W PSLV-C14 LEO RISAT-2 Apr 20, 2009 300 kg PSLV-C12 LEO IMS-1 Apr 28, 2008 83 kg 220 W PSLV-C9 LEO CARTOSAT – 2A Apr 28, 2008 690 Kg 900 W PSLV-C9 LEO
10. 10. Experimental SatellitesISRO has launched many small satellites for experimental purposes – Remote Sensing, Atmospheric Studies, Payload Development, Orbit Controls, recovery technology etc. Launch Date Launch Mass Power Launch Vehicle Orbit Type SRE – 1 Jan 10, 2007 550 kg Apple Jun 19, 1981 670 kg 210 Ariane -1(V- 3) GSO RS-1 Jul 18, 1980 35 kg 16 Watts RTP Aug 10, 1979 35 kg Aryabhata Apr 19, 1975 360 kg 46 Watts
11. 11. Satellite Navigation service  ISRO is establishing the Indian Regional Navigation Satellite System (IRNSS) to meet user requirements of the positioning, navigation and timing based on independent satellite navigation system.  Space Segment consists of seven satellites. All satellites will be visible at all times in the Indian region.  Ground Segment provides monitoring of the constellation status, computation of the orbital , clock parameters and navigation data uploading.
12. 12. Satellite Navigation service Launch Date Launch Mass Power Launch Vehicle Orbit Type Application IRNSS 1D Mar 28, 2015 PSLV-C27 GSO Navigation IRNSS 1C Nov 10, 2014 Navigation IRNSS-1B Apr 04, 2014 1432 kg 1660 W PSLV-C24 Navigation IRNSS-1A Jul 01, 2013 1425 kg 1660 W PSLV-C22 Navigation
13. 13. Scientific & Exploration  Research in areas like astronomy, astrophysics, planetary and earth sciences, atmospheric sciences and theoretical physics.  A series of sounding rockets are available for atmospheric experiments.  Several scientific instruments have been flown on satellites especially to direct celestial X-ray and gamma-ray bursts.
14. 14. Mars Orbiter Mission  India’s first interplanetary mission to planet Mars with an orbiter craft designed to orbit Mars in an elliptical orbit.  Configured to carry out observation of physical features of Mars and limited study of Martian atmosphere .  Payloads  Mars Colour Camera (MCC)  Thermal Infrared Imaging Spectrometer (TIS)  Methane Sensor for Mars (MSM)  Mars Exospheric Neutral Composition Analyser (MENCA)  Lyman Alpha Photometer (LAP)
15. 15. Chandrayaan-1  India’s first mission to Moon, was launched successfully on October 22, 2008 from Sriharikota.  The spacecraft was orbiting around the Moon at a height of 100 km from the lunar surface for chemical, mineralogical and photo-geologic mapping of the Moon.  After the successful completion of all the major mission objectives, the orbit has been raised to 200 km during May 2009.
16. 16. Small Satellites  To provide platform for stand-alone payloads for earth imaging and science missions . Indian Mini Satellite -1 (IMS-1)  IMS-1 bus – developed with payload capability of 30 kg.  First mission of the IMS-1 series was launched in 2008 as co-passenger along with Cartosat 2A. Indian Mini Satellite -2 (IMS-2) Bus  IMS-2 Bus – payload capability of around 200kg. The
17. 17. Small Satellites Launch Date Launch Mass Power Launc h Vehicl e Orbit Type Applicat ion SARAL Feb 25, 2013 407 kg 906 W PSLV- C20 LEO Earth Observat ion YOUTH SAT Apr 20, 2011 92 kg Solar Array genera ting 230 W, one 10.5 AH PSLV- C16
18. 18. Student Satellites Universities and educational institutions can venture into space technology :  Development of Payload Development of payloads may comprise of detectors, electronics and associated algorithms – experimental payload on the ISRO’s on-going projects.  Satellite Design & Fabrication by Universities/Institutions Universities can design, fabricate, test the satellite Bus & Payload and deliver the integrated spacecraft
19. 19. Student Satellites Launch Date Launch Mass Power Launch Vehicle Jugnu Oct 12, 2011 3 kg SRMSat Oct 12, 2011 10.9 kg YOUTHSA T Apr 20, 2011 92 kg Solar Array generatin g 230 W, one 10.5 AH Li-ion battery PSLV-C16 STUDSAT Jul 12, 2010 Less than 1 kg ANUSAT Apr 20, 40 kg
20. 20. SATELLITE LINK
21. 21. Satellite Communication  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.
22. 22. Satellite Comm v/s Terrestrial Comm  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.
23. 23. Disadvantages of Satellites  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.
24. 24. Satellite Communication – Services  Fixed Service Satellites (FSS) • Example: Point to Point Communication  Broadcast Service Satellites (BSS) • Example: Satellite Television/Radio called Direct Broadcast Service (DBS)/DTH.  Mobile Service Satellites (MSS) • Example: Satellite Phones
25. 25. Frequency Bands 9/13/201 6 Overview of Satellite Communications 25 Band Freq range Applications 1. VLF 10-30 KHz World wide Telegraphy 2. LF 30-300 KHz Marine & Navigation 3. MF 300-3000 KHz MW & SW Broadcasting 4. HF 3-30 MHz 5. VHF 30-300 MHz MARR, TV Radar, Aero plane, Navigation 6. UHF 300-3000 MHz TV, UHF 7. SHF (Super High Freq.) 3-30 GHz Microwave & Satellite 8. EHF (Extremely High Freq.) 30-300 GHz Experimental
26. 26. 9/13/201 6 Overview of Satellite Communications 26 M/W Frequency Bands  L 1-2 GHz  S 2-4 GHz  C 4-8 GHz  X 8-12 GHz  Ku 12-18 GHz  K 18-27 GHz  Ka 27-40 GHz  V 40-75 GHz  W 75-110 GHz  mm 110-300 GHz
27. 27. 9/13/201 6 Overview of Satellite Communications 27 C- Band : U/L : 5.925 – 6.425 GHz. D/L : 3.7 – 4.2 G Hz. Total 500 MHz BW. Frequency Bands For Satellite Communication Extended C- Band : U/L : 6.725 – 7.025 GHz. D/L : 4.5 – 4.8 G Hz. Additional 300 MHz BW.
28. 28. C-Band  C-band is mostly used for fixed services such as PSTN, Internet Trunking and mobile feeder links.  Transmissions are immune to atmospheric conditions such as snow and rain.  Earth Station antennas are large – typically 4.5 to 18 m in diameter.
29. 29. 9/13/201 6 Overview of Satellite Communications 29 Frequency Bands For Satellite Communication Ku band : U/L : 14.0 – 14.5 G Hz. D/L : 10.95 – 11.2 and 11.45 – 11.7 GHz. A total of 500 MHz BW in Ku band.
30. 30. Ku-Band  Generally used for fixed services such as Very Small Aperture Terminal (VSAT), corporate networks and small businesses that use a small transceiver linked to satellite .  Ku-band serves Internet trunking and video distribution applications.  Earth Stations are smaller as compared to C-band, with antenna diameter of 4 m or less.
31. 31. Ku band  Higher frequency of Ku-band makes it more susceptible to adverse weather conditions than C-band. Ku-band is generally offered in “Spot” beams.  Applications include VSAT, rural telephony, satellite news gathering, Videoconferencing and multimedia services.
32. 32. Ka -band  Ka-band operates in the 18-30 GHz range largely for broadband applications.  Used for high-bandwidth interactive services such as high-speed Internet, videoconferencing and multimedia applications.  Ka-band transmissions are even more sensitive to poor weather conditions than Ku-band.
33. 33. Beams  Satellites support a variety of “beam” types to allow the satellite to focus its power at different levels to particular locations.  This provides a trade-off between the size of the geographic area in which signals can be received and the amount of power used to send or receive the signal.  Beam types supported: C-Band Global C-Band Zone C-Band Hemi Ku-Band Spot
34. 34. “Global” beam  Radiated power of the satellite beam is directed at the equator and spreads outward.  Global beam provides widespread coverage but provides less power. This means that a larger antenna must be used with a global beam.  Used by carriers who require multiple points within coverage area and have access to a large antenna.
35. 35. Other Beams  Some satellite beams direct the satellite’s power to specific areas. These are called “Hemi,” “Zone” and “Spot” beams.  Hemi and Zone beams essentially offer approximately one half and one quarter of the coverage of a global beam, respectively.  Spot beams – in Ku band .They provide more power and, therefore, very small, low- cost antennas can be used. This makes it an excellent solution for corporate network applications.
36. 36. The Orbits 9/13/201 6 Overview of Satellite Communications 36
37. 37. 9/13/201 6 Overview of Satellite Communications 37 Earth Orbits for Satellites Orbit Definition Altitude Range (km) Period (Hours) (above surface of the earth) LEO 150 to 1,000 1.5 to 1.8 MEO 5,000 to 10,000 3.5 to 6 GEO 36,000 24  Geo-stationary Satellite: Precisely 35,768 km in the plane of the equator  Delay approx 240msec
38. 38. Geostationary Earth Orbit (GEO)  These satellites are in orbit 35,768 km above the earth’s surface along the equator.  Satellite in Geostationary orbit revolves 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.
39. 39. Geostationary Earth Orbit
40. 40. EARTHEARTH 36,000Km PERIOD 24 HRS EQUATOR GEO-STATIONARY ORBIT GLOBAL COVERAGE WITH GEOSTATIONARY SATELLITES CLARKE’S CONCEPT THE EARTH
41. 41. Geostationary Earth Orbit (GEO) Advantages  A GEO satellite’s distance from earth gives it a large coverage area.  GEO satellites have a 24 hour view of a particular area.  These factors make it ideal for satellite broadcast and other multipoint applications.
42. 42. Geostationary Earth Orbit (GEO) Disadvantages  A GEO satellite’s distance to earth causes 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.
43. 43. Geostationary Orbit (GEO)  The orbit is circular. The orbit is in equatorial plane i.e. directly above the equator and thus inclination is zero. There is ONLY one geostationary orbit.  The angular velocity of the satellite is equal to angular velocity of earth.  Period of revolution is equal to period of rotation of earth. Finish one revolution around the earth in exactly one day i.e. 23 hours, 56 Minutes and 4.1 seconds .  If the satellite is moving in the circular-equatorial orbit and its angular velocity is equal to earth’s angular velocity, the satellite is said to be moving along with the earth. This
44. 44. Geosynchronous Orbit  The orbit is NOT circular. The orbit is NOT in equatorial plane but it’s in inclined orbit. There are many geosynchronous orbits.  The angular velocity of the satellite is equal to angular velocity of earth.  Period of revolution is equal to period of rotation of earth i.e. one revolution around the earth in exactly one day i.e. 23 hours, 56 Minutes and 4.1 seconds. Yet it does NOT appear stationary from the earth. It looks oscillating but NOT stationary and that is why it is called Geosynchronous.  It is practically NOT possible to achieve an absolute
45. 45. Low Earth Orbit (LEO)  Satellites are much closer to the earth than GEO satellites, ranging from 500 to 1,500 km above the surface.  Satellites don’t stay in fixed position relative to the earth 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.
46. 46. Low Earth Orbit (LEO) •IRIDIUM with 66 satellites •GLOBALSTAR with 48 satellites
47. 47. Low Earth Orbit (LEO) Advantages  Satellite’s proximity to earth compared to a GEO satellite provides better signal strength and less time delay, which makes it better for point to point communication.  LEO satellite’s smaller area of coverage is less of a waste of bandwidth.
48. 48. Low Earth Orbit (LEO) Disadvantages  A network of LEO satellites is needed, which can be costly.  LEO satellites have to compensate for Doppler shifts caused by their relative movement.  Atmospheric drag affects LEO satellites, causing gradual orbital deterioration.  Low lifetime 5-7 years.  Highest rate of deposition of orbital debris.
49. 49. Low Earth Orbit (LEO)  Circular/slightly elliptical orbit under 2000 km  Orbit period ranges from 1.5 to 2 hours  Diameter of coverage is about 8000 km  Round-trip signal propagation delay less than 20 ms  Maximum satellite visible time up to 20 min  System must cope with large Doppler shifts  Atmospheric drag results in orbital deterioration
50. 50. MEO Satellite Characteristics  Circular orbit at an altitude in the range of 5000 to 12,000 km  Orbit period of 6 hours  Diameter of coverage is 10,000 to 15,000 km  Round trip signal propagation delay less than 50 ms  Maximum satellite visible time is a few hours
51. 51. Medium Earth Orbit (MEO) •ICO with 10 satellites
52. 52. Medium Earth Orbit (MEO)  Advantage : Satellite’s longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network.  Disadvantage : MEO satellite’s distance causes longer time delay and weaker received signal than a LEO satellite, though not as bad as a GEO satellite.
53. 53. Other Orbits  Molniya Orbit Satellites  Used by Russia for decades.  Elliptical orbit. The satellite remains in a nearly fixed position relative to earth for eight hours.  Three Molniya satellites can act like a GEO satellite.  Useful in near polar regions.
54. 54. Other Orbits  High Altitude Platform (HAP)  New idea in satellite communication.  A blimp or plane around 20 km above the earth’s 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.
55. 55. 9/13/201 6 Overview of Satellite Communications 56 Communication Satellite i) Communication Subsystem – consisting of a) Transmit/ Receive Antenna. b) Communication Transponders ii) Support Sub-system – consisting of a) Structure b) Attitude and Orbit Control System (AOCS) – AOCS is needed to get the satellite into the correct orbit and keep it there. c) Propulsion system d) Electric Power System e) Thermal control f) Telemetry and Tele-command system
56. 56. 9/13/201 6 Overview of Satellite Communications 57 A communication subsystem consists of – Antennas : Transmit and receive over wide range of microwave frequencies. Transponders : A set of transmitters and receivers that amplify and retransmit the incoming signal. Communication Subsystem A Transponder consists of a band pass filter, a down converter and an output amplifier.
57. 57. Support Subsystem
58. 58. 9/13/201 6 Overview of Satellite Communications 59 Satellites operating in C- band carry 12 transponders. 36 MHz is widely used as transponder bandwidth, 54 and 72 MHz adopted for some satellites.(36 MHz can carry 9000 voice channels) 24 transponders can be accommodated in 500 MHz BW through frequency reuse by orthogonal polarizations. Transponders 6 more Transponders ( Tx no. 13 to 18 ) are present in additional 300 MHz band in the extended C-band in INSAT systems. The narrower bandwidth is preferred for the transponder to avoid inter-modulation distortion likely to occur when high power amplifier ( TWT) is driven close to saturation.
59. 59. Satellite Earth Station  Earth Stations are used to communicate with satellites.  When a satellite is within an Earth Station’s line of sight, the earth station is said to have a view of the satellite.  It is possible for a satellite to communicate with more than one Earth Station at a time.  An Earth Station that follows a satellite not in geostationary orbit, is called a tracking station.  Earth stations use dish-shaped antenna. Diameter varies depending upon the applications, Space segment ,frequency band etc.9/13/201 6 Overview of Satellite Communications 60
60. 60. 9/13/201 6 Overview of Satellite Communications 61 Satellite Footprint Downlink EIRP (Effective Isotropic Radiated Power) is 32 dbw at Beam center. The footprint of a satellite is the ground area that its transponders offer coverage. Primary Coverage Area – 3 db contour EIRP 32 dbw . Secondary Coverage Area – 6 db contour EIRP 29 dbw Tertiary Coverage Area – 9 db contour EIRP 26 dbw
61. 61. 9/13/201 6 Overview of Satellite Communications 62 Satellite footprint on Asia Pacific Region
62. 62. INMARSAT  International Maritime Satellite Organisation – a satellite communications network for the maritime community.  The name was later changed to “International Mobile Satellite Organization” when it began to provide services to aircraft and portable users.  Service provider – M/s Tata Communications Ltd. (TCL).
63. 63. INMARSAT  TCL/VSNL was given the ILD licence to provide INMARSAT services .  TCL is providing Land Mobile services using INMARSAT-B, INMARSAT-C, INMARSAT-M, Mini-M & M-4 terminals to certain organizations after obtaining NOC from the DoT.  These INMARSAT services are being provided by TCL through their Land Earth Station (Gateway) at Arvi (Pune).
64. 64. INMARSAT Uses  Maritime Communications including ‘Global Maritime Distress and Safety System’ (GMDSS)- GMDSS is an internationally agreed set of safety procedures and communication protocols used to increase safety and make it easier to rescue distressed ships.  As land mobile for i. Rescue Operations during any disaster (e.g. in Uttarakhand, AP, Orissa) ii. Combat Operations (by security forces and paramilitary forces)
65. 65. INMARSAT  Provides satellite services with a constellation of four satellites which are located in the Geo-stationary earth orbit.  The constellation provide global coverage. The constellation I-3 satellites were launched in 1996. Still being used in India.  In 2005 , launched I-4 series of satellites for BGAN (Broadband Global Area Network).
66. 66. Global Service Reach Inmarsat 98% of the world’s landmass and all ocean regions GSM 10% of the world’s landmass
67. 67. BGAN Services • Basic Services – Inherently IP-based – Regular PSTN, ISDN and IP services – Internet access (including web browsing) – Intranet access (including virtual private networks) – Video Conferencing – Internet streaming (audio/video) – Data file transfer – E-mail and messaging (including GPRS/UMTS 2.5/3G SMS) – IP Facsimile
68. 68. Inmarsat-4  Orbital Positions  F1 : IOR  F2 : AOR-W  Prime Contractor : Astrium  10 year lifetime (minimum)  Up to 200 spot beams  Bandwidth : 34/34 MHz  Eirp:t
69. 69. Inmarsat-A
70. 70. Inmarsat-B
71. 71. Inmarsat-C
72. 72. Inmarsat Phone (mini-M)
73. 73. Direct-to-Home television (DTH)  TV Service that uses direct-broadcast satellites is known as direct broadcast satellite television (DBSTV) or direct-to-home television (DTH).  Refers to services transmitted by satellite in specific frequency bands: 11.7- 12.2 GHz.  DTH signals can be received at homes with dish antenna of diameter 60 to 90 cm.
74. 74. Direct-to-Home television (DTH)  DTH operators have introduced a large number of new interactive applications over delivery platforms.  India has the most competitive direct-broadcast satellite market with seven operators for more than 110 million television homes.  Number of Subscribers using DTH television is more than 60 million.
75. 75. Direct to Home TV
76. 76. TATA Sky INSAT 4A Reliance Big TV Measat 3 Sun Direct Measat3 Sun Direct HD INSAT 4B DD Direct Plus INSAT 4B DISH TV NSS6, Asiasat 5 DISH Tru HD Asiasat 5 Airtel Digital TV SES 7 Videocon ST2 Direct to Home TV
77. 77. Global positioning Service(GPS)  Satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the earth where there is an unobstructed line of sight to four or more GPS satellites.  United States government created the system, maintains it, and makes it freely accessible to anyone with a GPS receiver.  The system provides critical capabilities to military, civil, and commercial users around the world.
78. 78. Global positioning Service(GPS)  GPS concept is based on time.  The satellites carry very stable atomic clocks that are synchronized to each other and to ground clocks. Any drift from true time maintained on the ground is corrected daily. Likewise, the satellite locations are monitored precisely.  Number of satellites – 32  Orbit – MEO
79. 79. Global positioning Service(GPS)  GPS satellites continuously transmit their current time and position.  GPS receiver monitors multiple satellites and solves equations to determine the exact position of the receiver and its deviation from true time.  At a minimum, four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and clock deviation from satellite time).
80. 80. Global Positioning System (GPS)
81. 81. Global positioning Service(GPS)  Indian Regional Navigation Satellite System (IRNSS) is an autonomous satellite navigation system developed by ISRO which would be under complete control of Indian Govt.  The requirement has arisen because access to foreign controlled global navigation system (GPS) is not guaranteed in hostile situations.
82. 82. Global positioning Service(GPS)  IRNSS will provide two services – Standard Positioning Service for civilian use, Restricted Service for military users. Missile targeting could be an important military application.  IRNSS would have seven satellites, all are already placed in orbit.  The constellation of seven satellites is expected to operate from 2016 onwards.
83. 83. THANK YOU

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