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Lecture 11
 

Lecture 11

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    Lecture 11 Lecture 11 Presentation Transcript

    • Satellite Systems
      • 1945 Arthur C. Clarke publishes an essay about „Extra Terrestrial Relays“
      • 1957 first satellite SPUTNIK (Russia)
      • 1960 first reflecting communication satellite ECHO (USA)
      • 1963 first geostationary satellite SYNCOM
      • 1965 first commercial geostationary satellite Satellit „Early Bird“ (INTELSAT I): 240 duplex telephone channels or 1 TV channel, 1.5 years lifetime
      • 1976 three MARISAT satellites for maritime communication
      • 1982 first mobile satellite telephone system INMARSAT-A
      • 1988 first satellite system for mobile phones and data communication INMARSAT-C
      • 1993 first digital satellite telephone system
      • 1998 global satellite systems for small mobile phones
    • Applications
      • Traditionally
        • weather satellites
        • radio and TV broadcast satellites
        • military satellites
        • satellites for navigation and localization (e.g., GPS)
      • Telecommunication
        • global telephone connections
        • backbone for global networks
        • connections for communication in remote places or underdeveloped areas
        • global mobile communication
      •  satellite systems to extend cellular phone systems (e.g., GSM or AMPS)
    • Classical satellite systems base station or gateway Inter Satellite Link (ISL) Mobile User Link (MUL) Gateway Link (GWL) footprint small cells (spotbeams) User data PSTN ISDN GSM GWL MUL PSTN: Public Switched Telephone Network
    • Classical System
      • Foot Print : Area covered by a Satellite
      • Devices within the foot print communicate with the Satellite through ‘Mobile User Link’(MUL)
      • BASE Stn or Gateway : Gateway to other networks
      • Gateway Link(GWL) : Facilitates the Gateway to communicate with the Satellite.
      • Inter-Satellite Links(ISL): Satellites Communicate with each other through these links
        • Aid direct communication between users without base stations and other equipment.
    • Classical System
      • Some satellites have small antennas to create smaller cells using Spot Beams.
      • Seamless Operation : Many Gateways have been designed to have a seamless operation between all systems such as ISDN, PSTN, GSM, CDMA etc
    • Satellite Orbits
      • Earth Orbits the Sun
      • Moon Orbits the Earth.
      • Similarly, many Satellites orbit the earth.
      • The Satellites can pick up an orbit that goes around the Equator or they can go over earth’s north & South Poles.
      • They can pick up an orbit just a few hundred kms away or thousands of kms away from earth.
      • It all depends on the purpose for which the satellite is launched.
    • Satellite Orbits
      • Weather forecasting satellites are parked on the Geo-stationary orbit, exactly over the earth’s equator and make one orbit per day.
      • Hence the satellite seems to hover over the same spot on viewed from the earth all the time.
    • Basics
      • Satellites in circular orbits
        • attractive force F g = m g (R/r)²
        • centrifugal force F c = m r  ²
        • m: mass of the satellite
        • R: radius of the earth (R = 6370 km)
        • r: distance to the center of the earth
        • g: acceleration of gravity (g = 9.81 m/s²)
        •  : angular velocity (  = 2  f, f: rotation frequency)
      • Stable orbit
        • F g = F c
    • Satellite period and orbits 10 20 30 40 x10 6 m 24 20 16 12 8 4 radius satellite period [h] velocity [ x1000 km/h] synchronous distance 35,786 km
    • Basics
      • elliptical or circular orbits
      • complete rotation time depends on distance satellite-earth
      • inclination: angle between orbit and equator
      • elevation: angle between satellite and horizon
      • LOS (Line of Sight) to the satellite necessary for connection
        •  high elevation needed, less absorption due to e.g. buildings
      • Uplink: connection base station - satellite
      • Downlink: connection satellite - base station
      • typically separated frequencies for uplink and downlink
        • transponder used for sending/receiving and shifting of frequencies
        • transparent transponder: only shift of frequencies
        • regenerative transponder: additionally signal regeneration
    • Loss of Power
      • Attenuation or the Propagation Loss of the signal is defined as:
      • L = (4.  .r.f/c) 2
      • F : carrier frequency; c = speed of light.
      • Power of the received signal is inversely proportional to square of the distance between the satellite and the centre of earth.
    • Inclination inclination   satellite orbit perigee plane of satellite orbit equatorial plane
    • Elevation Elevation: angle  between center of satellite beam and surface  minimal elevation: elevation needed at least to communicate with the satellite footprint
    • Link Budget of Satellites
      • Parameters like attenuation or received power determined by four parameters:
      • sending power
      • gain of sending antenna
      • distance between sender and receiver
      • gain of receiving antenna
      • Problems
      • varying strength of received signal due to multipath propagation
      • interruptions due to shadowing of signal (no LOS)
      • Possible solutions
      • Link Margin to eliminate variations in signal strength
      • satellite diversity (usage of several visible satellites at the same time) helps to use less sending power
    • Atmospheric Attenuation Example: satellite systems at 4-6 GHz elevation of the satellite 5° 10° 20° 30° 40° 50° Attenuation of the signal in % 10 20 30 40 50 rain absorption fog absorption atmospheric absorption 
    • Orbits I
      • Four different types of satellite orbits can be identified depending on the shape and diameter of the orbit:
      • GEO: geostationary orbit, ca. 36000 km above earth surface
      • LEO (Low Earth Orbit): ca. 500 - 1500 km
      • MEO (Medium Earth Orbit) or ICO (Intermediate Circular Orbit): ca. 6000 - 20000 km
      • HEO (Highly Elliptical Orbit) elliptical orbits
    • Orbits II earth km 35768 10000 1000 LEO (Globalstar, Irdium) HEO inner and outer Van Allen belts MEO (ICO) GEO (Inmarsat) Van-Allen-Belts: ionized particles 2000 - 6000 km and 15000 - 30000 km above earth surface
    • Geostationary satellites
      • Orbit 35,786 km distance to earth surface, orbit in equatorial plane (inclination 0°)
      •  complete rotation exactly one day, satellite is synchronous to earth rotation
      • fix antenna positions, no adjusting necessary
      • satellites typically have a large footprint (up to 34% of earth surface!), therefore difficult to reuse frequencies
      • bad elevations in areas with latitude above 60° due to fixed position above the equator
      • high transmit power needed
      • high latency due to long distance (ca. 275 ms)
      •  not useful for global coverage for small mobile phones and data transmission, typically used for radio and TV transmission
    • Geostationary satellites
      • Northern and Southerin regions of the earth have problems receiving these satellites since due to low elevation angles beyond 60 deg.
      • Transmission quality is also reduced by shading of signals due to high rise buildings etc.
      • Battery power needed is around 10 W – quite high for mobike devices.
    • LEO systems
      • Orbit ca. 500 - 1500 km above earth surface
      • visibility of a satellite ca. 10 - 40 minutes
      • global radio coverage possible
      • latency comparable with terrestrial long distance connections, ca. 5 - 10 ms
      • smaller footprints, better frequency reuse
      • but now handover necessary from one satellite to another
      • many satellites necessary for global coverage
      • more complex systems due to moving satellites
      • Examples:
      • Iridium (start 1998, 66 satellites)
        • Bankruptcy in 2000, deal with US DoD (free use, saving from “deorbiting”)
      • Globalstar (start 1999, 48 satellites)
        • Not many customers (2001: 44000), low stand-by times for mobiles
    • MEO Systems
      • Orbit ca. 5000 - 12000 km above earth surface
      • comparison with LEO systems:
      • slower moving satellites
      • less satellites needed
      • simpler system design
      • for many connections no hand-over needed
      • higher latency, ca. 70 - 80 ms
      • higher sending power needed
      • special antennas for small footprints needed
      • Example:
      • ICO (Intermediate Circular Orbit, Inmarsat) start ca. 2000
        • Bankruptcy, planned joint ventures with Teledesic, Ellipso – cancelled again, start planned for 2003
    • Routing
      • One solution: inter satellite links (ISL)
      • reduced number of gateways needed
      • forward connections or data packets within the satellite network as long as possible
      • only one uplink and one downlink per direction needed for the connection of two mobile phones
      • Problems:
      • more complex focusing of antennas between satellites
      • high system complexity due to moving routers
      • higher fuel consumption
      • thus shorter lifetime
      • Iridium and Teledesic planned with ISL
      • Other systems use gateways and additionally terrestrial networks
    • Localization of Mobile Stations
      • Mechanisms similar to GSM
      • Gateways maintain registers with user data
        • HLR (Home Location Register): static user data
        • VLR (Visitor Location Register): (last known) location of the mobile station
        • SUMR (Satellite User Mapping Register):
          • satellite assigned to a mobile station
          • positions of all satellites
      • Registration of mobile stations
        • Localization of the mobile station via the satellite’s position
        • requesting user data from HLR
        • updating VLR and SUMR
      • Calling a mobile station
        • localization using HLR/VLR similar to GSM
        • connection setup using the appropriate satellite
    • Handover in satellite systems
      • Several additional situations for handover in satellite systems compared to cellular terrestrial mobile phone networks caused by the movement of the satellites
        • Intra satellite handover
          • handover from one spot beam to another
          • mobile station still in the footprint of the satellite, but in another cell
        • Inter satellite handover
          • handover from one satellite to another satellite
          • mobile station leaves the footprint of one satellite
        • Gateway handover
          • Handover from one gateway to another
          • mobile station still in the footprint of a satellite, but gateway leaves the footprint
        • Inter system handover
          • Handover from the satellite network to a terrestrial cellular network
          • mobile station can reach a terrestrial network again which might be cheaper, has a lower latency etc.
    • Overview of LEO/MEO Systems
    • ISRO
      • Indian space programme driven by vision of Dr Vikram Sarabhai considered as the father of Indian Space Programme.
      • "There are some who question the relevance of space activities in a developing nation. To us, there is no ambiguity of purpose. We do not have the fantasy of competing with the economically advanced nations in the exploration of the moon or the planets or manned space-flight. But we are convinced that if we are to play a meaningful role nationally, and in the community of nations, we must be second to none in the application of advanced technologies to the real problems of man and society. "
        • Government of India set up Space Commission and Department of Space (DOS) in June 1972. Indian Space Research Organisation (ISRO) under DOS executes Space programme through its establishments located in different places in India.
        • Main objective of space programme includes development of satellites , launch vehicles , Sounding Rockets and associated ground systems.
    • ISRO
      • Crossed several major milestones .
        • Experimental phase included Satellite Instructional Television Experiment (SITE) , Satellite Telcommunication Experiment (STEP) , remote sensing application projects, satellites like Aryabhata , Bhaskara , Rohini and APPLE and launch vehicles, SLV-3 and ASLV .
        • Present operational space systems include Indian National Satellite (INSAT) for tele-communication, television broadcasting, meteorology and disaster warning and Indian Remote Sensing Satellite (IRS) for resources monitoring and management .
        • Polar Satellite Launch Vehicle (PSLV) used for launching IRS Satellites and Geosynchronous Satellite Launch Vehicle (GSLV) , intended for launching INSAT class of satellites.
        • Space Science activities include SROSS and IRS-P3 satellites, participation in international science campaigns and ground systems like MST Radar.
        • ISRO's co-operative arrangements cover several countries and space agencies.
        • ISRO provides training in space field to personnel from other countries.
        • ISRO's hardware and services available commercially through Antrix Corporation.
    • ISRO
      • activities in a developing nation.                                                                 To us, there is no ambiguity of purpose. We do not have the fantasy of competing with the economically advanced nations in the exploration of the moon or the planets or manned space-flight. But we are convinced that if we are to play a meaningful role nationally, and in the community of nations, we must be second to none in the application of advanced technologies to the real problems of man and society. "
        • Government of India set up Space Commission and Department of Space (DOS) in June 1972. Indian Space Research Organisation (ISRO) under DOS executes Space programme through its establishments located in different
    • Indian National Satellite System (INSAT )
      • Established in 1983 with commissioning of INSAT-1B.
      • A joint venture of Department of Space (DOS), Department of Telecommunications, India Meteorological Department, All India Radio and Doordarshan. DOS responsible for establishment and operation of INSAT space segment.
      • INSAT space segment at present consists of INSAT-1D, last of the INSAT-1 series launched in 1990 and three ISRO-built satellites, INSAT-2A launched in July 1992, INSAT-2B launched in July 1993 and INSAT-2C launched on December 7, 1995.
      • INSAT-2DT acquired from ARABSAT.
      • INSAT-2E launched on April 3,1999.
      • ISRO has leased eleven 36 MHz equivalent units of C-band capacity on board INSAT-2E to INTELSAT organisation
      • INSAT-3B launched on March 22nd 2000.
    • Indian National Satellite System (INSAT )
      • INSAT-3A launched on April 10th 2003.
      • INSAT-3E launched on September 28th 2003.
      • INSAT-3C launched on January 24th 2002.
      • INSAT-2DT acquired from ARABSAT.
      • INSAT-2E launched on April 3,1999.
      • ISRO has leased eleven 36 MHz equivalent units of C-band capacity on board INSAT-2E to INTELSAT organisation
      • INSAT-3B launched on March 22nd 2000.
      • INSAT-3C launched on January 24th 2002.
      • INSAT-3A launched on April 10th 2003.
      • INSAT-3E launched on September 28th 2003.
    • Indian Remote Sensing Satellite (IRS) System
      • Commissioned with the launch of IRS-1A in March 1988
      • IRS system under National Natural Resources Management System (NNRMS) coordinated at national level by the Planning Committee of NNRMS (PC-NNRMS). 
      • At present has four satellites, IRS-1B launched in August 1991, IRS-1C launched in December 1995 and IRS-1D launched on September 29,1997. 
      • IRS-P3 and IRS-1D launched by India's Polar Satellite Launch Vehicle (PSLV).
      • OCEANSAT-1 with an Ocean Colour Monitor (OCM) and a Multi-frequency Scanning Microwave Radiometer (MSMR) launched by PSLV-C2.
      • RESOURCESAT-1 for agricultural applications launched by PSLV-C5 . 
    • Indian Remote Sensing Satellite (IRS) System
      • CARTOSAT-1 with a Very High Resolution Panchromatic camera for cartographic applications launched by PSLV-C6
      • Data from IRS satellites received and processed by the National Remote Sensing Agency, Hyderabad .
      • SI a US Company also receives and markets IRS data worldwide under a commercial contract with Antrix Corporation of the Department of Space . 
    • Stretched Rohini Satellite Series (SROSS)
      • 113 kg SROSS-C2 satellite, launched by ASLV-D4 on May 4, 1994 carries two scientific payloads, a Gamma-Ray Burst (GRB) experiment and a Retarding Potential Analyser (RPA). A similar satellite, SROSS-C had been launched by ASLV-D3 in May 1992. SROSS-C2 is in
    • Polar Satellite Launch Vehicle (PSLV
      • Developmental flights completed with successful third developmental launch in March 1996. 
      • Now available for launching 1,000-1,200 kg class of remote sensing satellites into polar sun-synchronous orbit. IRS-1D launched on September 29,1997.
      • IRS-P4(OCEANSAT) and two small satellites (KITSAT of Korea and TUBSAT of Germany) launched on on May 26,1999 by PSLV-C2 .
      • PSLV-C3 launched three satellites -- Technology Experiment Satellite (TES) of ISRO, BIRD of Germany and PROBA of Belgium - into their intended orbits on October 22, 2001.
    • Polar Satellite Launch Vehicle (PSLV
      • ISRO's Polar Satellite Launch Vehicle, PSLV-C4 launched KALPANA-1 satellite on September 12, 2002.
      • ISRO's Polar Satellite Launch Vehicle, PSLV-C5 launched RESOURCESAT-1 (IRS-P6) satellite on October 17, 2003.
      • ISRO's Polar Satellite Launch Vehicle, PSLV-C6 launched CARTOSAT-1 and HAMSAT satellites on May 5, 2005.
    • Geosynchronous Satellite Launch Vehicle (GSLV
      • For launching 2,000 kg class of communication satellites into geosynchronous transfer orbit.
      • A three stage vehicle; first stage is a 129 tonne solid propellant core motor with four liquid propellant strap-ons with 40 tonne propellant each, second stage is a liquid propulsion system with 37.5 tonne propellant and a cryogenic upper stage with 12 tonne of liquid oxygen and liquid hydrogen. 
    • Geosynchronous Satellite Launch Vehicle (GSLV
      • First developmental flight GSLV-D1 completed with successful launch on April 18, 2001.
      • Second developmental flight GSLV-D2 launched GSAT-2 satellite on May 8, 2003.
      • First operational flight of GSLV (GSLV-F01) and the third in the GSLV series launched EDUSAT satellite on September 20, 2004.