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IRIDIUM

IRIDIUM by David Lee 1012727 Oana Stanoiu 1875108 This report was prepared for Professor L. Orozco-Barbosa in partial fulfillment of the requirements for the course ELG/CEG 4183 Outline Background System overview Geosynchronous vs. Leo (low-earth orbiting) Satellite configuration

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IRIDIUM

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  1. IRIDIUM by David Lee 1012727 Oana Stanoiu 1875108 This report was prepared for Professor L. Orozco-Barbosa in partial fulfillment of the requirements for the course ELG/CEG 4183

  2. Outline • Background • System overview • Geosynchronous vs. Leo (low-earth orbiting) • Satellite configuration • Frequencies Used • Business Perspective • IRIDIUM vs. other satellite telecommunication networks (GlobalStar, Odyssey)

  3. Background • Why Iridium? • Derived from the chemical element Iridium which has atomic number 77 • Initially there were supposed to be 77 satellites • Driving forces: Major players and their roles • International consortium • Motorola was the initiator of the project • Based on GSM standards • Siemens GSM technology links the satellites to the public telephone and data networks through a system of 15 gateway switching centers

  4. System overview • System Architecture • Composed of: • Satellite system of 66 LEO • Operating in 6 orbital planes • Altitude of 780 km • Orbital period of 101 minutes • Terestrial gateways • Iridium handhelds

  5. GEO vs. LEO • Geo-stationary Earth orbital satellite • On a circular orbit in the equatorial plane at an altitude of 35786 km making 1 revolution in 24 hours. • Unable to service north or south latitudes > 70 degree and has long propagation delay (270ms, one way) • Need huge antenna for low-powered mobile terminals • No satellite tracking needed, relay communication 24 hours a day • Good for non RT, non-interactive application (i.e. TV broadcasting)

  6. GEO vs. LEO • Low Earth Orbital satellites • Excellent link feasibility with low delay due to low orbit • Small coverage cell is obtainable with small on-board antenna • Global coverage possible • Require large number of spacecraft (satellites) • Very complex space control system • Frequent handovers (~10 min between satellites, ~1-2 min between beams) • Low minimum angle

  7. Technology Description • Combination of TDMA and FDMA for the uplink and downlink to satellites • Support full-duplex voice channels at 4800 bps and half-duplex data channels at 2400-bps

  8. TDMA frame structure Guard Time Framing UL1 UL2 UL3 UL4 DL1 DL2 DL3 DL4 90ms

  9. Guard band 41.67kHz CH1 CH2 CH240 1626.5MHz 1616MHz 10.5MHz FDMA Structure

  10. Channel Frequency Reuse • Each IRIDIUM satellite has 3 phased array antennas with 16 spot beams 48 spot beams/satellite • Spot beams are assigned a fraction of the available frequency channels • Channels can be reused throughout the network by assigning them to cells that are far enough apart to minimize co-channel interference • IRIDIUM network uses a cluster factor of 12

  11. J E E E E D D D D F F F F L L L L A A A A G G G G C C C C K K K K B B B B H H H H J J J J I I I I Frequency Reuse Schema

  12. Link Strategy • IRIDIUM has 2 Intra-Orbit ISL and 2 Inter-Orbit ISL • Intra-Orbit ISLs connect satellites within the same orbit • Inter-Orbit ISLs connect satellites on different orbits

  13. IRIDIUM satellite configuration

  14. Performance • Cumulative outage • Terrestrial based network outage averages at 24 hours • The benchmark for cumulative outage is 55 minutes • IRIDIUM has a possible outage of 10 minutes

  15. Business Perspective • Early model • Need at least 1 million subscriber to break even (5 billion to build) • $3000 handset; $7.00/min; Internet access @ 10kbps • Current model (Iridium Satellite LLC) • Major sectors: Military (US: $72 mil); Industry(mining, offshore drilling rugs, CNN, aviation, maritime, entertainment) • Flat rate $1.5/min • Voice, data, and pager services • Satellite Lifetime (7 yrs), other competitors

  16. Business Perspective Cont. • Major Competitors • GlobalStar • Also struggling (only 13000 subscribers with $2 mil in revenue. October 2001 reported a 3rd quarter loss of > 211 million) • Voice and data, not truly global • 500 satellite phones as part of security telecommunications network during the Olympic games • Inmarsat • UK based, use geosynchronous satellites • Satellite communication for ships, video phone images

  17. IRIDIUM vs. other satellite telecommunication network • Geographical coverage • Iridium: truly global with 66 satellites; Others focuses on regions in the mid-latitudes (Globalstar has 24 satellites, Odyssey has 9) • Co-operation with terrestrial Networks • Iridium uses 1 gateway; Globalstar and Odyssey require maximum co-operation with terrestrial networks (no gateway, no service)

  18. IRIDIUM vs. other satellite telecommunication network • Propagation delay • Satellite to Earth: Iridium has the shortest • Terrestrial Networks: Iridium has the shortest since it has less terrestrial trail • Processing delay due to transmission systems and on-board processing: Iridium has the longest • Voice coding and decoding time (system independent)

  19. IRIDIUM vs. other satellite telecommunication network • Frequency bands and multiple access techniques • Iridium has a greater capacity (~0.3 mErlang/km2) than the Globalstar (~0.06 mErlang/km2) and Odyssey (~0.2 mErlang/km2) • Iridium uses TDMA access technique to coexist with the other systems while Globalstar and Odyssey’s S-band downlink is share with ISM applications leading to service degradation in populated urban area

  20. IRIDIUM vs. other satellite telecommunication network • Elevation angle and signal fading margin • Iridium (15 degree); Globalstar and Odyssey (30 degree 90% of the time) • Iridium has a higher fading margin (16 dB for voice, 35 dB for pagaing); Globalstar and Odyssey has less than 10 dB for voice

  21. Questions • 1) Why is LEO a better choice for global satellite telecommunication network than GEO (Geo-stationary Earth orbit)? • 2) Who was the initiator of the IRIDIUM program? • 3) Name two differences between IRIDIUM and GlobalStar satellite networks? • 4) What was the cause of the initial failure of the IRDIUM program? • 5) How many satellites are in the IRIDIUM satellite network? • 6) Define Erlang.

  22. References [1]Daoud, Fawzi. Hybrid satlellite/terrestial networks integration. Computer Networks: the International Journal of Distributed Informatique, vol.34, no.5, Nov. 2000, pp.781-97. Publisher: Elsevier, Netherlands. [2] Fossa, C. E., Raines, R.A., Gunsch, G.H., M. A. Temple, A Performance Analysis of the IRIDIUM® Low Earth Orbit Satellite System with a Degraded Satellite Consteleation, Mobile Computing & Communications Review, vol.2, no.4, Oct. 1998, pp.54-61. Publisher: ACM, USA. [3] Giusto, P. and Quaglione, G. Major alternatives for a global non-geostationary saeillite mobile network. Cselt Technical Reports (Centro Studi eLaboratori Telecomunicazioni), vol.22, no.1, Feb.1994, pp.1-14. Italy. [4] Hesseldahl, Arik. The Return of Iridium. Forbes.com Nov.30, 2001 10:00 am ET http://www.forbes.com/2001/11/30/1130tentech.html [5] Hesseldahl, Arik. The Return of Iridium. Forbes.com Nov.30, 2001 10:00 am ET http://www.forbes.com/2001/11/30/1130tentech.html [6] Ingley, C, Global Vision: Making the Right Connections, Satellite Communications, vol.23, no.2, Feb. 1999, pp.38-40, 42-3, 45. Publisher: Intertec Publishing, USA. [7] Keller, H., Salzwedel, H., Link Strategy for the Mobile Satellite System Iridium, 1996 IEEE 46th Vehicular Technology Conference. Mobile Technology for the Human Race (Cat. No.96CH35894). IEEE. Part vol.2, 1996, pp.1220-4 vol.2. New York, NY, USA. [8] Maine, Kris and Devieux, carrie. Overview of Iridium Satellite Network. WESCON/95 Conference Record (Cat. No.95CH35791).IEEE. 1995, pp.483-90. New York, NY, USA. [9] Otto, D, Schuster, S., Iridium – A Vision Becomes Reality, Telcom Report (English Edition), vol.18, no.3, May-June 1995, pp.11-13. Germany. [10] Sforza, H, A. Pandolfi, M. Laurenti, The IRIDIUM® Programme in the European PCN Scenario, Mobile and Personal Satellite Communications 2.Proceedings of the Second European Workshop onMobile/Personal Satcoms (EMPS'96). Springer- Verlag London. 1996, pp.537-49. London, UK. [11] Shin, J. and Byun, J. Seamless Roaming between IS41-based CDMA Cellular Network and GSM-based Iridium Network. 20th Annual Pacific Telecommunications Conference. PTC'98. Proceedings. Pacific Telecommun.Council. 1998, pp.279-84. Honolulu, HI, USA. [12] Thurston, P., Geometric Node Routing Algorithms for Low-Earth Orbit Global Satellite Communications Systems, WCNC. 1999 IEEE Wireless Communications and Networking Conference (Cat. No.99TH8466). IEEE. Part vol.1, 1999, pp.179-82 vol.1. Piscataway, NJ, USA.

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