Presentation on theme: "1 The Advent of Satellite Communication Satcom Vision and Development of Launch Technologies Oct. ‘45 - Arthur CLARKE: “Extraterrestrial relays”, Wireless."— Presentation transcript:
1 The Advent of Satellite Communication Satcom Vision and Development of Launch Technologies Oct. ‘45 - Arthur CLARKE: “Extraterrestrial relays”, Wireless World, p.305 Three manned GEO space station Oct. ‘54 - John PIERCE: “Telecommunications satellites” LEO or GEO satellites without man in space Oct. ‘57 - URSS: “Sputnik mission ” First artificial satellite (non TLC): 85 kg in Earth orbit Jul. ‘61 - John. F. KENNEDY: “Policy statement on communications satellites” Birth of Satellite Communications Aug. ‘62 - Law in the U.S.: “Communications Satellite Act” Birth of COMSAT Aug. ‘64 - Inter-governmental agreement : “Interim Arrangements for a Global Commercial Communications Satellite System” Birth of ICSC and INTELSAT
2 Milestones of Satellite Communications (1) : LEO and MEO experiments Pre-recorded message transmission Dec. ‘58 - SCORE (60 kg of payload launched on ATLAS at 190 km perigee km apogee) Oct. ‘60 - COURIER (227 kg, km) Passive reflection Aug. ‘60 - ECHO I (76 kg, km) Jan. ‘64 - ECHO II (248 kg, km) Telephone and TV transmission Jul. ‘62 - TELSTAR I (77 kg, km) Dec. ‘62 - RELAY I (78 kg, km) May ‘63 - TELSTAR II (79 kg, km) Jan. ‘64 - RELAY II (78 kg, km)
3 Milestones of Satellite Communications (2) : GEO experiments Jul. ‘63 - SYNCOM II (39 kg, almost GEO: i=33°) Aug. ‘64 - SYNCOM III (66 kg) 1965: The first HEO satellite (URSS) Apr. ‘65 - MOLNIYA I ( km, 12 hours) Clarke’s conception of GEO
4 Milestones of Satellite Communications (3) 1965: GEO operational systems Apr. ‘65 - INTELSAT I (“Early Bird”) Starts INTELSAT GEOs for intercontinental fixed services FIXED CONTINENTAL SERVICES In the U.S. regional systems start for fixed (continental) services INMARSAT GLOBAL SYSTEMS Fully operational GEO global systems, for mobile maritime service FIRST LAND MOBILE SATELLITE SYSTEM OMNITRACS starts to provide in North America land mobile satellite messaging and localization services ITALSAT (ITALY) The first satellite with on board processing and multibeam coverage
5 Service Evolution towards Multimedia/Personal Communications Converge at worldwide level ANYTIME ANYVOLUMEANYTYPE ANYWHERE M U L T I M E D I A PERSONALPERSONAL
7 Multimedia Satellite Services: Perspective View WRC-95: Ka-FREQUENCIES TO LEOs (11/95) ITALSAT LAUNCH (1/91) ACTS LAUNCH (9/93) SPACEWAY FCC FILING (12/93) 1995 TELEDESIC FCC FILING (3/94) ASTROLINK FOUNDED (7/99) FIRST COMMERCIAL SATELLITE LAUNCH (?) BOEING ENTERS TELEDESIC (4/97) WRC-97 REVISES Ka-BAND (11/97) CELESTRI MERGES INTO TELEDESIC (5/98) FIRST IRIDIUM SATELLITE LAUNCH (5/97) FCC DEADLINE FOR KA BAND FILING (9/95) 1997
8 Multimedia/Personal Satellite Services Rationale Global Information Infrastructure (GII) to every individual Broadband services Services Global Internet services Interactive/multimedia video Tele-medicine Distance learning Interactive home banking/shopping Satellite news gathering Disaster management etc.
9 Main Technologies for Multimedia Satellite Services On board antennas Phased and multibeam antenna to shape beams for specific footprint to focus beams (“hot spots”) to steer beams HPAs and beams forming networks Reconfigurable output power distribution to add flexibility in traffic management to improve satellite reliability Processing satellites On board processing and inter-satellite links to allow single-user routing to mix digital traffic typologies
10 Satellite Constellation Cost Drivers Satellite Antenna size Number of beams Power requirement Stabilization Lifetime Number of satellites Launch Satellite size Altitude Orbits type Terrestrial system Number of gateways Operation costs PTSN and trunking Network coordination and management Network maintenance Billing and customer services
11 Satellite Networks Basic Features âFavorable attributes of the satellite Coverage potentially offered to large regions Direct-to-user services Promptness of service implementation Service and traffic capacity reconfiguration âClassification of direct-to-user services One-way services (i.e. broadcasting) Two-way services (i.e. communication) One-wayTwo-way
12 One-way and Two-way Satellite Topologies: Transparent vs. Regenerative Repeaters a) Full coverage antenna and transparent transponder b) Multibeam: one receiver and one transmitter per beam, connected to a switching matrix
13 Orbits and Frequencies: the Capacity Issue Low Orbits Geostationary-Earth-Orbit (GEO) Low-Earth-Orbits: an alternative for high capacity global systems åCapacity grows with d -2 LEO/GEO capacity advantage is about 36 2 1300 High Frequencies Traditional L band (frequency, f, about 1-2 GHz): low capacity New Ka band and beyond (20-30 GHz and higher): high capacity åCapacity grows with f 3 Ka/L capacity advantage is about 20 3 8000 Low Orbits and High Frequencies Combing low orbits and high frequencies potentially provides a huge advantage åL-band GEO / Ka-band LEO capacity advantage is 10 million times
14 Capacity Advantage as a Function of Satellite Altitude Transmission capacity, C, can be expressed as: where means “proportional” and n is the number of “cells” For a given antenna size: A is the cell area is the angular width of the antenna beams d is the satellite altitude
15 Orbit Altitude Trade-offs As H is reduced we have the following advantages: The footprint of each on board antenna spot is reduced Reducing the footprint (“cell”) brings a larger frequency reuse (with the inverse of the square of cell radius). The free-space loss (FSL) is reduced Reducing the FSL allows to set less stringent requirements both on board the satellite and to the user terminal. Reducing the power per channel on board is a basic factor towards the optimum use of the spectrum (this is analogous to cellular systems). To the low power of the terminal the benefits of low consumption and less radiation hazard are associated. The propagation delay is reduced A short propagation delay allows more complex signal processing to contrast the channel impairments and/or allows the double-hop via satellite.
16 Capacity Advantage as a Function of Frequency Transmission capacity, C, can be expressed as: where B is the available band k is the number of times B is reused For a given antenna size: A is the cell area is the angular width of the antenna beams
17 The Radio Spectrum
18 Spectral Allocations Spectrum for non-GEO systems was considered in three World Radio Conferences (WARC’92, WRC’95 and WRC’97) and by the FCC (1994 and 1997) WARC’92: assigned the band MHz (“L band”) and the band MHz (“S band”) to LEO services on a primary use basis worldwide for up-link and down-link, respectively FCC (1994): divided the two band (L and S) and assigned the lower MHz part to CDMA systems (e.g. GLOBALSTAR) and the upper 5.15 MHz part to TDMA systems (IRIDIUM) WRC’95: took the following main decision: the band MHz was made available for ICO since the year 2000 bandwidth was allocated for the the non-GEO MSS service in several frequency bands (from 4 to 30 GHz) (TELEDESIC)
19 FCC L/S Band Spectral Allocations to LEOs ãFCC allocated bandwidth to MSS LEO systems in 1994 ãBands were split in two and assigned to systems adopting TDMA (IRIDIUM) and CDMA (GLOBALSAR) separately.
20 Spectral Allocations at Ka Band WRC’97 and FCC-1997
21 Orbit Classifications: General Based on the inclination, i, over the equatorial plane: Equatorial (i=0°) Polar (i=90°) Inclined (0°
"name": "21 Orbit Classifications: General Based on the inclination, i, over the equatorial plane: Equatorial (i=0°) Polar (i=90°) Inclined (0°
22 Orbit Classifications: Circular Orbits Based on the circular orbit altitude, H, over the Earth surface: Low-altitude Earth Orbit (LEO): 500 km < H < 1700 km Medium-altitude Earth Orbit (MEO): 5000 km < H < km Geostationary Earth Orbit (GEO): H = km When locating a satellite we wish to avoid: Atmosphere which is still dense at H< 250 km Van Allen Belts: –internal belt H km –external belt H km
23 DMDM 2· M mm H MM Main relationships: 1) 2) 3) where: H is the satellite altitude 2· M is the maximum nadir angle m is the minimum elevation angle 2 · M is the maximum subtended angle D M is the maximum satellite-to-terminal distance (edge of coverage) R E = 6378 km is the average Earth radius Satellite Link Geometry
25 Orbit Constellations Features Coverage Need to have a fully deployed constellation for real time services (e.g.: voice) with full Earth coverage Sparse constellations suitable for non real time data services To reduce the constellation size coverage of polar regions (lat. >70°) is generally avoided Main parameters for communications services: H, m Altitude, H H takes into account the need to avoid Van Allen Belts and atmospheric drag Elevation angle, m Minimum elevation angle, m, under which the terminal “sees” the satellite at the coverage border influences constellation size A small m, beneficial to reduce constellation size, is however in conflict with a low probability of obstruction (due to orography, etc.)
26 Circular Orbit Centrifugal Force = Gravitational Force m = satellite mass (don’t care!!) g 0 = 9.81 m/s 2 R E = 6378 km = Earth radius H = orbital height T = orbital period
27 Lower Bound on the Number of Satellites m = 70° m = 40° m = 10° Circular orbits Earth’s areaPole’s area Area to be covered (service area) Single satellite coverage area where is earth's spherical segment deepness where M = f ( m,H) and ’=20° ’’ MM S0S0 S’S’ RERE Satellite H
28 GEOs: Visibility from Earth Coverage provided by three INTELSAT satellites
29 Geometrical Characteristics for GEO Links (1) Plot shows the variation of range, R, from GEO satellite to Earth station with latitude and relative longitude L The maximum value of (R/R 0 ) 2 is which means a variation of 1.3 dB in Free Space Loss Plot shows the maximum elevation angle under which a terminal “sees” the satellite as a function of terminal latitude
30 Geometrical Characteristics for GEO Links (2) Figure allows, for the angle determination of azimuth, A, and elevation angle, E, of an Earth station, to point a GEO satellite Figure shows how to rotate the Earth station antenna around its boresight to achieve polarization match with a linearly polarized wave from satellite Assumes polarization plane of transmitted wave perpendicular to orbital plane
31 Highly Elliptical Orbits (HEOs) HEOs (i = 63.4°) are suitable to provide coverage at high latitudes (including North Pole in the northern hemisphere) Satellite handover: all traffic must be periodically transferred from the “setting” satellite to the “rising” satellite Depending on selected orbit (e.g. Molniya, Tundra, etc.) two or three satellites are sufficient for continuous time coverage of the service area. Due to very high apogee, the satellite is very slow along a large arc
32 HEO Satellites Mechanics Accounting for the Earth rotation the tree satellites appear as if they were an a single track Advantages vs. GEO: higher elevation angle, coverage of high latitude Disadvantages vs. GEO: large delay, larger Free Space Loss, larger number of satellites Fixed observerEarth-fixed observer
33 Effects of the Propagation Delay In a GEO link, one-way propagation delay is 240 < t d < 275 milliseconds, depending on location of Earth stations. Therefore, two-way (circuit) delay is about 500 ms Direct effect (psychological) and indirect effect (echo) can impact on subjective service quality. Direct effect pushes the unaware talker to repeat the voice message, so producing “garbling”. Indirect effect is a consequence of the conversion between two- wire and four-wire connections in telecommunications networks.
34 A Delay-related Problem in GEO Links: Echo To reduce echo disturbance, UIT recommends a maximum circuit delay of 400 ms. This prevents usage of two-hop GEO communications.
35 Echo Countermeasures Echo Suppressor Based on the “imprecise” assumption that when “talker A” is talking, “talker B” is listening, and vice versa. Not suitable for data transmission (i.e. computers). Echo Canceler Based on estimation of the echo and its cancellation with an out-of-phase replica. Suitable both for voice and for data.