Satellite communication (a tutorial)

28,116 views
27,902 views

Published on

This presentation was actually developed in 2005 (on the basis of free publically available data and then published online at www.rfcafe.com) for the student of University of Sindh, Jamshoro, Pakistan.

Now, upon request of many students this presentation is being uploaded again for educational purposes.

Published in: Education, Technology, Business
0 Comments
37 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
28,116
On SlideShare
0
From Embeds
0
Number of Embeds
52
Actions
Shares
0
Downloads
3,207
Comments
0
Likes
37
Embeds 0
No embeds

No notes for slide
  • Transponder intermodulation is specified as a limit of EIRP density transmitted from the transponder in a 4 kHz bandwidth at the beam edge. The limits are given in IESS 410 Tables 2a and 2b, for every satellite beam.
  • Satellite communication (a tutorial)

    1. 1. Tutorial Satellite Communication By Kamran Ahmed (kamrahmed@excite.com)
    2. 2. Course Contents • Overview of Satellite Systems • Orbits & Launching Methods • Orbital Mechanics • Orbital Perturbations • Satellite Visibility • Radio Wave Propagation • Polarization • Antenna • Link Budget • Interference • Channel Characterization
    3. 3. 1. Overview of Satellite Systems
    4. 4. Contents • • • • • • • • • • • What is satellite communication The Origin of Satellite Elements of Satellite Communication Key input data Early Satellite Systems System Design Considerations Major Problems for Satellite Limitation for Satellites Advantages of Satellite Different Applications Frequency Allocation & Regulatory Aspects
    5. 5. What is Satellite Communication… • A communication satellite is basically an electronic communication package placed in orbit whose prime objective is to initiate or assist another through space. • Satellite communication is one of the most impressive spin-offs from the space programs and has made a major contribution to the pattern of international communication. • The information transferred most often correspondence to voice (telephone), video (Television) and digital data.
    6. 6. Cont... • Communication satellite are off-course only one means of telecommunication transmission. The traditional means include copper wire and microwave pointto-point links. Newer techniques involves use of optics either point-to-point infrared or fiber optics. Point-to-point radio system such as short wave radio may also be used.
    7. 7. The origin of satellite • The concept of using object in space to reflect signals for communication was proved by Naval Research Lab in Washington D.C. when it use the Moon to establish a very low data rate link between Washington and Hawaii in late 1940’s. • Russian started the Space age by successfully launching SPUTNIK the first artificial spacecraft to orbit the earth, which transmitted telemetry information for 21 days in Oct. 1957. • The American followed by launching an experimental satellite EXPLORER In 1958. • In 1960 two satellite were deployed “Echo” & “Courier” • In 1963 first GSO “Syncom” • The first commercial GSO (Intelsat & Molnya) in 1965 these provides video (Television) and voice (Telephone) for their audience
    8. 8. Elements of Satellite Communications • The basic elements of a communication satellite service are divided between; • Space Segment • Ground Segment • The space segment consist of the spacecraft & launch mechanism and ground segment comprises the earth station and network control center of entire satellite system.
    9. 9. Satellite Communications System Uplink IDU Down Link RFT RFT IDU RF Transmit Earth Station Receive Earth Station
    10. 10. Concept Transponder downlink downlink uplink uplink IRRADIUM Earth station (site A) Earth station(site B)
    11. 11. Propagation Delay Single Hop 270 ms Double Hop 540 ms
    12. 12. Ground Station _ Anatomy Indoor Unit (IDU) IFL 70/140 MHz Antenna Sub-System Outdoor Unit (ODU) C/Ku
    13. 13. Satellite Services • • • • The ITU has grouped the satellite services in to three main groups Fixed Satellite Services (FSS) Broadcast Satellite Services (BSS) Mobile Satellite services (MSS)
    14. 14. Space Segment • Space segment consist of a satellite in suitable orbit. • Space segment classified on the basis of orbit; – – – – LEO MEO HEO GEO & GSO
    15. 15. Ground Segment • The ground segment of each service has distinct characteristics. • Services like; • FSS • BSS • MSS – Maritime, Aeronautical & Land base • DBS • Etc.
    16. 16. Satellite Footprints Satellite beam their signals in a straight path to the earth. The satellite focus these microwaves signals onto the specified portions of the earth’s surface to most effectively use the limited power of their transponders. These focused signals create unique beam patterns called “footprints.” Types of footprints: – Global beam footprint – Hemispheric Beam Footprint – Zone Beam Footprint
    17. 17. Satellite Footprints
    18. 18. Satellite Footprints
    19. 19. Satellite Footprints
    20. 20. Satellite Footprints
    21. 21. Key Input Data... Bands: C-Band ( Ku-Band ( Beams: Global ( ) Hemi ( ) Zone ( ) Spot ( ) ) )
    22. 22. National and Regional Systems 1 2 3 4 5 Anik, Canada Morelos, Mexico Panamsat, Americas Brasilsat, Brazil Eutelsat, Europe 6 7 8 9 10 Telecom, France Kopernikus, Germany Italsat, Italy Arabsat, Arab League Insat, India 11 12 13 14 Asiasat, East Asia CS, Japan Palapa, Indonesia Aussat, Australia
    23. 23. Early Satellites Satellite Launching Date Country/Organization Type Height (miles) RELAY 1962 USA/RCA & NASA Active Duplex SYNCOM 1963 USA/NASA Active Duplex MOLNIYA 1965 U.S.S.R Active Duplex High altitude elliptical First Soviet communication satellite used a high altitude elliptical orbit. EARLY BIRD 1965 INTELSAT/COMSAT Active Geostationary First commercial communication satellite; served the Atlantic ocean region; capacity to carry 240 voice channels INTELSAT 2 1966 INTELSAT/COMSAT Active Geostationary First multiple access commercial satellite with multidestination capability INTELSAT 3 1968 INTELSAT/COMSAT Active Geostationary 3 generation designed to carry 1200 voice circuits 942-5303 Comments 4.2/1.7 GHz satellite designed to carry telephone signals. Geostationary First Geostationary communication satellite used to transmit television signals from the Tokyo Olympics.
    24. 24. Early Satellites Satellite Launching Date Explorer 1958 ECHO Country/Organization Type Height (miles) Comments USA/NASA Broadcast 110 to 920 Very short life; Noted for re-broadcasting an on-board taped message from president Eisnhour 1960 USA/NASA Passive 1000 100-Foot diameter plastic balloon with an aluminum coating which reflect radio signals COURIER 1960 Department of defense Store & Repeat 600-700 TELSTAR 1962 USA/AT&T Active Duplex 682-4030 First radio repeater satellite. It accepted and stored upto 360,000 teletype words as it passed overhead and then broadcast to ground stations further along the orbit; only operated for 17 days. First satellite to receive and transmit simultaneously; Operated in 4/6 GHz band
    25. 25. Early Satellites Satellite Launching Date Country/Organization Type Height (miles) Comments INTELSAT 4 1971 INTELSAT/COMSAT Active Geostationary COMSAT’s 4th generation; designed to carry 6000 voice circuits. ANIK 1 1972 Canada/Telesat Active Geostationary World’s first domestic satellite; 5000 voice circuits capacity. WESTAR 1974 USA/Western Union Active Geostationary First US domestic satellite
    26. 26. Early Satellites • • • • US Navy bounced messages off the moon ECHO 1 “balloon” satellite - passive ECHO 2 - 2nd passive satellite All subsequent satellites used active communications
    27. 27. ECHO 1 • Photo from NASA
    28. 28. Early Satellites • Relay – 4000 miles orbit • Telstar – Allowed live transmission across the Atlantic • Syncom 2 – First Geosynchronous satellite
    29. 29. TELSTAR • Picture from NASA
    30. 30. SYNCOM 2 • Picture from NASA
    31. 31. Asiasat 2
    32. 32. System Design Consideration • • • • Services or Application Selection of RF Band Finance Further technical design considerations are:– Optimal modulation, coding scheme, type of service, permitted earth station size and complexity, shape of service area, landing rights, state of prevailing technology related both to spacecraft and ground station.
    33. 33. Major problems for satellite • Positioning in orbit in-term of Frequency & Orbit Selection • Stability • Power • Communications • Harsh environment • Interference Problem
    34. 34. Limitation of Satellites • High initial investment • New investment require in Ground Segment • Short life time • Spectrum crowding • Regulatory aspects (landing rights etc.) • Launch vehicle reliability
    35. 35. Advantages of Satellite • • • • • • Wide band capability Wide area coverage readily possible Distance-insensitive costs Counter inflationary cost history All user have same access possibilities Point to point, point to multipoint (broadcast) and multipoint to point (data collection) are all possible • Inherently suited for mobile application. • Compatible with all new technologies • Service directly to the users premises
    36. 36. Applications • Communication (truncking call) • Teleconference • Telemedicine • TV Broadcasting • Data communication • Telemetry(TEC, remote sensing etc) • • • • Weather telecast Navigation GPS Security/Calamity monitoring • Standard Time • Military • Remote Sensing
    37. 37. Frequency Allocations & Regulatory Aspects • Frequency bands for satellite services are shared with terrestrial services. • Satellite signal strength is constrained to avoid interference by it to others. • Thus a large antenna and sensitive receiver are needed at the earth station. • Frequency sharing techniques are an important study area. • Many satellites have to share a limited frequency band (and limited orbital arc) thus coordination in frequency and orbital location is important. • Frequency allocation are done by international agreements
    38. 38. Electromagnetic Spectrum
    39. 39. The Frequency Spectrum and Typical Applications Power Systems 102 AC 104 GPSMobil Glonass Mittel GalileoFunk Sat Welle Mikro TV TV Sun Welle IR Lamp AM UKW Studio 106 Broadcast 108 1010 Microwave 1012 1014 Infrared 1016 Ultraviolett X-Rays 1018 1020 Hz X-Ray
    40. 40. Radio Frequency Bands Band Number 4 5 6 7 8 9 10 11 Band Name Frequency Range Metric Subdivision VLF, Very low frequency LF, Low frequency MF, Medium frequency HF, High frequency VHF, Very high frequency UHF, Ultra high frequency SHF, Super high frequency EHF, Extra high frequency 3-30 KHz 30-300 KHz 300-3000 KHz 3-30 MHz 30-300 MHz 300-3000 MHz 3-30 GHz 30-300 GHz Myriametric waves Kilometric waves Hectometric waves Decametric waves Metric waves Decimetric waves Centimetric waves Decimillimetric waves
    41. 41. Satellite Operating Frequency Bands Frequency Range (GHz) 0.39-1.55 1.55-5.2 3.9-6.2 5.2-10.9 10.9-36.0 15.35-17.25 18.3-31.0 Band L S C X K Ku Ka Category MSS FSS & BSS FSS Military FSS & BSS FSS & BSS FSS
    42. 42. Frequency Allocation and Regulatory Aspects • Domestic e.g. Federal communication Commission (FCC) National Telecommunication and Information Administration (NITA) In Pakistan, PTA (Pakistan Telecommunication Authority) • International International Telecommunication Union (ITU) – Formed in 1932 from the International Telegraph Union – Consists of over 150 members nations – World Administrative Radio Conference (WARC) – International Radio Consultative Committee (CCIR) consists of 13 study groups.
    43. 43. ITU Regions ITU divides the surface area of the earth into three regions for the purpose of frequency allocation • Region 1: Pacific Ocean Region North and South America Greenland • Region 2: Atlantic Ocean Region Europe Africa Middle East Central Asia
    44. 44. ITU Regions (Continued) • Region 3: Indian Ocean Region Pakistan, India, Sub-continent , South East Asia & Australia
    45. 45. Frequency Allocations to Satellite Services
    46. 46. International Telecommunications Union Examples of Satellite Radio Services: - Fixed Satellite Service FSS - Mobile Satellite Service MSS - Broadcast Satellite Service BSS - Radio Navigation Sat. Serv. RNSS - Radio location Sat. Service RSS - Space Operation Service -... Earth observation Sat. Serv. ESS In total more than 18 radio services SOS
    47. 47. International Telecommunications Union Artikel S5 der Radio Regulations Region 1 Region 2 Region 3 19.7 - 20.1 GHz FIXED-SATELLITE (space-to-earth) 19.7 - 20.1 GHz FIXED-SATELLITE (space-to-earth) 19.7 - 20.1 GHz FIXED-SATELLITE (space-to-earth) Mobile-Satellite (space-to-earth) MOBILE-SATELLITE Mobile-Satellite (space-to-earth) (space-to-earth) S5.524 S5.524, S5.525, S5.526 S5.524 S5.527, S5.528, S5.529
    48. 48. International Telecommunications Union A license is required by every operator in order to operate a satellite system nationally; a licence may only be acquired if: - the operator can show that he has a contract with the system owner to be his service provider - the frequencies for the system have been cleared / coordinated / notified - that system is fully registered with the ITU -the operator has workers registered as operators A licence will be cancelled if: - there are no more registered operators to work the system - the service provider has breached ‘data protection laws’
    49. 49. 2. Orbits and Launching Methods
    50. 50. Contents • • • • • • • • • • • • • • • Different Types of orbit Satellite Orbits & Relative Periods GEO View & Coverage from GEO Some GEO Characteristics of GEO Transfer Orbit C & Ku Bands Satellites in Orbit Mega LEO, MEO, HEO & GEO Projects The Future Broadband LEO Launching Launch Vehicle Summary of Launchers Types of Launches
    51. 51. Different Types of Orbits • Circular orbits are simplest • Inclined orbits are useful for coverage of equatorial regions • Elliptical orbits can be used to give quasi stationary behaviour viewed from earth – using 3 or 4 satellites • Orbit changes can be used to extend the life of satellites
    52. 52. Cont… Several types • LEOs - Low Earth Orbit • MEOs - Medium Earth Orbit • HEOs – Highly Elliptical Orbit • GSO - Geostationary Earth Orbit
    53. 53. Cont…
    54. 54. LEO • • • • • • • Low Earth Orbit 200-3,000 km High orbit speed Many satellites Predominately mobile Iridium, Globalstar (space shuttle orbit)
    55. 55. MEO • • • • • • Medium Earth Orbit 6,000 – 12,000km New generation About 12 satellites Voice and mobile ICO (Odyssey), Orbcomm, Ellipso Ellipso
    56. 56. Sub-Satellite Track of a HEO
    57. 57. The 24 h HEO of Sirius
    58. 58. The 24 h HEO of Sirius
    59. 59. HEOs: Molnya and Tundra Molnya Period Apogee Perigee Inclination Tundra 12 h 39 500 km 1 000 km 63.4° 24 h 46 300 km 25 300 km 63.4°
    60. 60. Satellite Orbits and Periods Height of Orbit1 (km) Period Cell of Orbit Diameter (h) (km) 200 700 1000 1 414 10 000 20 000 35 786 1.5 1.6 1.8 1.9 5.8 11.9 24.0 1 3 154 5 720 6 719 7 806 14 935 16 922 18 100 Visible Numbers Part of Earth of Satellite % * 1.5 5.0 6.8 9.1 30.5 37.9 42.4 above the surface of the earth *minimum necessary for 0° elevation and 0 redundancy 66 20 15 11 4 3 3 Duration of Over flight (min) 7 14 18 22 130 300 24 h/d
    61. 61. GEOs • Originally proposed by Arthur C. Clarke • Circular orbits above the equator • Angular separation about 2 degrees allows 180 satellites • Orbital height above the earth about 23000 miles/35786.16km • Round trip time to satellite about 0.24 seconds
    62. 62. GEOs (2) • GEO satellites require more power for communications • The signal to noise ratio for GEOs is worse because of the distances involved • A few GEOs can cover most of the surface of the earth • Note that polar regions cannot be “seen” by GEOs
    63. 63. GEOs (3) • Since they appear stationary, GEOs do not require tracking • GEOs are good for broadcasting to wide areas • Currently 329 GEO are in orbit (ref: web site provided by Johnston)
    64. 64. The original vision • 1945 Arthur C Clark envisaged “extraterrestrial relays” • # of Satellites: 03 • Period: 23 h 56 min 4.091 s • Height: 36 000 km above equator • Speed of flight: 3.074 km/s
    65. 65. and then.. • 1957 Sputnik • a rush of experimental satellites in many orbits • Intelsat 1965 – 1st commercial GEO service • over 800 objects registered so far
    66. 66. GEO - geostationary earth orbit • characterised by: – delay (echo) ~0.5sec return – high power – 5-7 years life • • • • global and spot beams C and K band (4-6Ghz and 12-14Ghz) 2 – 3o spacing Currently more than 200 GEO satellites in operation
    67. 67. the view from 36,000km
    68. 68. Earth coverage with 2 spacecraft 90 70 50 30 10 -10 -30 -50 -70 -90 -170 -150 -130 -110 -90 -70 -50 -30 -10 10 30 50 70 90 110 130 Coverage of the inhabited world except for Polynesia 150 170 190
    69. 69. some GEO’s above us • • • • • • Optus * 3 AsiaSat * 3 PAS *2 Intelsat * 7 Inmarsat * 2 Palapa * 2 and others Some Service Providers: Netspeed Austar Optus Telstra iHug Newskies MediaSat NTL Heartland Xantic Stratos
    70. 70. Characteristics of a Geostationary Satellite Orbit • • • • • • Eccentricity (e) 0 Inclination of the orbital plane (i) 0º Period (T) 23h 56m 4s Semi-major axis (a) 42164 km Satellite altitude(R) 35786 km Satellite velocity (Vs) 3075 m/s µ=Gme=3.986x1014 m3/s2 F=GMm/r2 T=2π√ a3/µ e=c/a V= µ(2/r-1/a) m/s
    71. 71. The GEO Elevation , distance to the satellite Ro ζ ε d pRo Kgrav = m Me G / r2 Kzent = m r ω 2, = m v2 / r Angular velocity ω = 2π / T, T Period, v velocity Kgrav = Kzent und m Me g / r2 = m r ω 2 bzw. Me g / r2 = r ω2 r 3 = Me g T2 / ( 2π )2 The period T of the circular orbit (r in km, m = 398 601.8 km3/s2) is ──── ────── T = 2 π √ r 3 / m = 9.952 10-3 √ r 3 / km in Seconds p = 6.611
    72. 72. The GEO Ro ζ ε d pRo ∆lon = LongitudeE/S - LongitudeSatellite ∆lat = LatitudeE/S - LatitudeSatellite Space angle α: cos( α ) = cos ( ∆lon ) * cos( ∆lat ) ─────────────────────────────────────── Distance d: d = Ro √ 6.6112 – 2 * 6.611 * cos α + 1 Elevation ε: sin( ε ) = [ 6.6112 Ro2 – Ro2 – d2 ) / ( 2 Ro d ) ] Test: α = 81.3° α = 0° d = 41680 km and ε = 0° d = 35787 km and ε = 90°
    73. 73. The inclination (1) . ) The inclination: orbit remains geosynchroneous, 24 h; satellite moves North/South; inclination builds up 0.8°/year if not corrected contiuously T ne d pla ne incli he The equatorial plane
    74. 74. The inclination (2) . ) After 18 years some 15° of inclination will have built up; ne now the inclination reverses and decreases by 0.8°/year; d pla ine satellites with <15° inclination are geostationary by law. The incl The equatorial plane
    75. 75. Transfer Orbits
    76. 76. C-Band satellites in GEO Legende im Orbit im Bau ITU Appl. Legend on orbit under constr ITU Appl. (1995)
    77. 77. Ku-Band satellites in GEO Legende im Orbit im Bau ITU Appl. Legend on orbit under constr ITU Appl. (1995)
    78. 78. C and Ku-Band satellites in America
    79. 79. Comparison Chart Features GEO MEO LEO Heig ht (km’s ) Time per Orbit (hrs ) Speed (kms / hr) Time delay (ms ) Time in s ite of Gatew ay Satellites f or Global Coverag e 3 6 ,0 0 0 200-3000 24 6 ,0 0 0 1 2 ,0 0 0 5-12 1 1 ,0 0 0 1 9 ,0 0 0 2 7 ,0 0 0 250 80 10 Alw ays 2 - 4 hrs < 1 5 min 3 10-12 50-70 1 .5
    80. 80. Mega LEOs, MEOs, HEOs, and GEOs 1 2 3 4 5 6 7 8 9 10 11 TELEDESIC of microSoft with 288 LEOs at Ka-Band V-Band Supplement of TELEDESIC/microSoft with 72 LEOs im Q-Band GS-40 of Globalstar LP with 80 LEOs at Q-Band M-Star of Mororola with 72 LEOs at Q-Band LEO ONE of LEO ONE Corp. with 48 LEOs at Q-Band ORBLINK of Orblink LLC with 7 MEOs in Q-Band SkyBridge of ALCATEL witt 64 LEOs and 9 GEOs in Ku-Band WEST of MATRA with 10 MEOs and 12 GEOs in Ka-Band GESN of TRW with 15 MEOs and 4 GEOs in Q-Band CELESTRI of Motorola MOT with 63 LEOs and 10 GEOs in Ka-Band SpaceWay of Hughes Communications with 20 LEOs and 16 GEOs in KaBand 12 StarLynx of Hughes Communications with 20 MEOs and 4 GEOs in Q-Band 13 DenAli Telecom LLC PenTriad in HEO im Ku-, Ka-, V- and W-Band
    81. 81. The Future • given current-generation LEO’s and MEO’s are predominately used for mobile voice and low-speed data services (MPSS) – good voice coverage for remote regions – adjunct to GSM mobile networks ~ Globalstar
    82. 82. the future • continual development in VSAT (GEO) technology – bandwidth gains – multiple services = choice • Broadband LEOs – Teledesic • • • • fixed and transportable terminals 64k – 2M – and above (Gb) 288 satellites 2005 launch?? – SkyBridge • 80 satellites • 2004
    83. 83. what is SkyBridge? • SkyBridge is an Alcatel controlled company planning to establish a constellation of 80 satellites to provide broadband data communications direct to business & residential premises. • Satellites are Low Earth Orbit (LEO) at an altitude of 1500 km • offers “last mile” broadband access from 2004 – no long-haul trunking capability - connects users to terrestrial gateway • System cost is approx US$4.8bn
    84. 84. broadband LEO – low latency 36 000 km 1 500 km GEO : 500ms Astrolink Intelsat Spaceway LEO : 30ms SkyBridge Teledesic LEO round-trip propagation time comparable to terrestrial
    85. 85. Launching Step 1: satellite is released in the Low Earth Orbit by launch vehicle (click on the picture below) Step 2: The Payload Assist Module (PAM) rocket fires to place the satellite into the geostationary transfer orbit (GTO)
    86. 86. Launching (Continued) Step 3: Several days after the satellite gets into the GTO the Apogee Kick Motor (AKM) fires to put the satellite into a nearly circular orbit.
    87. 87. Launching (Continued) Step 4: Orbital Adjustment by firing the AKM to achieve a circular geosynchronus orbit. (click on the picture below)
    88. 88. Launch Vehicles Launch Vehicles Atlas II Country USA Delta II Proton Long H-2 March-3 USA Gross Weight Boast to GTO Ariane-4 Europe 460 t 3636 Kg 1,819 Kg 2,200 Kg Russia 680 t 2,000 Kg China JAPAN 202 t 260 T 650 Kg 2,200 kG
    89. 89. Launch Vehicle
    90. 90. Launch Vehicle
    91. 91. Summary of Launchers
    92. 92. Sea Launch
    93. 93. At the Equator equator 11 day travel, 3 days on site, 9 days back 1. and 2. stage fueled on launch site; 3. stage and satellite fueled in Long Beach
    94. 94. Sea Launch Lift-Off! Up to 6 t 3000 m deep water Commander is 5 km away for launch
    95. 95. The Launch Service Alliance ArianeSpace, Boeing Launch Services, and Mitsubishi Heavy Industries ↪ mutual backup to mitigate schedule risks, range issues, etc.
    96. 96. Summary of Launchers International Launch Services, ILS Lockheed Martin, USA, Khrunichev, RUS, Energia, RUS Atlas-IIARlo, Proton-Mhi Baikonur Launch Site
    97. 97. Types of Launches The Evolution: Land Launch since the 60ies Sea Launch since the 90ies Rail Launch since the 70ies Air Launch since the 80ies
    98. 98. Anatomy of a Satellite A communication satellite consists of the following subsystems: • Antenna_For receiving and transmitting signals. • Transponder_It contains the electronics for receiving the signals, amplifying them, changing their frequency and retransmitting them. • Power Generation and conditioning subsystem_For creating power and converting the generated power into a usable form to operate the satellite. • Command and Telemetry_For transmitting data about the satellite (status, health etc.) to the earth and receiving commands from earth. • Thrust subsystem_For making the adjustments to the satellite orbital position and altitude. • Stabilization subsystem_For keeping the satellite antennas pointing in exactly the right direction.
    99. 99. Common Abbreviations Orbits: GEO = Geostationary Earth Orbit HEO = Highly inclined Elliptical Orbit MEO = Medium altitude Earth Orbit LEO = Low altitude Earth Orbit IGSO = Inclined Geo-Synchroneous Orbit HAP = High Altitude Platform Services: BIG = Voice Telephony Super = Voice telephony into mobiles from GEO Little = Data only, typically store and forward Mega = Mega-bit/s services DBS = Direct Broadcast satellite television Service Dab = Digital Audio Broadcast satellite service Nav = Navigation service
    100. 100. glossary GEO – geostationary earth orbit – 36,000km MEO – Medium earth orbit – 6-12,000km LEO – Low earth orbit – 200-3,000km Broadcast – One to many simultaneous transmission, usually associated with older style analogue transmission Multicast – In communications networks, to transmit a message to multiple recipients at the same time. Multicast is a one-to-many transmission similar to broadcasting, except that multicasting means sending to specific groups, whereas broadcasting implies sending to everybody. When sending large volumes of data, multicast saves considerable bandwidth, because the bulk of the data is transmitted once from its source through major backbones and is multiplied, or distributed out, at switching points closer to the end users. 2-way – Infers forward and reverse transmission via the satellite, usually but not always asymmetric, i.e. high-speed download from the satellite and low speed from client to the satellite latency – The time between initiating a request for data and the beginning of the actual data transfer. A GEO satellite has a latency of approx 256ms resulting in a round trip delay of about half a second (echo) IP – Internet Protocol – the language of the Internet. The protocol stack is referred to as TCP / IP Fixed – refers to a satellite receiver being attached as a permanent mounting, as opposed to tracking. Mobile – Refers to a mobile satellite receiver such as a personal communicator or mobile phone. Usually associated with LEO and MEO services. Broadband – high speed transmission. The threshold is arguable, but is construed as being faster than dial-up ~ 64kbps and upwards. Some conventions suggest the threshold starts at 1.5 or 2Mbps. Orbit – The path of a celestial body or an artificial satellite as it revolves around another body. One complete revolution of such a body VSAT– Very small aperture terminal, refers to a small-dish service using a GEO satellite and a large central hub, usually 6 metres plus. DTH – Direct to home. A service bypassing normal terrestrial infrastructure such as a satellite TV receiver. As opposed to community satellite service where local distribution from a satellite receiver is done by cable, radio or other means.
    101. 101. 3. Orbital Mechanics
    102. 102. Contents • • • • • • • • • • • Kepler’s Laws Orbital Elements Epoch Orbital Inclination Right Ascension of Ascending Node (R.A.A.N.) Argument of Perigee Eccentricity Mean Motion Mean Anomaly Drag (optional) Apogee & Perigee Heights
    103. 103. Kepler’s Laws • LAW 1: The orbit of a planet about the Sun is an ellipse with the Sun's center of mass at one focus LAW 2: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time • LAW 3: The squares of the periods of the planets are proportional to the cubes of their semi-major axes
    104. 104. Kepler’s First Law • LAW 1: The orbit of a planet about the Sun is an ellipse with the Sun's center of mass at one focus. This is the equation for an ellipse:
    105. 105. Cont…. • Earth’s orbit has an eccentricity of 0.017 (nearly circular) • Pluto’s orbit has an eccentricity of 0.248 (the largest in our solar system) • Satellites also follow Kepler’s 1st Law – But Earth can replace sun at Focus
    106. 106. Kepler’s Second Law • LAW 2: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time
    107. 107. Cont… • So… Satellites go faster at Perigee than at Apogee • Reason: conservation of specific mechanical energy; i.e., З = KE + PE
    108. 108. Kepler’s Third Law LAW 3: The period of an orbit depends on the altitude of the orbit OR The square of the period is proportional to the cube of its mean distance from primary focus • T a2 / T b2 = R a3 / R b3
    109. 109. Cont… • Low Earth orbit: 90 minutes – 186 miles, 17,684 mph • Geosychronous: 24 hours – 22,236 miles, 6,857 mph • Moon: 28 days (one month) – 238,330 miles, 2,259 mph
    110. 110. Orbital Elements • The classic 'Keplerians' are the seven mathematical values which determine a spacecraft's orbit around the Earth. • In practice there are additional values which are required because the Earth isn't a perfect sphere, and other anomalies.
    111. 111. Cont… • Seven numbers are required to define a satellite orbit. This set of seven numbers is called the satellite orbital elements, or sometimes "Keplerian" elements (after Johann Kepler [15711630]), or just elements • These numbers define an ellipse, orient it about the earth, and place the satellite on the ellipse at a particular time. • In the Keplerian model, satellites orbit in an ellipse of constant shape and orientation. The Earth is at one focus of the ellipse, not the center (unless the orbit ellipse is actually a perfect circle)
    112. 112. Cont… The basic orbital elements are... 1. Epoch 2. Orbital Inclination 3. Right Ascension of Ascending Node (R.A.A.N.) 4. Argument of Perigee 5. Eccentricity 6. Mean Motion 7. Mean Anomaly 8. Drag (optional) Note:Satellite keplerians are also distributed by NASA in a format called the NASA twoline format.
    113. 113. Epoch • [aka "Epoch Time" or "T0"] • A set of orbital elements is a snapshot, at a particular time, of the orbit of a satellite. Epoch is simply a number which specifies the time at which the snapshot was taken Orbital Inclination • [aka "Inclination" or "I0"] • The orbit ellipse lies in a plane known as the orbital plane. The orbital plane always goes through the center of the earth, but may be tilted any angle relative to the equator. Inclination is the angle between the orbital plane and the equatorial plane. By convention, inclination is a number between 0 and 180 degrees.
    114. 114. Right Ascension of Ascending Node • [aka "RAAN" or "RA of Node" or “RAAN", and occasionally called "Longitude of Ascending Node"] • Right ascension is another fancy word for an angle, in this case, an angle measured in the equatorial plane from a reference point in the sky where right ascension is defined to be zero. Astronomers call this point the vernal equinox. • Finally, "right ascension of ascending node" is an angle, measured at the center of the earth, from the vernal equinox to the ascending node.
    115. 115. Apogee & Perigee A few words about elliptical orbits... The point where the satellite is closest to the earth is called perigee, although it's sometimes called periapsis or perifocus. We'll call it perigee. The point where the satellite is farthest from earth is called apogee (aka apoapsis, or apifocus).
    116. 116. Argument of Perigee • If we draw a line from perigee to apogee, this line is called the line-of-apsides (Sometimes the line-of-apsides is called the major-axis of the ellipse) • The line-of-apsides passes through the center of the earth. We've already identified another line passing through the center of the earth: the line of nodes. The angle between these two lines is called the argument of perigee • Where any two lines intersect, they form two supplementary angles, so to be specific, we say that argument of perigee is the angle (measured at the center of the earth) from the ascending node to perigee.
    117. 117. Cont… • In simple words the polar angle locating the perigee point of a satellite in the orbital plane; drawn between the ascending node, geocenter and perigee and measured from ascending node in direction of satellite motion.
    118. 118. Eccentricity • [aka "ecce" or "E0" or "e"] • Eccentricity tells us the "shape" of the ellipse. When e=0, the ellipse is a circle. When e is very near 1, the ellipse is very long and skinny. Mean Motion • [aka "N0"] (related to "orbit period" and "semimajor-axis") • Now we need to know the "size" of the orbit ellipse. In other words, how far away is the satellite?
    119. 119. • Kepler's third law of orbital motion gives us a precise relationship between the speed of the satellite and its distance from the earth. Satellites that are close to the earth orbit very quickly. Satellites far away orbit slowly. This means that we could accomplish the same thing by specifying either the speed at which the satellite is moving, or its distance from the earth! • Satellites in circular orbits travel at a constant speed. Simple. We just specify that speed, and we're done. Satellites in non-circular (i.e., eccentricity > 0) orbits move faster when they are closer to the earth, and slower when they are farther away. The common practice is to average the speed. You could call this number "average speed", but astronomers call it the "Mean Motion". Mean Motion is usually given in units of revolutions per day
    120. 120. • In this context, a revolution or period is defined as the time from one perigee to the next. • Sometimes "orbit period" is specified as an orbital element instead of Mean Motion. Period is simply the reciprocal of Mean Motion. A satellite with a Mean Motion of 2 revs per day, for example, has a period of 12 hours. • Sometimes semi-major-axis (SMA) is specified instead of Mean Motion. SMA is one-half the length (measured the long way) of the orbit ellipse, and is directly related to mean motion by a simple equation. • Typically, satellites have Mean Motions in the range of 1 rev/day to about 16 rev/day
    121. 121. Mean Anomaly • [aka "M0" or "MA" or "Phase"] • Now that we have the size, shape, and orientation of the orbit firmly established, the only thing left to do is specify where exactly the satellite is on this orbit ellipse at some particular time. • Anomaly is yet another astronomer-word for angle. Mean anomaly is simply an angle that marches uniformly in time from 0 to 360 degrees during one revolution. It is defined to be 0 degrees at perigee, and therefore is 180 degrees at apogee.
    122. 122. Drag • [aka "N1"] • Drag caused by the earth's atmosphere causes satellites to spiral downward. As they spiral downward, they speed up. The Drag orbital element simply tells us the rate at which Mean Motion is changing due to drag or other related effects. Precisely, Drag is one half the first time derivative of Mean Motion. • Its units are revolutions per day per day. It is typically a very small number. Common values for low-earth-orbiting satellites are on the order of 10^-4. Common values for high-orbiting satellites are on the order of 10^-7 or smaller.
    123. 123. Kepler Orbital Parameters (Kepler Elements) • Ω – right ascension of ascending node • i – inclination of orbital plane • ω – argument of perigee • a – semimajor axis of orbital ellipse • e – numerical eccentricity of ellipse • T0 – epoch of perigee passage Ref: www.amsat.org/amsat/keps/kepmodel.html#argp www.amsat.org/amsat/ftp/keps/current/amsat.all
    124. 124. Kepler Elements
    125. 125. 4. Orbital Perturbation
    126. 126. Contents • • • • • • • • • • Orbital perturbations Types of Orbital Perturbations The Non-Spherical Earth Atmospheric Disturbances Solar Radiation & Solar Winds Third Body Interaction Attitude Perturbations Aerodynamic Pressure Solar Pressure Earth Magnetic Field
    127. 127. Orbital perturbations • In this chapter we will discuss the most important disturbances. This is necessary to do because we want to know the lifetime of the satellite before it will tumble down to earth. • We will also see how the orbit changes due to the different disturbances. • One important thing to remember is that these calculations are for a cause to do the predicted orbit and lifetime more accurate.
    128. 128. Types of Orbital Perturbations • There are two types of Orbital Perturbations – gravitational, when considering third body interaction and the non-spherical shape of the earth. – non-gravitational like atmospheric drag, solar-radiation pressure and tidal friction. • These can also be classified as conservative or non-conservative disturbances forces. Where conservative forces depends only on the position, while non-conservative forces depends on both position and velocity.
    129. 129. The Non-Spherical Earth • The earth is far away from perfectly spherical. • One depends on the rotation, making the radius from center of the earth to the equator larger than from the center of the earth to the poles. – – – Gravitation potential Gravity harmonics Force approach
    130. 130. Atmospheric Disturbances • Although the atmosphere is almost empty you have to consider it. This is the most important disturbance, because it is the main cause in determining the lifetime of the satellite. • The drag that can be calculated is an empirical function based on Cd which is a constant depending on the shape of the body. • The also necessary density of the atmosphere depends on some different environmental factors such as the activity of the sun. The major part of the atmosphere below 1000 km consists of O2, N2, and He.
    131. 131. • The minor representative parts are O3, CO2, H2, NO,electrons, and both positive and negative ions. • The difficulty to determine the density is because of the chemical reactions especially photochemical reactions. These are driven by the sunlight, and therefore the activity of the sun is important. • The other chemical reaction in the atmosphere is diffusion. The minor constituents are controlled by photochemical
    132. 132. • In this case we use a mean value of the density. CD is the drag coefficient depending on the shape and surface but the best value is given in an actual test flight. But the value for a sphere is 2.2 and for a cylinder it is 3.0. Usually 2.2 is considered to give a conservative result.
    133. 133. Solar radiation and solar wind • Solar radiation is all kind of electromagnetic field emitted by the sun, from X-rays to radio waves. • The solar wind consists of particles emitted by the sun, mainly ionized nuclei and electrons. • Because of the charged particles in the solar wind it does not penetrate the magnetopause, except at the magnetic poles. The magnetopause starts about 10 earth radii from the center of the earth (Re = 8371) km. Therefore, the sun is more or less active. It has an activity cycle of 22 years between two
    134. 134. • Therefore the solar pressure is also not constant, but it fluctuate by <1%. The pressure is, P0 = 4.7 ·10-6 [Pa]. The perturbing forces can be calculated by:
    135. 135. • The effect due to the solar radiation pressure is, for a LEO, not that big. • The aerodynamic drag has a more disturbing effect. But at altitudes above 1000 km and an orbit close to the ecliptic plane it has a more distinct effect.
    136. 136. Third body interaction • How do the other planets disturb the satellite?
    137. 137. Attitude Perturbations • The disturbance in orientation or attitude is important to look at because we want to keep the orientation so it can perform the tasks • Here we consider the atmospherically drag, the solar pressure and the magnetic disturbance.
    138. 138. • Aerodynamic Pressure – The pressure due to the atmosphere affects the satellite, although one often think of space as a vacuum it has, or at least the environment where the satellite operates, has some kind of atmosphere. If the center of pressure of the body is different from the center of mass, the pressure acts on the body and the resultant of the forces is not through the center of mass and there are a torque due to the atmosphere. The force on a differential area can be expressed by;
    139. 139. Solar Pressure • Just like the pressure from the atmosphere a torque due to solar pressure act on the satellite. The pressure of the the sun and the difference of the center of pressure and the center of mass causes a torque on the satellite. The force on a differential area can be described with;
    140. 140. The total torque can be found in the same way as for the atmospheric torque.
    141. 141. Earth Magnetic Field • The magnetic field of the earth has two ways of disturbing the satellite. The first is when the satellite rotates in a magnetic field. The magnetic field induces eddy currents in the shell and due to the resistance of the shell it produces heat. The energy it takes to produce the heat is taken from the rotational energy but the effects are very small. In this case when we have a short life cycle of the satellite we do not have to take this aspect in our calculations. The torques due to eddy currents are;
    142. 142. • where ke is a constant depending on the satellite’s geometry (see table) and conductivity, B is the vector of the magnetic strength of the earth
    143. 143. 5. Satellite Visibility
    144. 144. Contents • • • • • • When are satellites visible? Factors Affecting the satellite visibility Orbit & Attitude Inclination Earth Shadow Ground Track Other factors
    145. 145. Limit of Visibility • When Are Satellites Visible? • Whether or not a satellite is visible to a given observer is dependent upon many factors such as observer location, time of day, satellite altitude, and sky condition. Knowing these details may aid an observer in determining the most favorable times for sightings and is most certainly necessary
    146. 146. Factors Affecting Satellite Visibility • Orbit Altitude And Inclination • Earth's Shadow • Ground Track • Other Factors
    147. 147. Orbit Altitude & Inclination • • • • GEO MEO LEO HEO
    148. 148. Earth's Shadow • The Earth's shadow must also be considered. When eclipsed, a satellite is naturally not visible. Such events are dependent upon the satellite's altitude, inclination, the time of year, and the observer's location
    149. 149. Ground Track • Precession Of course it is not simply a question of watching for a given satellite at the same time each night. Few satellites have an orbital period which is a simple fraction of one day, the geostationary satellites being the obvious exception. The orbital period is dictated by the satellite's altitude. The higher the altitude, the further it has to travel around the Earth and the longer it thus takes. Satellites in low Earth orbit complete one orbit in around 90 minutes, whereas at geostationary altitudes (about 36,000 km) one orbit takes 24 hours. • Many satellites in low Earth orbit go through a similar cycle of visibility. The cycle varies with orbital inclination, altitude, and observer location.
    150. 150. Other Factors • satellite suffers greater air resistance the lower its orbit. This bleeds off the orbital energy, lowering the orbit yet further as the satellite begins to brush the upper atmosphere at perigee. • The forces on the satellite due to the Earth (and Moon, Sun, etc.) vary throughout its orbit giving rise to continual change in the orbit.
    151. 151. 6. Radio Wave Propagation
    152. 152. Contents • Introduction • Atmospheric Losses – – – – – – – Beam-spreading Loss Polarization Loss Rayleigh fading Scintillation Loss Free-space loss Weather Loss Doppler Effect • Rain Attenuation • Ionospheric Losses
    153. 153. Introduction • This section discusses the basic effects of the propagation anomalies as they influence the communication satellite system performance • The greatest difference between the bands above 10 GHz and those between 1 and 10 Ghz • The 1-10 GHZ range is already extensively used by both terrestrial microwave and satellite services.although the noise level and attenuation are lower than the higher frequencies, the potential for interference from terrestrial point-to-point services has limited earth station locations.
    154. 154. • Above 10GHz the rain attenuation increases, but the chances of interference with other services are minimum. • At certain wavelengths signals encounter absorption bands due to atmospheric components (like water vapor and oxygen) within the range of 1-10 GHz • Frequencies above 30GHz have been underutilized, there is spectrum available, especially for services that do not pass through the atmosphere like ISL(Inter Satellite Link)
    155. 155. • The fundamental equation for the free-space position of the slant range losses(Lrange) is; Lrange = (4Π S/λ )2 where; S= Slant Range in m λ =Wavelength in m • At 6GHz the slant range attenuation is about 200db
    156. 156. Atmospheric Losses • In satellite communications, atmospheric losses results from the absorption of the Earth-satellite or satellite-Earth signals as they pass through the Earth's atmosphere. The value of the atmospheric loss is strongly dependent on frequency.
    157. 157. Atmospheric Losses
    158. 158. Atmospheric Losses – Beam-spreading Loss – Polarization Loss – Rayleigh fading – Scintillation Loss – Free-space loss – Weather Loss – Doppler Effect
    159. 159. Beam-spreading loss • In satellite communications, beamspreading loss results from the spreading of the earth-satellite signals as they pass through the Earth's atmosphere
    160. 160. Scintillation loss • In satellite communications, scintillation loss results from rapid variations in the signal’s amplitude and phase due to changes in the refractive index of the Earth's atmosphere.
    161. 161. Polarization loss • In satellite communications, polarization loss results from a rotation of the polarization of the signal as it passes through the Earth's atmosphere
    162. 162. Rayleigh Fading • Rayleigh fading is fading in a satellite communications channel due to the interference caused to the main signal by the same signal arriving over many different paths, resulting in out-of-phase components incident at the receiver. • Rayleigh fading occurs commonly in wireless communications channels, including satellite communications channels.
    163. 163. Free Space Losses • In satellite communications, free-space loss is the major loss suffered by signals in traveling over the Earth-satellite path. The loss is inversely proportional to the square of the distance traveled and inversely proportional to the square of the frequency used. That is, as the distance is doubled the received power is reduced by a factor of four. Similarly, as the frequency is doubled the received power is reduced by a factor of four. • Free-space loss for geo-stationary satellite communications satellites varies between 190-210 dB depending on the frequency used
    164. 164. Weather Losses • In satellite communications, weather loss results from attenuation of the Earthsatellite signals by hydrometers as they pass through the Earth's atmosphere
    165. 165. Brightness Temperature of the Earth 14 GHz (ESA/EUTELSAT-Modell)
    166. 166. Doppler Effect • The Doppler effect in satellite communications is the change in frequency of an electromagnetic signal that results from the relative speed of the satellite and the Earth terminal. When the orbital parameters of a satellite are known, Doppler shift can be used to determine the position of the Earth terminal. When an Earth terminal's position is known, Doppler shift can be used to estimate the orbital parameters of a satellite. When the satellite (or the Earth station) is moving quickly, the Doppler effect is an important consideration in satellite communications
    167. 167. Atmospheric and Rain Attenuation
    168. 168. Rain Attenuation • Rain is predominant loss element below 60GHz. • Fog is shown has attenuation 0.1 g /m3 • The total link attenuation is the sum of the losses due to slant range , the atmosphere, precipitation and any additional losses(such as scintillation etc.)
    169. 169. Climatic Zones A: is extremely dry climate, . . . P: extremely humid climate
    170. 170. Climatic Zones A C C D K E H K E M E P H H P H E E C D K K P D N C E P H D E F P N E F D M K A
    171. 171. Atmospheric and Rain Attenuation 20 mm/h Rain Attenuation 10 mm/h 100 Equatorial Latitudes Additional Attenuation in dB 10 100 10 Ionospheric Delay 1 Atmosph. Attenuation Medium Latitudes 1  5 GHz Frequency in GHz
    172. 172. Ionospheric Losses • Al lower frequencies (e.g 1.5 and 2.5 GHz) ionospheric effect may be encountered, particularly scintillation. • The magnitude of these losses vary considerably with the time of day and the sunspot activity level (the affect the ionosphere).
    173. 173. Ionospheric Losses
    174. 174. Ionospheric Losses • All radio waves propagated over ionospheric paths undergo energy losses before arriving at the receiving site. As we discussed earlier, absorption in the ionosphere and lower atmospheric levels account for a large part of these energy losses. • There are two other types of losses that also significantly affect the ionospheric propagation of radio waves. These losses are known as ground reflection loss and free space loss. • The combined effects of absorption, ground reflection loss, and free space loss account for most of the energy losses of radio transmissions propagated by the ionosphere
    175. 175. 7. Polarization
    176. 176. Contents • • • • • • • • Polarization Types of Polarization Antenna polarization Manual Polarization Switching Polarization of satellite signals Depolarization Cross polarization discrimination Ionospheric depolarization, rain & ice depolarization • XPD and Co-Polar Attenuation • Ionospheric Effect
    177. 177. Polarization • The polarization of an electromagnetic wave is defined as the orientation of the electric field vector. Recall that the electric field vector is perpendicular to both the direction of travel and the magnetic field vector. • The polarization is described by the geometric figure traced by the electric field vector upon a stationary plane perpendicular to the direction of propagation, as the wave travels through that plane.
    178. 178. Cont…
    179. 179. Cont… • Polarization is also describe as the "direction of vibration" on the radio wave. • It depends the orientation of elements of an antenna, when you set elements vertical, it generates verticalpolarized radio wave similarly when you set as horizontal, it generates horizontal-polarized. • In the case of YAGI antenna, the direction of Electronic-Field is same as the direction of its elements. • Radio stations have to set as a same direction of polarization for communication each other.
    180. 180. Types of Polarization • An electromagnetic wave is frequently composed of (or can be broken down into) two orthogonal. This may be due to the arrangement of power input leads to various points on a flat antenna, or due to an interaction of active elements in an array, or many other reasons. • The geometric figure traced by the sum of the electric field vectors over time is, in general, an ellipse as shown in Figure 2. Under certain conditions the ellipse may collapse into a straight line, in which case the polarization is called linear.
    181. 181. Cont… • In the other extreme, when the two components are of equal magnitude and 900 out of phase, the ellipse will become circular as shown in Figure 3. Thus linear and circular polarization are the two special cases of elliptical polarization. Linear polarization may be further classified as being vertical, horizontal, or slant.
    182. 182. Polarization and its types
    183. 183. Cont… • Polarization makes the beam more concentrated • FSS satellites use horizontal and vertical polarization, whereas DBS satellites use left- and right-hand circular polarization • To use the channels that are available for satellite broadcast as efficiently as possible, both horizontal and vertical polarization (and left- and right-hand circular polarization) can be applied simultaneously per channel or frequency. In such cases the frequency of one of the two is slightly altered, to prevent possible interference
    184. 184. Cont… • Horizontal and vertical transmissions will therefore not interfere with each another because they are differently polarized. This means twice as many programs can be transmitted per satellite • Consequently, via one and (almost) the same frequency the satellite can broadcast both a horizontal and a vertical polarized signal (H and V), or a left- and right-hand circular polarized signal (LH and RH).
    185. 185. Radio stations have to set as a same direction of polarization for communication each other. • When you try to hear the vertical-polarized wave with horizontal- polarized antenna, what will be happened? A theory tells it is impossible to receive. In fact, although it is possible, It becomes very difficult (very weak less than -20dB ). This is due to:– The radio waves do not travels with pure-polarized condition, and – There is no real antenna that has pure-polarized character. Anyway, you should to adjust the polarization for better communication.
    186. 186. Is Circular Polarization better choice for satellite? • Circular-polarization (CP) is another choice when you could not decide the polarization of your choice. • CP is the special style of polarization, the direction of Electric-Field rotates one times par one cycle. • The CP antenna can receive both horizontal and vertical polarized radio wave, even in the direction of slant-polarized. • CP is very popular technique for satellite communication both commercial and amateur satellite systems.
    187. 187. Antenna Polarization • Table 1 shows the theoretical ratio of power transmitted between antennas of different polarization. These ratios are seldom fully achieved due to effects such as reflection, refraction, and other wave interactions, so some practical ratios are also included.
    188. 188. Cont…
    189. 189. Cont… • The sense of antenna polarization is defined from a viewer positioned behind an antenna looking in the direction of propagation. The polarization is specified as a transmitting, not receiving antenna regardless of intended use. • We frequently use "hand rules" to describe the sense of polarization. The sense is defined by which hand would be used in order to point that thumb in the direction of propagation and point the fingers of the same hand in the direction of rotation of the E field vector.
    190. 190. Cont… • For example, referring to Figure 4, if your thumb is pointed in the direction of propagation and the rotation is counterclockwise looking in the direction of travel, then you have left hand circular polarization. • The polarization of a linearly polarized horn antenna can be directly determined by the orientation of the feed probe, which is in the direction of the E-field.
    191. 191. Cont… • In general, a flat surface or sphere will reflect a linearly polarized wave with the same polarization as received. A horizontally polarized wave may get extended range because of water and land surface reflections, but signal cancellation will probably result in "holes" in coverage. Reflections will reverse the sense of circular polarization.
    192. 192. Cont… • For a linearly polarized antenna, the radiation pattern is taken both for a co-polarized and cross polarized response. • The polarization quality is expressed by the ratio of these two responses. The ratio between the responses must typically be great (30 dB or greater) for an application such as cross polarized jamming • For general applications, the ratio indicates system power loss due to polarization mismatch. • For circularly polarized antennas, radiation patterns are usually taken with a rotating linearly polarized reference antenna.
    193. 193. Manual Polarization Switching • The CP antenna reduces QSB so it might be better for comfortable operation, but the CP antenna is bigger and more complicated than the simple linearpolarized antenna. Also the big and complicated antenna will be expensive. 3dB loss will be a problem with some limited conditions. • There is another choice. Setup a pair of vertical/Horizontal polarized independent antenna and switch them at your shack. You select where either is better during its pass. This is the theory of "Divercity" reception
    194. 194. Polarization of satellite signal • Applied for geo-stationary satellites • “Horizontal”polarization = parallel to the equatorial plane • “Vertical”polarization = parallel to the Earth's axis • Polarization angle at earth station – – – – – r = local gravity direction k = the direction of the wave propagation p = unit polarization vector f = k x r, normal to the reference plane x = the angle between the reference plane (r and k) and the polarization vector
    195. 195. Depolarization • The electric field E1 is depolarized after going through a depolarizing medium. • The result is, as shown in the figure, an orthogonal (E12) component may be generated. • E11 is called the co-polar component and E12 is called the cross-polar component. • This phenomenon can cause interference.
    196. 196. Cont…
    197. 197. Cross-Polarization Discrimination (XPD) • One measure to quantify the effects of polarization is called the cross-polarization discrimination (XPD)
    198. 198. Cross-polarization discrimination observations - rain depolarization • Looking at XPD as a function of the co-polar attenuation (A), it can be concluded that: – XPD degrades at a given co-polar attenuation as the frequency decreases – XPD degrades with increasing co-polar attenuation – XPD for the Vertical Polarization wave is better than that for Horizontal Polarization – XPD for the Vertical Polarization and the Horizontal Polarization waves are better that the Circular Polarization
    199. 199. XPD and co-polar attenuation A θ -> the elevation angle in degrees τ −> the polarization tilt angle τ = 45 for circular polarization
    200. 200. Ionospheric effects • Faraday’s effects – The rotation of a linearly polarized wave due to the earth’s magnetic field is called the Faraday’s effect. It is proportional to the 1/f2 factor. • Ionospheric scintillation – Due to the refractive index variations in the ionosphere caused by local concentrations of ionization. It is also proportional to the 1/f2 factor.
    201. 201. 8. Antenna
    202. 202. Contents • • • • • • • • • Antenna Some Basic Definitions Radiation Parameters Radiation Patterns Types of Radiation Patterns Antenna Radiation Pattern Nulls & Lobes Antenna Beamwidth Types of Ground Station Antenna used in SatCom Types of Space Segment Antenna used in SatCom
    203. 203. Antenna • Antennas form a very important element in communication system, either terrestrial or extra terrestrial, depending on the mission type and requirements • "That part of a transmitting or receiving system which is designed to radiate or to receive electromagnetic waves". • we use antennas to overcome our inability to lay a physical interconnection between two remote locations or an antenna can also be viewed as a transitional structure (transducer) between free-space and a transmission line (such as a coaxial line). • Antennas cannot add power, instead they can only focus and shape the radiated power in space e.g. it enhances the power in some wanted directions and suppresses the power in other directions
    204. 204. Some Basic Definitions • Suppose we have an antenna located at the origin of a spherical co-ordinate system, further assume that the antenna is transmitting and the observations are made for a very large distance; • Let Po (Watts) be the accepted power in the antenna and Pr (Watts) be the radiated power, then the radiating efficiency ή as; • ή = Pr / Po z θ Ant Location ç z r P y
    205. 205. Radiation Intensity • We define Radiation Intensity f (θ,Ф) or Θ(θ,Ф) (watts/steradians) Pr = • The Average radiation intensity is; Θavg = Pr / 4π
    206. 206. Antenna Directivity (Measure of the focusing property of an antenna) • • "The directivity of an antenna is defined as the ratio of the radiation intensity in a given direction from the antenna, to the radiation intensity averaged over all directions. This average radiation intensity is equal to the total power of the antenna divided by (4 pi). If the direction is not specified, the directivity refers to the direction of maximum radiation intensity". D (θ,Ф) = {Θ(θ,Ф) / Θavg} or D (θ,Ф) = 4π {Θ(θ,Ф) / Pr} ≈ θ is the elevation angle ≈ φ is the azimuth • where D is the directivity. Generally D > 1, except in the case of an isotropic antenna for which D = 1. An antenna with directivity D >> 1 is called a directive antenna.
    207. 207. Cont…
    208. 208. Gain (Measure of Directivity) • The Gain G(θ,ф) is the ability to concentrate the power accepted by the antenna in a particular direction. It is related to the Directivity and Power Radiation efficiency or in other words Power Radiation Intensity as follow; G(θ,ф)= ή D(θ,ф) for loss less antenna ή =1 G(θ,ф)=4π{Θ(θ,Ф) / Pr} • With respect to the antenna's dimensions, G= ή{4πA / λ2} A is the aperture area of the antenna λ is the wavelength of the operational frequency η is the antenna efficiency (usually between
    209. 209. Cont… • Basically there are only two types of antennas: • dipole antenna (Hertzian) • vertical antenna (Marconi) • All antennas can be broken down to one of these types (although some say that there is only one - the dipole) • In addition to this we have a theoretical perfect antenna (non-existent) that radiates equally in all directions with 100% efficiency. This antenna is called an isotropic radiator.
    210. 210. Cont… (Basic Antenna types)
    211. 211. Gain presented as 3D gain The gain can also be presented as a 3D gain. The radius of the spheroid is proportional to the antenna gain.
    212. 212. Gain in theory • Since all real antennas will radiate more in some directions than in others, you can say that gain is the amount of power you can reach in one direction at the expense of the power lost in the others. When talking about gain it is always the main lobe that is discussed • Gain may be expressed as dBi or dBd. The first is gain compared to the isotropic radiator and the second gain is compared to a halfwave dipole in free space (0 dBd=2.15 dBi)
    213. 213. Power Density • The power density P(θ,ф) is related to radiation intensity as follows; P(θ,ф)= {Θ(θ,Ф) / r2} or P(θ,ф)= {G(θ,Ф) Po/ 4πr2} • The factor Po/ 4πr2 represent the power density that results if the power accepted by the antenna were radiated by loss-less isotropic antenna
    214. 214. Equivalent Isotopic Radiated Power (EIRP) • The maximum power flux density at some distance “r” from a transmitting antenna of gain “G” is; • An isotropic radiator with input power equal to GPS would produce the same flux density. Hence,
    215. 215. Antenna Effective Area • Measure of the effective absorption area presented by an antenna to an incident plane wave. • Depends on the antenna gain and wavelength λ 2 Ae = G (ϑ , ϕ ) [m ] 4π 2 • Aperture efficiency: ηa = Ae / A A: physical area of antenna’s aperture, (m2)
    216. 216. Transmission losses • Free Space Transmission [FSL] – More to follow • Feeder Losses [RFL] – Between the receive antenna and the receive proper • Antenna Misalignment Losses [AML] • Fixed Atmospheric & Ionospheric Losses – Absorption losses – Depolarization losses
    217. 217. Power transfer between two antennas • For two antennas in free space separated by large distance R • The received power is equal to a product of power density of the incident wave and the effective aperture area of the receiving antennas Pr = PAe or Pr = {(GtPtGrλ2) / (16π2R2)}
    218. 218. Antenna Bandwidth • • • • The bandwidth of an antenna is defined as ”The range of frequencies within which the performance of the antenna, with respect to some characteristic, conforms to a specified standard”. The reason for this qualitative definition is that all the antenna parameters are changed with frequency and the importance of the different parameters as gain, return loss, beamwidth, side-lobe level etc. much depends on the application. For example, the bandwidth of an antenna for gain (-1dB from the maximum) is defined as where fU is the upper frequency, fL is the lower frequency, and fC is the center frequency. Another example is the bandwidth related to the mismatch loss defined by the SWR .
    219. 219. Reciprocity • • ALL the major properties of a linear passive antenna are identical whether it is used in transmit or receive mode. There is only one exception to this rule called "reciprocity", and that is when the antenna contains magnetically biased magnetic materials such as ferrites with resonantly rotating electron spin systems. The physical reason for reciprocity is that the only difference between outgoing and incoming waves lies in the arrow of time. Since the electromagnetic equations are invariant except for the signs of magnetic fields and currents, under time reversal, there can be no difference between transmit and receive mode in the physical current and field distributions. However, if we have a magnet providing a steady bias field, under time reversed conditions we would have to reverse the direction of this bias field. But for incoming and outgoing waves, the bias field direction remains the same. Thus it is possible for the system to be non-reciprocal.
    220. 220. Cont… • Of course, antennas containing amplifiers, or diodes, or spark gaps, may well not be reciprocal for obvious reasons. Also, practical antenna installations having metal-oxide-metal contacts, "rusty bolts", dry soldered joints and other electrical contact imperfections are also likely to behave differently under transmit and receive modes of operation
    221. 221. Radiation Parameters • Radiation Pattern measurement – Graphical representation of the field magnitude at a fixed distance from an antenna as a function of direction i.e. angular variation of the test antennas radiation. • Gain measurement – Absolute measurement that gives the angular variation of the test antenna’s radiation. Needed to fully characterize the radiation properties of the test antenna.
    222. 222. Radiation Parameters • Polarization – Defined as the polarization of the electromagnetic wave radiated by the antenna along a vector originating the antenna along the primary direction of propagation. The direction of the oscillating electrical field vector i.e. orientation of the E-filed. – Four basic types of polarization Vertical-, horizontal-linear polarization and Lefthand elliptical, Right-hand elliptical polarization.
    223. 223. Radiation Parameters
    224. 224. Radiation Pattern • Radiation pattern characteristics/parameters: – – – – – – Half-power beam width Main lobe Side lobes Antenna directivity Gain function Boresight (Direction of maximum gain) – Polarization – Distortion – XPD(cross polarization
    225. 225. Radiation Pattern • Antenna radiation pattern is three-dimensional, but is needed to describe them as two-dimensional paper. The most popular technique is to record signal level along great circle or conical cuts through the radiation pattern. In other words, one angular coordinate is held fixed, while the other is varies. • Radiation Pattern = Radiation Intensity as function of the azimuth/ elevation angles or In different words when power radiation intensity and power density are presented as relative scale, they are referred to as antenna radiation pattern. • A family of such two-dimensional patterns then can be used to describe the complete three dimensional patterns • The main lobe of the radiation pattern is in the direction of maximum gain
    226. 226. Types of Radiation Pattern • There are many types of antenna radiation patterns, most common are; • Omnidirectional (azimuthal plane) beam • Pencil beam • Fan beam • Shaped beam
    227. 227. Omnidirectional Antenna and Coverage Patterns The Omnidirectional beam is most popular in communication and broadcast applications. The azimuthal pattern is circular, but the elevation pattern will have some directivity to increase the gain in the horizontal directions
    228. 228. Pencil Beam Pencil beam is applied to a highly directive antenna pattern consisting of a major lobe contained with in it cone of small solid angle. Usually the beam is circularly symmetric about the direction of peak intensity
    229. 229. Fan Beam A fan beam is narrows in one direction and wide in the other. A typical use of a fan beam would be in search or surveillance radar
    230. 230. Shaped Beam Shaped beams are also used in search and surveillance
    231. 231. Cont… • • • • Radiation patterns generally defined as the far field power or field strength produced by the antenna as a function of the direction (Azimuth and elevation) measured from the antenna position. The behavior of the fields is changed with the distance from the antenna, and generally three regions are defined: Reactive near-field region - The region in the space immediately surrounding the antenna in which the reactive field dominated the radiating field (d <λ/(2π)). Radiating near-field region - Beyond the former region and for which d <2D2/ λ where r is the distance from the antenna, D is the largest dimension of the antenna and λ is the wavelength. This region is called also Fresnel region. In this region the radiating field begins to dominate. Far-field region - Beyond this region, the reactive field become negligible and also the radial part of the fields. This region is called also Fraunhofer region. – Generally measurements are taken in the far field region. In case of large planar antennas it is more convenient to make near field measurements and to calculate the far field.
    232. 232. Antenna Radiation Pattern Lobes and Nulls • A radiation lobe can be defined as a portion of radiation pattern bounded by regions of relatively weak radiation intensity. The main lobe is a high radiating energy region. Other lobes are called sidelobes, and the lobe radiating in the counter direction to the desired radiation direction is called back lobe. Regions for which the radiation is very weak are called nulls.
    233. 233. Antenna Beamwidth. • Antenna beamwidth is defined as the angle θ between half power points on the main beam. In case that we have a power pattern in [dB] units, it means that we measure the angle between two 3dB points.
    234. 234. Measuring E and H field of antenna
    235. 235. E field cut of dipole antenna
    236. 236. Half-power beam width • It is the angular beam width at 3 dB. It can be approximated as, • D is the antenna's diameter. ∀ λ is the operational wavelength.
    237. 237. Half-power beam width
    238. 238. Short Dipole in Free Space FF 1 H V Relative Gain 1 -1 0 0 90 180 270 360 Degrees Horizontal plane: GVi /GVimax = 1 Vertical plane: GHi /GHimax = |sin θ|
    239. 239. Elements of Radiation Pattern Main lobe Emax • • Emax /√2 • Nulls • Sidelobes -180 0 Beamwidth Gain Beam width Nulls (positions) Side-lobe levels 180 (envelope) • Front-to-back ratio
    240. 240. Antenna Mask (Example 1) 0 -10 -15 180 120 60 0 -60 -120 -20 -180 Isotropic gain, dB -5 • Typical relative directivitymask of receiving antenna (Yagi ant., TV dcm waves) Azimith angle, degrees [CCIR doc. 11/645, 17-Oct 1989)
    241. 241. Antenna Mask (Example 2) 0 0dB RR/1998 APS30 Fig.9 -10 Relative gain (dB) COPOLAR -20 -3dB Phi0/2 Phi -30 -40 CROSSPOLAR -50 0.1 1 10 100 Phi/Phi0 Reference pattern for co-polar and cross-polar components for satellite transmitting antennas in Regions 1 and 3 (Broadcasting ~12 GHz)
    242. 242. Types of Ground Antennas Used in Satellite Missions • Different satellite missions have different allotted frequency slots by ITU, each slot behaves differently between ground and earth segment in terms of dispersion, attenuation and noise accumulation • Generally at frequencies below 1GHz, TTT&C are running, the antenna may then be arrays of dipoles, helices and yagi-uda arrays, such type of antenna systems have wider beamwidth and medium gain. Deploying them in an array pattern results in increased gain and fanned and shaped beams thus enabling them for comparatively easy tracking • At frequencies above 1GHz the electromagnetic waves become highly directional but more susceptible to attenuation, fading and dispersion, therefore, horn and parabolic antennas are most commonly used. The most popular and widely used are the aperture antennas given bellow;
    243. 243. Types of Ground Antennas Used in Satellite Missions • Axially Symmetric Fed Antenna – This is the most common type of antennas found on roof tops or back yards of homes. They come in different configurations. Axis symmetric point focus feed. Front feed and Vortex feed • Cassegrain Feed Antenna – The second common configuration used particularly in large antennas is the Cassegrain antenna. Here the feed is located at the vertex of the parabolid and illuminates a hyperbolic shaped subreflector located at the focal area. The benefit here is that the electronics is located at a more accessible part of the antenna but with some sacrifice in sidelobe level because of the blockage .
    244. 244. Types of Ground Antennas Used in Satellite Missions • Gregorian Feed Antenna – In Gregorian configuration the feed is at the focal point of an ellipse and the elliptical sub-reflector at its other focus. With this configuration there is an improvement in the far-outside lobe level • Offset Aperture Antennas – These configurations indicate that the feed are on axis . The same generic types may also be used with offset feeds. The removal of feed from a collimated beam improves the side lobe level and has better effect of reducing mutual interference from adjacent satellites.
    245. 245. Reflector antennas
    246. 246. Crossed Yagi antennas for circular polarisation and right-handed and left-handed helical antennas
    247. 247. Cassegrain Feed Antenna Comparison between the measured antenna gain pattern and the predicted one for small offaxis angles
    248. 248. Front Fed Antenna A Front-Fed Offset Reflector Antenna with Multiple-Feed Horns (Courtesy Alenia Spazio)
    249. 249. Gregorian Feed Antenna
    250. 250. Offset Parabolic Reflector
    251. 251. Offset Parabolic Antennae
    252. 252. Satellite Antennas • The physical dimensions of the spacecraft and the availability of limited power restrict use of large antennas. • Medium gain antennas are used instead which include modified parabolic antennas for large area coverage • In LEO missions, the satellite may be two axis stabilized, the rotation being on the axis with largest inertia, the antenna gain pattern may not remain uniform when received at the ground station. Therefore, a rotating antenna whose rotation is in the opposite direction of the satellite rotation is used, such type of antenna is called “Despun antenna” • Circular polarization may employed for TT&C purposes or image transmission like weather satellite • Helical antennas are used for circularly polarized EM wave pattern, these antennas has larger beamwidth, therefore, tracking by the ground station becomes easier
    253. 253. Satellite Antennas • In GEO satellites, DVB and VSAT applications are dominant • In broadcast services satellite has to cover larger area , linearly polarized array antennas are used. For broadcast services the transmitting antennas may consist of array of Horn Antennas, Helical Antennas or Disk-on-Rod Antennas. Power beam form the antennas can be steered to cover specific area on the earth’s surface by switching on or off different antennas from the array on the satellite.
    254. 254. 18 dBi X-band pyramidal horn antenna
    255. 255. Helical Antenna
    256. 256. 9. Link Budget
    257. 257. Contents • • • • • • • • • • • • • • Introduction General Architecture Signal Power Calculation EIRP Noise Calculation Thermal Noise Effective Temperature Noise Temperature G/T Link Analysis Eb/No Carrier Parameters BER Rain Attenuation and Margin
    258. 258. Link Budget
    259. 259. Introduction Overall design of a complete satellite communications system involves many complex trade-offs to obtain a costeffective solutions Factors which dominate are –Downlink EIRP, G/T and SFD of Satellite –Earth Station Antenna –Frequency –Interference
    260. 260. General Architecture EIRP down Uplink Downlink G/T & SFD Uplink Path Loss Rain Attenuation Downlink Path Loss Rain Attenuation EIRP Up Gt G/T ES Pt HPA / Transceiver LNA / LNB
    261. 261. Transmit Earth Station – Antenna Gain – Power of Amplifier Uplink – Path Loss – Rain Attenuation
    262. 262. Satellite – G/T – EIRP – SFD (Equivalent Isotropic Radiated Power) (Saturated Flux Density) – Amplifier Characteristic Downlink – Path Loss – Rain Attenuation
    263. 263. Receiving Earth Station – Antenna Gain – LNA /LNB Noise Temperature – Other Equipment
    264. 264. Signal Power Calculation Antenna Gain G = η (Π * d / λ) 2 [dBi] Where, λ=C/f, C = Speed of light f = frequency of interest η = efficiency of antenna (%), d = diameter of antenna (m)
    265. 265. Signal Power Calculation Antenna Beam width θ 3dB = 70 * C / df Where, C= 3x108 m/s (Velocity of Light) [degrees]
    266. 266. EIRP Is the effective radiated power from the transmitting side and is the product of the antenna gain and the transmitting power, expressed as EIRP = Gt + Pt –Lf Where, Lf is the Feed Losses [dB]
    267. 267. Signal Power (Pr) Pr = EIRP – Path Loss + Gr (sat) [dB] Where, Path Loss = (4ΠD / λ) 2 D is the Slant Range (m)
    268. 268. Noise Calculation
    269. 269. Thermal Noise Is the noise of a system generated by the random movement of electronics, expressed as Noise Power = KTB Where, K= (-228.6 dBJ/K) T= Equivalent Noise Temperature (K) B= Noise Bandwidth of a receiver
    270. 270. Effective Temperature Te = T1 + (T2/G1) Where, T1= Temperature of LNA T2= Temperature of D/C G1= Gain of LNA
    271. 271. Noise Temperature Ts = Tant / Lf+(1-1/Lf)Tf Where , Tant = Temperature of antenna Lf = Feed Losses Tf = Feed Temperature
    272. 272. Effective Temperature Tsys = Ts + Te • • • Being a first stage in the receiving chain, LNA is the major factor for the System Temperature Calculation Lower the noise figure of LNA lower the system temperature Antenna temperature depends on the elevation angle from the earth station to satellite
    273. 273. G/T (Gain to System Noise Temperature) – This is the Figure of merit of any receiving system – It is the ratio of gain of the system and system noise temperature G/T = G-10log (Tsys) [dB/K]
    274. 274. Link Analysis C/N Uplink (C/N)u = (EIRP)e-(Path Loss)u+(G/T)sat-K-Noise BW [dB] C/N Downlink (C/N)d = (EIRP)sat-(Path Loss)d+(G/T)e-K-Noise BW [dB] C/N Total (C/N)T-1 = (C/N)u-1 + (C/N)d-1 + [C/I)IM-1 + [C/I]adj-1 + [C/I]xp-1 [dB]
    275. 275. Eb/No (Energy per bit per Noise Power Density) – Is the performance criterion for any desire BER – It is the measure at the input to the receiver – Is used as the basic measure of how strong the signal is – Directly related to the amount of power transmitted from the uplink station Eb/No = (C/N)T + Noise BW – Information Rate
    276. 276. Carrier Parameters • Solution - Carrier Performance: – Eb/No Threshold – Bit Error Rate (BER) – Rain Attenuation
    277. 277. Bit Error Rate (BER) – Why is it used? - To represent the amount of errors occurring in a transmission - To express the link quality – What is it? - BER is an equipment characteristic - BER is directly related to Eb/No - BER improves as the Eb/No gets larger P = 1/2 e -Eb/No (with P = Probability of error)
    278. 278. Carrier Parameters • Performance: – Application specific • Digital voice links: – BER threshold 10-3 • Data links: - BER threshold: 10-4
    279. 279. Carrier Parameters • Performance: – Typical Eb/No values for different FEC Eb/No for FEC 1/2 (dB) Eb/No for FEC 3/4 (dB) Eb/No for FEC 7/8 (dB) BER 6.5 7.1 7.6 9.9 8.0 8.7 9.2 11.0 9.1 9.7 10.4 12.1 10-6 10-7 10-8 10-10
    280. 280. Rain Attenuation • Performance - Rain Attenuation: – Availability TO • Rain Margins – Typically 99.60 % for Ku-Band – Typically 99.96 % for C-Band E/S • Performance - Additional Margins: – Adjacent Satellite Interference (ASI) – Interference Margins SA L TE E LIT
    281. 281. Summary; Transmission Parameter for Link Budgets C = 10 log (c) in dBW c = 100.1 C in W N = 10 log (n) in dBW n = 100.1 N in W C-N = C - N in dB EIRP = P + G - V in dBW PL = FD + AD + RD in dB G-T = G - T in dBi/K N = T + K + B in dBW C ‑N [dB] = EIRP ‑ PL + G‑T K ‑ B [dBW] [dB] [dBi/K] [dBWs/K] [dBHz]
    282. 282. Cont... EIRP = P + G - V in dBW, Equivalent Isotropic Radiated Power G-T = G - T in dBi/K, Figure of Merit PL = FD + AD + RD in dB, Pathlosses N = T + K + B in dBW,Noise Power. = No + B; No Noise Power Density dBW/Hz C-N = C - N in dB, Signal to Noise Ratio Eb-No =Energy per bit to noise power density, in dB BER = Bit Error Rate, e.g.: 10-5
    283. 283. 10. Interference
    284. 284. Contents • • • • • • • • • • • • • Interference in Satellites Interference Types Sources of Interference Causes of Interference FM Interference Cross Polarization Interference Digital & CW Interference Intermodulation Interference Raised Noise Floor Spikes & Unknown Adjacent Satellite Interference Adjacent Transponder Interference Co-Channel Interference
    285. 285. Interference in Satellite • Interference is mainly concern on; – Interference Type – Sources of Interference – Causes of Interference
    286. 286. Interference Interference Type: • Digital • Spike • Cross Polarization • TDMA • FM TV • Intermodulation • Unknown
    287. 287. Interference Source of Interference: •Neighboring Customer •Adjacent Satellite •Self-Customer •Opposite Polarization •Others External Factors: 40.22% Internal Factors: 59.78%
    288. 288. Interference Causes of Interference: •Human Error: 29.89% •Equipment Error: 21.74% •Adjacent Satellite: 16.85% •Customer Cooperation: 8.15% •Others: 23.37% Internal Factors: 59.78%
    289. 289. Types of Interference • • • • • • • • • FM Cross Polarization Digital CW Intermodulation Raised Noise Floor TV/FM TDMA Spikes & Unknown
    290. 290. FM Interference I Base band IF Up converter 70 MHz RF HPA 6 GHz FM signal:88 MHz to 108 MHz 70 MHz 6 GHz FM Radio Signal
    291. 291. FM Interference II f (MHz) 70 f (MHz) 88 108 90 + f (MHz) 70 IF 90 f (GHz) 6.0 RF 6.09
    292. 292. FM Interference III Source: • Terrestrial FM Radio Broadcast • Introduced at the IF level of the Earth Station
    293. 293. FM Interference IV Cause: • Poor Connection between BB and RF equipment, so FM broadcast is induced into the system and eventually transmitted to the satellite. • Poor quality accessory between BB and RF • Poor grounding system
    294. 294. FM Interference V Prevention: • • • • Select accessories with standard specifications Good Earth Station installation Good grounding system Coordinate with PCNS to perform UAT and interference checking when a new station is installed
    295. 295. Cross Polarization Interfrence Source: • If XPD level of an uplink antenna is less than 30 dB, antenna will transmit both vertical and horizontal polarizations • Therefore, cross pole will occur at the other satellite or transponder with opposite pole and will interfere the existing carrier
    296. 296. Cross Polarization Interfrence Cause: • Poor antenna pointing • Poor cross pole isolation • Sudden change in the antenna pointing due to mistake or storm • Carrier uplink without performing proper UAT with PCNS
    297. 297. Cross Polarization Interfrence Prevention: • Do not uplink the carrier without performing UAT with PCNS • DO not uplink un-modulated carrier for UAT before PCNS’s directions • Perform Regular Preventive maintenance
    298. 298. Digital & CW Interference Source: • Earth Station Equipment
    299. 299. Digital & CW Interference Cause: • Transmission of wrong carrier frequency by the user • Unauthorized access • Uplink CW for UAT before calling PCNS • Equipment malfunction
    300. 300. Digital & CW Interference Prevention: • Verify U/L frequency before transponder access • Do not uplink un-modulated carrier (CW) before PCNS directions • Perform UAT • Request PCNS if customer wants to uplink a new carrier for special purpose at some vacant slot • Perform Preventive Maintenance periodically
    301. 301. Intermodulation Interference Description: • If more than one carrier are transmitted by a single HPA, mixing or Intermodulation (IM) processes take place • This results in Intermodulation products which are displaced from the carriers at multiples of the difference frequencies • The power level of the Intermodulation products are dependent on the relative power level of the carrier and the linearity of TWTA or SSPA
    302. 302. Intermodulation Interference Description: • The frequencies of the Intermodulation products are: – 2f1-f2 – 2f2-f1 f1: frequency of carrier #1 f2: frequency of carrier #2 • It can occur at both E/S and Satellite
    303. 303. Intermodulation Interference Cause: • U/L power level of the each carrier is set so high that the Intermodulation occurs • U/L power level is increased without considering the the possibility of intermodulation • Increasing the U/L power without informing PCNS
    304. 304. Intermodulation Interference How does it affects • It reduces the Eb/No of your carrier using at the same frequency • May raise the Noise Floor of some slots • Existing uplink power at E/S would be used more than normal • Therefore, you have to replace new RFT to get more power when you would want to put new carriers into it
    305. 305. Intermodulation Interference Prevention: • Verify the link budget of the station transmitting more than one carrier before transponder access • Aggregate input back-off for HPA or RFT at E/S must be defined and informed to up linker • Do not increase U/L power without informing PCNS • Do not operate with overused power
    306. 306. Raised Noise Floor Source: • Earth Station Equipment
    307. 307. Raised Noise Floor Cause: • E/S equipment configuration was not set up properly • The gain of U/L equipment such as U/C or HPA was not set suitably • The U/L power is too high
    308. 308. Raised Noise Floor Prevention: • Use good E/S setup • Set suitable gain of E/S equipment • Do not increase the U/L power without informing PCNS • Verify uplink noise level at the output of HPA before transponder access
    309. 309. Spike and Unknown Description: • Unpredictable Frequency, Bandwidth, Time • Some of them may occur at out of assigned transponder
    310. 310. Spike and Unknown Cause: • Most of them are caused by the U/L equipment error (both base band and RF equipment) • It does not affect all carriers transmitted by itself
    311. 311. Spike and Unknown Investigation: • Only RF equipment such as U/C, HPA, Transceiver needs turning off • Turning of Base band equipment such as Modem, Exciter, Modulator cannot prove the source of interference
    312. 312. Spike and Unknown Prevention: • Perform Preventive Maintenance periodically • Operate all U/L equipment under suitable conditions as directed by operational manual of the equipment • Find out root cause if it disappeared with unknown reason or equipment reset in order to perform prevention
    313. 313. Sources of Interference • Co-Channel Interference Wanted Carrier T x p 1 2 /1 2 T x p 2 2 /2 2 Unwanted Carrier
    314. 314. Sources of Interference • TWTA Intermodulation Wanted Carrier Unwanted Carrier … T x p 1 2 /1 2 ...
    315. 315. Transponder Parameters • Intermodulation (IM) – What is it? – Why does it exist? - Potential source of noise - Different signals are sent simultaneously – How is it avoidable? - By reducing the saturation E.I.R.P. E.I.R.P.Operation = E.I.R.P.Saturation - OBO
    316. 316. Sources of Interference • Adjacent Satellite Interference (ASI) SATELLITE SPACING SATELLITE ANTENNA WANTED SIGNALS UNWANTED SIGNALS RADIO LINK
    317. 317. Sources of Interference • Adjacent Transponder Interference (Multipath) 1 -2 3 -4 R C V R 1 -2 S SP A 1 -2 IM U X 1 -2 . . . S M 3 -4 S SP A 3 -4 3 -4 W H . . . S a te llite d is h 1 -2 O M U X 3 -4 W H S a t e llit e d is h S a te llite d is h S a te llite d is h
    318. 318. Sources of Interference • Satellite: – Co-Channel Interference – TWTA Intermodulation – Adjacent Satellite Interference – Adjacent Transponder Interference - “Multipath” • Path Losses: – Up link thermal Noise – Down link thermal Noise • Earth Station: – HPA Intermodulation • Outside: – Sun Interference – Terrestrial Interference
    319. 319. 11. Channel Characterization
    320. 320. Contents • • • • • • • • • • • The sequence of signal processing and transmission Multiplexing & Multiple Access FDMA TDMA CDMA Comparison in TDMA, FDMA & CDMA Channel Coding & Modulation Channel Reservation Channel Coding Modulation Techniques The Baseband Eye Pattern
    321. 321. The Sequence of Signal Processing and Transmission Transmission Frequency Conversion Modulation Interleaver Channel Coding Multiplexing Encryption Source Coding Digitization Frequency Conversion Demodulation De-Interleaving Channel Decoding Demultiplexing Decryption Source Decoding Display
    322. 322. Signal processing and transmission Digitisation higher reliability, low cost, less susceptible to Source Coding to reduce bit rate for transmission Encryption for communications privacy Multiplexing for efficient transmission of multiple channels ChannelCoding for error free transmission Interleaving for robust error correction Modulation imparting baseband information to a carrier Frequency Conversion to operate at radio frequencies noise,
    323. 323. Multiplexing and Multiple Access • For the majority of data communications that take place, there is a requirement for several users to share a common channel resource at the same time. • For multiple users to be able to share a common resource in a managed and effective way requires some form of access protocol that defines when or how the sharing is to take place and the means by which messages from individual users are to be identified upon receipt. These sharing process come to be known as multiplexing and multiple access in digital communications.
    324. 324. Multiple Access and Multiplexing • Multiple Access:is the ability for several earth stations to transmit their respective carriers simultaneously into the same satellite transponder • Multiplexing:is the reversible operation of combining several information-bearing signals to form a single, more complex signal.
    325. 325. Multiple Access and Multiplexing Multiple Access at radio frequency Multiplexing at baseband TDMA - TDM FDMA - FDM CDMA - CDM
    326. 326. FDMA • Used extensively in the early telephone and wireless multiuser communication systems • If a channel, such as a cable, has a transmission bandwidth W Hz, and individual users require B Hz to achieve their required information rate, then the channel in theory should be able to support W/B users • Near-Far problem
    327. 327. Frequency Division Multiple Access; FDMA Uplink Downlink Guard Band ... f1 f2 f3..... fM f1 f2 f3 fM Frequency
    328. 328. TDMA • The basic principle behind time division multiplexing is that the user has access to a modem operating at a rate several times that required to support his own data throughput, such that he can send his information in a time slot that is shorter than his own message transaction. Other users can then be assigned similar time slots on the same channel. Clearly if the data rate on the channel is w bits/second, and each individual user requires only b bits/second, then the system can support w/b simultaneous users. • In TDM systems, users are assigned a time slot for the duration of their call whether they require it or not.
    329. 329. TDMA TDMA Near – Far Effect in TDMA
    330. 330. Example of a TDMA system • The GSM digital cellular system is a very good example of a TDMA
    331. 331. Time Division Multiple Access; TDMA Upli nk Downlink Guard Time ... t1 t2 t3..... tM t1 T2 t3 tM Time
    332. 332. Time Division Multiplexing ... burst1 to Joe burst2 to Bill burst3 to Tim a coherent stream of data burstn to who?
    333. 333. Time Division Multiple Access; TDMA

    ×