Satellite Communications © 2012 Raymond P. Jefferis III Lect01 Satellite Communications Introduction General concepts Needs, advantages, and disadvantages Satellite characteristics Orbits Earth coverage System components and design Power sources Communication characteristics Spectrum and Bandwidth Channel capacity Frequency and Wavelength Path losses Antennas and beam shaping GPS Satellite - NASA Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

© 2012 Raymond P. Jefferis III Lect01 Text Text Satellite Communications, Second Edition, T. Pratt, C. Bostian, and J. Allnut, John Wilen & Sons, 2003. Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

Other Useful References Ippolito, Louis J., Jr., Satellite Communications Systems Engineering, John Wiley, 2008. Kraus, J. D., Electromagnetics, McGraw-Hill, 1953.  Kraus, J. D., and Marhefka, R. J., Antennas for All Applications, Third Edition, McGraw-Hill, 2002.  Morgan, W. L. , and Gordon, G. D., Communications Satellite Handbook, John Wiley & Sons, 1989. Proakis, J. G., and Salehi, M., Communication Systems Engineering, Second Edition, Prentice-Hall, 2002. Roddy, D, Satellite Communications, Fourth Edition, Mc Graw-Hill, 1989. Stark, H., Tuteur, F. B., and Anderson, J. B., Modern Electrical Communications, Second Edition, Prentice-Hall, 1988. Tomasi, W., Advanced Electronic Communications Systems, Fifth Edition, Prentice-Hall, 2001. Lect 01 © 2012 Raymond P. Jefferis III

General Concepts of Satellites: © 2012 Raymond P. Jefferis III Lect01 General Concepts of Satellites: They orbit around the earth Have various orbital paths (to be discussed) They carry their own source of power They can communicate with: Ground stations fixed on earth surface Moving platforms (Non-orbital) Other orbiting satellites Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

Needs, Advantages & Disadvantages © 2012 Raymond P. Jefferis III Lect01 Needs, Advantages & Disadvantages • Communications needs Advantages of using satellites Disadvantages of using satellites Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

Satellite Communications Needs Space vehicle to be used as communications platform (Earth-Space-Earth, Space-Earth, Space-Space) Space vehicle to be used as sensor platform with communications Ground station(s) (Tx/Rx) Ground receivers (Rx only) Lect 01 © 2012 Raymond P. Jefferis III

List Advantages & Disadvantages List these on the sheet supplied. Five minutes allowed. Lect 01 © 2012 Raymond P. Jefferis III

Advantages of Using Satellites High channel capacity (>100 Mb/s) Low error rates (Pe ~ 10-6) Stable cost environment (no long-distance cables or national boundaries) Wide area coverage (whole North America, for instance) Coverage can be shaped by antenna patterns Lect 01 © 2012 Raymond P. Jefferis III

Disadvantages of Using Satellites Expensive to launch Expensive ground stations required Cannot be maintained Limited frequency spectrum Limited orbital space (geosynchronous) Constant ground monitoring required for positioning and operational control Lect 01 © 2012 Raymond P. Jefferis III

Satellite Characteristics © 2012 Raymond P. Jefferis III Lect01 Satellite Characteristics Orbiting platforms for data gathering and communications – position holding/tracking VHF, UHF, and microwave radiation used for communications with Ground Station(s) Signal path losses - power limitations Systems difficult to repair and maintain Sensitive political environment, with competing interests and relatively limited preferred space Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

Mission Dependent Characteristics Orbital parameters Height (velocity & period related to this) Orientation (determined by application) Location (especially for geostationary orbits) Power sources Solar (principal), nuclear, chemical power Stored gas/ion sources for position adjustment Lect 01 © 2012 Raymond P. Jefferis III

Satellite Application Examples © 2012 Raymond P. Jefferis III Lect01 Satellite Application Examples Telecommunications Military communications Navigation systems Remote sensing and surveillance Radio / Television Broadcasting Astronomical research Weather observation Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

© 2012 Raymond P. Jefferis III Orbits Have particular advantages and disadvantages (See text Chapter 1) Are determined by satellite mission Keppler’s Laws of planetary motion describe certain orbital properties (Covered in Lecture 2) Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Orbital Properties Altitude (radius to center of the earth) Inclination with respect to the earth axis Period of rotation about the earth Ground coverage by the satellite Communications path length(s) Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Types of Orbit Dr. Leila Z. Ribeiro, George Mason University Lect 01 © 2012 Raymond P. Jefferis III

Missions Associated with Orbit Types GEO Primarily commercial communications MEO Military and research uses LEO Remote sensing Global Positioning Systems Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III LEO and MEO Features Earth coverage requires multiple passes Typical pass requires about 90 minutes Signal paths relatively short (lower losses) Small area, high resolution ground image Earth station tracking required Multiple satellites for continuous coverage (Decreases with increasing altitude - “Telstar”) Lect 01 © 2012 Raymond P. Jefferis III

The Geostationary (Clarke) Orbit Arthur C. Clarke, Wireless World, February, 1945, p58. Lect 01 © 2012 Raymond P. Jefferis III

Geo-Synchronous Satellite (GEO) Features Appears fixed over point on earth equator Each satellite can cover 120 degrees latitude Orbital Radius = 42,164.17 km Earth Radius = 6,378.137 km (avg) Period (Sidereal Day) = 23.9344696 hr (86164.090530833 seconds) Long signal path - large path losses Lect 01 © 2012 Raymond P. Jefferis III

GEO Features (continued) Ground image area (instantaneous) Ground track coverage (multiple orbits) Stationarity (geostationary orbit) Space coverage (satellite-satellite) Lect 01 © 2012 Raymond P. Jefferis III

Orbital Altitudes and Problems © 2012 Raymond P. Jefferis III Lect01 Orbital Altitudes and Problems Low Earth Orbit (LEO) 80 - 500 km altitude Atmospheric drag below 300 km Medium Earth Orbit (MEO) 2000 - 35000 km altitude Van Allen radiation between 200 - 1000 km Geostationary Orbit (GEO) 35,786 km altitude (42,164.57 km radius) Difficult orbital insertion and maintenance Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

© 2012 Raymond P. Jefferis III Orbital Inclinations Equatorial Prograde – inclined toward the east Retrograde – inclined toward the west Inclined Various inclination angles with respect to the spin axis of the earth, including polar Geostationary (on equator; no inclination) Sun synchronous Lect 01 © 2012 Raymond P. Jefferis III

Earth Coverage Calculation By the Law of Sines: and, The elevation angle is approximately, Lect 01 © 2012 Raymond P. Jefferis III

Earth Coverage Calculation (continued) The total coverage area on the surface of the earth, using the previously calculated value of δ) is given by the equation, Lect 01 © 2012 Raymond P. Jefferis III

Try the Calculation Yourself Show Lect01S24calc.nb Mathematica®®program Lect 01 © 2012 Raymond P. Jefferis III

Sample Calculation [Mathematica®] re = 6378.137; (* km *) delta = 32.4171; (* degrees *) area = 2 p re^2 (1 - Cos[delta Degree]); Print["Area = ", area, “[km^2]"] Area = 3.98313*10^7 [km^2] Lect 01 © 2012 Raymond P. Jefferis III

Alternate Earth Coverage Calculation Coverage variation as a function of satellite altitude (rsat) rsat is the radius to the satellite from the center of the earth Lect 01 © 2012 Raymond P. Jefferis III

Calculation: CoverageArea.nb re = 6378.137; (* km *) rs = re + hs; alpha = ArcSin[re/rs] ad = alpha/Degree delta = ArcSin[(rs/re)*Sin[alpha]] - alpha dd = delta/Degree A = 2 p re^2 (1.0 - Cos[delta]) Plot[A, {hs, 1000, 2000}, AxesLabel -> "Coverage [km^2]", Frame -> True, FrameLabel -> {"Altitude [km]", "Coverage [km^2]"}] Lect 01 © 2012 Raymond P. Jefferis III

Earth Coverage vs Satellite Altitude Lect 01 © 2012 Raymond P. Jefferis III

Advanced Earth Coverage Calculations © 2012 Raymond P. Jefferis III Lect01 Advanced Earth Coverage Calculations In: Orbital Mechanics with MATLAB http://www.cdeagle.com/html/ommatlab.html Recommended download: Coverage Characteristics of Earth Satellites http://www.cdeagle.com/ommatlab/coverage.pdf Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

“Satellite System” Components © 2012 Raymond P. Jefferis III Lect01 “Satellite System” Components Satellite(s) Earth station(s) Computer systems Information network (Example: Internet) Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

Satellite System Design © 2012 Raymond P. Jefferis III Lect01 Satellite System Design Satellite network with earth stations. Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

© 2012 Raymond P. Jefferis III Lect01 Satellite Components Receiver (receives on an uplink) Receiving antenna Signal processing (decode, security, encode, other) Transmitter (transmits on a downlink) Transmitting antenna (beam shaping) Power and environmental control systems Attitude control (De)multiplexing (used in rotating satellites) Position holding (mission dependent option) Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

Simple Satellite Schematic © 2012 Raymond P. Jefferis III Lect01 Simple Satellite Schematic Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

Satellite Power Sources Solar power panels (near-earth satellites) Power degrades over time - relatively long Radioactive isotopes (deep space probes) Lower power over very long life, rarely used. Fuel cells (space stations with resupply) High power but need maintenance and chemical resupply, rarely used. Example: International Space Station Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Solar Power Power available in orbit: ~1400 watts of sunlight per square meter Conversion efficiency: ~25% Useful power: ~350 Watts/square meter Panel steering required for maximum power Typical power levels: 2 - 75 kW Photocell output degrades over time Lect 01 © 2012 Raymond P. Jefferis III

Typical Solar Power Panel Example Type: GaAs/Ge Voltage: 53.1 Volts Power: 1940 Watts ( Effective Load + Source Resistance: 1.45341 Ω ) Geostationary Operational Environmental Satellites (GOES) - Ground testing of solar panels, NASA Lect 01 © 2012 Raymond P. Jefferis III

Satellite Communication Characteristics Via electromagnetic waves (“radio”) Typically at microwave frequencies High losses due to path length Many interference sources Attenuation due to atmosphere and weather High-gain antennas needed (“dish”) to make up for path loss and noise Lect 01 © 2012 Raymond P. Jefferis III

Communication Characteristics (continued) Spectrum and Bandwidth Channel capacity Frequency and Wavelength Path losses Lect 01 © 2012 Raymond P. Jefferis III

Spectrum and Bandwidth • Electromagnetic spectrum allocations (“DC to light” – see next slide) Bandwidth: the size or “width” (in Hertz) of a spectrum frequency band Frequency band: a range of frequencies in the available spectrum. • Channel capacity increases with the bandwidth (see Slide 42) Lect 01 © 2012 Raymond P. Jefferis III

Electromagnetic Spectrum Wikipedia Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Channel Capacity The number of error free bits of information transmitted and received per second Shannon (BSTJ, Vol. 27,1938) The capacity C [bits/s] of a channel with bandwidth W, and signal/noise power ratio S/N is Lect 01 © 2012 Raymond P. Jefferis III

Frequency and Wavelength Formula Microwave energy, at a given frequency, f [Hz] Moves at a velocity, v [m/s] And has a wavelength (distance between peak intensities), λ [m] Formula: λ = v / f (v = c for space) Note: The speed of light, c, in a vacuum (space) is fixed at, c = 299 792 458 [m/s] Lect 01 © 2012 Raymond P. Jefferis III

Frequencies of Interest for Satellites Generally between 300 MHz and 300 GHz. The microwave spectrum Allows efficient generation of signal power Energy radiated into space Energy may be focused (beam shaping) Efficient reception over a specified area. Properties vary according to the frequency used: Propagation effects (diffraction, noise, fading) Antenna Sizes Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Microwaves Include frequencies from 0.3 GHz to 300 GHz. - Line of sight propagation (space and atmosphere). - Blockage by dense media (hills, buildings, rain) - Wide bandwidths compared to lower frequency bands. - Compact antennas, directionality possible. Reduced efficiency of generation 1 GHz to 170 GHZ spectrum divided into bands with letter designations (see next slide) Lect 01 © 2012 Raymond P. Jefferis III

Designated Microwave Bands Standard designations For microwave bands Common bands for satellite communication are the L, C and Ku bands. Wikipedia Lect 01 © 2012 Raymond P. Jefferis III

Common Microwave Frequency Allocations L band 0.950 - 1.450 GHz Note: GPS at 1.57542 GHz C band 3.7 - 4.2 GHz (Downlink) 5.925 - 6.425 GHz (Uplink) Ku band 11.7 - 12.2 GHz (Downlink) 14 - 14.5 GHz (Uplink) Lect 01 © 2012 Raymond P. Jefferis III

Common Microwave Frequency Allocations Ka band 18.3 - 18.8, 19.7 - 20.2 GHz (Downlink) 30 GHz (Uplink) V band 40 - 75 GHz 60 GHz allocated for unlicensed (WiFi) use 70, 80, and 90 GHz for other wireless Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III L-Band GPS Receiver Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III L-Band Frequencies: 0.950 – 1.450 GHz (λ ~30cm) Uses: Amateur radio communications GPS devices Features: Patch antenna used for GPS receivers Low rain fade - Low atmospheric atten. (long paths) Low power Small receiver configurations Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III C-Band Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III C-Band Frequencies: 3.7 - 6.425 GHz (λ ~5cm) Uses: TV reception (motels) IEEE-802.11 WiFi VSAT Features: Large dish antenna needed (3m diameter) Low rain fade - Low atmospheric atten. (long paths) Low power - terrestrial microwave interferences Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Lect01 Ku-Band Lect 01 © 2012 Raymond P. Jefferis III Satellite Communications

© 2012 Raymond P. Jefferis III Ku-Band Frequencies: 12 - 18 GHz (λ ~ 2cm) Uses: Remote TV broadcasting Satellite communications VSAT Features: Rain, snow, ice (on dish) susceptibility Small antenna size - high antenna gain High power allowed Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Ka-Band Frequencies: 18 - 40 GHz (λ ~ 1cm) Uses: High-resolution radar Communications systems Deep space communications Features: Obstacles interfere (buildings, vegetation, etc.) Atmospheric absorption Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III V-Band Frequencies: 40 to 75 GHz. (λ ~ 5 mm) Uses: Millimeter wave radar research (very expensive!) High capacity millimeter wave communications Point-to-point fixed wireless systems (WiFi) Features: Rain fade Obstacles block path Atmospheric absorption Expensive equipment Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Millimeter Waves Planck space exploration satellite Planck is a flagship mission of the European Space Agency (Esa). It was launched in May 2009 and moved to an observing position more than a million km from Earth on its "night side".It carries two instruments that observe the sky across nine frequency bands. The High Frequency Instrument (HFI) operates between 100 and 857 GHz (wavelengths of 3mm to 0.35mm), and the Low Frequency Instrument (LFI) operates between 30 and 70 GHz (wavelengths of 10mm to 4mm). Johnson noise problems addressed Some of its detectors operate at minus 273.05C Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Path Losses The loss of a radiated signal with distance Losses increase with frequency Satellites typically require long path lengths ( Path lengths can be over 42,000 km ) Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Causes of Path Loss Dispersion with distance Atmospheric absorption (Calculated in Lecture 11) Rain, snow, ice, & cloud attenuation (Calculated in Lecture 12) Atmospheric noise effects resulting in increased Bit Error Rate (BER) (Calculated in Lecture 6) Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Simple Path Loss Model Free-space power loss = (4πd / λ)2 In dB this becomes, where: d is the path distance in km f is the frequency in MHz Lect 01 © 2012 Raymond P. Jefferis III

Calculation of Sample Path Loss Model Ku band geosynchronous satellite: f = 15,000 MHz d = 42,000 km LossdB = 32.44 + 20 log10(40,000) + 20 log10(15,000) = 208 dB Atmospheric losses must be added to this Lect 01 © 2012 Raymond P. Jefferis III

Atmospheric Attenuation (Loss) 53.5 - 65.2 GHz H2O 22.2 GHz Microwave Attenuation [dB/km] vs Frequency [GHz], Wikipedia Lect 01 © 2012 Raymond P. Jefferis III

H2O vs Dry Air Absorption (Loss) Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Remedies for Path Loss High gain antennas High transmitter power Low-noise receivers Tracking of steered antennas Modulation techniques Error correcting codes Frequency selection Beam shaping to focus energy Lect 01 © 2012 Raymond P. Jefferis III

Constraints Limiting Path Loss Remedies Maximal antenna sizes push satellite radio wavelengths below 2m. Requirements for antenna gain, due to communication path losses, reduce the practical wavelengths to below 20cm. (Diameter, d, of many wavelengths, λ) Dish-Antenna Power Gain = η(πd/λ)2 (where η is antenna efficiency) Lect 01 © 2012 Raymond P. Jefferis III

Antenna Gain Calculation Ku-Band antenna Diameter 80 cm (d/λ = 40), η = 0.6 (about 40 wavelengths at 15GHz) Power Gain = 0.6*(3.14*40)2 = 15775 GdB = 10 log10[Power Gain ] = 40 dB Note: Losses and sidelobe effects can reduce this gain to 60% or less of its possible value. Lect 01 © 2012 Raymond P. Jefferis III

Antenna Gain Efficiency Loss From text, p115 d / λ = 5.6 (4GHz), η = 0.35 GaindB = 10 log10η(πd/λ)2 = 20.9 dB From text, p116 d = 9m, λ = 0.075m (4GHz), η = 0.6 GaindB = 10 log10η (πd/λ)2 = 49.3 dB Note: Smaller antenna has lower efficiency. Lect 01 © 2012 Raymond P. Jefferis III

Beam Shaping through Antenna Design Antenna radiation patterns (the beam) can be shaped to redistribute the radiated energy, by antenna design Shaping radiation patterns can increase signal strength in selected areas Allows for more signal energy where higher noise levels are expected Allows energy to be conserved for areas of low noise or low economic concern Lect 01 © 2012 Raymond P. Jefferis III

Intelsat Galaxy-11 Example Location: 91W Power: Solar, 10.4 KW Antennas: C-Band: 2.4m Ku-Band: 1.8m Transponders: 24 channels C-Band: 20W each 24 channels Ku-Band: 75W (data) 16 channels Ku-Band: 140W (TV video) Lect 01 © 2012 Raymond P. Jefferis III

Intelsat Galaxy-11 C-Band Coverage Lect 01 © 2012 Raymond P. Jefferis III

Intelsat Galaxy-11 Ku-Band Coverage Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Conclusions Design constraints limit the power avaiable to satellite communications equipment Path losses limit communication capacity High gain antennas can overcome some limitations Antenna patterns can be shaped to favor desired locations on the earth Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Questions? Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III Reminders Check access to a math package (Mathematica® or MATLAB®) Do homework Lect 01 © 2012 Raymond P. Jefferis III

© 2012 Raymond P. Jefferis III End Lect 01 © 2012 Raymond P. Jefferis III