Satellite Communication Prepared By: Ismail Mehrez - Mohamed Khaled

Satellite Communications * 4/25/201707/16/96 Satellite Communications General concepts Satellite characteristics System components Orbits Power sources Communications Frequencies Path losses GPS Satellite - NASA *

General Concepts Satellite is in the orbit of the earth * 4/25/201707/16/96 General Concepts Satellite is in the orbit of the earth Special orbits have particularly useful properties Carries its own source of power Communications possible with: Ground station fixed on earth surface Moving platform (Non-orbital) Another orbiting satellite *

Satellite Characteristics Orbital parameters Height Orientation Location Power sources Principally solar power Stored gas/ion sources for position adjustment VHF, UHF, and microwave radiation used for communications with Ground Station(s) Signal path losses - power limitations

Types of Orbits

Types of Orbit Dr. Leila Z. Ribeiro, George Mason University

Orbital Altitudes and Problems * 4/25/201707/16/96 Orbital Altitudes and Problems Low Earth Orbit (LEO) 80 - 500 km altitude Atmospheric drag below 300 km Medium Earth Orbit (MEO) 8000 - 18000 km altitude Van Allen radiation Geostationary Orbit (GEO) 35,786 km altitude Difficult orbital insertion and maintenance A layer of energetic charged particles that is held in place around a magnetized planet by its magnetic field *

Important Angles By the Law of Sines: and, The elevation angle is approximately, Elevation Angle Inclination Angle

Coverage vs Satellite Altitude

System Components Satellite(s) Ground station(s) Computer systems * 4/25/201707/16/96 System Components Satellite(s) Ground station(s) Computer systems Information network *

Basic Satellite Network * 4/25/201707/16/96 Basic Satellite Network Satellite network with earth stations. *

Satellite Components Receiving antenna Receiver * 4/25/201707/16/96 Satellite Components Receiving antenna Receiver Processing (decode, security, encode, other) Transmitter Transmitting antenna Power and environmental control systems Possible position control (geosynchronous) *

Simple Satellite Schematic * 4/25/201707/16/96 Simple Satellite Schematic *

* 4/25/201707/16/96 System Block Diagram *

Satellite Power Sources * 4/25/201707/16/96 Satellite Power Sources Solar panels (near-earth satellites) Power degrades over time - relatively long Radioactive isotopes (deep space probes) Lower power over very long life Fuel cells (space stations with resupply) High power but need maintenance and chemical resupply isotope with an unstable nucleus, characterized by excess energy *

Communications Link 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

Channel Capacity The capacity C [bits/s] of a channel with bandwidth W, and signal/noise power ratio S/N is Wavelength = Velocity/Frequency where, velocity ≈ velocity of light in vacuum ( about 3 x 108 meters/sec)

Satellite Communications Frequencies Generally between 300 MHz and 300 GHz. i.e. The microwave spectrum - Line of sight propagation (space and atmosphere). - Blockage by dense media (hills, buildings) Wide bandwidths compared to lower frequency bands. Properties vary according to the frequency used: Propagation effects (diffraction, noise, fading) Antenna Sizes

Electromagnetic Spectrum Wikipedia

Designated Microwave Bands Standard designations For microwave bands Common bands for satellite communication are the L, C and Ku bands. Wikipedia

Antenna Power Gain Dish-Antenna Power Gain: G = A is the area of the antenna aperture D is the diameter of the parabolic reflector lambda is the wavelength of the radio waves. eA: is a dimensionless parameter between 0 and 1 called the aperture efficiency.

Antenna Gain Example Example: Calculate the Power gain of a Ku-Band antenna With average aperture efficiency of 0.6 at a wavelength of 0.02m. The diameter of the reflector is known to be 80cm. Solution: Power Gain = 0.6*(3.14*40)2 = 9465 GdB = 10 log10[Power Gain ] = 40 dB

Antenna Gain Efficiency Example 2: Repeat example 1 with D = 9m Solution: GaindB = 10 log10EA (pd/l)2 = 60 dB Conclusion?..... Bigger antennas have higher gain.

Path Loss Losses increase with frequency Long path lengths (dispersion with distance) ( Path lengths can be over 42,000 km ) Atmospheric absorption Rain, snow, ice, & cloud attenuation

Antenna Gain and Link Losses Pt = transmitted power Pr - received power At = transmit antenna aperture Ar = receive antenna aperture Lp = path loss La = atmospheric attenuation loss Ld = diffraction losses

Simple Path Loss Model where: d is the path distance in m Free-space power loss = (4pd / l)2 In dB this becomes, where: d is the path distance in m f is the frequency in Hz

Sample Path Loss Example Calculate the power loss of a Ku band geosynchronous satellite with the given parameters: f = 15,000 MHz d = 42,000 km Solution: LossdB = 20 log10(40,000) + 20 log10(15,000) – 147.55 = 208 dB

* 4/25/201707/16/96 Bit Error Rate Graph is the signal-to-noise ratio (SNR) of a modulated signal *

Remedies for Path Loss High gain antennas High transmitter power Low-noise receivers Error correcting codes Frequency selection

Application Examples Telecommunications Military communications * 4/25/201707/16/96 Application Examples Telecommunications Military communications Navigation systems Remote sensing and surveillance Radio / Television Broadcasting Astronomical research Weather observation *

Advantages of 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

Disadvantages of Satellites Expensive to launch Expensive ground stations required Very hard to be maintained Limited frequency spectrum Limited orbital space (geosynchronous) Constant ground monitoring required for positioning and operational control Sensitive political environment, with competing interests and relatively limited preferred space

Satellite Communications Needs Space vehicle used as communications platform (Earth-Space-Earth, Space-Earth, Space-Space) Ground station(s) (Tx/Rx)

* 4/25/201707/16/96 References Text Satellite Communications, Second Edition, T. Pratt, C. Bostian, and J. Allnut, John Wilen & Sons, 2003. *

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.