# EELE 5490, Fall, 2009 Wireless Communications

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EELE 5490, Fall, 2009 Wireless Communications
Ali S. Afana Department of Electrical Engineering Class 5 Dec. 4th, 2009 1

Speed, Wavelength, Frequency
Light speed = Wavelength x Frequency = 3 x 108 m/s = 300,000 km/s System Frequency Wavelength AC current 60 Hz 5,000 km FM radio 100 MHz 3 m Cellular 800 MHz 37.5 cm Ka band satellite 20 GHz 15 mm Ultraviolet light 1015 Hz 10-7 m

Type of waves

Radio Frequency Bands Classification Band Initials Frequency Range
Characteristics Extremely low ELF < 300 Hz Ground wave Infra low ILF 300 Hz - 3 kHz Very low VLF 3 kHz - 30 kHz Low LF 30 kHz kHz Medium MF 300 kHz - 3 MHz Ground/Sky wave High HF 3 MHz - 30 MHz Sky wave Very high VHF 30 MHz MHz Space wave Ultra high UHF 300 MHz - 3 GHz Super high SHF 3 GHz - 30 GHz Extremely high EHF 30 GHz GHz Tremendously high THF 300 GHz GHz

Large-scale small-scale propagation

Models are Specialized
Different scales Large scale (averaged over meters) Small scale (order of wavelength) Different environmental characteristics Outdoor, indoor, land, sea, space, etc. Different application areas macrocell (2km), microcell(500m), picocell

Free space propagation model
Assumes far-field (Fraunhofer region) d >> D and d >>  , where D is the largest linear dimension of antenna  is the carrier wavelength No interference, no obstructions Black board 4.2 Effective isotropic radiated power Effective radiated power Path loss Fraunhofer region/far field In log scale Example 4.1 and 4.2

Friis Transmission Equation
No 2 No 1 G1, A1 G2, A2 From previous section If antenna 1 were isotropic then power density at distance d is W0 = Pt / 4πd2 As antenna 1 is directive then this will be increased by Gt so that W0 = PtG1 / 4πd2 The power transferred to the load of antenna 2 is Pr = W0A2 = PtG1A2 / 4πd2

Pr / Pt =G1G2 ( λ / 4πd )2 No 2 No 1 G1, A1 G2, A2 Now we know that
So that Pr / Pt = G1A2 / 4πd2 =G1G2 ( λ2 / 4π 4πd2 ) Pr / Pt =G1G2 ( λ / 4πd )2

Refraction Conductors & Dielectric materials (refraction) Propagation wave impinges on an object which is large as compared to wavelength - e.g., the surface of the Earth, buildings, walls, etc. Diffraction Radio path between transmitter and receiver obstructed by surface with sharp irregular edges Waves bend around the obstacle, even when LOS (line of sight) does not exist Scattering Objects smaller than the wavelength of the propagation wave - e.g. foliage, street signs, lamp posts “Clutter” is small relative to wavelength

Refraction Perfect conductors reflect with no attenuation
Like light to the mirror Dielectrics reflect a fraction of incident energy “Grazing angles” reflect max* Steep angles transmit max* Like light to the water Reflection induces 180 phase shift Why? See yourself in the mirror q qr qt

Reflection from smooth surface

Typical electromagnetic properties

Classical 2-ray ground bounce model
One line of sight and one ground bound

Method of image

Simplified model Far field simplified model Example 4.6

Questions?