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EELE 5490, Fall, 2009 Wireless Communications

EELE 5490, Fall, 2009 Wireless Communications. Ali S. Afana Department of Electrical Engineering Class 5 Dec. 4 th , 2009. Speed, Wavelength, Frequency. Light speed = Wavelength x Frequency = 3 x 108 m/s = 300,000 km/s. Type of waves. Radio Frequency Bands.

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EELE 5490, Fall, 2009 Wireless Communications

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

  2. Speed, Wavelength, Frequency • Light speed = Wavelength x Frequency = 3 x 108 m/s = 300,000 km/s

  3. Type of waves

  4. Radio Frequency Bands

  5. Large-scale small-scale propagation

  6. 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

  7. 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

  8. Friis Transmission Equation No 2 No 1 G2, A2 G1, A1 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

  9. No 2 No 1 G2, A2 G1, A1 Now we know that G2 = 4πA2 / λ2 So that Pr / Pt = G1A2 / 4πd2 =G1G2 ( λ2 / 4π4πd2 ) Pr / Pt =G1G2 ( λ / 4πd )2

  10. Radio Propagation Mechanisms • 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

  11. 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

  12. Reflection from smooth surface

  13. Typical electromagnetic properties

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

  15. Method of image

  16. Simplified model • Far field simplified model • Example 4.6

  17. Questions?

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