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Exploring Wireless Communication: Wavelength, Frequency, and Propagation Models

Delve into radio frequency bands, wave characteristics, and propagation models in wireless communications, including reflection, diffraction, and scattering. Understand key concepts like the Friis Transmission Equation and Radio Propagation Mechanisms.

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Exploring Wireless Communication: Wavelength, Frequency, and Propagation Models

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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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