Chapter 2 Wireles Propagation Characteristics.pptVIP

Chapter 2: Wireless Propagation Characteristics Prof. Pingan Li Propagation in Multipath Environments Mobile Commun. Environments Path loss Shadow Multi-path fading Time spread Doppler spread Doppler frequency shift 3-level Model General 3-level Model Path loss model is used for system planning, cell coverage link budget (what is the frequency reuse factor?) Shadowing is used for power control design 2nd order interference and TX power analysis more detailed link budget and cell coverage analysis Multipath fading is used for physical layer modem design --- coder, modulator, interleaver, etc Path Loss Model Free space loss path model Too simple, unrealistic Ray tracing model Based on site-specific information Empirical model (Statistical model ) Based on channel parameter detection Environment-limited Free Space (LOS) Model Path loss for unobstructed LOS path Power falls off: Proportional to d2 Proportional toλ2(inversely proportional to f2 ) Free Space Model (LoS) Path loss for unobstructed LoS path Power falls off in proportion to d2 Line-of-Sight Equations Optical line of sight Effective, or radio, line of sight d = distance between antenna and horizon (km) h = antenna height (m) K = adjustment factor to account for refraction, rule of thumb K = 4/3 Line-of-Sight Equations Maximum distance between two antennas for LOS propagation: h1 = height of antenna one h2 = height of antenna two Free Space Loss Consider an Isotropic point source fed by a transmitter of Pt Watts The energy per unit area of the surface of the sphere with radius d Hence, at a distance d, an receive antenna with effective aperture Ae obtain a total power Free Space Loss Define an antenna gain as Hence, the received power Free Space Loss Free space loss, ideal isotropic antenna Pt = signal power at transmitting antenna Pr = signal power at receiving antenna ? = carrier wavelength d = propagation distance between antennas c = speed of light (? 3 ×10 8 m/s) where d and ? are in