ECE637 : Fundamentals of Wireless Communications Lecture 2: Wireless propagation Aliazam Abbasfar

Outline Class arrangements Radio propagation and fading Path loss models

Radio propagation and fading Rays coming from different paths Reflections Refractions scattering Large scale fading Path loss shadowing Small scale fading Multi-path fading Slow Pr/Pt Very slow Fast d

Path loss models Maxwell’s equations Ray tracing Empirical models Too complex Ray tracing Site-specific Empirical models Simplified model

Free space model (LOS) For each ray free space model applies Signal attenuation and delay Electric far field is inversely proportional to distance and proportional to l Path loss :

Two-path propagation Ground reflection Ground bounce approximately cancels LOS path above critical distance RX power Power falls off Proportional to d4 and independent of l (f)

Ray tracing Models all signal components Reflections Scattering Diffraction More info needed detailed geometry dielectric properties Simpler than Maxwell’s equations

Empirical models Statistical models Based on measurements Predicts local mean signal power Based on measurements Okumura Hata … Simplified model d < d0 : near-field g : path loss exponent

Shadowing Variation in large scale path loss Statistical modeling Blockage Reflection, refraction, and scattering Statistical modeling Log-normal distribution Verified empirically for both indoor and outdoor Two parameters : m and s

Outage probability/Cell coverage Outage probability ( at a given distance) Probability received power below given minimum pout( Pmin, d) = p(pr(d) <Pmin ) = p(PL > pt-Pmin ) Cell coverage

Reading Ch. 2 Goldsmith Ch. 2 Tse