02.Raiopropagationfundamentals.pptVIP

Module 2 – Radio propagation fundamentals Module Contents Propagation mechanisms Multipath And Fading Propagation Slope And Different Environments Module Contents Propagation mechanisms Basics: deciBel (dB) Radio channel Reflections Diffractions Scattering Multipath And Fading Propagation Slope And Different Environments deciBel (dB) – Definition deciBel (dB) – Conversion Calculations in dB (deciBel) Logarithmic scale Always with respect to a reference dBW = dB above Watt dBm = dB above mWatt dBi = dB above isotropic dBd = dB above dipole dBmV/m = dB above mV/m Rule-of-thumb: +3dB = factor 2 +7 dB = factor 5 +10 dB = factor 10 -3dB = factor 1/2 -7 dB = factor 1/5 -10 dB = factor 1/10 Radio Channel – Main Characteristics Linear In field strength Reciprocal UL DL channel same (if in same frequency) Dispersive In time (echo, multipath propagation) In spectrum (wideband channel) Propagation Mechanisms – (1/2) Free-space propagation Signal strength decreases exponentially with distance Reflection Specular reflection amplitude A ? a*A (a 1) phase f ? - f polarisation material dependant phase shift Diffuse reflection amplitude A ? a *A (a 1) phase f ? random phase polarisation random Propagation Mechanisms – (2/2) Absorption Heavy amplitude attenuation Material dependant phase shifts Depolarisation Diffraction Wedge - model Knife edge Multiple knife edges Scattering – Macrocell Scattering local to mobile Causes fading Small delay and angle spreads Doppler spread causes time varying effects Scattering local to base station No additional Doppler spread Small delay spread Large angle spread Remote scattering Independent path fading No additional Doppler spread Large delay spread Large angle spread Scattering – Microcell Many local scatterers: Large angle spread Low delay spread Medium or high Doppler spread Module Contents Reflections, Diffractions And Scattering Multipath and Fading Delay – Time dispersion Angle – Angular Spr