04-09-2012, 04:34 PM
wireless mobile communications
wireless mobile.ppt (Size: 2.47 MB / Downloads: 37)
Mobile Radio Propagation
Large Scale Propagation Effects
Distance dependent loss
Reflection
Diffraction
Scattering
Useful in estimating radio coverage
Small Scale Propagation Effects
Rapid fluctuations of received signal strength over short durations or short distances
Multipath propagation – time dispersive
Mobility – frequency dispersive
Radio Propagation Mechanisms
Reflection
Propagating EM wave impinges on an object which is large as compared to its wavelength
- e.g., the surface of the Earth, buildings, walls, etc.
Conductors & Dielectric materials (refraction)
Diffraction
Radio path between transmitter and receiver is obstructed by a surface with sharp irregular edges
Waves bend around the obstacle, even when LOS (line of sight) does not exist
Fresnel zones
Scattering
Objects smaller than the wavelength of the propagating wave
- e.g. foliage, street signs, lamp posts
“Clutter” is small relative to wavelength
Diffraction
Diffraction occurs when waves hit the edge of an obstacle
“Secondary” waves propagate into the shadowed region
Water wave example
Diffraction is caused by the propagation of secondary wavelets into a shadowed region.
Excess path length results in a phase shift
The field strength of a diffracted wave in the shadowed region is the vector sum of the electric field components of all the secondary wavelets in the space around the obstacle.
Huygen’s principle: all points on a wavefront can be considered as point sources for the production of secondary wavelets, and that these wavelets combine to produce a new wavefront in the direction of propagation.
Signal Penetration into Buildings
RF penetration has been found to be a function of frequency as well as height within the building. Signal strength received inside a building increases with height, and penetration loss decreases with increasing frequency.
Walker’s work shows that building penetration loss decrease at a rate of 1.9 dB per floor from the ground level up to the 15th floor and then began increasing above the 15th floor. The increase in penetration loss at higher floors was attributed to shadowing effects of adjacent buildings.
Some devices to conduct the signals into the buildings
wireless mobile.ppt (Size: 2.47 MB / Downloads: 37)
Mobile Radio Propagation
Large Scale Propagation Effects
Distance dependent loss
Reflection
Diffraction
Scattering
Useful in estimating radio coverage
Small Scale Propagation Effects
Rapid fluctuations of received signal strength over short durations or short distances
Multipath propagation – time dispersive
Mobility – frequency dispersive
Radio Propagation Mechanisms
Reflection
Propagating EM wave impinges on an object which is large as compared to its wavelength
- e.g., the surface of the Earth, buildings, walls, etc.
Conductors & Dielectric materials (refraction)
Diffraction
Radio path between transmitter and receiver is obstructed by a surface with sharp irregular edges
Waves bend around the obstacle, even when LOS (line of sight) does not exist
Fresnel zones
Scattering
Objects smaller than the wavelength of the propagating wave
- e.g. foliage, street signs, lamp posts
“Clutter” is small relative to wavelength
Diffraction
Diffraction occurs when waves hit the edge of an obstacle
“Secondary” waves propagate into the shadowed region
Water wave example
Diffraction is caused by the propagation of secondary wavelets into a shadowed region.
Excess path length results in a phase shift
The field strength of a diffracted wave in the shadowed region is the vector sum of the electric field components of all the secondary wavelets in the space around the obstacle.
Huygen’s principle: all points on a wavefront can be considered as point sources for the production of secondary wavelets, and that these wavelets combine to produce a new wavefront in the direction of propagation.
Signal Penetration into Buildings
RF penetration has been found to be a function of frequency as well as height within the building. Signal strength received inside a building increases with height, and penetration loss decreases with increasing frequency.
Walker’s work shows that building penetration loss decrease at a rate of 1.9 dB per floor from the ground level up to the 15th floor and then began increasing above the 15th floor. The increase in penetration loss at higher floors was attributed to shadowing effects of adjacent buildings.
Some devices to conduct the signals into the buildings