Radio Propagation

• Large scale fades

– Attenuation: in free space, power degrades by 1/d2

– Shadows: signals blocked by obstructing structures

• Small scale fades

– Multipath effects:

» Rapid changes in signal strength over a small area or

time interval

» Random frequency modulation due to varying

Doppler shifts on different multipath signals

» Time dispersion (echoes) caused by multipath

propagation delays

– Even when mobile is stationary, the received signals may

fade due to movement of surrounding objects-Radio Propagation

•　Large scale fades

– Attenuation: in free space, power degrades by 1/d2

– Shadows: signals blocked by obstructing structures

•　Small scale fades

– Multipath effects:

»　Rapid changes in signal strength over a small area or

time interval

»　Random frequency modulation due to varying

Doppler shifts on different multipath signals

»　Time dispersion (echoes) caused by multipath

propagation delays

– Even when mobile is stationary, the received signals may

fade due to movement of surrounding objects