|
www.WirelessCommunication.NL
Chapter: Wireless Channels
|
Hear a discussion of the basic model behind Rayleigh fading.
Rayleigh fading is caused by multipath reception. The mobile antenna receives a large number, say N, reflected and scattered waves. Because of wave cancellation effects, the instantaneous received power seen by a moving antenna becomes a random variable, dependent on the location of the antenna.
In case of an unmodulated carrier, the transmitted signal has the form
.
Next we'll discuss the basic mechanisms of mobile reception.
arrive from an angle 
relative to the direction of the motion of the antenna.
The Doppler shift of this wave is
,
where v is the speed of the antenna.
Animation and Figure: Phasor diagram of a set of scattered waves (in blue),
resulting a Rayleigh-fading envelope (in black).
Check out the Java animated version
for details.
The received unmodulated signal r(t) can be expressed as
An inphase-quadrature representation of the form
can be found with in-phase component
and quadrature phase component
.
This propagation model allows us, for instance,
If the set of reflected waves are dominated by one strong component, Rician fading is a more appropriate model.
