TEL AVIV UNIVERSITY Gaddi Blumrosen

Where these components are referred to as:
s ( , ) is large scale fading (called also Long term fading or shadowing)
and caused by reflection and diffraction from constant large scatterers,
sometimes called shadowing effect.
is small scale fading (called also Short term fading) is caused by
variations of scatterers surrounding the transmitter and or the receiver.
tr
l ( , ) tr
Note:
In some notations in literature, large scale fading is referred to as slow fading and
Small scale fading is referred to as fast fading.
With the far field assumption, we can express the fading as function of the angle from
the vertical to the ULA axis (see figure 1) and time
( t, )
s ( t,
)
l
( t,
)
(2.5)
Fig. 2 below (taken from [23]), shows short term fading , long term fading and mean
path loss as a function of source distance in a typical wireless channel.
Figure 2: LOS, slow and fast fading
Fading can be viewed also in time, frequency and space domains.
Time-selective fading
Time-selective fading is caused by variations in time due to scatterers surrounding the
transmitter and or receiver. Coherence time, Tc
, is the time separation for which
time-space correlation function of the channel impulse response at two times is
sufficiently correlated (exceeding pre-determined threshold). The Coherence time is