8. introduction to small scale fading

1. WIRELESS COMMUNICATION
SERIES
Introduction to
Small Scale Fading

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3. • Definition:
• Small Scale fading or simply fading , is used to
describe the rapid fluctuations of the
amplitude and phase over a short period of
time or distance.
• Causes:
• Fading is caused by interference between two
or more versions of the transmitted signals
which arrives at the receiver at slightly different
times. These waves are called the multipath
waves that are combined at the receiver end.
• Effects:
• As the result of signal combining, there will be a
change in amplitude and phase depending on
• Distribution of intensity
• Relative propagation time
• Bandwidth of propagated signal

4. • Multipath Propagation:
• Presence of reflecting objects and scatters in the channel creates a constantly
changing environment that affects the signal in terms of amplitude, phase and
time.
• This leads to a situation that the receiver could receive multiple copies of
transmitted waves that have difference phase and time of arrival and creates
Signal smearing.
• Speed of Mobile:
• The relative motion between the base station and the mobile station results in
random frequency modulation due to different Doppler shifts on each of the
multipath component.

6. • Speed of surrounding objects:
• If the objects in the radio channel are in motion, they include time varying Doppler shift
on multipath components.
Movement of surrounding > Mobile User  Fading
Movement of surrounding < Mobile User  Ignored
• Transmission Bandwidth of the signal:
Bandwidth of the Signal > Bandwidth of the Channel
Signal is affected rapidly and smearing will also be high.
Bandwidth of the Signal < Bandwidth of the Channel
 Fading is not significant

7. Definition of Small Scale Fading
Causes of Small Scale Fading
Effects of Small Scale Fading
Factors Influencing the Small Scale Fading
Multipath Propagation
Speed of the Mobile  Gives Raise to Doppler Shifts
Speed of Surrounding
Transmission Bandwidth of the signal