There are two main types of fading that occur in wireless networks: large-scale and small-scale fading. Large-scale fading is caused by obstacles between the transmitter and receiver that block the signal. It includes path loss and shadowing. Small-scale fading occurs over very small changes in time and position due to multipath propagation. Multipath fading can be flat or frequency-selective depending on how each frequency component is affected. Fading can also be categorized as fast or slow based on how quickly the signal strength varies over frequency.

1. WIRELESS NETWORKS
TYPES OF FADING
FARAH AKIF
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2. FADING
 In wireless communication, fading is the variation of the attenuation of the
signal with various variables
 These variables include time, geographical position, and radio frequency
 A fading channel is a communication channel that experiences fading
 In wireless systems, fading may either be due to multipath propagation,
referred to as multipath-induced fading, weather (particularly rain), or
shadowing from obstacles affecting the wave propagation, sometimes
referred to as shadow fading
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3. TYPES OF FADING
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5. FADING, WHY?
 Fading is caused by destructive interference between two or more versions of
the transmitted signal being slightly out of phase due to different
propagation time
 This is also called multipath fading
 The different components are due to reflection and scattering from trees
buildings and hills etc.
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6. LARGE SCALE FADING
 Large scale fading occurs when an obstacle gets positioned between the
wireless device and the signal transmitter
 This interference causes significant reduction in signal strength because the
wave is shadowed or blocked by the obstacle
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7. LARGE SCALE FADING – PATH LOSS
 Path loss is the reduction in the power density of electromagnetic signal as it
propagates through free space
 Path loss models describe the signal attenuation between a transmit and a
receive antenna as a function of the propagation distance and other
parameters
 Some models include many details of the terrain profile to estimate the signal
attenuation
 Whereas others just consider carrier frequency and distance
 Antenna height is another critical parameter
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9. LARGE SCALE FADING – SHADOWING
 In wireless communication, shadowing is the deviation of received
electromagnetic signal from an average value (received signal strength
threshold)
 Long term shadow fading due to variations in radio signal power due to
encounters with terrain obstructions such as hills or manmade structures such
as buildings
 The measured signal power differ substantially at different locations even
though at the same radial distance from a transmitter
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10. SMALL SCALE FADING
 Short term fluctuation in signal amplitude caused by local multipath
 At the receiver the radio waves generated by same transmitted signal may
come from
 Different directions
 With different propagation delays
 With different amplitudes
 With different phases
 Each factor given above is random
 The multipath components combine vectorially at the receiver and
produce a fade or distortion
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11. SMALL SCALE FADING – MULTIPATH DELAY SPREAD
 Multipath delay spread is a measure of the multipath richness of a
communication channel
 In general it can be interpreted as the difference between the time of arrival
of the earliest significant multipath component and the time of arrival of the
last multipath component
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12. SMALL SCALE FADING – MULTIPATH DELAY SPREAD
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13. SMALL SCALE FADING – DOPPLER SPREAD
 Time varying fading due to motion of a scatter or the motion of a transmitter
or receiver or both results in Doppler Spread
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15. FLAT FADING
 Flat fading or non-selective fading is that type of fading in which all frequency
components of the received signal fluctuate in the same proportion
simultaneously
 i.e. fading will effect each frequency component equally
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16. FREQUENCY SELECTIVE FADING
 Frequency selective fading is the type of fading in which all the frequency
components of the received signal fluctuate in different proportions
 i.e. fading will effect each frequency component differently
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17. FAST FADING
 It varies quickly with the frequency
 Fast fading originates due to effects of constructive and destructive
interference patterns which is caused due to multipath
 Has high doppler spread
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18. SLOW FADING
 It does not vary quickly with the frequency
 It originates due to effect of mobility
 It is result of signal path change due to shadowing and obstructions such as
tree or buildings etc.
 Low doppler spread
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19. FAST VS SLOW FADING
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