What Are Different Types Of Small Scale Fading?


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Kaleem Raza Profile
Kaleem Raza answered
There are many natural factors in the radio propagation channels influence small scale fading. Some of the common factors of influencing the small scale fading include:

Multi-path propagation
Due to the reflecting objects and scatters in the channels creates a changing environment which will reduce the signals power in amplitude, phase, and time. Including different multi-path components and amplitude of random phase cause the variation of the signals.

Speed of the mobile.
Between the mobile and base station the relative motion results the random frequency modulation due to the Doppler's shift. Whether Doppler shift will be positive or negative it's depending on the mobile receiver is moving towards or away form base station.

Speed of surrounding objects.
Objects are in the range of radio channels are in motion; if the objects in the area moves at a higher rate than the mobile, the small fading effects will be dominate.

The transmission bandwidth of the signal.
The bandwidth of the transmitted radio signal is greater than the bandwidth of multi-path channel, that causing receiving signal distorted. The bandwidth of channel can be quantified by the coherence of bandwidth.
Kaleem Raza Profile
Kaleem Raza answered
An expression fading is used to explain the quick changes in a amplitude and the phase of radio signal over a limited time period or traveling area, this phenomena works with obstructions in the path from the base station to the mobile unit, after the receiving different kinds of the similar signal in a various intervals of time. Outcome of the arrived multiple versions of the broadcast signal on different times at the receiving and interfering among these waves causes fading.
There are different types of small scale fading:
1- Small scale fading based on multi-path time delay spread.
(A) Flat fading:
• BW of signal < BW of Channel
• Delay spread < symbol period

(B) Frequency selective fading:
• BW of signal < BW of Channel
• Delay spread < symbol period
2- Small scale fading based on Doppler spread:
(A) Fast fading
• High Doppler spread
• Coherence Time < symbol period
• Channel variation faster then base-band signal variation

(B) Slow fading
• Low Doppler spread
• Ccoherence Time > symbol period
• Channel variation slower then base-band signal variation

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