Difference between small scale fading and large scale fading

This page compares small scale fading Vs large scale fading in wireless communication and mentions difference between small scale fading and large scale fading.

The time variation of received signal power due to changes in transmission medium or paths or obstacles is known as fading. Wireless system consists of transmitter, receiver and channel. In fixed scenario, fading depends on variation in the channel parameters due to atmospheric conditions such as rainfall, lightening etc. In mobile scenario, fading depends on variation in the channel parameters due to obstacles over the path which are varying with respect to time. Moreover path loss leads to attenuation of the transmitted signal before it reaches receiver.

Fading types

Based on channel model parameters and position or movement of transmitter/receiver, there are different fading types as mentioned. Fading occurs due to reflections from ground and surrounding buildings as as well as scattered signals from trees, people and towers present in the large area. Refer article on types of fading and fading basics>>. Let us understand small scale fading and large scale fading.

Small scale fading

• Small scale fading is concerned with rapid fluctuations of received signal strength over very short distance and short time period.
•  These multipath fading types depend on propagation environment.
• It is divided into two main categories viz. multipath delay spread and doppler spread.
• Based on multipath delay spread there are two types of small scale fading viz. flat fading and frequency selective fading.
• Doppler spread is divided into fast fading and slow fading.

Large scale fading

• Large scale fading occurs when an obstacle comes in between transmitter and receiver. This interference type causes significant amount of signal strength reduction. This is because EM wave is shadowed or blocked by the obstacle. It is related to large fluctuations of the signal over distance.
• It includes path loss and shadowing effects.
• The free space path loss can be expressed as follows.
➤ Pt/Pr = {(4 * π * d)2/ λ2} = (4*π*f*d)2/c2
•  Shadowing is deviation of received power of EM signal from average value. It is result of obstacles over the path between transmitter and receiver. It depends on geographical position as well as radio frequency of EM (ElectroMagnetic) waves.

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