What is Fading?

In Wireless Communication, fading refers to the attenuation of the transmitted signal power due to various variables during wireless propagation. These variables can be atmospheric conditions such as rainfall and lightning, geographical position, time, radio frequency etc. The channel between transmitter and receiver can also be time varying or fixed depending upon whether the transmitter/receiver are fixed or moving with respect to each other which can cause fading to occur. 

Transmitted signals encounter multiple reflectors in the environment during its propagation before reaching the receiver. This creates multiple paths and as a result, the receiver sees multiple copies of the transmitted signal, each traversing in a different path. Each signal copy experiences different attenuation, delays and phase shifts while propagating. This can result in either constructive or destructive interference, amplifying or attenuating the signal power seen at the receiver. Strong destructive interference is frequently referred to as a deep fade.

Fading can cause decline in performance in a wireless communication system because it results in the loss of signal power thus reducing the Signal to Noise Ratio (SNR). It can even cause temporary failure of communication due to a severe drop in SNR. The signal loss can be over some or all over the bandwidth depending on the causes of fading. Fading can also be a problem as it changes over time. Communication systems are often designed to adapt to such impairments, but the fading can change faster than the adaptations can be made. This can adversely affect the link’s performance.

Click here to read about the different types of fading.