SMALL SCALE FADING

The term fading is used to describe rapid fluctuation of the amplitude of a radio signal over a short period of time or travel distance.Fading is caused by distinctive interference between two or more versions of the transmitted signal being slightly out of phase due to different propagation time.

Factors Influencing Small Scale Fading

1.Multipath propagation

The presence of reflecting objects & scatter on the space between transmitter and receiver creates a constantly changing channel environment.It also causes the signal at receiver to fade or distort.

2.Speed of mobile receiver.

• The relative motion between the transmitter & receiver results in a random frequency modulation due to different doppler shifts on each of the multipath signals.

• Doppler shifts may be positive or negative depending on direction of movement of mobile.

3.Speed of surrounding objects.

• If the speed of surrounding object is greater than mobile the fading is dominated by those objects.
• If the surrounding objects are slower than the mobile then their effects can be ignored.

4. The transition bandwidth

• Depends on the relation between the signal bandwidth and the coherence bandwidth of the channel,the signal is either distorted or faded.

• If the signal bandwidth is greater than coherence bandwidth it creates distortion.

• If the signal bandwidth is smaller than coherence bandwidth it creates small scale fading.