1
2.6kviews
Explain the factor influencing small scale fading
2 Answers
1
211views

The following physical factors influence small-scale fading in the radio propagation channel:

  1. Multipath propagation - Multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths.
    The presence of reflecting objects and scatterers in the channel produces the following undesirable characteristics:
    1. Creates a constantly changing environment that dissipates the signal energy leading to weaker signal reaching the receiver,
    2. Introduces phase variations in the received signal and
    3. Changes in the time of arrival of the various multipath components of the signal.

The random phase and amplitude of different multipath components cause fluctuations in signal strength, thereby introducing small scale fading, signal distortion or both. Multipath propagation often lengthens the time required for the baseband portion of the signal to reach the receiver which can cause signal smearing due to intersymbol interference.

  1. Speed of the mobile - The relative motion between the base station and the mobile results in random frequency modulation due to different doppler shifts on each of the multipath components. Doppler shift will be positive or negative depending on whether the mobile receiver is moving towards or away from the base station.
  2. Speed of surrounding objects - If objects in the radio channel are in motion, they induce a time varying Doppler shift on multipath components. If the surrounding objects move at a greater rate than the mobile, then this effect dominates fading.
  3. Transmission Bandwidth of the signal - If the transmitted radio signal bandwidth is greater than the bandwidth of the multipath channel (quantified by coherence bandwidth), the received signal will be distorted, but the received signal strength will not fade over a local area.
1
113views

There are several physical factors that influence small scale fading. The main factors influencing small-scale fading are as follows:

Multipath propagation:

  • In the channel due to the presence of reflecting objects and scatters a constantly changing environment creates that dissipates the signal energy in amplitude, phase, and time.
  • These effects result in multiple versions of the transmitted signal that arrive at the receiving antenna.
  • The random phase and amplitudes of the different multipath components cause fluctuations in signal strength, thereby inducing small-scale fading, signal distortion, or both.
  • Multipath propagation often lengthens the time required for the baseband portion of the signal to reach the receiver which can cause signal smearing due to intersymbol interference.

Speed of the mobile:

  • The relative motion between the base station and the mobile results in random frequency modulation due to different Doppler shifts on each of the multipath components.

  • Doppler shift will be positive or negative depending on whether the mobile receiver is moving toward or away from the base station.

Speed of surrounding objects:

  • If objects in the radio channel are in motion, they induce a time varying Doppler shift on multipath components resulting in fading.

  • If the surrounding objects move at a greater rate than the mobile, then this effect dominates the small-scale fading.

The transmission bandwidth of the signal:

  • If the transmitted radiosignal bandwidth is greater than the "bandwidth" of the multipath channel,the received signal will be distorted, but the received signal strength will notfade much over a local area (i.e., the small-scale signal fading will not be significant).
Please log in to add an answer.