Terminology » RF Basics » Level Crossing Rate (LCR) vs. Average Fade Duration (AFD)

Level Crossing Rate (LCR) vs. Average Fade Duration (AFD)

wireless communication radio propagation signal fading level crossing rate average fade duration

This page explains the concepts of Level Crossing Rate (LCR) and Average Fade Duration (AFD) and highlights the differences between them. These concepts are important in understanding radio propagation.

Level Crossing Rate (LCR)

  • It measures the average number of times a signal crosses a specific level.
  • It can be defined mathematically as follows:

Level Crossing Rate Alt text: Level Crossing Rate

  • N_R is expressed in units of fades per second, while LCR is expressed in crossings per second.

Average Fade Duration (AFD)

  • It measures the average time period during which the signal remains below a specific level.
  • Both LCR and AFD are useful for designing signaling formats and diversity schemes in cellular systems.
  • AFD is expressed in units of seconds. The Average Fade Duration can be calculated using the following formula:

Average Fade Duration Alt text: Average Fade Duration

  • Here, �? = R / R_rms is the value of the specified amplitude level
  • R is normalized to the local RMS amplitude of the fading envelope.
  • R_rms is based on the Rayleigh distribution of the received signal envelope.