OE-7.3 Mobile Radio Propagation & Fading

Work through these

• Introduction to radio wave propagation; large-scale path loss

  What happens to a signal on the way, at the scale of the whole path. The distinction between large-scale and small-scale effects organises the whole topic.

• The free space propagation model

  The ideal case with nothing in the way, which no real link ever is. It is the reference every real measurement is quoted against.

• The three basic propagation mechanisms: reflection, diffraction, scattering

  The three things that happen when a wave meets an object, depending on its size relative to the wavelength. Between them they explain why a signal reaches places with no line of sight.

• Small-scale multipath propagation

  Several copies of the same signal arriving at slightly different times. This is the cause of nearly everything difficult in mobile radio.

• Factors influencing small-scale fading

  What decides how bad the effect above gets: speed, bandwidth and the environment. It sets up the classification two items down.

• Doppler shift

  The frequency change caused by motion, familiar from sound and consequential here. It sets how fast the channel changes, which decides how often it must be re-estimated.

• Types of small-scale fading

  The four cases, sorted by whether the trouble is in time or in frequency. Getting this classification straight is what makes the mitigation techniques in the next topic make sense.