Line of sight power variation in the air to ground channel

The paper investigates the variation of the received line-of-sight (LoS) power due to ground multipath propagation for the L-band air to ground radio channel. Within, both theoretical as well as results taken from flight trial measurements are presented. In theory, ground multipath propagation leads to periodic amplification and attenuation of the received LoS power. Measurement data presented within the paper confirms that in general, the variation can be well modeled by introducing an additional ground multipath component. Nevertheless, in reality strong signal variations do not appear as often as expected, i.e. the reflection off the ground is strongly attenuated. Two main reasons can be identified attenuation. First, ground multipath propagation can be blocked by nearby buildings, terrain features or vegetation. Second, a rough ground surfaces causes the incident radio waves to be reflected in all directions. This effect is called scattering and results in only a small portion of the power being received at the aircraft