Radio wave can be propagated from the transmitting antenna to the receiving antenna in many ways: perpendicular incidence wave or ground refraction wave, diffraction wave, troposphere reflection wave, ionosphere reflection wave, as shown in the diagram. As for radio wave, the most simple propagation mode between the transmitter and the receiver is free space propagation.
One is perpendicular incidence wave; the other is ground reflection wave. The result of overlaying the perpendicular incidence wave
and the reflection wave may strengthen the signal, or weaken the signal, which is known as multi-path effect. Diffraction wave is the main radio wave signal source for shadow areas such building interior.
The strength of the diffraction wave is much dependent of the propagation environment. The higher the frequency is, the weaker the diffraction signal will be. The troposphere reflection wave derives from the troposphere. The heterogeneous media in the troposphere changes from time to time for weather reasons.
Its reflectance decreases with the increase of height. This slowly changing reflectance causes the radio wave to curve. The troposphere mode is applicable to the wireless communication where the wavelength is less than 10m (i.e., frequency is greater than 30MHz).
Ionosphere reflection propagation:
When the wavelength of the radio wave is less than 1m (frequency is greater than 300MHz), the ionosphere is the reflector. There may be one or multiple hops in the radio wave reflected from the ionosphere, so this propagation is applicable to long-distance communication. Like the troposphere, the ionosphere also presents the continuous fluctuation feature.
In a typical cellular mobile communication environment, a mobile station is always far shorter than a BTS. The direct path between the transmitter and the receiver is blocked by buildings or other objects.
Therefore, the communication between the cellular BTS and the mobile station is performed via many other paths than the direct path. In the UHF band, the electromagnetic wave from the transmitter to the receiver is primarily propagated by means of scattering, namely, the electromagnetic wave is reflected from the building plane or refracted from the man-made or natural objects.