Path loss

The path loss L describes the loss of electromagnetic power between a transmitter P and a receiver. A small path loss usually indicates good reception situation.

The path loss all losses on the way from the sender to the receiver are included, such as free space loss, absorption loss when penetrating media (atmosphere), losses due to diffraction and shadowing as well as losses due to reflections within the Fresnel zone.

Compared with unwanted signals at radiation coupling a sufficiently large path loss on the coupling path between the source (transmitter) and interference sink (receiver) a characteristic of electromagnetic compatibility. The increase in the path loss, for example by increasing the spatial distance between drain and source is then interference suppression.

Propagation model calculations

There are basically two different ways to determine the path loss for a wireless communication channel. Once the deterministic method, in which the propagation conditions physically analyzed, and then their influence will be charged. This is only to a limited extent and only leads to the goal, if minimum disruption of lateral spread. In practice, this is usually only useful for connections between earth station and satellite and radio connections on the Earth's surface with an extremely short distance ( for example, a wireless mouse ).

Another method uses stochastic and statistical means. These calculations are performed with computer programs, where a terrain profile as well as conditions in the area are based on, for example. Most of these methods are based on extensive research into the propagation conditions. There are known several wave propagation models:

  • The wave propagation model of Lee;
  • Okumura - Hata model, the;
  • The COST - Walfisch - Ikegami model;
  • The COST -231 HATA model.

As a result proportionalities between the path loss and the distance will be issued. This can be between to. Some models 'll add a so-called environmental correction factor -2 to -20 dB.

Components of the path loss

There are many causes for the results summarized in a path loss attenuation of electromagnetic waves:

Free-space propagation

The path loss in decibels is at a propagation in free space without interference:

  • F: frequency
  • D: distance between transmitter and receiver
  • C: speed of light

The free space propagation occur, for example in the radio link between two satellites which have an optical clear view with each other. Only in this special case, the path loss is characterized solely by the free-space loss.

Two-way propagation

The above-mentioned Equation for the free space. Spreads the shaft via an electrically conductive plane, it is usually from the receiver both directly and indirectly, reflected from the plane received. This is called two-way propagation.

HS and hE indicate the height of the transmitting and receiving antenna to the plane. When spread over the plain, the path loss increases much faster ( to the power of 4) than in free space ( with the power of 2 ).

Fresnelzone Multipath propagation Fading
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