Path Loss

Path loss models describe the signal attenuation between transmit and receive antenna as a function of the propagation distance and other parameters. Some models can include many details of the terrain profile to estimate the signal attenuation.

Propagation prediction

Topographical terrain data is used extensively to predict propagation conditions, before installing cellular base stations.	Source: Siemens TORNADO D Cellular Planning Tool
In a rough coverage estimation, pathloss is computed using a basic propagation model, with considering the topogrphy in great detail. Real-life cell substantially differ from the theoretical hexagonal lay-out.	Source: Siemens TORNADO D Cellular Planning Tool
Pathloss is computed from the terrain features and antenna data. This determines to coverage of each base station	Source: Siemens TORNADO D Cellular Planning Tool

Example

In the above example, the most appropriate path loss model depends on the location:

At location 1, free space loss is likely to give an accurate estimate of path loss.
At location 2 and 3, a strong line-of-sight is present, but ground reflections can significantly influence path loss. The plane earth loss model appears appropriate
At location 4, free space loss needs to be corrected for significant diffraction losses, caused by trees cutting into the direct line of sight.
Path loss prediction at location 5, 6 and 7 is more difficult than at the other locations. Ground reflection and diffraction losses interact.

Path-loss law

Figure: Average path loss versus distance in UHF bands, measured in Northern Germany.
(a, green): forestrial terrain
(b, orange): open area
(grey): Average of (a) and (b)
(black): Egli's model

Models such as the Egli Path Loss Law can be used for a rough coverage estimation. Results generated by the TORNADO D planning tool by Siemens AG for cellular telephone at 900 MHz. (Qatar, Arabian Peninsula )
Source: Siemens TORNADO D Cellular Planning Tool

Received signal power and attenuation

Path loss is one of the mechanisms causing attenuation between the transmitter power amplifier and receiver front end. Some other effects are listed below, with an indication of the order of magnitude in a GSM-like system (see also pdf slides on GSM frequency planning).

Losses in the antenna feeder (0 .. 4 dB)
Losses in transmit filters, particularly if the antenna radiates signal of multiple transmitters (0 .. 3 dB)
Antenna directionality gain (0 .. 12 dB)
Losses in duplex filter
Fade margins to anticipate for multipath (9 .. 19 dB) and shadow losses (5 dB)
Penetration losses if the receiver is indoors, typically about 10 dB for 900 MHz cellular

www.WirelessCommunication.NL

Chapter: Wireless Channels. Section: Path Loss.

Path Loss

Propagation prediction

Example

Path-loss law

Received signal power and attenuation

www.WirelessCommunication.NL © Jean-Paul M.G. Linnartz, 1993, 1995.

Chapter: Wireless Channels.
Section: Path Loss.