[1] Path loss is a major component in the analysis and design of the link budget of a telecommunication system.
Path loss is also influenced by terrain contours, environment (urban or rural, vegetation and foliage), propagation medium (dry or moist air), the distance between the transmitter and the receiver, and the height and location of antennas.
There are several factors that affect this: In understanding path loss and minimizing it, there are four key factors to consider in designing a wireless communication system: 1) Determining the required transmitter power: The transmitter must have enough power to overcome the path loss in order for the signal to reach the receiver with sufficient strength.
The signal radiated by a transmitter may also travel along many and different paths to a receiver simultaneously; this effect is called multipath.
Small-scale fading refers to the rapid changes in radio signal amplitude in a short period of time or distance of travel.
In the study of wireless communications, path loss can be represented by the path loss exponent, whose value is normally in the range of 2 to 4 (where 2 is for propagation in free space, 4 is for relatively lossy environments and for the case of full specular reflection from the earth surface—the so-called flat earth model).
Radio and antenna engineers use the following simplified formula (derived from the Friis Transmission Formula) for the signal path loss between the feed points of two isotropic antennas in free space: Path loss in dB: where
Exact prediction is possible only for simpler cases, such as the above-mentioned free space propagation or the flat-earth model.
Statistical methods (also called stochastic or empirical) are based on measured and averaged losses along typical classes of radio links.
For FM radio and TV broadcasting the path loss is most commonly predicted using the ITU model as described in P.1546 (successor to P.370) recommendation.
These methods are expected to produce more accurate and reliable predictions of the path loss than the empirical methods; however, they are significantly more expensive in computational effort and depend on the detailed and accurate description of all objects in the propagation space, such as buildings, roofs, windows, doors, and walls.
The path loss in other frequency bands (medium wave (MW), shortwave (SW or HF), microwave (SHF)) is predicted with similar methods, though the concrete algorithms and formulas may be very different from those for VHF/UHF.
[citation needed] Easy approximations for calculating the path loss over distances significantly shorter than the distance to the radio horizon: In cellular networks, such as UMTS and GSM, which operate in the UHF band, the value of the path loss in built-up areas can reach 110–140 dB for the first kilometer of the link between the base transceiver station (BTS) and the mobile.