Editing Path loss (section)

==Examples==
{{Unreferenced section|date=August 2017}}
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&nbsp;dB for the first kilometer of the link between the [[base transceiver station]] (BTS) and the [[mobile phone|mobile]]. The path loss for the first ten kilometers may be 150–190&nbsp;dB (''Note'': These values are very approximate and are given here only as an illustration of the range in which the numbers used to express the path loss values ''can eventually be'', these are not definitive or binding figures—the path loss may be very different for the same distance along two different paths and it can be different even along the same path if measured at different times.)

In the radio wave environment for mobile services  the mobile antenna is close to the ground. [[Line-of-sight propagation]] (LOS) models are highly modified. The signal path from the BTS antenna normally elevated above the roof tops is refracted down into the local physical environment (hills, trees, houses) and the LOS signal seldom reaches the antenna. The environment will produce several deflections of the direct signal onto the antenna, where typically 2–5 deflected signal components will be vectorially added.

These refraction and deflection processes cause loss of signal strength, which changes when the mobile antenna moves (Rayleigh fading), causing instantaneous variations of up to 20&nbsp;dB. The network is therefore designed to provide an excess of signal strength compared to LOS of 8–25&nbsp;dB depending on the nature of the physical environment, and another 10&nbsp;dB to overcome the fading due to movement.