Line of sight (LOS) is the level of obstruction on the path between two points.
The level of obstruction in a LOS determines not only the visibility from one point to another but also the quality of signal reception for wireless transmissions, such as Wi-Fi. Clear LOS is necessary for infrared wireless networking or LED-based Li-Fi.
Analysis of line of site is particularly important for planning wireless network deployment. A clear line of site between two antennas is ideal for the best reception. However, a radio signal can permeate and bend or bounce around some obstruction, unlike line of sight for an eye. LOS is often categorized with separate abbreviations for the different levels of obstruction. A fully open path is the situation abbreviated as LOS. A near line of site with partial obstructions is abbreviated as nLOS and a completely blocked non-line of sight as NLOS.
Radio frequencies penetrate more materials than photons but this penetration is not uniform and depends on density of the materials or having holes large enough for the radio waves to penetrate. A wood wall is much easier penetrated by radio than concrete, for example, and metals are even less penetrable. The dependency on density means that a clear LOS matters and that if there are any obstructions, what those obstructions are made of matters as well.
To improve the performance of a wireless network, reducing the amount of equipment required and thus the cost, it’s important to carefully consider LOS obstructions and their materials, as well as interfering networks and radio noise from other electronic and mechanical equipment around wireless gateways or antennas.