# Line of Sight (LOS)

*Line of Sight* · Wireless

> Line of sight (LOS) means an unobstructed direct path exists between two antennas. It is the basic requirement for high-frequency wireless links.

Line of sight means there is no object between transmitter and receiver that blocks the signal. Wireless planning distinguishes two notions. Optical line of sight means one point can be seen from the other. Radio line of sight additionally requires the first Fresnel zone to be sufficiently clear. A link that is visually clear is not necessarily clear for radio.

Links are commonly classified in three groups. Clear LOS has an open path. In nLOS (near line of sight) the Fresnel zone is partly obstructed. In NLOS the direct path is fully blocked and the signal arrives only through reflection and diffraction. OFDM-based sub-6 GHz systems tolerate nLOS conditions to a degree, whereas high frequencies such as 24, 60 and 80 GHz demand an almost perfect LOS. A single tree can break the link.

LOS analysis builds a path profile between two points from a digital elevation model (terrain) and, ideally, a digital surface model that includes buildings and vegetation. The profile shows earth curvature, antenna heights and the Fresnel zone together. The most reliable approach is to confirm the desktop analysis in the field with a rooftop visual check, binoculars, drone imagery or a temporary test link.

LOS can change over time. Trees coming into leaf in summer, new buildings or working cranes can degrade a previously healthy link. Designs should therefore leave sufficient antenna height and fade margin, and critical links should have an alternative route or backup connection planned.

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Canonical: https://internetten.com.tr/en/glossary/line-of-sight-los