nonLOS

Non-LOS, or non-line-of-sight, describes conditions in which a direct, unobstructed path between transmitter and receiver is blocked by obstacles such as buildings, terrain, or indoor walls. In wireless communications and sensing, LOS is preferred for signal strength and reliability, but many real-world environments involve NLOS, making indirect paths the norm.

Propagation in NLOS relies on indirect routes created by reflections, diffractions, and scattering. Signals reach the receiver via these multipath components. Higher frequency bands, especially millimeter waves, are more easily blocked, while lower frequencies can partly penetrate or bend around obstacles. In urban, indoor, or densely built settings, NLOS is common and can still yield workable links through multipath and diversity techniques.

To cope with NLOS, systems use relays, repeaters, and network densification to create new paths. Beamforming and MIMO exploit multipath to improve quality. Reflective surfaces and programmable metasurfaces can steer or reshape propagation. In sensing and localization, NLOS poses biases and uncertainty; algorithms aim to identify NLOS paths and mitigate effects or use indirect reflections for positioning.

Modeling and analysis employ empirical path-loss models, ray tracing, and measurement data. Standards for cellular and Wi-Fi networks incorporate NLOS scenarios in performance assessments. Non-LOS is a central consideration in the design and operation of wireless systems and sensing, influencing deployment choices, architectures, and processing algorithms.