What is LoS?
LoS (Line of Sight) refers to a propagation condition where the transmitter and receiver have a clear, unobstructed direct path between them. In LoS conditions, the direct path carries the strongest signal component and propagation loss follows a predictable free-space path loss model. LoS is the preferred propagation condition for 5G NR deployments — particularly at mmWave frequencies (FR2) where signal penetration through obstacles is very limited and the direct path dominates link budget.
How Does LoS Work?
In LoS propagation, the received signal consists of a strong direct ray plus weaker reflected and scattered components. The path loss follows the Friis transmission equation: PL = 20·log₁₀(4πd/λ), where d is distance and λ is wavelength. For 5G at 3.5 GHz, free-space path loss at 100m is approximately 74 dB; at 28 GHz (mmWave), it increases to approximately 92 dB. 3GPP channel models (TR 38.901) define separate LoS and NLoS probability models for different environments (urban macro, urban micro, indoor, rural). The LoS probability decreases with distance and is lower in dense urban environments. Fresnel zone clearance is the practical criterion for LoS — the first Fresnel zone must be at least 60% clear of obstructions.
Use Cases
5G NR network planning and link budget analysis, mmWave deployment site selection, FWA (Fixed Wireless Access) link design, backhaul and fronthaul microwave link planning, and propagation model calibration for coverage simulation.
3GPP / Standards Reference
3GPP TR 38.901 (Channel model for 0.5–100 GHz — LoS probability models), ITU-R P.1411 (Short-range outdoor propagation)
Related Terms
NLOS | mmWave | FR2 | FWA | EIRP
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This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
