What is NLOS?
NLOS (Non-Line of Sight) refers to a radio propagation condition where the direct path between transmitter and receiver is obstructed by physical obstacles such as buildings, terrain, vegetation, or other structures. In NLOS conditions, the signal reaches the receiver only through reflection, diffraction, and scattering — resulting in significantly higher path loss, greater delay spread, and more severe fading compared to LoS conditions. NLOS propagation is the dominant condition in most urban and indoor 5G deployments and is particularly challenging at mmWave frequencies.
How Does NLOS Work?
In NLOS, the received signal is composed entirely of reflected, diffracted, and scattered multipath components — with no dominant direct path. This results in Rayleigh fading (random amplitude fluctuations) as the multipath components add constructively and destructively. Path loss in NLOS is typically 10–30 dB higher than LoS at the same distance, with the excess loss increasing at higher frequencies. At mmWave, NLOS conditions can cause 20–40 dB additional loss compared to LoS, often making communication impossible without beam management (finding the best reflected path). 3GPP channel models define NLOS path loss equations and LoS/NLOS probability functions for each deployment scenario (UMa, UMi, InH, RMa).
Use Cases
5G NR coverage planning in urban environments, mmWave deployment feasibility analysis, beam management and tracking for NLOS mmWave users, relay and RIS (Reconfigurable Intelligent Surface) deployment for NLOS coverage enhancement, and indoor coverage planning.
3GPP / Standards Reference
3GPP TR 38.901 (Channel model — NLOS path loss models), ITU-R P.1411 (Short-range outdoor NLOS propagation)
Related Terms
LoS | mmWave | Beamforming | FR2 | Cell Tower
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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.
