A spectrum overlay technique is a strategy in spectrum management where a secondary user utilizes a channel allocated to a primary user only when it is unoccupied. Spectrum overlay techniques rely on a detection and avoidance mechanism like DFS (Dynamic Frequency Selection). In this approach, the secondary user monitors the frequency spectrum, and if it detects activity by a primary user, it refrains from using that channel.

For instance, this mechanism is employed by RLANs (Radio Local Area Networks) operating in the 5 GHz frequency range. RLANs utilize a frequency band that is also utilized by radar systems.