DFS is short for Dynamic Frequency Selection. It is a communication technique in which transmitters actively “listen” to the RF environment and dynamically choose transmit channels based on the environment’s characteristics.
Unlicensed devices, typically as WLANs/ WiMax application, are being allowed to operate in the same frequency spectrum that is currently allocated to licensed devices as radar systems. Due to radar systems are guaranteed to have spectrum protection. So the unlicensed devices must choose other operating channel that covers a frequency range not currently utilized by nearby operational radar to ensure they do not interfere with operating radar systems. The DFS standards (like ETSI 301893 V1.7.1, FCC 06-96, and Japan MIC) define a set of radar profiles, against which unlicensed commercial devices must be validated to ensure proper systematic radar avoidance.