In some countries, unlicensed spectrum used by WiFi networks is shared with radar systems. WiFi networks that operate in such bands employ radar detection and avoidance. A WiFi transceiver spends a certain channel sojourn (dwell) time scanning a channel prior to starting communication on it. A full scan takes about seven seconds, a user-perceptible delay.
This disclosure describes techniques to reduce scan time by leveraging radar detection procedures that have already been completed by nearby access points. If a nearby access point has recently transmitted a frame or emits a wide-band transmission, it is an indication that the nearby access point has confirmed that the channel is clear of radar. Therefore, a device that is about to initiate a full scan can abbreviate its scan duration substantially. With implementation of the techniques of this disclosure, scan times drop from seven seconds to under two seconds.
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Lee, Jiwoong, "Fast WiFi scanning", Technical Disclosure Commons, (December 19, 2018)