A device (400) scans and classifies each channel within a spectrum of channels (215-270) as being occupied or unoccupied (255), and, if occupied, whether it is occupied by a primary user (240), a secondary user (230), or an unknown user (260). As a secondary device (400), transmissions are avoided on channels occupied by primary users (490). The device selectively joins an existing network of secondary devices, or establishes a new network on an unoccupied channel (125), based on the quality of service (QoS) that the channel can provide and/or other factors. If the device is paired with a target device (115), the paired device advertises itself on a selected channel (345-360) for a period that is at least as long as the time required to scan all channels, to facilitate discovery in the event that the target device is also in a search mode. The advertising duration randomly alternates (345) among integer multiples of the scan duration.