A communication unit operates in a wireless-networking environment and maintains a mapping for active channels and associated network identifiers. The communication unit may associate with a wireless network using the mapping for one or more of the active channels having a selected network identifier. For associations and reassociations with wireless networks, the communication unit may selectively scan the channels having mapping stored in a table to more quickly identify active channels and thereby reduce scan time. In some embodiments, an access point may perform channel-width measurements and radar detection using the bitmap.