A method for wireless communications, comprising: receiving, at an apparatus, a beacon frame comprising an indication of a time which a message with a field indicating a current version of an unused frequency spectrum map will arrive, and further receiving based on said time, the message with a field indicating a current version of an unused frequency spectrum map, the unused frequency spectrum map indicating channels usable for the wireless communications; determining whether the current version of the unused frequency spectrum map is different than a previous version of the unused frequency spectrum map; and using a channel for the wireless communications based on the determination; and, wherein the message comprises at least one of: an indication that the message is a contact verification signal, CVS, wherein the indication comprises an information element, IE, identifier, ID; a length field indicating a length of the field indicating the current version of the unused frequency spectrum map; a beacon frame or a broadcast management frame, wherein the beacon frame or the broadcast management frame comprises a Management Message Integrity Check, MIC, Information Element, MMIE; or a frame with at least one of a first field indicating that the message is a Public Action message or a second field indicating that the message comprises the first field indicating the current version of the unused frequency spectrum map. receiving, at an apparatus, a beacon frame comprising an indication of a time which a message with a field indicating a current version of an unused frequency spectrum map will arrive, and further receiving based on said time, the message with a field indicating a current version of an unused frequency spectrum map, the unused frequency spectrum map indicating channels usable for the wireless communications; determining whether the current version of the unused frequency spectrum map is different than a previous version of the unused frequency spectrum map; and using a channel for the wireless communications based on the determination; and, wherein the message comprises at least one of: an indication that the message is a contact verification signal, CVS, wherein the indication comprises an information element, IE, identifier, ID; a length field indicating a length of the field indicating the current version of the unused frequency spectrum map; a beacon frame or a broadcast management frame, wherein the beacon frame or the broadcast management frame comprises a Management Message Integrity Check, MIC, Information Element, MMIE; or a frame with at least one of a first field indicating that the message is a Public Action message or a second field indicating that the message comprises the first field indicating the current version of the unused frequency spectrum map. an indication that the message is a contact verification signal, CVS, wherein the indication comprises an information element, IE, identifier, ID; a length field indicating a length of the field indicating the current version of the unused frequency spectrum map; a beacon frame or a broadcast management frame, wherein the beacon frame or the broadcast management frame comprises a Management Message Integrity Check, MIC, Information Element, MMIE; or a frame with at least one of a first field indicating that the message is a Public Action message or a second field indicating that the message comprises the first field indicating the current version of the unused frequency spectrum map.