Abstract: A method for facilitating the more efficient opportunistic use of one or more frequency division multiplexed (FDM) channels in a frequency band by a group of two or more secondary users (SU) that have formed a point-to-multipoint, centralized ad hoc network, with one SU acting as a central node and the remaining SU acting as remote nodes. Each SU adheres to a predetermined protocol utilizing synchronized time slots in each of the channels being used by the network, each time slot having at least one data transmission period and at least one primary user detection period during which no SU transmits. The central SU node determines channel availability. Remote SU nodes may listen for primary user transmissions in a channel and inform the central SU node of detected activity. Remote nodes contend for transmission during a data transmission period of a time slot unless the channel has been reserved by a remote node after successful transmission in the data transmission period of a preceding time slot.