Systems and methods for detecting unused channels in a cognitive radio system are described. In one method, data is communicated on a particular channel for a secondary receiver. In addition, a set of channels is iteratively scanned by collecting samples for each channel and for each iteration of the scanning. Here, iterations of the scanning progressively removes channels from the set of channels based on the collected samples and updates states of the channels in the set based on the collected samples to obtain a set of candidate channels. In response to detecting a pre-determined condition, communications on the particular channel are precluded and at least one of the candidate channels is evaluated by collecting additional samples on each of the channels. Further, at least one of the candidate channels is selected based on the evaluation for utilization by the one or more secondary receivers for data communication.