In this paper the capability of a cognitive radio network to discover available frequency channels in the spectrum
licensed to a primary user (e.g., digital TV) is analyzed. We rely on cooperative sensing where fusion of individual sensing
outcomes is based on the r-out-of-k decision rule. The study is carried out assuming the point of view of a tagged network
of cognitive devices that is surrounded by other uncoordinated transmitters competing for accessing the same portion of the
spectrum. The contributions of this work are the following.
First, the introduction of a three-state model of the wireless hannel. Second, modeling the sensing process by means of
the general framework provided by urn occupancy problems accessed in non-uniform fashion. Third, the evaluation of the
number of available channels in the presence of interference limiting spectrum availability. Finally, the proposal of a cognitive
protocol to mitigate the interference. Results are given for a specific case of interest where all networks are supposed ECMA-
392 standard compliant.