A method for performing cooperative spectrum sensing in a cognitive radio system, comprising; measuring, by cognitive user devices, an energy of a communications channel to a primary user device from the cognitive user device; characterised in that the cognitive user devices comprise at least two different clusters of cognitive user devices, and for each cluster: determining a cluster head device including determining an optimal cognitive user device of the cluster based on a comparison of the cognitive user devices in the cluster; receiving, by the cluster head device for the cluster from each cognitive device within the cluster, a signal representing a function of the energy measured by each of the cognitive user devices; and based on the signals received from each of the cognitive user devices within the cluster, making a decision by the cluster head device whether the primary user device is present in a designated portion of network spectrum; receiving, from each cluster head device of the at least two clusters by a common receiver, a signal representative of the decision made by the cluster head device; and based on the signals representing the decisions of the cluster head devices, determining by the common receiver whether the primary user device is present in the designated portion of the network spectrum. measuring, by cognitive user devices, an energy of a communications channel to a primary user device from the cognitive user device; characterised in that the cognitive user devices comprise at least two different clusters of cognitive user devices, and for each cluster: determining a cluster head device including determining an optimal cognitive user device of the cluster based on a comparison of the cognitive user devices in the cluster; receiving, by the cluster head device for the cluster from each cognitive device within the cluster, a signal representing a function of the energy measured by each of the cognitive user devices; and based on the signals received from each of the cognitive user devices within the cluster, making a decision by the cluster head device whether the primary user device is present in a designated portion of network spectrum; receiving, from each cluster head device of the at least two clusters by a common receiver, a signal representative of the decision made by the cluster head device; and based on the signals representing the decisions of the cluster head devices, determining by the common receiver whether the primary user device is present in the designated portion of the network spectrum. determining a cluster head device including determining an optimal cognitive user device of the cluster based on a comparison of the cognitive user devices in the cluster; receiving, by the cluster head device for the cluster from each cognitive device within the cluster, a signal representing a function of the energy measured by each of the cognitive user devices; and based on the signals received from each of the cognitive user devices within the cluster, making a decision by the cluster head device whether the primary user device is present in a designated portion of network spectrum; receiving, from each cluster head device of the at least two clusters by a common receiver, a signal representative of the decision made by the cluster head device; and based on the signals representing the decisions of the cluster head devices, determining by the common receiver whether the primary user device is present in the designated portion of the network spectrum.