Multi-band direction-sensitive cognitive radio node

Cognitive radio (CR) nodes should be ultimately able to resolve all information-relevant resources (frequency, space, polarization et cetera) available to unlicensed users for communication at a certain location in a given time slot. We propose a cognitive radio node that is capable of resolving simultaneously frequency and spatial resources with the help of a multi-band direction-sensitive antenna, a commercial wideband transceiver, and energy detection. The antenna system is resonant at three selectable frequency bands and divides space in three switchable sectors d₁, d₂, and d₃, hence providing nine degrees of freedom altogether. The proposed CR node is tested in an Over-The-Air test setup consisting of eight transmit antennas placed around the node in a circular arrangement. The transmit antennas are fed with unique wideband signals at different center frequencies, emulating the activities of eight static primary users. The proposed CR node is used to sense frequency/direction spectrum utilization using energy detection. The results show that the CR node successfully identifies primary users´ activity with a sufficient dynamic range.