Joint Angular-Frequency Power Spectrum Sensing Based on K-Means Clustering

The critical component in the cognitive radio (CR) network is spectrum sensing (SS) used to locate the accessible spectrum and to minimize interference with the licensed users (LUs). The CR SS could take into account the direction-of-arrival (DoA) of signals sent by LUs from the perspective of a secondary user (SU) to further improve the spectrum utility. This prevents the SU to interfere the LU signals by occupying a frequency band that the LU is currently using but aiming its transmission at a specific angle away from the LU. We use a uniform linear array, sample the signal received by each antenna, compute the correlation between samples, apply classical beamforming, and compute the discrete Fourier transform to reconstruct the complete two-dimensional angular-frequency power spectrum. In order to determine whether LUs or other SUs are currently occupying a certain frequency band or not, we use K-means clustering to compute the detection threshold. Numerical studies are carried out to demonstrate that the threshold based on the K-means clustering is applicable to detect signals from LUs based on the result of frequency and DoA power SS.