“…The accuracy of the spectrum maps achieved by using the model-based methods was poor due to the lack of flexibilities in the radio propagation. In contrast, the crowdsourcing-based methods constructed the spectrum maps more accurately via regression techniques or machine learning [5], such as matrix recovery [6], Kriging interpolation [7], the inverse distance weighted (IDW) interpolation [8], kernel-based learning [9], [10] and some data-driven methods proposed to further improve the accuracy [11], [12]. However, the spatial-correlationbased schemes only use spatial interpolation and cannot obtain the spectrum maps when there is no signal information about the target frequency.…”