The increased number of wireless communication systems in the last decades raised the problem of the limited resources in the frequency domain. Cognitive Radio (CR) technology, based on a dynamic spectrum access (DSA), is a possible solution for improving the efficiency of spectrum usage. A necessary step in order to identify suitable frequency bands for opportunistic usage is to evaluate the degree in which licensed bands are currently used. This paper presents results of two measurement campaigns conducted in Romania in urban and rural environments, covering the frequency range from 25 MHz up to 3.4 GHz. The results are confronted with the frequency allocation table published by the national authority for radio communications and a comparison and analysis of the obtained data are being made

Keywords: Cognitive radio, Dynamic spectrum access, Energy detection, Measurement campaign, Spectrum occupancy