Cognitive Radio (CR) has been recently proposed as a possible solution to the problem of spectrum scarcity in
wireless systems. In a cognitive radio network the (unlicensed) secondary users can access the unused frequency bands
assigned to (licensed) primary users, on a non-interfering basis. Spectrum sensing is the fundamental functionality of CR
systems that allows secondary users to autonomously identify the unused frequency bands that can be safely exploited for
cognitive communications. This paper presents a review of the state of the art solutions and recent patents in the field of
spectrum sensing for cognitive radio networks. A comparison between different strategies is carried out to evidence both
the advantages and drawbacks of each method.
Keywords: Cognitive radio, databases for sensing, primary detection, signal detection, spectrum holes, spectrum sensing.
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