Review of spectrum sensing in cognitive radio

The frequency spectrum bandwidth used in modern wireless systems is limited while the number of wireless systems is rapidly increasing. In order to alleviate the spectrum scarcity, secondary systems can opportunistically access the temporarily unused licensed bands of primary systems which are known as spectrum holes or white spaces, by altering their transmitting parameters so that the interference is minimal to primary user while coordinating access to this channel with other cognitive radio (CR) users in the vicinity. Spectrum sensing is necessary to enable dynamic spectrum access without interfering with primary users. This optimizes the use of available radio frequency spectrum while minimizing interference to other licensed or unlicensed users by detecting and utilizing only the white spaces. This paper explores various sensing methods, their performance, applicability and effectiveness under different transmission conditions and advantages and disadvantages incorporated with each sensing method.