  In this chapter, we present the state of the art of the spectrum sensing
techniques for cognitive radio networks as well and their comparisons. The rest
of the chapter is organized as below: Section I.1, Section I.2, and Section I.3
present the spectrum management problem and the cognitive radio cycle as well
as the compressive sensing solution; Section II.1 describes the spectrum
sensing model; Section II.2 presents the existing spectrum sensing techniques,
including energy, autocorrelation, Euclidian distance, wavelet, and matched
filter based sensing. Finally, a conclusion is given at the end of the chapter.
