Spectrum Sensing is widely used in smart or cognitiveradio transmission system in order to allocate unusedbandwidth by a primary user to a secondary user. The allocationscheme depends on determining a threshold reflecting theexistence or not of the primary user. This manuscript deals withthis problem by proposing two major contributions: the first oneis a novel mechanism to calculate the threshold based on a knowndistribution of the correlation function between the pilot and thereceived signal. Our main finding is that the threshold couldbe, in some circumstances, independent from the SNR whichrelieves the detector from processing threshold updates in casewhen the SNR frequently varies. In the second contribution weuse the Waveform technique in order to detect the existing or notof Primary user signals while a secondary user is transmittingwithout interrupting the detection mechanism of the primaryuser. Contrary to existing methods, which require a silence periodof secondary users in order to sense the activity of the primaryuser, our approach does not need this period which enhances thetotal transmission rate.Our simulation results corroborate the two proposed approaches.Simulation results are presented and discussed.