In this paper, the simulation of cognitive radio system to must detect the presence of primary user to avoid interference. Spectrum sensing to detect the spectrum holes (unused bands of the spectrum) providing high spectral resolution capability. Allowing the secondary users to operate at the spectrum vacant bands which allocated the primary users. They should spot the spectrum holes and the idle state of the primary users in order to exploit the free bands and also promptly vacate the band as soon as the primary user becomes active.