| It is widely recognized that the utilization of radio spectrum by licensed wireless systems, e.g., TV broadcasting, is quite low. Specially, in any given time and spatial regions, there are frequency bands where there is no signal occupancy then There has been recent interest in improving a spectrum utilization by allowing for secondary usage using the cognitive radios (CRs). The most important thing in cognitive radios (CRs) use spectrum sensing to determine the frequency bands that are vacant of the licensed signal transmissions and transmit on such portions to meet regulatory constraints of avoiding harmful interference to licensed systems. In the future the cognitive radios (CRs) will be capable to scanning the wide band of frequencies, in the order of a few GHz, and employ adaptive waveforms for transmission depending on estimated spectrum of licensed systems.The present dissertation is showing the performance of the cognitive network is improved with the consideration of cooperative spectrum sensing scheme using new cooperative strategy. This optimization strategy can be improved the spectrum sensing opportunities. In our mentioned strategy we can show that the probability of detection is increases for a given of probability of false alarm and can be reduce the detection time and improve the agility gain.Then we proposed a new scheme for spectrum sensing in two cases. In first scheme, when the primary signal information is known to the secondary users, so we are about to use the code value with match filter to detect the primary user, on the other hand, when the primary user signal information is unknown so we proposed a new strategy for energy detection in both non-cooperation and cooperation schemes. Then we will prove by simulation results that the new scheme is better than the conventional energy detection, we can show that we have increases in probability of detection and the agility gain, and we have reduce in the detection time and the probability of misdetection.
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