Spectrum sensing is a fundamental technology in cognitive radio(CR) networks，where the CRs act as secondary users(Sus) that opportunistically access frequency bands when the primary users(Pus) are not present. The secondary users thus sense for the presence of primary users continually. If the primary users are detected，the secondary users must immediately stop using that channel. Two parameters are cardinal to attaining spectrum sensing: probability of correct detection，Pd and probability of false alarm，Pf. From the Pus’ perspective，the higher the probability of correct detection，the better the Pus’ are protected from interference from Sus. For the Sus，the lower the probability of false alarm，the higher the opportunity to reuse the channels when available，leading to increased throughput for the secondary network. Depending on which user is of utmost priority，either a predetermined probability of correct detection or false alarm can be set. In this thesis，the optimization of each of the two probabilities having set the other to a fixed value using cooperative sensing is studied. By way of computer simulation based on a IEEE 802.22 WRAN network it is shown that cooperating only a certain number of secondary users and not all gives optimum performance in either case.