| Cognitive wireless network(CWN) evolves into one of the frontier re-search fields of communication technologies because it provides high band-width to cognitive users via heterogeneous wireless architectures and dynamic spectrum access techniques.To prevent interference to the licensed users, spectrum sensing has to be performed by the cognitive users in CWN. Local spectrum sensing can’t solve the problem of hidden terminal because of the influence of channel fading characteristics. As an approach to improve the accuracy of the sensing results, cooperative spectrum sensing, where a cognitive base station (CBS) fuses the local sensing results from the cognitive users to obtain a final decision, has also been extensively studied. Cooperative spectrum sensing is mostly focused on increasing the sensing performance for one channel. Nevertheless, it is less likely that a single terminal can perform wideband detection in one sensing slot due to hardware and energy constraints. To tackle this dilemma, coordinated spectrum sensing has been adopted. In coordinated spectrum sensing, the entire spectrum of interest is divided into several narrow subchannels. Then, each cognitive user is only assigned to detect one subchannel. The CBS gather each subchannel detection information to gain the whole wideband spectrum usage.The main contributions of this dissertation are listed as follows:1. When the number of cognitive users N is more than the number of subchannels M, cognitive users assignment strategy for coordinated spectrum sensing is proposed. A metric called ineffective transmission-effective trans-mission ratio (ITETR) is proposed to evaluate the performance of the cogni-tive users assignment strategy. A mathematical analysis as well as the related closed-form solution in the simplified case are provided when all cognitive users have the same sensing performance for the same subchannel. Based on this analysis, an improved greedy algorithm-based strategy is proposed to de-termine the sub-optimal solution for the more general case, i.e., each cognitive users exhibits different sensing performance for the same subchannel. Sim-ulation results show that the proposed strategy can significantly improve the ITETR of CWN when different channels possess different utilizations.2. A spectrum sensing sequence based on the priori knowledge of licensed users and cognitive users is proposed when N=1.When2<N<M, different spectrum sensing strategies are proposed in competitive multi-users scenari-o and non-competitive multi-users scenario. Simulation results show that the proposed strategy can improve spectrum sensing efficiency and traffic efficien-cy.3. Spectrum sensing sleep mechanism in CWN are examined to decrease sensing energy consumption. According to access requirement from cognitive users, two traffic scenarios of CWN are defined, namely, light traffic scenari-o and heavy traffic scenario. For the two traffic scenarios, different spectrum sensing sleep mechanisms have been proposed. In light traffic scenario, only some of the several subchannels execute spectrum sensing to meet the access requirement from the cognitive users, while the rest of subchannels are not executed spectrum sensing. The optimal number of sensing subchannels is ob-tained in this scenario. In heavy traffic scenario, utilizing the idle and busy char-acteristic of the subchannel, cognitive users that are assigned to the subchannel will keep a certain sleep duration when the subchannels state is switched from idle to busy/busy to idle. The optimal sleep duration is proved to be existence and the closed-form solution is given. The simulation results showed that the proposed sleep mechanisms can achieve remarkable energy-saving ability with negligible performance of system loss. |
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