On Spectrum Sensing With Inactive Secondary Users In Cognitive Radio Networks

With the rapid development of communication technology, spectrum becomes avery scarce resource. The application of the wireless communication is restricted byspectrum utilization. Cognitive radio is widely regarded as one of the key technolo-gies, which can improve the spectrum utilization by using the available spectrum moreefficiently through opportunistic spectrum usage. Spectrum sensing plays an impor-tant role in cognitive radio networks. Available spectrum resources will appear whenthe channels allocated to primary users are idle. Similarly, the sensing performanceis improved by utilizing the inactive secondary users. This dissertation deals with thesensing policies in cognitive radio networks, such as cooperative sensing, joint sens-ing and the allocation of the inactive secondary users. The main achievements of thisdissertation are listed as follows:1. A sensing model is proposed by using the inactive secondary users in theoverlay transmission mode. Combining the additional cost with the throughput of cog-nitive radio network, a length of sensing period optimization issue is proposed basedon inactive secondary users in cognitive radio network. Under the fairness constraints,an optimization issue is proposed by allowing the inactive secondary users to coop-erate or not, the proposed optimization issue can improve both the throughput andthe efficiency. Both the mathematical analysis and simulations show that the inactivesecondary users can improve the sensing performance.2. A length of sensing period optimization issue is proposed by considering theinter-cell interference in the underlay transmission mode. When the inter-cell interfer-ence is existed, a scheme which can change the transmission mode between overlayand underlay based on the pilot sensing was proposed. Considering the SINR of pri-mary user satisfies the outage probability, the optimization problem of transmit powerof secondary user was changed into a tradeoff problem between sensing and through-put. Then the maximum network throughput is formulated as an object function. Afteranalyzing the optimization problem, an effective algorithm of the length of sensingperiod for maximizing the throughput was found. Simulations results show that theproposed policy based on sensing period can improve the sensing performance.3. Due to the uncertainty of primary users’ states, random sensing policy isconvenient to implement but cannot find vacant channels rapidly. A joint random sens-ing policy by using the inactive secondary users in cognitive networks was proposed. After utilizing inactive secondary users to detect, sensing performance of cognitivenetworks can be deduced by modeling the list of available channels stored in cog-nitive base station as markov model. Based on the fairness principle, an availablechannels allocation strategy was proposed for active secondary users. Both the theo-retical analysis and simulations results show that sensing with inactive cognitive userscan reduce the service overhead and improve the cognitive network throughput. Afterconsidering the report overhead of secondary users, the optimal number of inactiveusers was obtained which yields the highest throughput of cognitive network throughan optimization algorithm.4. In cognitive radio networks, A novel scheme which utilizes inactive secondaryusers efficiently has been proposed to manage the problem caused by optimal sensingorder in joint allocated sensing policy. the primary The users’ traffic patterns wasmodeled as continuous-time Markov chains. Considering the influence of sensingperformance, the throughput of cognitive radio networks is formulated as an objectfunction, and an optimal sensing order is obtained. As the difference between up linkand down link, We get an optimal sensing strategy in up link mode and a suboptimalsensing strategy with low complexity in down link mode. The numerical simulationresults show that the proposed order based on spectrum sensing scheme can achievehigher throughput,larger channel utilization and lower sensing overhead as comparedwith the spectrum sensing scheme without using the optimal order sensing. Afterconsidering the report overhead of SUs, the optimal number of inactive SUs for themaximum throughput can be found.5. In cognitive radio network，each active secondary user wants to get muchchannel information. An allocation algorithm based on the auction theory is proposedto solve the ownership of inactive secondary users. The payoffs of transmission vol-ume action and satisfaction degree action were studied under the second-price auc-tion mode. An auction algorithm based on reserve price, budget constraint and fair-ness limit was proposed. The numerical simulation results show that the schemebased on auction algorithm can achieve higher performance as compared with otherschemes.