Dynamic Spectrum Access Mechanisms For Cognitive Radio Based On Queueingtheory And Game Theory

In order to meet the increasing requirements of wireless applications, cognitive radio network(CRN) has been proposed to overcome the inefficiency of the traditional static spectrum allocation policy and facilitate spectrum sharing between primary users(PU) and secondary users(SU) through dynamic spectrum access technology. Dynamic spectrum access technology still faces many challenges. Besides the technical aspects, new spectrum policy and economic model matching the characteristics of spectrum sharing should be also considered for practical designs. Therefore, the dynamic spectrum access schemes for cognitive radio are described from both technical and economic concerns in this dissertation.First, based on the queueing theory, an adaptive spectrum decision algorithm for the multi-channel wireless networks is given to reduce the overall system time of SU by considering that the preempted SU have to retransmit the whole packets,. The system model is presented by employing the preemptive repeat identical priority M/G/1 queueing theory. And then the sensing-based and the probability-based spectrum access schemes for SU are designed according to the system model. The probability-based spectrum access scheme with suitable parameters can evenly distribute the traffic loads of SU to various channels, ther eby shortening the overall system time. Moreover, the sensing-based spectrum access scheme can perform sequential sensing to increase the chances to find the idle channels, thereby reducing the system time. Comparing the overall system time resulting from both the spectrum decision schemes, SU can adaptively adopt the best channel selection scheme to minimize the overall system time. Simulation results show that the proposed algorithm can significantly decrease the average overall system time of SU compared with the random access scheme and the sensing-based channel selection scheme.Second, the spectrum access control policy for SU is investigated based on the spectrum pricing scheme from the economic perspective, so as to realize rational spectrum allocation. The spectrum access process of SU can be treated as a non-cooperative game. SU can decide whether to access the spectrum or not. However, if all SU aim at maximizing their own individual utility, the overall utility of the system will decrease so the pricing scheme must be used to incite SU to behave in ways that improve the overall performance. Due to the various information obtained by SU in different network environments, different access models are established for the distributed CRN and the centralized CRN. In the centralized CRN, SU can receive information on the channel state and the current queue length from the central controller, so the observable queue model can be used for it. And in the distributed CRN, SU are not informed of the queue length information, so the unobservable queue model is used for the probability-based spectrum access scheme and the partially observable queue for the sensing-based spectrum access scheme. Depending on the various analysis models, this dissertation compares the equilibrium and the socially optimal strategies and derives the corresponding spectrum pricing scheme. Simulation results validate the theoretical analysis and show that the proposed pricing scheme can improve the overall social benefit compared with the free spectrum access scheme. In addition, the numerical results also display that revealing more information about the state of the system to SU can help them make better decision to increase the overall social benefit.Last, by taking into account the fact that the real-time traffic or the delay-sensitive traffic usually has to meet some delay constrains, the corresponding spectrum access control scheme is investigated based on the game theory and the queueing theory. For the delay-sensitive traffic, SU may make the abandonment decision and exit from the waiting queue if the waiting time exceeds the tolerance limit in the practical problem, even though SU have decided to access the channel. Therefore, based on the queueing model with balking and reneging, the expression for the average overall system time of SU is derived by level crossing method. Then the nash equilibrium and socially optimal access strategy are analyzed. Furthermore, the corresponding pricing scheme is developed to increase the social wel fare. Simulation results show that the proposed pricing scheme can significantly improve the overall social benefit compared with free spectrum access scheme.