The Study Of Joint Resource Allocation Policy In Cognitive Radio Networks Based On Cooperative DF Relay

In order to improve the spectrum efficiency, secondary users are allowed to utilize the licensed spectrum of primary users dynamically in cognitive radio (CR) networks. CR technology has received wide concern recently as a key technology for solving the problem of spectrum shortage. The Orthogonal Frequency Division Multiplexing (OFDM) technology, the representative of multicarrier technology, owning powerful ability of overcoming multipath interference, has been widely applied in wireless communication systems. In multicarrier CR system based on cooperative relay technology, the core concern of resource allocation research is how to utilize power and subcarriers more effectively, and how to improve both the efficiency of resource and the performance of system.Therefore, for a cooperative relay CR communication system which has multiusers and multi-carriers, this thesis formulates optimization problems by using convex optimization theory. And we studyed the resource allocation policies under the premise of considering the users’fairness and guaranteeing the delay requirement, aiming to improve the performances of both the primary and secondary system as much as possible. Finally we simulated the proposed policy and analyzed it in detail. The main works can be summarized as follows:(1) This paper introduced the mathematical foundation of resource allocation research in wireless communication system including game theory, convex optimization theory, Tylor expansion and Monte Carlo method.(2) On the basis of the proposed CR communication system model, we formulated the optimization problem of minimizing the β-fair cost of the average transmit powers while fulfilling the rate constraints of both the primary and secondary system, focusing on the fairness between secondary users. Furthermore, we divided the original problem into three equivalent sub-problems using Lagrangian dual method. The optimal power and subcarriers allocation between secondary users were obtained by using Karush-Kuhn-Tucker (KKT) conditions. Moreover, sub-gradient iterative algorithm was adopted in numerical solution and simulation. The numerical results were provided to show that the system could achieve a tradeoff between energy efficiency and fairness in our proposed policy compared to subcarrier-fixed allocation policy and constant power allocation policy.(3) Based on above resource allocation research in physical layer, we studied the cross-layer resource allocation policy with delay quality of service (QoS) requirement in upper layer after introducing the concept of effective capacity. We formulated the optimization problem of minimizing the average transmit powers while fulfilling the effective capacity of both the primary and secondary system. For further research, we transformed the original problem into a simplified problem using Tylor expansion, and solved this new problem utilizing Lagrangian dual method. At the same time, we proposed a suboptimal scheme allocating the subcarriers to the optimal channels, which can reduce the computational complexity of the whole problem. At last, stimulation results told us that our proposed scheme could save much more power assumption of secondary system than other schemes with upper-layer delay QoS requirement. The performance of the suboptimal scheme is only next to the optimal scheme.