Research On Key Technologies For Cognitive Radio System

In order to improve the efficiency of system bandwidth and protect the user’s quality of service, several key issues of congnitve radio have been studied in this thesis, which includes spectrum sensing, spectrum allocation, channel allocation and power control. The contributions and results are listed as follows:Other than the traditional method, a new in-band spectrum sensing technique based on linear self-signal elimination in cognitive radio is proposed in this work. The method eliminates the self-signal in the received signal through the linear weighting of the adjacent reception symbol by using the AR model of wireless fading channel. Based on the Neyman-Pearson criterion an optimum detector for spectrum sensing of the residual signal is presented. The simulation results demonstrate that the proposed method is better than the existing in-band spectrum sensing methods without Quiet Period when the Doppler frequency shift is large. The algorithm achieves an acceptable detection performance for IEEE802.22system and improves the performance of spectrum sensing.For the requirements of improving spectrum utilization, reducing power consumption and guaranteeing quality of service for cognitive radio, two algorithms are developed by using orthogonal frequency division multiplexing. The proposed algorithms solve the problem of spectrum sharing between the cognitive radio and the orthogonal frequency division multiplexing. Compared with the traditional static spectrum allocation algorithm based on the FDMA, the proposed algorithms can satisfy the QoS requirements, and improve the system capacity by nearly30%. A spectrum allocation model of cognitive user is built based on the study. It solves the balance of chain game model by introducing appropriate coordination mechanism. Simulation results verify the advantage from the aspects of mathematical expectation of payoff, channel usage and communication time.In order to solve the channel assignment problem in multi-radio multi-channel network, a game-theoretical formulation is presented. Firstly, a utility function is constructed which considers the channel load-balance and fairness among players. Secondly, a channel assignment model is built based on the non-cooperative game. Thirdly, a novel channel assignment algorithm with fairness and load-balance is proposed. The simulations verify that the proposed algorithm can achieve the load balance of the channel and fully guarantee the validity and fairness of the users.A heuristic algorithm is proposed to solve the problem of optimal power control with QoS constraint for OFDM based cognitive radio network. As a result, the cognitive radio network achieves the optimal power allocation. In order to solve the problem of channel allocation and power control of cognitive wireless network, an optimal mathematical model for common channel and power allocation is presented in this paper. The model utilizes the interference power model under imperfect spectrum sensing. Using penalty function to simplify the nominal mixed integer programming to be an unconstrained nonlinear programming, an optimal allocation approach based on genetic algorithm is proposed. The proposed algorithm can achieve the jointly optimal allocation for power control and channel resource, reduce the power interference for the primary user, and reach the maximum throughput of cognitive users under imperfect spectrum sensing.