Research On Spectrum Sensing Technologies In Cognitive Radio

With wireless communications technology development, the demands on the wireless spectrum resources are continuously increased, which leads to spectrum scarcity phenomenon looming, and the current fixed spectrum allocation mechanism also limits the full use of the spectrum resource, leading to the poor spectrum utilization. The proposed cognitive radio technology provides a new way to address the scarcity of spectrum resources and low utilization of the spectrum, is considered to be the best method to solve the above problem. As a key technology of cognitive radio, spectrum sensing is the primary premise of achieving cognitive radio applications and improving the cognitive system spectrum utilization. This thesis mainly studies on spectrum sensing technology in cognitive radio, the main completed work contains of two parts .In part one, this thesis proposes the cooperative spectrum sensing algorithm based on the cholesky factorization of covariance matrix by extending the single user spectrum sensing to multi-user cooperative spectrum sensing spectrum. The proposed algorithm can improve the sensing performance by joint detection using multi-user information. In addition, this thesis also proposes an improved cooperative spectrum sensing algorithm based on the cholesky factorization of covariance matrix. The proposed improved algorithm can effectively reduce the computational complexity by selecting the stronger relevant signal for detection among cognitive users.In part two, based on multi-carrier detection model for OFDM system, this thesis gives multi-carrier joint spectrum sensing algorithm. Applied to the OFDM system with limited energy consumption, the multi-carrier joint spectrum sensing algorithm under the energy-constrained for OFDM system is proposed. Both the sensing time and the decision threshold parameters of each carrier are optimized, under the case of the energy-constrained, to maximize the total throughput of the system. The simulation results illustrate that multi-carrier joint spectrum sensing algorithm can achieve more throughput than traditional spectrum sensing algorithm, comparing with energy equipartition spectrum sensing algorithm, the multi-carrier joint spectrum sensing method under the energy-constrained for OFDM system not only has higher throughput, but also save more energy.The organization of this thesis is as follows. Chapter one briefly describes the background and significance of this theme and situation and main work of this thesis. Chapter two summarizes the spectrum sensing technology theory in cognitive radio. Chapter three studies the cooperative spectrum sensing based on the covariance matrix. Chapter four studies the spectrum sensing for OFDM cognitive radio system. The last chapter presents the summary and prospect of this thesis.