The Research Of Cooperative Spectrum Sensing Scheme Based On Relay Transmission

With the rapid development of wireless communication technology, the demand for spectrum resources is strong increasingly. Cognitive radio arises to be an important solution to the spectrum scarcity problem by finding spectrum space holes. Spectrum sensing is one of the most important constituents for the establishment of cognitive radio networks which could identify the available spectrum and prevent the harmful interference with licensed users. Ensuring cooperation among secondary users could gain improved detection performance, reduce the probability of false alarm and missed detection probability, some experts focus on the cooperative spectrum sensing technique.In the system of cooperative spectrum sensing, if the channel between cognitive user and the fusion decision center exists stumbling block, the reliability of cooperative spectrum sensing will be reduced greatly, the case can cause the loss of some sensing information.To reduce the probability of false alarm and missed probability, the scheme is discussed about cooperative spectrum sensing based on cooperative relay transmission. Combination of orthogonal frequency division multiplexing, pre-coding and cyclic delay diversity techniques, cooperative spectrum sensing and cooperative relay transmission are fully considered and properly combined to solve the problem about the loss of sensing information. The main research work are as follows.In this thesis, algorithms of local detection are discussed. Due to the limitation of local detection, cooperative spectrum sensing is studied to improve the detection performance and fusion rules are summed up. And then, some simple model of relay transmission are discussed. A cooperative communication network is proposed, this is the theoretical foundation for the core part of the thesis.The thesis is discussed about cooperative spectrum sensing, when the channels exist stumbling block. The model about cooperative spectrum sensing is conducted. The entire cooperative spectrum sensing process is divided into four time slots to complete. In the first slot, each cognitive user independently detected, within the rest of the three slots, combined the relay transmission technology, cognitive user send the information to the fusion center to do the finally judgment. In this scheme, frequency diversity gain is achieved through coded transmission, while the cyclic delay technology is used repeatedly to improve the detection performance, and reduce the detection complexity.Simulation results show that the proposed scheme can improve the system performance,reduce the probability of false alarm and missed probability.