The Spectrum Sharing Algorithm Of Cognitive Radio Based On OFDM

With the development of wireless communication technology, spectrum resource has been more widely employed. The utilization of spectrum resource is low because of the static fixed spectrum allocation policy. Cognitive radio is a new method to solve the shortage of spectrum resource and to improve the spectrum efficiency. In this thesis, we proposed spectrum allocation and spectrum sharing model in cognitive radio system by combining OFDM to improve the system capacity and spectrum efficiency.First of all, we introduce the research background and current development of cognitive radio, and then we proposed a system model of cognitive radio based on OFDM.Secondly, we introduce the energy detection, matched filter detection and cyclostationary feature detection separately. Then we obtain the relationship between the detection probability and signal to noise ratio (SNR) of cognitive users according to energy detection in Gaussian white noise channel. In addition, we proposed the detection of multi-user collaboration method to improve the system performance in cognitive radio network. Thirdly, we introduce the classifications of spectrum allocation in cognitive radio, and proposed a dynamic spectrum allocation model of single user based on OFDM. In this thesis, by fixing the transmission power of cognitive user, we focus on greedy algorithm and improved grouping greedy algorithm to maximize the system capacity. Simulation shows: greedy algorithm can reduce the computation and ensure that the allocated bit is an integer. The fixed sub-carrier grouping algorithm can reduce the complexity of system design greatly with a little loss of system capacity. The adaptive grouping algorithm not only reduce the number of iterations efficiently, but also expand the threshold range to optimize the system performance.Finally, we introduce the spectrum sharing processing in cognitive radio, and then proposed a dynamic spectrum sharing model of multi-users based on OFDM. Based on fixing the transmission rate of cognitive users, we focus on Wong algorithm, secondly allocation algorithm and time sharing based on time accessing algorithm to minimize the transmission power of cognitive users. Simulation shows: the secondly allocation algorithm can reduce the complexity of Wong algorithm efficiently, time sharing algorithm can improve the communication performance of low channel gain users, which indicates the fairness principals and improves the spectrum efficiency. In addition, we introduce the definition of spectrum handoff and spectrum handoff algorithm to achieve a flexible management of spectrum handoff.