Energy Efficiency Resource Allocation In Cognitive Radio System Based On OFDM

With the rapid development of wireless communication technology,the demand for wireless communication services is getting higher and higher,so that the wireless spectrum resources become increasingly nervous.Cognitive radio technology is proposed to solve this problem effectively,which has been got the extensive concern of academic circles.In cognitive radio networks,the limited spectrum resources and the fixed allocation mechanism makes the existing spectrum utilization very low.How to make use of the various resources efficiently and improve the energy efficiency(EE)of the system without interfering with the normal communication of the main user becomes the most urgent task in the research of the cognitive radio network.In this thesis,the problem of low utilization of spectrum resources has carried on the thorough research.Firstly,cognitive radio technology is introduced,which includes overlay and underlay transmission methods.But the disadvantage is that there is interference between the primary user and the secondary user.Cooperative relay technology is an effective in alleviating this problem,it can weaken the wireless link in the path of weakness,thereby enhancing the reliability of the transmission link.OFDM technology does a great contribution to eliminate the interference between the channels and improve the data transmission rate.Therefore,for maximizing energy efficiency,combining cognitive radio technology,OFDM technology and cooperative relay technology,a resource allocation strategy is proposed to solve the problem of low resource utilization and improve the system energy efficiency.The main work and achievements of this paper are as follows:1.A strategy based on hybrid overlay/underlay transmission protocol is proposed to maximize the energy efficiency of the main user under frequency division multiplexing.We solve the resource optimization problem into several sub-problems.Firstly,a heuristic algorithm is used to subcarrier pairing,which reduces the complexity of the algorithm.Since the number of subcarrier pairs is not large,the subcarrier selection can be performed using the exhaustive method.Traverse all subcarrier pairs,calculate the energy efficiency of each subcarrier pair,and select the subcarrier pair with the optimal energy efficiency.Finally,the Lagrange multipliermethod is used to determine the subcarrier power allocation and to select the best relay.This algorithm is specifically designed for hybrid overlay/underlay transmission protocols.The simulation results show that the hybrid overlay/underlay transmission protocol achieves higher energy efficiency than traditional overlay and underlay techniques.2.A heuristic subcarrier pairing algorithm is proposed to solve the problem of energy efficiency maximization at a lower cost.The energy efficiency problem is optimized by combining the improved water filling algorithm and the Lagrangian dual algorithm.Different from the classical water injection algorithm which using the transmission power as the water surface,this paper selects the target rate of the main user as the water surface,you can only use one parameter(water level)to represent the channel power allocation of,and obtain the rate of each subcarrier with optimal energy efficiency.The subcarrier pairing is performed according to the subcarrier matching index size,which simplifies the algorithm complexity.In this paper,the proposed algorithm has some comparison with the existing algorithm,simulation results show that in the same environment,the proposed algorithm is better than the existing literature on the system stability and overall energy efficiency,the performance of the system is optimized.