Research On Resource Allocation Algorithm In OFDM-Based Cognitive Radio Networks

With the rapid development of wireless communication service,the problem of spectrum resource shortage is becoming more and more serious.The traditional fixed spectrum allocation mode leads to significant imbalance in spectrum utilization.As an intelligent spectrum sharing technology,cognitive radio(CR)technology can dynamically detect the idle spectrum resources in authorized bands and reutilize them,which greatly optimizes the management of radio spectrum resources and improves the spectrum utilization.Orthogonal Frequency Division Multiplexing(OFDM)technology is considered to be the ideal air interface for CR,for its flexible resource scheduling ability and good adaptability.Focused on the multi-user resource allocation problem in OFDM-based CR networks,rational and efficient resource allocation algorithms are designed based on the system modeling established from spectrum efficiency and energy efficiency respectively.The main work and contributions are as follows:1.A resource allocation model for the OFDM-based CR networks with certain channel state information is formulated,which aims to maximize the spectrum efficiency under the constraint conditions of the transmission power budget of the system and the interference threshold of primary users.A distributed resource allocation algorithm is proposed.The subcarrier allocation based on maximum transmission rate is presented,and then the modified linear water-filling algorithm is adopted for power allocation.Simulation results show that the proposed algorithm can achieve satisfactory spectrum efficiency and can effectively reduce the computational complexity compared with the optimal power allocation algorithm.2.Under the resource allocation model for the OFDM-based CR networks with certain channel state information,the constraint condition of proportional fairness among secondary users is added to maximize the spectrum efficiency.Intelligent optimization algorithms are adopted to allocate resource.Firstly,a subcarrier allocation scheme based on genetic algorithm is designed.Then,particle swarm optimization combined with multistage punishment function is applied to allocate power.Simulation results show that the proposed algorithm can obtain the spectrum efficiency close to the optimal power allocation method,whilst it can improve proportional fairness among secondary users with low computation complexity.3.A resource allocation model for the OFDM-based CR networks with uncertain channel state information is formulated,which aims to maximize the energy efficiency under the constraint conditions of power budget of the system,the interference threshold of primary users,proportional fairness among secondary users and minimum transmission rate of the system.In view of the fact that the exact channel state information cannot be available in the real system,the interference constraint of the primary users is converted to a probability constraint,and then the non convex problem is tackled to a convex form by the Bernstein approximation.A subcarrier allocation algorithm based on maximum energy efficiency and an optimal power allocation algorithm based on Quasi Newton interior point algorithm are proposed.Simulation results show that the proposed algorithm can approach the optimal solution of the system and reduce the computational complexity effectively.