Study On Spectrum Resource Allocation Algorithms For OFDM-based Cognitive Radio Systems

With the rapid development of wireless communication technology,the demand of spectrum resources is increasing rapidly.However,the current fixed spectrum allocation method severely restricts the sustainable development of wireless communication and service applications.Cognitive radio(CR)technology is a revolutionary technology in the field of wireless communication,which allows secondary users to utilize the vacant spectrum opportunistically under the premise of guaranteeing the quality of service of primary users,so as to improve the spectrum resource utilization in nature.Spectrum allocation is one of the key technologies in CR which is an important step for realization of CR.However,the flexible selecting frequency programs of orthogonal frequency division multiplexing(OFDM)technology provide a good platform for achieving CR systems.Therefore,it is of great significance to study the spectrum resource allocation algorithms for OFDM-based cognitive radio(CR-OFDM)systems.The main work of this paper is as follows:(1)The research background and significance of spectrum resource allocation for CR-OFDM systems are elaborated.Research status at home and abroad is summarized.The fundamental knowledge of spectrum resource allocation technology is introduced.(2)Aiming at the spectrum resource allocation problem of multiple secondary users for CR-OFDM systems,a joint subcarrier and power allocation method is proposed.This algorithm is divided into two sub problems by using the two step method:subcarrier allocation and power allocation.Firstly,according to the capacity requirements of secondary users,the fairness proportional factor is introduced into the subcarrier allocation process and allocats the subcarrier resources for the secondary users.Then on this basis,the lower limit of power constraint of the allocated subcarriers to each secondary user which combines with the transmit power requirements of the secondary users is increased and uses the ladder power allocation algorithm to solve the power allocation optimization problem for subcarriers.Simulation results show that the proposed algorithm can guarantee the fairness of capacity allocation among the secondary users and ensure the required quality of service for each secondary user.Moreover,the algorithm has the low computational complexity,which is conducive to practical application.(3)Aiming at the spectrum resource allocation problem of multi-objective for CR-OFDM systems,a spectrum allocation algorithm based on particle swarm optimization is proposed.Firstly,jointly maximizing the cognitive system throughput and minimizing its total transmit power as the objective to formulate a multi-objective optimization problem.After that,the multi-objective optimization problem is transformed into a single objective optimization problem by using linear weighting method.Because of the search ability of the particle swarm optimization is efficient and fast,and it is used to allocate the spectrum resources for the subcarriers occupied by the secondary user.To avoid falling into the local optimal solution,the proposed algorithm selects the global extreme value and individual extreme value of particles by implementing mutation operation to position vector and the optimization process of the joint spectrum resource allocation is realized.Simulation results show that the proposed algorithm has good flexibility and applicability,and it can be well applied to practical communication systems.