Research On Resource Allocation Algorithm In OFMD-based Cognitive Radio Networks

Cognitive radio(CR)technology allows the active detection of cognitive users and utilization of idle spectrum resources,alleviates the lack of spectrum resource,and provides a new method to improve the spectrum utilization.Orthogonal frequency division multiplexing(OFDM)technology is a multicarrier modulation and multiplexing technology,which can manage radio resource flexibly and is appropriate to be used in CR networks to further improve the network agility and spectrum utilization.In an OFDM-based CR network,resource allocation is one of the key techniques which directly affect the performance of the network.This paper focuses on the problem of resource allocation in OFDM-based CR networks,the main work is as follows:1.A resource allocation algorithm based on energy efficiency is proposed.In the downlink of an underlay OFDM-based CR network,taking the total transmit power of the CR network and the primary users' interference threshold as the constraints,we construct the resource allocation problem with the total energy efficiency of the cognitive network as the optimization objective.We develop a resource allocation algorithm which is divided into two steps: an improved heuristic algorithm is used to solve the subcarrier assignment problem first,and then an improved Dinkelbach algorithm based on fractional programming is employed to solve the power allocation problem.Numerical results demonstrate that the proposed scheme can enhance the system energy efficiency significantly and produce less interference to primary users.2.A resource allocation algorithm based on imperfect spectrum sensing is proposed.In the uplink of an overlay OFDM-based CR network with imperfect spectrum sensing,we introduce the false detection probability and false alarm probability,calculate the interference to the primary users introduced by the secondary users,and formulate the resource allocation problem to maximize the CR system capacity.The proposed resource allocation algorithm is divided into three steps as power preallocation,subcarrier assignment and power adjustment.The numerical results verify the effectiveness of the proposed algorithm in the case of imperfect spectrum sensing.