Resource Allocation In Cognitive Radio With Imperfect Spectrum Sensing

With the rapid development of cognitive radio technology,how to make an efficient use of the spectrum resources has become the focus of the whole society,since the spectrum is one kind of the non-renewable resources.Spectrum sensing technique is one of the key technologies of cognitive radio.Before accessing the frequency band,the secondary user needs to detect and analyze the primary user's status and then make the decision on whether to access it or not.Besides,in order not to affect the normal communication of the primary user,we need to make a reasonable allocation and limit the transmit power on the foundation of the results of the spectrum sensing.In this paper,based on the orthogonal frequency division multiplexing(OFDM)cognitive radio system,a research has been put into the spectrum sharing model.In the previous studies,under the imperfect spectrum sensing circumstances,the protection method to the primary user is very scarce and inefficient.On the basis of the above,the following work has been done in this paper:1)According to the spectrum sharing model,under the premise that the secondary user's transmit power is constrained,an interference power constraint has been added to further protect the primary user's normal communication,and the objective function is optimized.As the primary user's transmit power is limited,the relationship between the cognitive radio system's throughput and the spectrum sensing time can be represented by a convex function.But coupled with the interference power constraint,this question is transformed into non-convex optimization problem.In this paper we assume that the number of sub-channels of the OFDM cognitive radio system is large enough and satisfy the spectrum sharing conditions,thus the non-convex problem can be transformed into a convex optimization problem,and then the expression of optimum power can be obtained.2)Based on the above,we proposed a new protection strategy: Rate Loss Constraint.The primary user's rate loss,during its work process,should be as small as possible,so that we can protect the primary user's normal communication.Subsequently the proposed new ideas were discussed,and the objective function was optimized,and finally simulations were made to verify the correctness and validity of the proposed ideas.3)The impact on the system was compared between the Interference power constraint and rate loss constraint,the performance of both of them analyzed as well.Then through the derivation of the theoretical formula,the relationship between them were obtained: the upper-bound that the cognitive radio system can be withstood is associated with the interference power threshold.The simulations had been made to the proposed ideas.The results show that there exists a relationship between their thresholdsprove that the new strategy can effectively protect the normal communication of the primary user,and the system performance had been significantly improved.