Reserch On Power Allocation Of Cognitive Radio Based On Water-filling Algorithm

With the rapid development of wireless communication technology, the wirelessbusiness is growing prosperity, and the number of users is increasing. However, due tothe limitations of existing technology of taking advantage of the spectrum resource, theavailable spectrum resource is limited, and has become saturated. But, the researchingresults show that, spectrum resources utilization is very low for unreasonable spectrumallocation policy. Therefore, to improve the utilization of the available spectrumresources is increasingly urgent. The Cognitive Radio technology based on SoftwareDefined Radio is not only able to detect idle and access to channel to transmit data, butalso adaptively adjust the parameters of the communications equipment according to thechanges in the communications environment. So that efficient use of spectrum resourceswill be achieved. This thesis studys Cognitive Radio spectrum sharing among secondaryusers and primary users, i.e. the secondary user is capable of realizing optimal powerallocation within the tolerable interference constraint of the primary user.Firstly, from three different aspects, this thesis studys the theory related toCognitive Radio power allocation. The first aspect describes Cognitive Radiospectrum sharing from different perspectives, focused on the underlay andoverlay spectrum sharing of the hierarchical access model. The second aspectdescribes power allocation based on cooperation and non-cooperative model.Then, research and analyze the existing mode. The third area of research will beused for the mathematical theory of this article, including the gradient descentmethod, sub-gradient method, the Lagrange dual function.Secondly, in OFDM system, this thesis studys the secondary user power allocationunder the overlay spectrum sharing model based on cooperation. According to thecharacteristics of OFDM system, this thesis analyzes the interference betweensecondary users and primary users and establishes the interference model. On the basisof the interference model, the cognitive system model is established. For solving themodel, power constraint scenario is firstly considered. This paper proposes thedifferentiated adjustment of water-filling line algorithm which greatly reduces powerallocation algorithm complexity. Then, taking into account power constraint andinterference constraint, Lagrange duality principle and sub-gradient algorithm areapplied to optimize the power allocation of secondary user. Then, two cases arecompared to analyze the impact of restrictions constraint on the secondary user’behavior.Finally, the secondary user power allocation based on cooperation underlay spectrum sharing model isresearched. Considering power constraint, multi-water lineiterative algorithm is proposed on the basis of differentiated adjustment of water-fillingline algorithm, which achieves the most optimal allocation of secondary user power.Then, taking into account power constraint and interference constraint, this thesisproposes the shared spectrum iterative algorithm based on the differentiated adjustmentof water-filling line algorithm. According to the simulation results, secondary usersmaximizing their own interests are analyzed under the underlay spectrum sharingmodel.