Study On Resource Allocation Algorithm In Cooperative OFDM Cognitive Radio System

With the rapid development of mobile communication technology, in addition tothe basic short message service and voice business, mobile terminals have alsoincreased many multimedia services, such as the web browsing, video communicationand online shopping, which makes the wireless spectrum resource become more andmore scarce. As a new wireless communication design concept, cognitive radio hashigher flexibility and intelligence. It can perceive the wireless communicationenvironment and adjust the system parameters real-time and adaptively according tothe cognitive information. Cognitive radio can realize spectrum sharing dynamicallybetween primary users and cognitive users, which can improve the system spectrumefficiency.At the same time, people have a greater expectation for the future wirelesscommunication quality. They hope that the future wireless communication system canachieve a higher rate, a higher capacity, a broader coverage and a lower cost. So thecooperative communication technology arises at the historic moment. Cooperativecommunication technology can form a virtual multi-antenna system by sharing theantenna or other resource, which can obtain diversity gain like MIMO system. It canimprove the system performance in all respects.Recently, people begin to pay more attention to the organic combination of thecooperative communication technology and the cognitive radio technology. It canimprove the performance of the system greatly on the premise of efficient use ofspectrum resource. Especially the fourth generation mobile communication system (4G) will be put into use, and Orthogonal Frequency Division Multiplexing (OFDM) isone of the key technologies in4G system. How to introduce the OFDM technologyinto cooperative cognitive radio system has become a current research hotspot. Wecan improve the performance of the cooperative OFDM cognitive radio systemeffectively through the resource optimization allocation.In this paper, the following problems have been studied based on the resourceallocation in cooperative OFDM cognitive radio system:First of all, cooperative communication technology and cognitive radiotechnology have been studied in this paper. The system model has been built based onDF relay assisted OFDM cognitive radio system.Then, the dynamic resource allocation in cooperative OFDM cognitive radiosystem has been studied, which mainly includes relay selection and power allocation. Most current relay and power allocation algorithms use Lagrange dual decompositiontechnique to find the optimal solutions. This approach has better performance withhigher computational complexity. Aiming at the problem, this paper proposed a lowcomputational complexity resource allocation algorithm. The proposed algorithmrelaxes the integrality constraint on the relay selection factor and takes bothsubcarriers channel conditions and the interference to the primary users introduced bythe secondary users into account in the relay selection. A sub-optimal powerallocation scheme is given on the basis of the properties of total system power andinterference constraint: the proposed algorithm considers the initial power allocationfirstly, in which only a constraint is considered every time. We find the solutionsbased on KKT conditions. And then the residual power is allocated again. Comparedto the traditional resource allocation algorithms, system capacity is guaranteed withlower computational complexity. So the proposed algorithm is more conducive toimplement in the actual communication system.Finally, the simulation results verify the validity of the algorithm proposed inthis paper. Simulation results show that the proposed algorithm can ensure that theinterference introduced to the primary users is within the threshold and improve thesystem capacity of the secondary users at the same time, which proves it is feasible.