Research On Power Allocation In Cognitive Radio Networks

With the great advance and development of global technology, wireless service businessincreases rapidly. Nevertheless, existing wireless spectrum allocation strategy is mostlyfixed and the utilization frequency is low. Therefore, the abundant frequency is idles as thesame time the requirement of frequency is ceaselessly increasing which leads to low usageefficiency. The appearance of cognitive radio technology settles this problem radically.Cognitive radio makes the cognitive users, i.e the secondary users, measure and senses thespare frequencies authorized and make use of the spectrums after confirming that thisaction would not take interference to the authorized users, i.e the primary users. So thespectrum usage efficiency can be ameliorated. While the world is getting loudly thatpower should be cut down with high efficiency which leads the power control to animportant study point of cognitive radio. As a big part of communication technology,cooperative communication technology can efficiently improve the transmission speed ofdata and achieve the diversity gain that obviously improves the system performance ofcommunication system. So cooperative communication technology is investigated widelyin cognitive radio field.With the foundation of cognitive radio networks, we do a detailed work on powerallocation, cooperative communication and joint both technologies. According to thedifferent system framework of cognitive radio networks, we study the power allocationproblem in the non-cooperative environment and cooperative environment.This thesis first study the non-cooperative environment, and optimization goal is tomaximize system throughput while fulfills the requirement that secondary users can’t takethe interference beyond the threshold to the primary users. Then we use the geometricprogramming method to transform the power optimization problem to the convex problemand present an auxiliary value, and then we use the dual decomposition method todecompose the coupling connection so that the problem can be resolved. After that, weresearch on how to allocate the power within the cooperative environment. We proposetwo algorithms to handle this problem. One is to maximize the system throughput andfulfill the requirement that secondary users can’t take the interference beyond thethreshold to the primary users along with within the range of maximum total power. It transforms the problem function equivalently to make iterative calculation. One is tomaximize the access secondary users. Then we transform the optimization problemequivalently and induct the auxiliary parameter to make iterative calculation. Bothalgorithms aim at the QoS requirement of secondary users so as to improve the wholenetwork performance. In the end, simulation is running out the results for different modelsand analyses are given to comment these results.