Stdudy On User Selection And Power Allocation Based On Interference Alignment In Cognitive Radio Network

Nowadays, under the rapid development of information industry background, wireless spectrum resources become increasingly limited, cognitive radio(CR) as an new smart spectrum access technology is proposed which can sense the various kinds of information continuously from the external environment and select the suitable spectrum to work in order to achieve optimum spectrum utilization and solve the problem of spectrum scarcity by learning, analyzing and judging. Interference among the primary user(PU) and secondary users(SUs) is inevitable when the SUs share the PU's spectrum, interference alignment(IA) as an effective method to solve the interference problem is widely used.However the signal to interference plus noise ratio (SINR) of the system will decrease under some channel. Power allocation(PA) make the potential feasibility to further improve performance of the system. In a practical cognitive radio networks, users are always randomly located in an area, the distance between each user is not equal, there are many SUs in a certain area, the spectrum resources of PU are limited. The probability of all the SUs access the PU's spectrum is low, while the unselected users are remaining idle which is a waste of the wireless resources. Hence how to select the suitable users and optimize power among users in CR system has been deeply studied in this thesis. The main contents of this paper are as follows:(l)Establish the user selection model of CR network based on IA. In a practical CR networks, users are always randomly located in an area, considering interference temperature constraints of PU, therefore an optimal user selection and power allocation algorithm in CR network based on IA is proposed. When the PU communicate individually, an adaptive communication model algorithm is proposed;(2)A suboptimal algorithm is proposed based on the algorithm which is discussed in (1). If the SUs which are closer to PU communicate in CR network, they must lead a lot of interference to PU, so the proposed algorithm chooses the farther SUs to communicate under the insurance of the PU's performance. The suboptimal algorithm can reduce the computational complexity and the loss of performance which is little compared with the optimal algorithm.(3)Each transmitter of the CR network is assumed to have a constant power source, it is a waste of the wireless resources if the unselected users are idle, the unselected SUs have the ability to harvest energy. It is natural that the unselected SUs can harvest energy from the nearby transmitters, and recharge their batteries.When the distance between PU and unselected SUs is far enough or there is idle spectrum of PU, they can communicate with the energy they have harvested. Estabnish the energy harvested model by the unselected users and simulation results show the performance of energy harvested by the unselected SUs under different conditions.