| In recent years, more and more wireless communication equipments access spectrum, whichleads limited spectrum resources to be increasingly scarce because of traditional static allocationstrategy. With this policy, non-authorized users can not access the licensed spectrum bands, whichbrings valuable spectrum in the idle state. Spectrum sensing and spectrum sharing enable cognitiveusers to fully use the spectrum holes and improve spectrum utilization. Therefore, the transmissionpower of each cognitive user should be controlled in order to reduce interference to authorized userand ensure the QoS of the cognitive users.Based on game theory, thesis studies the power control algorithms in cognitive radio. Firstly, itanalyzes and compares the performance of the K-G algorithm and the classic SINR balancingalgorithm. Because the K-G algorithm can not guarantee the fairness of the system, the KG-CPalgorithm is proposed, then the existence and unique of the Nash equilibrium in KG-CP algorithmare proved. The simulation shows that the KG-CP algorithm can reduce the transmit power ofcognitive user, ensure fairness of the system and also has a better performance in the case ofmulti-user communication.Secondly, based on the NBS model, a new power control algorithm is proposed. The newalgorithm can achieve optimal strategy by Lagrange multiplier. By the simulation, the newcooperative game algorithm shows a lower transmit power level than NBS algorithm, and guaranteethe SINR of the users which are far away from the base station.In summary, power control can reduce user’s transmit power level and minimize the interferencebetween users. And the capacity of cognitive network system can be improved. |
