The Study Of Spectrum Sharing In Cognitive Radio Based On Game Theory

Cognitive radio,which is an new intelligent wireless communication technique, can adapt system operation parameters by sensing the environment's variations. Spectrum sensing, power control and dynamic spectrum allocation are the key technology of the cognitive radio. The problem of spectrum allocation in the cognitive radio is considered in this thesis.Game theory is an efficient method in helping decision-makers to analyze and make decisions by mathematical models. As a new technology, which can sense available radio frequency spectrum and adapt operating parameters to wireless communication in real-time, cognitive radio is related to the choice of strategies, and spectrum choosing is one of these.Based on the game theory, the technology of spectrum sharing in the cognitive radio is analyzed and the improvements of the algorithm are made. The main work is as follows: (1) The problem of spectrum sharing between secondary users is studied based on the price. According to the price which is an important factor in the spectrum sharing and given by the primary user, every secondary user compete the spectrum with each other to maximize their own profit. There is no any factor which can reflect the wishes of the primary user in the price function of the original algorithm. This thesis considers the wishes of the primary user and makes improvements on the primary user's price function which shows the wishes of primary users in the spectrum sharing. Thus different secondary users have different price functions which can be adjusted according to the wishes of the primary user. The existence and uniqueness of Nash equilibrium are also discussed. Simulation results show that the shared spectrum depends on the wishes of primary users besides the secondary channel qualities.(2) A new spectrum sharing algorithm based on supply and demand balance in cognitive radio networks is proposed. A supply and demand model between primary users and secondary users is established to decide the price of free spectrum leased by primary users. Considering the three factors——total bandwidth of primary users, secondary terminal remaining battery capacity and reliance of different secondary users——which would have influence on the spectrum allocation, a new secondary utility and spectrum sharing algorithm are designed. The existence and uniqueness of Nash equilibrium are proved from both theoretic and simulated aspects. The simulation results show that primary users could receive maximum revenues by allocating spectrum in equilibrium price, and the spectrum shared by secondary users is directly affected by the reliance and remaining battery capacity of secondary users. (3) A game-theoretic joint rate and power control problem in the spectrum sharing is discussed. Based on the shortage of the current interference temperature model that reduces the interferences taken to primary users, this thesis strengthens those users'subjectivities in power control. Besides the game among secondary users to reduce their interferences due to the others by the adjustments in transmission powers and rates, the primary users detect the inferences taken by secondary users and use an interference punishment factor which designed under the premise that the inferences do not exceed the threshold. The more interference that the secondary user affects primary users, the more seriously that the secondary user will be punished. In this way, the transmission powers of secondary users and interferences that primary users affected will be reduced. The simulation results show that the proposed game-theoretic interference method could reduce interference and improve utility of primary users by decreasing secondary transmission powers. At the same time, the interferences among secondary users could also be reduced, and the received signal to interference will achieve some improvements.(4) The cooperative spectrum sharing in cognitive radio systems is investigated. Based on the Nash bargaining in cooperative game, an improved utility function is proposed to maximize the profit product of all secondary users. The cooperative game algorithm for spectrum allocation in cognitive radio is used, and the priority of secondary users introduced. The existence and uniqueness of Nash bargaining solution for the new utility in cooperative game are also shown. Simulation results indicate that the new algorithm can reflect the secondary users'priority of spectrum allocation by setting the parameters and make the spectrum allocation more effective and fair.