The Study Of The Power Control In Cognitive Radio Based On Game Theory

With the rapid development of wireless communication technologies and the increasing broadband communication demands, the shortage of spectrum resource is becoming an outstanding problem day by day. However, many frequency bands are not used efficiently most of time and there exists a big waste of spectrum because of the fixed spectrum allocation policy. Cognitive radio (CR) is a revolutionary technology that promises to alleviate the radio spectrum shortage problem by improving the spectrum utilization.CR is a new novel intelligent wireless communication technique which can adopt a series of key technologies such as spectrum sensing, power control and spectrum management, spectrum sharing, spectrum handoff etc to utilize the unused licensed spectrum of licensed users, in this way, CR can realize dynamic spectrum access and improve the spectrum utilization.From the perspective of characteristic in CR, this thesis develops a deep research on the key technology of CR which is transmitting power control. This thesis does detailed research on distributed power control algorithm of CR by means of game theory. The NPG algorithm is deduced in the perspective of physical meaning, and then the NPGP algorithm is researched and proved which can improve the communication performance of the NPG algorithm by using MATLAB simulation. To further enhance the communication performance of CR, the NPGP sigmoid-NL algorithm is proposed. The MATLAB simulation results show that the utility of the improved NPGP sigmoid algorithm will improve and the CR users'transmitting powers will decrease by decreasing the value of"Nash Equilibrium threshold factor".Then, the thesis does research on power control algorithm when CR users are in the manner of Underlay mode of spectrum sharing. The logarithmic utility power control algorithm is proposed, which combines the characteristic of non-negative variables of logarithmic function. Through theoretic analysis and MATLAB simulation, we can prove that the proposed algorithm can guarantee all the CR users'SIR needs, which are greater than or equal to the target SIR values. Besides, when there are only a few of CR users, the logarithmic utility algorithm can make the CR users to achieve higher SIR values so as to meet the high SIR needs of high-speed data communications.