Research On Power Control For Cooperative Communications Based On Cognitive Radio System

In recent years, wireless communication plays an increasingly important role in people's daily life and social development, which makes wireless communication technology develop at a high-speed. However, wireless communications rely on radio spectrum, the frequency as a kind of natural resources is very limited. The existing spectrum allocation method is unreasonable, which leads to the scarcity of spectrum resources and a very low utilization of licensed spectrum. Recently, cognitive radio (CR) technology becomes a research hot spot, which requires no fixed spectrum allocation and communicates in the free band through the perception of the surrounding electromagnetic environment, and then improved spectrum efficiency. It is considered as the best technology to solve those problems mentioned before.Power control technology is one of the key problems in CR and wireless communication. Reasonable adjustments to the user's transmit power can not only ensure the normal communication of primary users, but also meet the needs of CR users. Cooperative communication technology in recent years has developed fast, whose basic idea is that the users forward the information for each other in wireless network to obtain greater spatial diversity. In this paper, power control for cooperative communications based on CR system is studied to improve network throughput and achieve a better optimization of transmission power under the premise of primary users'normal communication. Fairness among CR users should be considered too.The study comprises two parts, cognitive radio hardware and software. Works and innovations are as follows:The first part focuses on the use of power control technology to improve the performance of wireless communication systems.Firstly, based on the OPCSS algorithm and the Decode-and-Forward in cooperative communication, a new OPCSS-DF algorithm is proposed. The simulation results show that the proposed algorithm improves system performance and spatial diversity, which makes the range of applications of this algorithm wider.Secondly, based on Goodman's non-cooperative power control game, a new power control game algorithm suitable for CR system was proposed by improving the pricing function. The existence and uniqueness of the Nash equilibrium is proved too. The simulation results indicate that compared with several classical non-cooperative game algorithms the new algorithm not only reduces the transmission power efficiently and improves the user's income, but also shows a good convergence .Thus,it is suitable for CR system which has high demand of time-delay character.The second part is the research of cognitive radio hardware platform and the verification of theoretical results. The CR MAC layer communications union on hardware and software platform is designed and studied, the final test results show that the communications union works effectively, not only meets the needs of mobile station for multiple services, but also completes the performance indicators set initially. This paper lays a good foundation for the further research on cognitive radio.At the end, a summary is given and the future research directions are pointed out.