The Research Of Key Technologies For Cognitive Radio Networks

With the rapid development of wireless communication technologies and the increasing broadband communication demands, the shortage of spectrum is becoming an outstanding problem. On one hand, the conflicion between spectrum supply and demand is increasing. On the other hand, according to the survey of related organizations the utilization of licensed spectrums is very low under the present static spectrum management mode. Under the above background, the cognitve radio (CR) technology is prposed, which aims at enhancing the utilization of licensed spectrum with intelligent using the unused spectrum of licensed systems.CR becomes a hot topic in wireless communication research. Related research are undergoing by scholars from universities all over the world. But the CR technology is also in the beginning stage and there are many drowbacks need to be improved. In this paper, our researches focus on CR power control scheme, MAC layer sensing efficiency and spectrum sharing in IEEE 802.22 systems. The game theory and auction theory in microeconomics are introduced to inspire new ideas. Several new algorithms are proposed and the performances are verified through computer simulations. The researches have meaningful value for the realization of CR systems.The work in this dissertation is concluded as following points.Firstly, the research progress of CR is discussed detailedly, and the characteristic and technology challeges are analyzed.Secondaly, in chaper 3, we considered decentralized cognitive radio networks, and we especially focusd on the multiple measurement points scenario. Interference temperature model is proposed for spectrum sharing. Based on interference temperature model, the problem of spectrum sharing can be formulated as a power optimization problem at physical layer. Game theory is used to investigate the distributed power control for providing the maximum throughput in cognitive radio networks. A tax-based power control game algorithm is introduced to implement power allocation optimization in a distributed mode, and guarantees the convergence to globally optimal power allocations.Thirdly, chapter 4 discussed the MAC layer spectrum sensing in cognitive radio network. Efficient MAC layer spectrum sensing scheme can improve sensing performances and find more available spectrum opportunities. Focusing on solving MAC layer the sensing period optimization problem, we proposed an adaptive sensing period adjustment algorithm. The proposed algorithm realized the automation adjusting of sensing period based on the channel model of primary users, and found more opportunities than fixed period sensing.Fourthly, in chapter 5 we studied the spectrum sharing problem among different IEEE 802.22 WRAN cells. Aiming at efficiently solving the spectrum sharing problem, a dynamic spectrum renting scheme is proposed. Based on auction theory, the proposed spectrum renting algorithm obtains higher spectrum utilization and higher auction benefit, and guarantees no interference between competitive WRAN base stations.Finally, a conclusion is drawn for the dissertation, and valuable research directions in the future are presented.