Gelecek-nesil bilişsel kablosuz ağlar için gelişmiş haberleşme teknikleri

As wireless devices become ubiquitous, demand for the electromagnetic spectrum has increased to a level that leads to two problems in wireless communications. First problem is spectrum scarcity problem. Since most of the spectrum is allocated to licensed users, unlicensed users are facing with the problem of insufficient spectrum bands. Electromagnetic spectrum band is scarce, hence, it must be utilized efficiently. Although unlicensed spectrum bands are overcrowded, licensed ones are underutilized. Second problem is inefficient spectrum utilization. Cognitive radio technology stands as a promising approach to overcome these problems and to enable next-generation cognitive wireless networks, which are the wireless networks with spectrum-awareness. This technology enables using the licensed spectrum bands in an opportunistic manner with limited interference to the licensed users. In this thesis, cognitive radio is adopted in different types of wireless networks to realize next-generation cognitive wireless networks. Due to greatness of the domain of next-generation cognitive wireless networks, this thesis focuses on a subset of these networks. Hence, this thesis investigates four different wireless networks with cognitive radio capability for next-generation cognitive wireless networks. Advanced communication techniques are proposed and analyzed in these four main pillars of wireless networks. First pillar of next-generation cognitive wireless networks is cognitive radio ad hoc and sensor networks. Spectrum opportunity characterization is performed, mobility-aware clustering protocol is proposed, clustering in multi-channel spectrum-aware environment is investigated, energy optimal transmission range is found, network coding is studied for multicast communication in this type of networks. Second pillar of them is wireless networked control systems with cognitive radio capability. Maximum coverage area and maximum energy-efficiency under Kalman filter convergence with maximum cost-efficiency are studied. Third pillar is cognitive wireless multimedia networks. Challenges and requirements are analyzed to enable spectrum-aware communications in cognitive wireless multimedia networks. Existing solutions are investigated and open research issues are determined. Last pillar is Internet of Things. Spectrum scarcity problem is worsened by this paradigm, and nodes within Internet of Things are resource-constrianed. Hence, it benefits from cognitive radio technology to overcome these challenges. Hence, network coding application is utilized to decrease transmission efforts, and energy harvesting in the domain of smart grid and smart cities is investigated to overcome limited energy supply challenge. The analysis and studies in this thesis help realization of next-generation cognitive wireless networks. The thesis also points out open research issues and how cognitive radio can be applied in next-generation wireless networks.