Research On Key Technologies For Cognitive Radio System

Cognitive radio is a new wireless communication technology proposed recently, whose main objective is to make best efficient utilization of the precious spectrum resource. In cognitive radio, the primary user has arbitrary authority on spectrum, and its communication process will not be interrupted by other users. The cognitive users sense the environment, study from the sensing result, discover the spectrum vacancy and lease the idle channel under the premise of not interfering with the primary user's communication. When detection primary user's access into system, the cognitive user has to interrupt its task in time, withdraw from the leasing channel, and wait until the next spectrum opportunity.The key technologies of cognitive radio involve spectrum sensing, spectrum allo-cation and cognitive QoS. Spectrum sensing is the foundation of cognitive radio sys-tem. It's main role is to discover the spectrum opportunity quickly and precisely. Based on spectrum sensing, spectrum allocation collects cognitive user's requirement and dis-tribute spectrum opportunities to different cognitive users under certain strategy. The cognitive QoS guarantees the cognitive user's QoS during its communication process. This dissertation centers on the above three key technologies and is carried out in the following five aspects:O We study the feedback based sensing method. Based on the basic feedback topology, we derive the sensing decision rules. To cope with the energy and space overhead in basic feedback topology, we further discuss the feedback topology without sensing history and feedback topology with one step sensing history. Theoretical and experimental results show that by introducing the feedback mechanism, the cognitive user's sensing accuracy is improved.②We study the the scheduling base centralized spectrum allocation. We con-struct the cognitive scheduling model. Based on the model, we propose a "hybrid priority dynamic scheduling" policy. We further provide and prove the optimal de-creasingω/p scheduling rule. Theoretical and experimental results show that, under our scheduling rule, the cognitive user can finish its task within a shorter period of time, the communication system's service rate and spectrum utilization rate are increased.③We study the game theory based distributed spectrum allocation. We proposed the chain store game model. To deal with pure strategy Nash equilibrium and mixed strategy Nash equilibrium's shortcomings, we introduce the collaborative mechanism and use the correlated equilibrium to solve the model. Theoretical and experimental results show that we achieve improvements in payoff function, channel utilization and communication time under chain store game model.④We study the cognitive user's service interruption process. We propose a new QoS parameter, average nested interrupted times, in wireless communication system. By modeling the cognitive radio system as both M/G/1 and M/G/k queues, we solve the explicit expressions of the parameter. This new QoS parameter is an important complement to the theoretical study of service interruption. It also has a significant guidance in cognitive user's channel selection and spectrum allocation strategies.⑤We study the cognitive user's channel switch process. We propose a "ran-dom once switch" policy. We further build a channel superposition theory based semi-Markov multi-channel switch model, which is used to analyze cognitive user's service waiting time and switch overhead during its spectrum leasing process. Theoretical and experimental results show that under "random once switch" policy, the cognitive user has a smaller service waiting time and switch overhead.In this dissertation, the key technologies of cognitive radio system are studied. The feedback sensing topology is designed for spectrum sensing; the scheduling model is adopted to study the centralized spectrum allocation problem; the chain store game with collaborative mechanism is explored to discuss the distributed dynamic spectrum allocation problem; the service interruption is explicitly deduced under the queueing models to analyze the cognitive QoS; a novel channel superposition theory based semi-Markov multi-channel switch model is built to analyze cognitive user's QoS. Based on theoretical analysis and aiming to solving the concrete problem in wireless com-munication, our work are significant in both of cognitive radio research's theory and applications.