Localization Of Primary User And Applications Of Location Information In Cognitive Radio Networks

The available spectrums are very limited due to the character of electromagnetic wave itself. But along with the increasing applications of wireless communication, especially with the sharp increasing applications on the wireless internet in recent years, large amount of wireless spectrum resource is required. Because of the fixed allocation rule which is currently wide used, the available radio spectrum has been assigned almost completely in every country. Cognitive radio technology can utilize the licensed users'frequency for transmission and avoid interferences on licensed users. This technology provides an effective solution to solve the problem between the increasing wireless applications and the limited resource. In this thesis, we have studied the location information collection and utilization including the primary user localization algorithm, location-based spectrum allocation algorithm, and the impacts of the localization error on the secondary network performance.First, motivated by the sensor network localization algorithms, considering the requirements of localization in cognitive radio networks, we have studied the received signal strength based localization algorithm and the node selection algorithm. A localization algorithm without requirement of iteration is proposed under the condition that the transmitting signal strength is known. The relationship between model error brought in the process of linearization and received signal strength is analyzed. Based on estimation theory, the relationship between the lower bound of estimation performance and geometry structure is analyzed with the consideration of the geometry structure performance in localization. Then, based on the model error and geometry analysis, a node selection algorithm is proposed to reduce the error and avoid the poor geometry. Thus, the localization accuracy is improved. On the other hand, the proposed algorithm greatly reduces the computational scale and the computation amount is largely reduced. Therefore, node energy consumption is reduced and the network lifetime is prolonged.Second, we have studied the localization problem for a class of localization algorithms widely used in wireless sensor networks without primary user's emission signal strength. The model error is analyzed. Taking into account the relationship between the lower bound of the geometry structure and the estimated lower bound, the relationship between the model error and the geometry structure is studied. A node selection algorithm is proposed to achieve a good compromise between the model accuracy and the geometry performance. Thereby, the localization accuracy is improved and the complexity of the algorithm is reduced.Third, we have studied the location-based spectrum allocation for heterogeneous channels. Considering the distinction between the available spectrums and the difference on the radius of transmission and interference between the spectrum frequencies may be large, a more applicable standard for the "spectrum scarcity" character in cognitive radio networks, which classify channels according to the channel frequency, is proposed. In resource allocation problem, taking into account the spatial reuse, we proposed a location based method and it can improve the efficiency of spectrum utilization.Finally, the impacts of the location error on the cognitive radio network performance have been studied. By considering the downlink transmission in an OFDMA based cognitive radio network, we analyze the performance changes of resource allocation and secondary user networks when there exists the location error on the primary use. We focus on the effects of localization error for interference radius. Based on the "water filling" theory in power allocation problems, the upper bound on the impacts of localization error on secondary users are derived under the condition that location error interval is known. The conditions are proposed for the assessment of effects on the secondary uses networks. A feasible method to judge the impact degree of location error is given based on our proposed conditions. It is also proved that our localization and node selection method are applicable in spectrum spatial reusing.