Research On Spectrum Access Method Based On Spectrum Situation In Cognitive Radio Networks

In cognitive radio networks, the spectrum situation is the current status and future trend of radio spectrum resource in temporal, frequency and spatial domain. It reflects the current spectrum characteristics and is the important basis of spectrum access. In this thesis, the spectrum access problem is investigated both in small scale cognitive radio network and large scale cognitive radio network based on the spectrum situation in temporal, frequency and spatial domain. The main research contents are:In small scale cognitive radio networks, the network radius and the distance of secondary users is small. The spectrum situation detected by secondary users is similar, so secondary users use spectrum holes mainly in temporal and frequency domain. In this thesis, a mixed spectrum access scheme based on the temporal-frequency situation of channel is proposed. It models the channel state with two state Markov process. The state of the channel in the temporal and frequency dimensions is estimated.The secondary users select Overlay or Underlay access mode according to the channel state. Then the transmit power of secondary users is optimized by the principle of the maximum capacity. The influence of spectrum sensing error detection and false alarm on spectrum access is considered. The theoretical analysis and simulation results indicate that the mixed spectrum access system has higher capacity than single Overlay or Underlay system.The spectrum situation map can effectively estimate the interference of different locations and guide the secondary users of different locations for spectrum access and power control. In view of the traditional interpolation method, the accuracy of spectrum situation map is low and the number of sampling nodes is large. In this thesis, a method to construct spectrum situation map based on the information of primary user is proposed. For the emission power unknown, it establishes the location model by the least square method baesd on the signal strength which is received by the secondary users, then estimates the information of primary user such as the location and the transmit power by the Lagrange function method. Finally, according to the spatial information and communication model, the spectrum situation map is constructed directly. The simulation results show that the performance of Receiver Operating Characteristic(ROC) in the algorithm is better than the traditional interpolation method.In large scale cognitive radio networks, the different spectrum environments surrounding the secondary users create vast spatial potentials for access. A space spectrum access method based on the location information is proposed. It analyses the relations between the primary network coverage, the distance between primary and secondary users and the cognitive network capacity. It realizes power control according to the three location relations between primary and secondary users. The concurrent communication interference problem of the primary and secondary users in the space is sovled. It can guide the secondary users for power control and spectrum access. The simulation results indicate that the proposed methd can provide more spatial spectrum access opportunities for secondary users and achieve higher cognitive system capacity.