With the development of wireless communication technology, the number of wireless users has increased dramatically, making spectrum resources more and more tense. How to fully improve the utilization of wireless spectrum has become a technical problem to be solved. Cognitive radio technology proposes a new solution. The core idea is to enable wireless communication equipment to have the ability to discover "spectral holes" and make rational use of the "holes" found. Although cognitive radio technology can manage limited spectrum resources in a more flexible manner, it is necessary to solve key technical problems including spectrum detection, adaptive spectrum resource allocation and wireless spectrum management in order to actually apply it to practical communication systems. With the rapid development of wireless communication technology, spectrum resources have become increasingly tight. Especially with the development of wireless local area network (WLAN) technology and wireless personal area network (WPAN) technology, more and more people use these technologies to access the Internet wirelessly. Most of these network technologies work using unlicensed bands (UFBs). Due to the rapid development of WLAN and WRAN wireless communication services, the unlicensed frequency bands in which these networks operate have become increasingly saturated. Other communication services (such as TV broadcasting services) require communication networks to provide certain protection from interference from other communication services. In order to provide good protection, the frequency management department specifically allocates a specific licensed band (LFB) for use by specific communication services. Compared to the licensed band, the unlicensed band has much less spectrum resources (most of the spectrum resources are used for licensed bands). The utilization of a significant amount of licensed spectrum resources is very low. Thus, the fact that some parts of the spectrum resources are relatively small but the amount of traffic carried on them is large, while the utilization of other licensed spectrum resources is very low. Therefore, it can be concluded that based on the current spectrum resource allocation method, a considerable portion of the spectrum resource utilization rate is very low. In order to solve the problem of lack of spectrum resources, the basic idea is to maximize the utilization of existing spectrum. To this end, the concept of cognitive radio has been proposed. The basic starting point of cognitive radio is that in order to improve spectrum utilization, cognitive wireless communication devices can operate in an authorized frequency band in an "opportunsTIc Way" manner. Of course, this must be based on the fact that the licensed band is useless or only a small number of communication services are active. Such spectral resources that can be utilized in the air, time, and frequency domains are referred to as "spectral holes." The core idea of ​​cognitive radio is to enable wireless communication devices to have the ability to discover "spectral holes" and make rational use of them. When an unauthorized communication user uses an authorized spectrum resource by "borrowing", it must be ensured that his communication does not affect the communication of other authorized users. To do this, unauthorized users must use the discovered "spectral holes" in accordance with certain rules. In cognitive radio, such rules are loaded onto a communication terminal in a machine understandable form, such as an XML language. Since these rules can be constantly adjusted according to the spectrum utilization, the load and distribution of communication services, etc., these rules allow spectrum managers to manage valuable spectrum resources in a more flexible manner. As can be seen from the above description, in order to improve the spectrum utilization, the detected "spectral holes" can be fully utilized. This is an application of cognitive radio technology. However, the cognitive radio proposed as a new concept has a wider coverage. The basic definition of cognitive radio can be summarized as [1]: CogniTIve Radio is an intelligent communication system that can sense the external communication environment. Through learning, cognitive radio systems constantly perceive external environmental changes and adapt to environmental changes by adaptively adjusting their own internal communication mechanisms. Such adaptive adjustment is on the one hand to improve the stability of the system, and on the other hand to improve the utilization of spectrum resources. From this it can be concluded that the characteristics of cognitive radio are: *Awareness of the environment * Ability to learn about environmental change *Adaptability to environmental changes * High reliability of communication quality * Make full use of spectrum resources *Reconfigurability of system function modules Cognitive radio was developed by MITRE consultant, Dr. Joseph Mitola of the Royal Swedish Institute of Technology and GERALD Q MAGUIRE, Professor JR. in the IEEE Personal CommunicaTIons magazine in August 1999 [2], which is further for software radio. Extension. Cognitive radio uses a radio-domain model-based approach to infer the rules governing the use of the radio spectrum (such as radio frequency bands, air interfaces, protocols, and spatial and temporal modes), via Radio Knowledge Representation Language (RKRL) [3], Knowledge of radio rules, equipment, software modules, radio propagation characteristics, networks, user needs and application scenarios to enhance the flexibility of personal services and enable software radio technology to better meet user needs.
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