5、认知无线电面临的问题及未来发展认知无线电中存在着主用户隐藏问题。许

5. Problems faced by cognitive radio and future development <br>There are hidden problems of master users in cognitive radio. Many factors can cause the main user to hide the problem. The multipath fading of the main user during signal transmission or the presence of occlusion between the main user and the cognitive user will cause the system to fail to correctly make spectrum decisions. If the main user cannot be found correctly, it will cause the cognitive user to interfere with the main user [17]. <br>There are still problems in the detection of spread spectrum signals by cognitive radio. At present, fixed frequency signals and spread spectrum signals are used in communication systems. The devices using fixed frequency signals work on a single frequency or channel. Devices using spread-spectrum technology work on different frequencies or channels. Frequency hopping spread spectrum and direct sequence spread spectrum are the most common spreading methods currently used for spread spectrum signals. Frequency-hopping spread-spectrum equipment can change its own frequency to use different narrow-band channels when it is working, which makes it difficult for the system to perceive the primary user. Although direct-sequence spread spectrum equipment does not change channels but uses a single channel during operation, the power distribution range of the main users using spread spectrum signals is relatively large, which will also cause cognitive users to have difficulties in perceiving the main users [18 ]. <br>Cognitive radio also faces some problems in communication security. In a real communication environment, there may be malicious users. They can launch attacks through some means, such as by imitating the main user and launching the main user simulation attack to the cognitive user. Malicious users can imitate the main user to mislead the communication system to make wrong spectrum detection results, which reduces the detection performance of the system [19]. <br>Although cognitive radio has some problems, it has shown great potential in wireless and mobile communications. <br>Through artificial intelligence and signal processing technology, cognitive radio can not only be applied to simple spectrum testing, but also extend to the perception of the performance of the entire system, and make the wireless communication system more widely used in the future, intelligent and humanized. Through theoretical research and application development, cognitive radio can be developed in the following areas: (1) Development of basic theory of cognitive radio and related application technologies, spectrum sensing, adaptive allocation of spectrum resources, and dynamic spectrum management . (2) Development of test verification system. For example: CORVUS system and thread pool system [5], these systems are mainly for the test platform provided to verify the basic theory of cognitive radio.<br>(3) Integration with existing systems. Although the current view holds that the popularity of cognitive radio does not require any changes from licensed users, how to allow licensed users to use the same frequency band with other unlicensed users is a problem. At present, <br>some research work is considering integrating cognitive radio into the already deployed communication system and has achieved some results.

5. Cognitive Radio's Problems and Future Development<br>There is a problem of main user hiding in cognitive radio. Many factors can cause the main user to hide the problem. Multi-path fading by the primary user during signal transmission or the masking between the primary user and the cognitive user can cause the system to fail to make the correct spectrum judgment. Failure to properly detect the presence of the primary user can cause interference between the cognitive user and the primary user.<br>There are still problems with cognitive radio stortation signal detection. Fixed frequency signals and spread-frequency signals are currently used in communication systems. Devices that use fixed frequency signals operate on a single frequency or channel. Devices that use spread-band technology operate on different frequencies or channels. Jump frequency expansion and direct sequence spread frequency are the most commonly used expansion mode of the current spread signal. The frequency-hopping device can change its frequency to use different narrowband channels when it is working, which makes it difficult for the system to perceive the main user. Direct sequence spread spectrum equipment does not change channels when working but uses a single channel, but the main user using the spread signal has a relatively large power distribution range, which will also lead to cognitive users in the perception of the main user there is difficulty.<br>Cognitive radio also faces some problems in communication security. There may be malicious users in a real communication environment. They can launch attacks by imitating the primary user and launching a master user simulation attack to the cognitive user. A malicious user can impersonate the primary user and mislead the communication system into making incorrect spectral detection results, which reduces the detection performance of the system.<br>Although cognitive radio has some problems, it has shown great potential in the field of wireless and mobile communication.<br>Through artificial intelligence and signal processing technology, cognitive radio can not only be applied to simple spectrum testing, but also extend to the perception of the performance of the whole system, and make wireless communication system more widely, intelligent and user-friendly in the future. Through theoretical research and application development, cognitive radio can be developed in the following fields: (1) the basic theory of cognitive radio and the development of related application technology, spectrum perception, adaptive allocation of spectrum resources and dynamic spectrum management. (2) The development of the test verification system. For example, CORVUS systems and thread pool systems, which are the main purpose of validating the basic theory of cognitive radio to provide a test platform.<br>(3) Integration with existing systems. While the current view is that the popularity of cognitive radio does not require any change from licensed users, how to get licensed users to use the same band with other non-licensed users is a problem. At present,<br>Some research is considering the integration of cognitive radios into deployed communications systems and has yielded some results.

5. Problems and future development of cognitive radio<br>In cognitive radio, there is the problem of master user hiding. Many factors may lead to the hidden problem of the primary user. The main user's multi-path fading or the occlusion between the main user and the cognitive user will lead to the system can not make the spectrum decision correctly. If the existence of the primary user cannot be found correctly, cognitive users will interfere with the primary user [17].<br>There are still some problems in the detection of spread spectrum signal in cognitive radio. At present, fixed frequency signal and spread spectrum signal are used in communication system. The equipment using fixed frequency signal works on a single frequency or channel. Devices using spread spectrum technology work on different frequencies or channels. Frequency hopping spread spectrum and direct sequence spread spectrum are the most commonly used spread spectrum methods. Frequency hopping spread spectrum equipment can transform its own frequency to use different narrow-band channels when it works, which makes it difficult for the system to sense the main user. Although DSSS equipment uses a single channel instead of changing the channel, the power distribution range of the main user using the spread spectrum signal is relatively large, which also causes difficulties for cognitive users to perceive the main user [18].<br>Cognitive radio also faces some problems in communication security. There may be malicious users in the real communication environment. They can attack by some means, such as imitating the primary user and launching the primary user simulation attack to the cognitive user. Malicious users can imitate the primary user to mislead the communication system to make wrong spectrum detection results, which reduces the detection performance of the system [19].<br>Although cognitive radio has some problems, it has shown great potential in the field of wireless and mobile communication.<br>Through artificial intelligence and signal processing technology, cognitive radio can not only be applied to simple spectrum test, but also can be extended to the perception of the whole system performance, and make the wireless communication system more extensive, intelligent and humanized in the future. Through theoretical research and application development, cognitive radio can be developed in the following areas: (1) the development of basic theory and related application technology of cognitive radio, the development of spectrum sensing, adaptive allocation of spectrum resources and dynamic spectrum management technology. (2) Development of test and verification system. For example, Corvus system and thread pool system [5], these systems are mainly test platforms to verify the basic theory of cognitive radio.<br>(3) Integration with existing systems. Although the current view is that the popularity of cognitive radio does not need any change from the licensed users, how to make the licensed users and other non licensed users use the same frequency band together is a problem. At present,<br>Some research work is considering the integration of cognitive radio into the deployed communication system and some results have been achieved.<br>