| In the face of the increasingly complex electromagnetic environment in modern communication, fixed-frequency communication has suffered a great threat. When the frequencies are disturbed, communication can not be carried out as normal. In order to improve anti-jamming, anti-fading and security of communication, frequency hopping, as one of spread spectrum communications, has already chosen to be a usual way in communication. However, the information of the frequencies can not be transmitted when the frequencies of hopping frequency are disturbed. Cognitive radio, which is mainly divided into cognitive and reconstruction two functions, is proposed to solve the lack of spectrum resources and the low utilization rate. It is an intelligent wireless communication system which can learn from the surrounding environment by sensing it and change its parameters of internal condition to adapt to the changing electromagnetic environment in time..Firstly, this paper discusses the significance of combining cognitive radio technology and frequency hopping communication system. Cognitive communication system is proposed. Cognitive function of cognitive radio is used to detect interference signals in the electromagnetic environment, while reconstruction function is used to change the internal parameters of the communication in order to select the best hopping frequency table to avoid interfering signals. The system structure of cognitive hopping communication, the specific working processes, the key technologies and technical indicators are all described in detail. Common disturbance types and their mathematical models in the frequency-hopping communication system are introduced. The key technology of cognitive function is spectrum sensing. It can find out spectrum holes by using perceptron algorithm to detect the condition of spectrum in the electromagnetic environment. This paper focuses on spectrum sensing technology in the cognitive communication. Then, several main principles and mathematical models of spectrum sensing algorithms are described in detail while multi-node cooperative spectrum sensing algorithm is simply introduced. The energy detection method and the cyclostationary feature detection method which are applied in CR communication are simulated and analyzed by MATLAB. All phase FFT is put forward due to spectrum leakage caused by data truncation in the FFT process,which is used in spectrum sensing algorithm. This paper optimizes spectrum sensing algorithm.The principle and mathematical models of spectrum sensing algorithm based on all phase FFT are proposed. Through the analysis of the simulation performance can be seen that this method effectively inhibits the spectrum leakage and improves the accuracy of spectrum detection. It can provide more reliable information of spectrum for spectrum analysis and intelligent learning on cognitive radio, and thus to avoid interference and improve the quality of communication. |
