Research On Satellite Frequency Hopping Technology Based On Chaotic Sequence

Satellite communications can obtain a great coverage area at a lower cost,and can effectively complement the terrestrial communication system which is limited by geographical and political factors.As terrestrial communication systems reach saturation,the establishment of an integrated air-space communication network has become an important direction for the development of communication technology.Subject to the complex communication environment and the development of communication interference technology,the security problem of satellite communications is also increasingly prominent.Due to the wide coverage area of satellite communication system,communication signals are easily detected,intercepted and interfered by noncooperating parties.Although the traditional spread spectrum technology has improved the security performance,it no longer has sufficient security due to the development of low interception probability signal detection technology.Although frequency hopping techniques can improve anti-interception capability,traditional frequency hopping systems also face great challenges with the development of adaptive jamming techniques.In this thesis,we propose a frequency hopping system scheme that combines chaotic sequences as the generation method of frequency hopping sequences.The chaotic sequence is generated by using time information mapping as the initial value,and the control sequence uses time-varying pseudo-random codes to select the spread code and frequency hopping point of the current signal on the basis of traditional spread spectrum communication to enhance the confidentiality performance of the system.In traditional frequency hopping system,the switching period of the synchronous frequency set is usually long for the convenience of reception.The tracking interference based on neural network can use the neural network to capture the synchronous frequency points and predict the synchronous frequency hopping sequence.In this paper,we simulate the prediction method of the interferer and use the GRU network to predict the frequency hopping sequence with a large sliding window and adjust the synchronous frequency set switching period according to the results,which improves the antiinterference capability of the frequency hopping system.Due to the updated iterations of chaotic sequence prediction and frequency hopping sequence prediction techniques based on neural network technology,deciphering the traditional pseudo-random sequence has become a very mature technology.In order to further improve the anti-prediction capability of the frequency hopping communication system,this thesis studies a variety of chaotic mappings,and combines the performance requirements of frequency hopping sequences to propose a new high-complexity chaotic mapping,which greatly improves the anti-prediction performance of chaotic frequency hopping sequences and makes the chaotic frequency hopping system effectively against real-time tracking interference.Meanwhile,due to the harsh channel environment of satellite communication,a combination of multiple technical solutions is usually required to effectively suppress the effects caused by low signal-to-noise ratio.Although the spread spectrum technology can bring gain to the system,it also increases the difficulty of reception.In this paper,we adopt PMF-FFT algorithm for capture and FLL-PLL algorithm for tracking,and design a capture and tracking algorithm that can be applied to the frequency hopping system,which effectively improves the performance of the system.