The Design And Implementation Of Chaotic Spread Spectrum System In UAV TT&C Link

With the progress of science and technology and the need of military operations,UAVs are used more and more widely in military applications.The UAV TT&C data link takes on the data sending and receiving task,which is the "nerve center" of the UAV system,and needs high security.In the electromagnetic spectrum warfare,great challenges has been brought to anti-jamming UAV data transmission system in which the direct sequence spread spectrum technology has been adopted.Therefore,the research on anti-jamming and LPI technology in UAV TT&C data link has become an important direction of UAV system research.The production of chaotic sequences has the characteristics of sensitive to the initial values,so many different sequences of non periodicity and similar noise characteristics can be produced by the same generator with different initial values.In recent years,with the development of chaos theory,more and more researchers put forward the thought that the chaotic sequences can be applied to the UAV TT&C system.Spread spectrum communication using chaotic sequences,can achieve the military application of high confidentiality,anti-interference,low intercept purposes.These studies focus on Chebyshev mapping,Logistic mapping,improved Logistic mapping,Tent mapping and other models.A large number of statistical properties of theoretical analysis and spread spectrum feasibility studies are carried out.The improved Logistic chaotic spread spectrum sequence is adopted in this paper,and the binary quantization of the real valued sequence is realized by using the L bits quantization method,and its excellent correlation characteristics are verified.On the basis of considering the complexity of engineering implementation,a synchronization scheme of chaotic spread spectrum system based on synchronization with short code sequences is proposed.The short code synchronization is realized by matched filtering method.The corresponding short code aided synchronization flow chart is designed,and the long code eigenvalue is introduced into the frame structure design to realize the auxiliary synchronization guidance of short code.In the design of data frame structure,the characteristics of burst communication in data link are mainly considered,and short frame structure is adopted.DPSK modulation is adopted to avoid the phase ambiguity caused by the time adjustment and lead to data error.The demodulation of information is realized by using Costas loop.The full digital Costas loop for spread spectrum communication system is studied,which overcomes the disadvantage of higher requirement for SNR when the classical Costas loop works normally.And demodulation algorithm of improved Costas loop is implemented by simulation analysis and FPGA,and through the simulation and board level debugging,verify the correctness of binary quantization algorithm,verify the demodulation circuit of spread spectrum system Costas loop in low SNR signal demodulation and short code auxiliary function of chaos sequence spread spectrum communication system synchronization.Through anti-jamming experiment,the anti-jamming gain of the system is 25 dB.