Differential Self-Encoded Spread Spectrum System For Ground-to-Air Communication

With the rapid development of UAV,it has been widely used in military and civil fields.As an important part of UAV Communication system,data link effectively guarantees the efficient information transmission between UAV and control center.With the advantages of strong anti-interference ability,low probability of being intercepted and good covert communication performance,Direct Sequence Spread Spectrum system plays an important role in the process of data link security communication.Among which,the Code Hopping Spread Spectrum system which can realize the dynamic change of spread spectrum sequence further improves the anti-interference and anti-interception performance of communication system.Code Hopping Spread Spectrum system can be divided into two kinds of communication systems which include Pre-encoded Spread Spectrum and Self-encoded Spread Spectrum.However,both Pre-encoded Spread Spectrum and Self-encoded Spread Spectrum has the problem of synchronization.In order to reduce the synchronization difficulty of Code Hopping Spread Spectrum system and improve covert communication performance of data link,carrying out in-depth research on Differential Self-encoded Spread Spectrum system is of great significance significance and practical application value for ground-to-air communication.Based on the advantages of Code Hopping Spread Spectrum system and combined with the differential system that is based on G function,the Differential Self-encoded Spread Spectrum system is analyzed in detail.Thereinto,we focus on the research of Differential Self-encoded Spread Spectrum transmission mechanism and complete the deduction of the relevant formulas which are about the process of communication signal transmission.What is more,communication characteristics are analyzed too.Furthermore,the spread spectrum method based on Differential Self-encoded Spread Spectrum is studied deeply.According to the mapping rules of G function,pseudo-random that control hop change is replaced by signal code sequence.The G function of time-frequency disturbance is improved and the design of spread spectrum sequence selection function is completed.At the same time,according to the reversibility of G function,the inverse analytic function of spread spectrum sequence selection function is completed.Based on Chi-square test and averaged periodic graph method,the performance of spread spectrum sequence selection function is analyzed,including one-dimensional uniformity,twodimensional continuity and randomness.The acquisition of Differential Self-encoded Spread Spectrum signal is completed by multi-branch parallel loop correlation acquisition method.Combined with MATLAB simulation results,the correctness and rationality of Differential Self-encoded Spread Spectrum method are verified.Besides,under different interference conditions,the anti-jamming and anti-interception performance of Differential Self-encoded Spread Spectrum method is tested by using common interference signals of Direct Sequence Spread Spectrum system.On this basis,key functional modules such as spread spectrum sequence selection function unit,carrier synchronization unit and multi-branch parallel circulation correlation capture unit are designed and implemented based on FPGA hardware design platform.And Modelsim se10.c software is used to verify the rationality and validity of the unit designed.