| Spread spectrum communication technology is widely used in anti-interference communication,which can superimpose the pseudo-random sequence of high rate on the original information of low rate.The receiver side follows the inverse process to despread and accumulate the spread spectrum signal to recover the original information,which has better anti-interference capability and spectrum hiding capability.In addition,the pseudorandom sequence used for spreading can also encrypt the original information if it has a long period,and without knowing the generation method,even if it is intercepted by the enemy,it cannot be deciphered to obtain key information.Frequency hopping technology,as a derivative of spread spectrum,can control the carrier frequency by pseudo-random sequence to jump according to certain rules,which plays a role in avoiding interference.However,with the rapid development of technology,the emergence of deep learning and neural network technology equipped with supercomputers has been able to decipher some traditional spread spectrum sequences with clear mathematical structure,short period and small code space,which poses a great threat to the security of spread spectrum communication systems.Although chaotic sequences with infinitely long theoretical periods have been proposed in academia to improve the system’s decipherability,chaotic systems still face high complexity,severe period degradation,and synchronization difficulties in the implementation of digital circuits.To address the above problems,this paper firstly proposes a spreading-hopping sequence generation method based on Residue Number System(RNS)and permutation polynomials,and optimizes the sequence with good performance and designs a mapping method for the spreading-hopping sequence to make it more suitable for spread spectrum communication systems.Then a long-period spread spectrum hopping system synchronization scheme is designed for the spread spectrum hopping sequence,which improves the system secrecy performance and reduces the system complexity at the same time.The main work of this paper is as follows:(1)Based on the design of the residual system,a sequence with good performance is selected for the application of spread spectrum synchronization;the mapping method of the frequency hopping sequence is designed to improve the deciphering resistance and reduce the loss of balance,compared with the traditional mapping method,the loss of balance is reduced by 30% when the sequence length is 4096;the optimized structure of the hybrid spread spectrum hopping sequence generator for digital circuit implementation is proposed.(2)A time-of-day(TOD)-based synchronization scheme for long-period spreadspectrum hopping systems is designed by combining the characteristics of the spreadspectrum hopping sequence generator,mapping the sequence phase by the high clock information of TOD,and capturing the received signal in a single-channel slow-scan manner using a special frame format to reduce the hardware complexity.Based on this,the system transceiver simulation modeling is carried out to test the capture performance and BER performance of the system,and an improved early-late gate tracking method is proposed,which improves the BER performance by 0.5 d B compared with the conventional early-late gate at low SNR.(3)The RNS-based spread spectrum hopping communication system is designed and implemented for FPGA,and the system is tested on ZC706 and AD9361 platforms to verify the correctness of the system. |
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