Research On Self-encoded Spread Spectrum Communication System

The essence of spread spectrum communication is to use the broadband transmission technology to exchange for the benefits of SNR,and it has good anti-interference ability.It is widely used in military communications and other fields.Classical spread spectrum communication generally uses deterministic and periodic pseudo-random codes as spreading sequences,which are easily copied and deciphered by the enemy,and the security of information transmission is poor.In this context,self-coded spread spectrum technology came into being.This technology guarantees complete randomness,dynamic variability of the spread spectrum sequence,and low signal interception.It is applicable to military communications with high security requirements.In this thesis,the in-depth study of self-encoded spread spectrum communication systems has important theoretical and practical value.Firstly,the basic principle of the spread spectrum communication technology and its anti-interference characteristics and low probability of interception are analyzed.Several commonly used spread spectrum sequences in direct sequence spread spectrum communication are studied.The advantages and disadvantages of each sequence are given through simulation comparison.The security problems in the classical DSSS system are analyzed,and then the concept of self-coded spread spectrum communication is derived.Secondly,the basic principle of self-coded spread spectrum communication is analyzed in detail,and the advantages of the self-encoded spread spectrum communication system are illustrated by comparison with the direct-sequence spread spectrum system.The probability distribution and statistical characteristics of the self-encoded spread spectrum sequence are analyzed.The anti-jamming ability of Gaussian white noise,single-frequency interference,narrow-band interference,multi-path interference and multiple-access interference of self-coded spread spectrum systems was studied.The theoretical analysis and simulation experiments were performed to verify the results.Compared with traditional spread spectrum communication,self-encoded spread spectrum communication not only has superior confidentiality,but also has similar anti-jamming capability as the classical direct-sequence system under high SNR conditions.However,under the condition of low SNR,the performance of self-encoded spread-spectrum communication is drastically reduced,which has a threshold effect,that is,its unique self-interference problem.In this regard,a self-encoding system based on a fixed and random spreading sequence is proposed,which can greatly reduce the influence of the error on updating the spreading sequence and achieve the purpose of suppressing error propagation.On the other hand,an external feedback self-encoding system based on polar code is proposed.This scheme achieves a perfect fusion of both ends of transceiving and error correction encoding and decoding,so that the advantages of error correction encoding and decoding are fully realized,and improves the self-interference problems.Then,for the problem that the initial spreading sequence in the self-encoded spread spectrum communication must be known,a receiving scheme based on genetic algorithm is proposed so that the system can regenerate the initial spreading sequence without any prior knowledge,further improving System security.Finally,the common synchronization acquisition techniques in classical spread spectrum communication are analyzed in detail.Combined with the characteristics of self-encoding spread spectrum communication technology,a synchronization acquisition method based on periodic transmission synchronization codes is proposed and its feasibility is verified by simulation.