Research And Application On Shift Keying And Spread Spectrum Code In The Chaotic Communication System

In recent years, with the requirement for the quality of the communication technologygetting higher and higher in the civilian especially military fields, chaotic technology withits inherent characteristics, which can provide strong secrecy and anti-interference abilityin the communication system, is widely used. For the moment, the theoretical research ofchaotic communication has had mature technical solutions and its practical value hasbecome increasingly prominent.The main hot research areas in chaotic digital communication systems are parametermodulation, chaos shift keying and chaos spreading spectrum. On the basis of chaos shiftkeying and spread spectrum systems，this paper does in-depth research work respectivelyin both the existing FM-DCSK modulation technology and produce of chaotic spreadspectrum sequence, and then proposes an optimized and improved solution.In order to solve the problem that variance is not zero in the CSK and DCSK system,FM-DCSK scheme is presented. However, in actual communication channels, bit errorperformance is influenced by the channel distortion and noise interference in FM-DCSKmodulation system. In response to this problem, this paper proposes improved FM-DCSKsystem scheme. In response to this problem, this paper proposes improved FM-DCSKsystem scheme. In shortly, system receiving terminal makes use of the characteristics ofretransmission mechanism of reference signal and the modulated signal in FM-DCSKmodulation system, carries out phase inversion on the received signal and then performscorrelation with the original Received signal at the half bit period, which demodulates thereceived signal and recovers the information signal. After that, based on the improvedmodulation system, this paper derives the BER of the system, simulates and compares theBER performance between the existing chaotic modulation system and improvedmodulation in terms of SNR, spreading factor and correlation coefficient, and thenanalyzes and tests performance advantage of the improved FM-DCSK system. Since selection of chaotic spread spectrum sequences is a key factor to affect theperformance of chaotic spread spectrum communication system, this paper makesimprovement and optimization in chaotic spread spectrum sequence. Because chaoticspreading sequence generated by chaotic maps is real-valued, so it needs to be quantifiedinto a sequence of numbers. The traditional quantitative method uses Binary quantitativemethod, and each iteration only produces a code, which needs a great amount ofcomputing. Later, bit quantitative method is used to solve this problem, but eachiteration can only produce the L-bit codes and the length can not be changed. In this paper,an improved algorithm is presented based on bit quantitative method that all the bitsequence generated by iteration in Bit quantitative method are connected, and then weget sequences average according to the numbers of users, so that the spread spectrumsystem just need one initial value, can get any length of spread spectrum sequences, whichreduces the iteration times, and reduces the amount of computation. Then according to theprinciple of optimization of chaotic spread spectrum sequences, we screen out improvedsequence that is more suitable for spread spectrum code, and make performance analysis ofoptimal chaotic spread spectrum sequences.Finally, according to understanding and researching the theory of Chaotic spreadspectrum communication, the paper derives and analyzes theoretically the BER of theChaotic DS-CDMA system in theory, and establishes MonteCarlo simulation model of thesystem. After that, this paper puts the improved Logistic chaotic sequences along withconventional Logistic sequences as spreading codes applied to the chaos DS-CDMAsystems. According to Monte Carlo simulation model, this paper, respectively in singleuser and multiple user cases, analyzed the BER performance both in the two kind ofchaotic spread spectrum system in SNR, spreading factors and the number of users threeaspects, and verified the superiority of the improved chaotic spread spectrum sequences.