Research On Chaotic Digital Modulation System Based On DCSK

Differential Chaos Shift Keying(DCSK)adopts non-coherent demodulation.On the basis of retaining the good characteristics of chaotic signals,channel estimation and spreading code synchronization are not needed,DCSK has low implementation cost,robust to multipath fading environment,and good application prospects.Due to the use of Transmitted-Reference(T-R)mode,half of the time and power transmission chaotic reference signals,the system has low data rate,high energy consumption,low information security,and low bit error rate(BER)performance.In order to find a feasible solution to slove these problems,an intensive study on chaotic digital modulation system based on DCSK is conducted.The main research work of this thesis includes the following three aspects:(1)The related theoretical knowledge of chaos is researched and the modulation and demodulation principles of several typical chaotic digital modulation systems are introduced.Gaussian Approximation(GA)method is used for theoretical analysis and calculation.Furthermore,the advantages and disadvantages of DCSK system is studied to find the entry point for further improvement of the system.(2)In order to improve the bit transmission rate and Security of the DCSK system,a short reference DCSK based on scrambling matrix(SMSR-DCSK)is studied.Based on the forward shift matrix,a simple and orthogonal scrambling matrix is designed,which can disrupt the sequence of chaotic sequences and reduce the correlation between chaotic reference signals and information signals,By using Gaussian approximation(GA)method,the BER formula of system is derived in Additive Gaussian White Noise(AWGN)channel and Rayleigh fading channel,and the optimal performance parameters are solved accordingly.Monte Carlo simulation experiments were used to verify the theoretical analysis results,and the influence of power and reference sequence length on system performance was analyzed.Furthermore,the comparison with the anti-noise performance of typical systems was completed.The theoretical and simulation results show that compared with DCSK and SR-DCSK systems,the SMSR-DCSK system has a significant improvement in both Security and BER performance.(3)In order to improve the BER performance of Orthogonal Frequency Division Multiplexing DCSK(OFDM-DCSK),the OFDM-DCSK system with repeated spreading sequence and noise reduction(RSNR-OFDM-DCSK)is studied.The system allocates reference subcarriers and data subcarriers in an optimal manner and achieves noise reduction through diversity.Wherein the DCSK modulated signal is transmitted on the reference subcarrier,and the generated repeated spreading sequence is modulated and transmitted on the data subcarrier.Gaussian approximation and Monte Carlo simulation are used to study the system performance in AWGN channel and Rayleigh fading channel.Furthermore,the effects of FFT points,semi-spreading factor,number of data carriers,number of DCSK carriers and signal-to-noise ratio on BER performance of the system are analyzed.The theoretical and simulation results show that the RSNR-OFDM-DCSK system can significantly improve the BER performance compared with DCSK and OFDM-DCSK.