The Key Techniques In CDSK Chaotic Communication System

Correlation-Delay-Shift-Keying(CDSK) is a typical noncoherent chaotic digital modulation technique. In this chaotic communication system, the reference signal and the information-bearing signal are added together during a certain time delay. As a consequence, each transmitted signal includes one reference signal and one information-bearing signal. Compared with Differential-Chaos-Shift-Keying(DCSK), since no individual reference signal is sent, CDSK has better bandwidth efficiency; due to no switch between reference signal and information-bearing signal, CDSK allows the transmitter and receiver for continuous operation; due to no correlation between the transmitted signals in different moments, the transmitted information of CDSK is more difficult to be intercepted.However, because the reference signal is not strictly orthogonal to the information-bearing signal, the cross-correlation between the adjacent chaotic signal(Intrasignal Interference, ISI) will be introduced into the demodulation at the receiver. Therefore, the Bit-Error Ratio(BER) of CDSK is higher than that of the conventional digital communication scheme. If CDSK is applied to the multiuser system, its ISI component will rise along with the number of users. In order to improve the BER performance of CDSK, Gaussian approximation and Monte Carlo simulation are adopted to study the chaotic digital modulation technologies based on CDSK. The main contributions and contents are listed as follows:1. To increase the useful signal component and get an outstanding BER performance in contrast to the conventional Single-Input-Single-Output CDSK, we propose the Multiple-Input-Single-Output CDSK(MISO-CDSK) and Single-Input-Multiple-Output CDSK(SIMO-CDSK). Gaussian approximation method is adopted here to obtain the exact performance analysis and the BER formula derivation of the proposed systems over additive white Gaussian noise(AWGN) and Rayleigh flat fading channels. All the analytical results are validated by Monte Carlo simulation. Analytical and simulation results show that: due to the significant increment of useful signal component in demodulation, the proposed MISO-CDSK and SIMO-CDSK have an outstanding BER performance in comparison to the conventional SISO-CDSK communication system, and the improvement of the proposed systems will increase along with the number of antennas. For the two systems, we will find that: since the BER performance of SIMO-CDSK is not influenced by the delayed signal and its normalized capacity increases along with the number of receiver antennas, the performance of SIMO-CDSK is better than that of MISO-CDSK.2. To decrease the ISI component and noise interference component in CDSK chaotic communication system, Reference-Adaptive CDSK(RA-CDSK) and its Single-Input-MultipleOutput system(SIMO-RA-CDSK) are proposed. According to the relationship between adjacent information symbols, RA-CDSK employs the information-bearing signal or the sequence generated by discrete-time chaotic circuit as the reference signal for the next bit period. Compared with CDSK, since the reference signal can be used to bear information, the uncertainty caused by intrasignal interference and noise interference is made lower during the demodulation. Gaussian approximation method is adopted here to obtain the exact performance analysis and the BER formula derivation of RA-CDSK and SIMO-RA-CDSK system over additive white Gaussian noise(AWGN) and Rayleigh flat fading channels. All the analytical results are validated by Monte Carlo simulation. Analytical and simulation results show that: due to less interference in RA-CDSK, the BER performance of RA-CDSK is always much better than CDSK, GCDSK; with the same number of receiver antennas, the BER performance of SIMO-RA-CDSK system is better than that of SIMO-CDSK system; the normalized capacity of SIMO-RA-CDSK increases along with the number of receiver antennas.3. To eliminate the ISI component, a novel CDSK communication scheme with no intrasignal(CDSK-NII) and its Single-Input-Multiple-Output system(SIMO-CDSK-NII) are proposed. By utilizing the repeated chaotic sequence as the reference signal and taking advantage of the zero-sum sequence to ensure the reference signal strictly orthogonal to the information-bearing signal, the proposed scheme can eliminate the ISI component during the demodulation. Gaussian approximation method is adopted here to obtain the exact performance analysis and the BER formula derivation of CDSK-NII and SIMO-CDSK-NII system over additive white Gaussian noise(AWGN) and Rayleigh flat fading channels. All the analytical results are validated by Monte Carlo simulation. Analytical and simulation results show that: due to no ISI component during the demodulation, the BER performance of CDSK-NII is much better than CDSK and generalized CDSK(GCDSK); by selecting the reasonable length of multiframe, the BER performance of CDSK-NII system can even outperform RA-CDSK; with the same number of receiver antennas, the BER performance of SIMO-CDSK-NII system can be better than that of SIMO-RA-CDSK system; the normalized capacity of SIMO-CDSK-NII increases along with the number of receiver antennas.4. To apply the operation principle of CDSK-NII to the multiuser system, Multiple-access CDSK with No Intrasignal(MA-CDSK-NII) is proposed. This scheme assigns to each user a pair of Walsh code sequences. By alternately selecting one of a pair of Walsh code sequences to modulate the reference signal, MA-CDSK-NII can ensure the strict orthogonality between the signals from different users. Consequently, MA-CDSK-NII can wholly eliminate the intrasignal interference during the demodulation in multiuser condition. Gaussian approximation method is adopted here to obtain the exact performance analysis and the BER formula derivation of the proposed system over additive white Gaussian noise(AWGN) and Rayleigh flat fading channels. All the analytical results are validated by Monte Carlo simulation. Analytical and simulation results show that: with the same number of users, the BER performance of MA-CDSK-NII system is better than that of MA-CDSK system and MA-GCDSK system.