Research On MIMO And Multiple Access Technique In Chaos Shift Keying

Chaos has some excellent characteristics which can be applied to lots of different fields. Chaos shift keying(CSK) is considered as one of the three typical chaos secret communication technologies which have been widely researched in secret communication field due to chaotic signals' nonperiodic, wideband, intrinsic random and good correlation characteristics. Differential chaos shift keying(DCSK) and correlation delay shift keying(CDSK) are considered as two key technologies of CSK which can overcome the difficult problem of chaos synchronization. The chaos communication without synchronization between transmitter and receiver can be realized which makes CSK more practical and therefore obtains wider application prospect.DCSK system has some drawbacks on data security and transmission rate. In CDSK system it brings a lot of noise item which raises the bit error rate(BER) of CDSK. In addition, CDSK still has some flaws on data security and transmission rate. Therefore, in this thesis, CSK technology is deeply studied by combing with existing multiple input multiple output(MIMO) and multiple access technique. The main work of this thesis is listed as below:(1) Combined with the MIMO technique,a novel multiple input multiple output-frequency modulation – segment shift correlation delay shift keying scheme(MIMO-FM-SSCDSK) is studied in this thesis, which can increase the transmission rate by using multiple channel. It can significantly improve the system security because multipath chaos signal and the signal which carrying information are mixed together. If the eavesdropper wants to steal and demodulate the information form transmitter, it needs to intercept and capture multiple channel received signal simultaneously which becomes very difficult in MIMO-FM-SSCDSK. The proposed system's anti-noise performance and influence of channel numbers on system's BER in AWGN channel are analyzed, and compared with the frequency modulation- correlation delay shift keying(FM-CDSK) system. Simulation results show that, not only the BER of MIMO-FM-SSCDSK system but also the security of MIMO-FM-SSCDSK system is better than the FM-CDSK.(2) Combined with the multiple access technique a novel multiple user-frequency modulation- differential chaos shift keying(MU-FM-DCSK) system is researched in this thesis. The multiple access technique(multiple users) can distinguish different users by multiplying different adjustment parameters, and further demodulating the transmitted signal in receiver by level decision, which makes the system more practical. Compared with the traditional DCSK system, the transmission rate of the researched system increases exponentially, and it also reduces the interception probability of information because of mixed multiple users' information signals. Moreover, the performance of anti-noise and influence of channel numbers on system BER are analyzed deeply, and the security between researched system and the FM-DCSK system in AWGN channel are compared. Simulation results indicate that MU-FM-DCSK system has better BER performance, even outperforms that of the existing multiple user chaos shift keying system and the security of researched system is better than the FM-DCSK system.(3) The effect of related parameter on chaos shift keying system is analyzed deeply. Spreading factor is one of the most important parameters, with the increase of spreading factor, system BER will be improved. However, other system parameters and performance will be limited when the spreading factor tends to infinity. Therefore, there is an optimal spreading factor which can optimize the system performance. Utilizing the knowledge of deriving the derivative extreme value in higher mathematics, the equation of system BER can be derived and then the optimal spreading factor for chaos shift keying system can be obtained theoretically. Simulation results verify the effectiveness of optimal spreading factor in AWGN channel.