Research On Chaotic Digital Modulations Based On DCSK

Differential chaos shift keying (DCSK) technology employs non-periodic and wideband chaoticsignals as carriers so as to achieve the effect of spectrum spreading in the same process of digitalmodulation. Equipped with lower interception probability and immunity to multipath effects whichare desirable virtues of traditional spread spectrum systems, DCSK shows other unique advantages,including better privacy, simple circuits, low peak to average power ratio (PAPR), no need forchannel estimation or spreading code synchronization, potential to reduce mutual user inferences inmulti-user applications. As a result, this technology has tempting prospects in real applications.Due to the fact that DCSK wastes almost half bit duration and half power on sending chaoticcarriers that carry no data information, DCSK communication systems show some flaws in data rate,data security and bit error rate (BER) performance. To find feasible solutions to these problems,Gaussian approximation method, numerical integration method, exact performance analysis methodand Monte Carlo simulation are adopted in this dissertation to deeply study the chaotic digitalmodulation technologies based on DCSK. The main contents and contributions are listed as follows:(1) Double bit rate differential chaos shift keying (DBR-DCSK) scheme is proposed to increasethe data rate in DCSK communication systems. Gaussian approximation, numerical integration andexact performance analysis method designed for analyzing the BER performance of multiple accessantipodal chaos shift keying communication system are used in BER formula derivation of theproposed system over additive white Gaussian noise (AWGN) and Rayleigh flat fading channels.All analytical results are validated by Monte Carlo simulation. The relationship between the lengthof chaotic sequence and system BER performance is studied, and the BER performance of theproposed system is compared with other systems. Analysis and simulation results reveal: comparedto DCSK, DBR-DCSK can not only obtain better data privacy and higher data rate, but also achieveapproximate1dB performance improvement at certain signal to noise ratio (SNR) levels.(2) New strategies are explored to reduce or eliminate the adverse effect brought by the intra-signal interference components in decision variables on BER performance of DBR-DCSK. First, asimple algorithm is designed to reduce the intra-signal interferences, and the corresponding detectoris also constructed. In the proposed algorithm, all intra-signal interference components in decisionvariables are estimated/reconstructed by using received reference signals, the estimated componentsare removed from all decision variables before they are fed into final decision circuit. The BER performance of the new detector is studied over AWGN channel by both exact performance analysismethod and Monte Carlo simulation, which reveals that our new detector can improve the BERperformance of DBR-DCSK at certain SNR levels; with noise suppressing block, our new detectorcan greatly enhance the BER performance of DBR-DCSK at any SNR levels; this performanceenhancement becomes more and more evident as SNR increases. Second, a novel DBR-DCSKscheme with no intra-signal interference is proposed. In this new scheme, signal format of chaoticcarriers is changed so that two modulated chaotic signals in same time slot are always kept to beorthogonal and intra-signal interferences are removed completely from all DBR-DCSK decisionvariables. The BER performance of this new system is studied over AWGN channel by numericalintegration method and Monte Carlo simulation. Analysis and simulation results show that theproposed system not only inherits the original advantages of DBR-DCSK but also outperformsDBR-DCSK in BER performance. Besides, this BER performance enhancement appears to be moreand more obvious when SNR level increases or the length of chaotic sequence shrinks.(3) Reference-modulated differential chaos shift keying (RM-DCSK) scheme is proposed tosimplify DBR-DCSK transceiver structures. By using Gaussian approximation, exact performanceanalysis method and Monte Carlo simulation, the noise performance of RM-DCSK is studied overAWGN and Rayleigh flat fading channels, and the relationship between the length of chaoticsequence and system BER performance is also analyzed. The results show that RM-DCSK achievesgood privacy, same data rate and almost identical BER performance in comparison to DBR-DCSK.(4) To increase the data rate in code-shifted differential chaos shift keying (CS-DCSK), a novelorthogonal differential chaos shift keying (ODCSK) scheme is proposed. The BER performance ofODCSK is studied by Gaussian approximation method, numerical integration method and MonteCarlo simulation over AWGN channel. The influences of spreading factor, length of Walshsequence and length of chaotic sequence onto system BER performance are analyzed, and the noiseperformance of this new system is also compared with that of CS-DCSK. The results show that thenew system achieves not only higher data rate but also better BER performance in comparison withCS-DCSK at certain SNR levels and spreading factors.