Performances Analysis Of Chaos Shift Keying Communication Systems And Their Implementation Research

Chaotic signals, generated by a deterministic nonlinear system, not only have an inherently white-noise like broadband and aperiodic nature but have random-signals like auto- and cross-correlation properties. Furthermore, one-dimension chaos-based systems can offer potential advantages, such as simplicity and high speed. So, chaotic signals generated by one dimension chaotic map have the important features in spread-spectrum communication and security communication. Chaos shift keying (CSK) is one of the most common base-band communication schemes that chaotic signals are applied. Among these chaos-based shift keying systems, noncoherent (or differential) chaos shift keying (DCSK), which does not require synchronization, is more practical for implementation and has deserved considerable attention.Usually, Gaussian Approximation (GA) method is applied to investigate the performances of DCSK in multipath fading channels. The theoretical results obtained from the GA method are matching the simulation ones when the spreading factors are large enough. However, they are apart from the simulation results when the spreading factors are small. An exact analytical method is used here to substitute the GA method. The theoretical results obtained from the exact analytical method are match with the simulation ones in all cases.Ones always took assumption that the chaos auto-correlation side lobe is zero when they investigate the performances of DCSK in fading channel with delay spread. However, the effect of some chaos auto-correlation side lobe is not negligible. This is considered in our research and a revised theoretical bit error rate (BER) formula which is more universal for DCSK in the fading delay environment is evaluated.Multiple-access (MA) ability is an important feature for modern communication systems. Recently, a number of MA-DCSK communication schemes have been proposed in order to achieve a good balance between system BER performances and hardware costs. An improved MA-DCSK is presented in this paper, which is based on chaotic binary sequence and Walsh codes, for convenience, we call it BWMA-DCSK. The system's BER performances are analyzed and are compared with that of a classical MA-DCSK. The comparison result shows that the BER performances of the BWMA-DCSK system are better than the classical MA-DCSK system as all users use different chaotic initial value. The improved MA-DCSK system BER performances are drastically improved when all users use the same initial value.The performances of a single user DCSK in fading channels or fading channels with delay spread were investigated thoroughly before. However, there is no literature considers the BER performances of MA-DCSK system in fading environments. The performances of several MA-DCSK systems in fading or fading with delay spread channels are investigated in this paper in detail. The BER formulas are derived and the simulation results are presented. The BER performances of these MA-DCSK systems over these channels are compared, respectively. The comparison results shows that the classical MA-DCSK system degrades least in the fading or the fading with delay spread channels.Up to now, the previous implementation research work is mainly concentrate on a single user DCSK system. In this paper we designed digital circuits for the BWMA-DCSK system and the classical MA-DCSK system mentioned above. Firstly, we obtained the periodicities of two precision-limited chaotic maps for different number of precision by computer simulation; and from these periodicities we derived a statistical raw between the maximum periodicities and the precision; Secondly, by comparing the digital circuits performances and the hardware overheads of the two chaotic systems, we chose a chaotic system which is more suitable for practical use for the chaotic signals generator; we compared the digital circuits performances and the hardware overheads of the modulations and demodulations of the two MA-DCSK systems. Finally, we implemented the two MA-DCSK systems on an Altera FPGA device; the implementation results show that the BWMA-DCSK can achieve higher system clock frequency and faster data transmission rate than the classical MA-DCSK system under the same circumstances.