ABSTRACT
Previous digital communication technology continually used a linear system theory and linearity in order to improve its performance, and nonlinear system was used to reach specific level of linear system. However, as this technology reaches basic limit, people have started to improve performance of nonlinear communication systems applying chaos communication systems to nonlinear system[1]. Chaos communication system is nonlinear system, and has the characteristics such as non-periodic, wide-band, non-predictability and easy implementation. Also, chaos communication system is decided by initial conditions of equation, and it has sensitive characteristic according to initial condition, because chaos signal is changed into different signal when initial condition is changed [2]. By combining characteristics of chaos signals with a digital communication technology, it becomes dicult to detect other transmitted signals, interference waves, and it has strong features in the multi-path interference. As a result, research can improve security to reduce the probability of eavesdropping [3]. However, generally speaking, security of chaos communication system is superior to digital communication system, but BER performance is not good. In case of CDSK system, chaos signal is transmitted with reference signal. So, it has many self-interference signals. As a result, BER performance is bad according to evaluation[4]. For BER performance improvement of chaos communication system, many researches are being
done. If we do the research on the existing chaos system, many chaos map and modulation methods will be used to evaluate BER performance. We found chaos map and modulation methods. By using it, a BER performance is the best. Moreover, the encoded system used the chaos signal or research applying the security system was accomplished.
