Chaotic communications without synchronization

There has been tremendous interest worldwide in the possibility of exploiting chaos in wideband communication systems. Many different demodulation techniques have been proposed up to date. They can be divided into two basic categories. In the first approach, like the conventional coherent demodulation techniques, the chaotic signal has to be recovered from the received noisy signal by synchronization. However, the chaotic synchronization techniques published to date are so sensitive to the channel noise and/or distortion that these techniques cannot be used in radio communications. In the second approach, the demodulation is carried out without synchronization. This paper surveys the different chaotic communication techniques that can be implemented without synchronization and compares the noise performance of the different methods. Finally, a novel modulation scheme (FM differential chaos shift keying or FM-DCSK) is introduced, where the data rate is not limited by the inherent nonperiodic property of the chaotic signal.