Combined Equalization and Demodulation of Chaotic Direct Sequence Spread Spectrum Signals for Multipath Channels

摘要

Due to the inherent noise-like characteristic of chaotic signals and their sensitivity to the initial value, chaotic direct sequence spread spectrum (CD3S) signals have the advantages of a low probability of intercept (LPI) and a high level of security. Demodulation of non-cooperated CD3S signals is then a challenging issue. If the signal is sent though multipath channels, it is even more difficult for the receiver to demodulate it blindly. Based on the existing theories and methods, we focus more on signals passing through multipath channels. This paper presents an approach to achieve blind equalization and demodulation of CD3S signals through multipath channels. Multiple unscented Kalman filters (UKFs) are used to equalize and demodulate the CD3S signals for the unknown channel. This method can effectively demodulate the signals without any knowledge of the chaotic transmitter's parameters, initial value, state equation, or the channel coefficients, even when the signal is severely distorted by the multipath channel. Simulation results demonstrate that this method gives faster convergence and better demodulation performance than existing methods for various channel conditions.