Combined Equalization and Demodulation of Chaotic Direct Sequence Spread Spectrum Signals for Multipath Channels
- PDF / 825,460 Bytes
- 13 Pages / 439.37 x 666.142 pts Page_size
- 58 Downloads / 211 Views
Combined Equalization and Demodulation of Chaotic Direct Sequence Spread Spectrum Signals for Multipath Channels Xinzhi Xu · Jingbo Guo
Received: 17 August 2012 / Revised: 11 April 2013 © Springer Science+Business Media New York 2013
Abstract 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. Keywords Chaotic direct sequence spread spectrum communication · Multipath channel · Combined equalization and demodulation · Unscented Kalman filter 1 Introduction In recent years, chaotic communications have generated much interest because of their wide spread spectrum, low probability of intercept, and their sensitivity to the initial conditions. Since chaos was first introduced into communications [16], several X. Xu · J. Guo () Department of Electrical Engineering, Tsinghua University, Beijing, China e-mail: [email protected] X. Xu e-mail: [email protected]
Circuits Syst Signal Process
different modulation schemes have been proposed, such as chaos masking [4, 14, 18], chaos shift keying [5, 10, 21], chaotic parameter modulation [11, 12, 22], and chaotic spread spectrum communication [1, 6, 7, 13, 15]. Unlike sinusoidal signals, chaotic signals are more difficult to estimate as carriers [17]. The chaotic direct sequence spread spectrum (CD3S) communication method [1, 6, 7, 13, 15] has a simple structure which is easy to implement while providing good security. These advantages have created a flurry of interest in the research community since it was originally proposed by Heidari-Bateni and McGillem [6] and Parlitz and Ergezinger [15] simultaneously. Most of the research on CD3S communications has compared the performance of chaotic communications with conventional communications in an ideal channel or an additive white Gaussian noise (AWGN) channel. Hu and Guo [7] proposed a modified unscented Kalman filter (UKF) chaos fitting method to demodulate CD3S signals through AWGN
Data Loading...
