Combined demodulation with adaptive blind-channel equalization for chaotic-modulation communication systems

The problem of combining demodulation with adaptive blind- channel equalization for chaos communication systems is investigated in this brief. The proposed demodulator is designed to combat frequency- selective and/or time-selective channel distortions for chaos communica- tion systems including chaotic parameter modulation and differential chaos shift keying. Assuming that the channel coefficients can be described by linear autoregressive models, a state-space representation of the frequency- selective and/or time-selective channel impulse responses can be obtained. The whole chaos communication system is then formulated as a nonlinear state-space model, and the receiver with channel equalization is therefore a nonlinear state-estimation problem. A nonlinear adaptive algorithm based on extended Kalman filter (EKF) technique is proposed here to track the channel coefficients and to retrieve the message signal. Sensitivity analysis of the proposed EKF demodulator is carried out, and its performance in realistic frequency-selective and time-selective channels is evaluated using numerical simulations. Index Terms—Blind-channel equalization, chaos, chaos communica- tions, chaotic parameter modulation (CPM), differential chaos shift keying (DCSK), extended Kalman filter (EKF), wireline and wireless channels.