Chaotic communications through arbitrary attenuation: a hardware demonstration

A chaotic communications baseband system has been designed and implemented in hardware that transmits, synchronizes, and recovers a data message over arbitrary amounts of attenuation in the presence of noise. The hardware demonstration system includes data bit generation, chaotic modulation, D/A conversion, physical attenuation, A/D conversion, and message recovery. This proof-of-concept system was implemented on computer-based DSP evaluation modules. It utilizes a duobinary signal structure as well as software algorithms to track and compensate for transmit-receive sample clock mismatch, eliminate intrinsic intersymbol interference, and adjust sample point values to the correct pulse peak amplitude. The signal amplitude restorer is the critical enabling component for chaotic synchronization and demodulation. It exploits the transmit probability density function to adjust received pulses to within tenths of a dB of a desired level. The primary result is the demonstrated ability of nonlinear dynamical chaos-based systems to successfully communicate through physical channels across arbitrary propagation distances. A second achievement is reliable message recovery at low received SNR with respect to the evaluation module noise floor