Design, Analysis, and Performance of a Noise Modulated Covert Communications System

Ultrawideband (UWB) random noise signals provide secure communications because they cannot, in general, be detected using conventional receivers and are jam-resistant. We describe the theoretical underpinnings of a novel spread spectrum technique that can be used for covert communications using transmissions over orthogonal polarization channels. The noise key and the noise-like modulated signal are transmitted over orthogonal polarizations to mimic unpolarized noise. Since the transmitted signal is featureless and appears unpolarized and noise-like, linearly polarized receivers are unable to identify, detect, or otherwise extract useful information from the signal. The wide bandwidth of the transmitting signal provides significant immunity from interference. Dispersive effects caused by the atmosphere and other factors are significantly reduced since both polarization channels operate over the same frequency band. The received signals are mixed together to accomplish demodulation. Excellent bit error rate performance is achieved even under adverse propagation conditions.