Secure Spread Spectrum Communication Using Ultrawideband Random Noise Signals

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 technique is based on the use of heterodyne correlation techniques to inject coherence in a random noise signal. The transmitted signal is featureless and appears unpolarized and noise-like; thus linearly polarized receivers are unable to identify, detect, or otherwise extract useful information from the signal. The system is immune from interference caused by high power linearly polarized signals. Dispersive effects caused by the atmosphere and other factors are significantly reduced since both polarization channels operate over the same frequency band. Our results indicate that the proposed scheme can recover voice and data signals with superior fidelity. Simulations show that we can achieve BER values of 10 at an SNR of around -6 dB without channel coding and BER values sufficient for data and video at much lower SNRs when channel coding is employed, which indicates excellent performance under covert conditions such as operating under the enemy receiver's thermal noise floor. We also show preliminary field test results with the baseband processing implemented within a software defined radio architecture that clearly validate the system concept